Luminous Landscape Forum
Equipment & Techniques => Cameras, Lenses and Shooting gear => Topic started by: Dan Kehlenbach on April 08, 2009, 11:46:22 am
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Hello:
I recently purchased a Panasonic G1 and have been very impressed so far with its performance.
I do have a question about depth of field with the micro four-thirds format:
Since the distance from the lens to the sensor is shorter, and since the 4/3 sensor is smaller than my APS-C Canon DSLR, will there be an inherent increase in depth of field for a given f-stop? Would there be such things as "f-stop equivalents" between micro four-thirds and APS-C sensors?
Thanks for your help.
Dan Kehlenbach
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It's about a stop.
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will there be an inherent increase in depth of field for a given f-stop? Would there be such things as "f-stop equivalents" between micro four-thirds and APS-C sensors?
Here is my rule of thumb (but beware; many forum wars have been fought on this topic!)
Short answer:
About 2/3 stop difference between Four Thirds and EF-S or DX, 2 stops from Four Thirds to 35mm (24x36mm).
So for example, the f/2.8-3.5 lenses for Four Thirds are comparable to f/3.5-4.5 lenses for EF-S/DX for DOF wide open.
Long answer:
When photographing the same FOV with different formats, and so using focal lengths that differ in proportion to format size, you will get equal DOF if you adjust the f-stop in proportion to the change in focal length.
In other words, the same conversion factor for "equivalent focal lengths" (same FOV) also converts for "equivalent f-stops": equivalent for DOF at least(*).
Since the format conversion factors are
4/3 -> 35mm: 2x
4/3 -> EF-S: 1.25x
4/3 -> DX: 1.33x
EF-S -> 35mm: 1.6x
DX -> 35mm 1.5x
the corresponding corrections in f-stops are roughly
4/3 -> 35mm: 2 stops
4/3 -> EF-S: 0.64 stops
4/3 -> DX: 0.82 stops
EF-S -> 35mm: 1.36 stops
DX -> 35mm 1.19 stops
So about 2/3 stop between Four Thirds and either EF-S or DX.
(*) Equivalent for diffraction effects too, and maybe for "speed", once ISO speed differences are allowed for.
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Thanks for the help - I am looking forward to getting out with the camera and experimenting a bit with some landscapes and close-ups.
All my best,
Dan Kehlenbach
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It's also easy to remember this way: While a 14mm lens has the same apparent field of view on m4/3 as a 28mm lens would on 35mm, it's still a 14mm lens, and will have the same dof as a 14 mm lens on 35mm. A 50mm lens on m4/3 will have the field of view of a 100mm lens on 35mm, but still the dof of a 50mm lens. Field of view changes with sensor size, while dof is constant based on lens focal length and aperture, regardless of sensor size.
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Err1ksen,
Your explanation certainly makes sense. I am wondering how much difference the lens-to-sensor distance makes in DOF. In Panasonic's other 4/3 camera (L10, I believe), the distance from the lens to the sensor is 40mm while the G1 is 20mm.
[attachment=12874:MicroFou...Diag_001.jpg]
I am looking forward to getting out and experimenting.
Thanks.
Dan Kehlenbach
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It's also easy to remember this way: While a 14mm lens has the same apparent field of view on m4/3 as a 28mm lens would on 35mm, it's still a 14mm lens, and will have the same dof as a 14 mm lens on 35mm.
That is very misleading, because the image used from the 14mm lens in 4/3 is only half the width and height of that from the 14mm lens in 35mm format, so when printed at the same size, it must be enlarged twice as much. That extra enlargement doubles out of focus effects too, and so gives half as much DOF as 14mm in the larger format, and also a very different FOV, if comparing with equal f-stop.
But on the other hand, doubling focal length from 14mm to 28mm at equal f-stop reduces DOF by a factor of four (it goes with the square of focal length.) And doubling f-stop doubles DOF (with same focal length same degree of enlargement.)
So, doing the comparison sanely, viewing equal sized images of the same subject from the same distance:
- 14mm in 4/3 has half the DOF of 14mm in 35mm at the same f-stop
- 28mm in 35mm format has one quarter the DOF of 14mm in 35mm format at the same f-stop
- 28mm in 35mm format has twice the DOF of 28mm in 35mm format at half the f-stop
and thus
- 14mm in 4/3 has twice the DOF of 28mm in 35mm at the same f-stop
- 14mm in 4/3 has the same DOF of 28mm in 35mm at twice the f-stop. E.g 14mm f/4 in 4/3 vs 28mm f/8 in 35mm.
The last is my rule of thumb, doubling focal length and f-stop for equal FOV and equal DOF (and equal diffraction effects.)
Hopefully we will not now return to debating whether it is more reasonable to compare images with completely different field of view from the different formats, or to compare crops to equally sized portions of the differently sized sensors!
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I am wondering how much difference the lens-to-sensor distance makes in DOF. In Panasonic's other 4/3 camera (L10, I believe), the distance from the lens to the sensor is 40mm while the G1 is 20mm.
That is only distance from the lens mount to the sensor; it has no effect of optical properties like DOF, which will be the same for equal focal length, equal aperture, equal subject distance in any 4/3" format camera.
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I am wondering how much difference the lens-to-sensor distance makes in DOF.
From a DOF perspective, it has absolutely zero effect. But what that will do, would be to alter the design of the lens itself (especially true for the really challenging ultra-wides and wides), since the new design will not have to compensate for that extra distance to accomodate the mirror. Also, the design itself becomes a lot more simpler, with less propensity for coma and other distortions.
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Here is my rule of thumb (but beware; many forum wars have been fought on this topic!)
So about 2/3 stop between Four Thirds and either EF-S or DX.
BJL,
The G1 sensor size is 18mmx13.5mm. The Canon EF-S sensor is 22.3mmx14.9mm. The DoF difference between the 4/3rds format and specifically the EF-S cropped format, which is slightly smaller than the DX format, should therefore range between 22.3/18=1.2x and 14.9/13.5=1.1x, depending on the previsualised aspect ratio of the composition.
Assuming one maximises the sensor area in relation to the composition (using a zoom) and assuming one crops only to change the aspect ratio, then the DoF advantage of the G1 in relation to the Canon EF-S cropped format will be, at most, slightly more than 1/3rd of a stop and, at least, slightly less than 1/3rd of a stop.
The best approximation would therefore be 1/3rd of a stop difference, in relation to the Canon APS-C format. Nothing to shout about really. Agreed?
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The G1 sensor size is 18mmx13.5mm. The Canon EF-S sensor is 22.3mmx14.9mm.
No, the 12.1MP image from the G1 sensor comes from a 17.3x13mm "active area": the nominal 18x13.5mm of 4/3" format maybe covers the total pixel count of 13.1MP. So the sensor height and width ratios EF-S/G1 are about and 1.15 and 1.3, with diagonal ratio of 1.24 (26.8mm/21.6mm). That 1.24 is very close to the 1.26 linear factor for 2/3 stop, but if you prefer the extremes, 1.15 is 2/5 stop and 1.3 is 3/4 stop. (A factor if 1.4 is one stop.)
(I used 22.5x15mm for EF-S, but recent EF-S have the slightly smaller dimensions that you gave.)
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No, the 12.1MP image from the G1 sensor comes from a 17.3x13mm "active area": the nominal 18x13.5mm of 4/3" format maybe covers the total pixel count of 13.1MP. So the sensor height and width ratios EF-S/G1 are about and 1.15 and 1.3, with diagonal ratio of 1.24 (26.8mm/21.6mm). That 1.24 is very close to the 1.26 linear factor for 2/3 stop, but if you prefer the extremes, 1.15 is 2/5 stop and 1.3 is 3/4 stop. (A factor if 1.4 is one stop.)
(I used 22.5x15mm for EF-S, but recent EF-S have the slightly smaller dimensions that you gave.)
That's very misleading of Dpreview to quote the total sensor area for the Panasonic G1 and GH1 yet on the same style and format of introductory specification sheet quote the smaller 'active' sensor area of the Canon APS-C formats, without mentioning the distinction.
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That's very misleading of Dpreview to quote the total sensor area for the Panasonic G1 and GH1.
Yes; or just plain confused: DPReview often uses the traditional (total?) 18x13.5 dimensions, even in its "pixel density" calculations, ignoring the dimensions given in spec. sheets for many Four Thirds cameras, including in some of its own reviews, like for the E-30, which has basically the same sensor as the G1: http://www.dpreview.com/reviews/olympuse30/page3.asp (http://www.dpreview.com/reviews/olympuse30/page3.asp)
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That 1.24 is very close to the 1.26 linear factor for 2/3 stop, but if you prefer the extremes, 1.15 is 2/5 stop and 1.3 is 3/4 stop. (A factor if 1.4 is one stop.)
(I used 22.5x15mm for EF-S, but recent EF-S have the slightly smaller dimensions that you gave.)
Let's not quibble. Let's call it 2/3rds of a stop advantage. Moving on to the ramifications of the greater DoF of the 4/3rds format, I think we are all searching for the sort of performance in the lighter camera that can equal the performance of the heavier model.
How would a G1 with 14-54/F2.8-3.5, or 14-42/F3.5-5.6, compare with a 50D with EF-S 17-55/F2.8? Where are the tough comparisons?
It seems to me that a 50D at 17mm and F3.5 might produce a cleaner and sharper result than a G1 or E-620 at 14mm and F2.8. DoF should be about the same, but in low light I suspect the 50D will surpass the 4/3rds format.
When DoF can be sacrificed, or when a shallower DoF is desired, the 50D at 17mm and F2.8 will outperform any 4/3rds camera and lens combination, I suspect.
A 4/3rds format lens equivalent to the EF-S 17-55/2.8 would be a 14-44/F2.2 across the whole range. It doesn't exist.
If we compare the 4/3rds format with full frame 35mm of the same pixel count, for example, the Nikon D700 and G1 or E-620, I suspect the gap widens. With a 2 stop difference in DoF, I'm prepared to accept that a G1 or E-620 at ISO 1600 might be at least as good as a D700 at ISO 6400 regarding noise, but where's the equivalent Zuiko lens to Nikkor 14-24/2.8? It would need to be a 7-12/F1.4. The closest is 7-14/F4.
Another issue is of course resolution at the DoF equivalent F stop. Is the Zuiko 7-14 at 7mm and F4 sufficiently sharp to compete with the Nikkor 14-24 at 14mm and F8? If it is, is it also sufficiently sharp to compete with the Nikkor 14-24 at F4 and F5.6 in circumstances when a shallow DoF is okay?
If a Zuiko 7-12mm/F1.4 were a feasible proposition, woulkd it be about 50% sharper at F1.4, from corner to corner, than the Nikkor 14-24/2.8 at F2.8.? It would need to be to delvier equally sharp image resolution at the 12mp level.
I don't wish to appear dogmatic about such issues, but the great dearth of direct and competently executed comparisons on the interent give me reason to suspect there's really no contest.
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Let's not quibble. Let's call it 2/3rds of a stop advantage.
No quibble from me: that 's the facts!
Moving on to the ramifications of the greater DoF of the 4/3rds format, I think we are all searching for the sort of performance in the lighter camera ...
How would a G1 with 14-54/F2.8-3.5, or 14-42/F3.5-5.6, compare with a 50D with EF-S 17-55/F2.8?
If the interest is a lighter camera (or even in similarly priced kits), lens weight (and cost) matter too, so the EF-S 17-55/F2.8 is the wrong lens to be using: that choice clearly gives better low light performance from a heavier, more expensive kit, just as one expects by changing to a lens with substantially larger aperture diameter and front element size. (The 50D is probably the wrong body too: maybe the smaller, cheaper 500D?)
How about trying to stay in roughly the same size and weight range with something like
50D or 500D body with EF-S 18-55 f/3.5-5.6 IS vs G1 body with Panasonic 14-45/F3.5-5.6 (45, not 42) or E-620 with Olympus 14-42/F3.5-5.6
or
50D or 500D body with EF-S 17-85 f/4-5.6 IS vs E-620 with Olympus 14-54/F2.8-3.5 (or G1 w/ 14-54/F2.8-3.5, but then IS is lost)
The latter pairing actually shifts the DOF control advantage to the 4/3 kit, and maybe the wide open low light performance too, because that Canon 17-85/4-5.6 has uniquely small maximum aperture diameters for its class and price range.
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It would need to be a 7-12/F1.4. The closest is 7-14/F4.
Oh yeah, you are really going to be working the DOF hard with a 7mm lens..... I can't see where its going to make much difference if its f1.4 or f4, who is going to use a 7mm lens when they need shallow DOF? I don't think the sums are reflecting the real world, in which many people who use Olympus lenses have given up worrying if they are 'sufficiently sharp' to compete, because 'sharpness', or lack of it, is why they dumped Canon or Nikon in the first place.
Steve
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No quibble from me: that 's the facts!
BJL,
That's not quite correct. Those are the mathematical calculations based upon the simplest of formulas. In practice there are other factors, including lens design and distance to subject, which influence those theoretical DoF differences.
I've noticed myself, when comparing the noise differences between the 40D, 50D and 5D, after appropriate adjustment of ISO and aperture to equalize shutter speed, that the 1.6x factor applied to F stop # often does not result in equal DoF between the cropped format and full frame.
In other words, using the same zoom lens (Canon 24-105), adjusting FL to equalise FoV, stopping down by 1 & 1/3rd stops on the 5D whilst increasing ISO by 1 & 1/3rd EV to maintain the same shutter speed, results in the 5D image having noticeably less DoF.
Focussing on subjects at fairly close distances of 6 to 12ft (in my living room), there appears to be something like a 2 stop difference in DoF between the Canon APS-C format and FF 35mm. That is, the same difference that your formulas attribute to the 4/3rds format versus FF 35mm.
Now, I haven't taken the trouble to compare DoF with the plane of focus at numerous distances, from near to far. I've got other things to do. But it would be an interesting exrecise for someone with the time.
If the interest is a lighter camera (or even in similarly priced kits), lens weight (and cost) matter too, so the EF-S 17-55/F2.8 is the wrong lens to be using: that choice clearly gives better low light performance from a heavier, more expensive kit, just as one expects by changing to a lens with substantially larger aperture diameter and front element size. (The 50D is probably the wrong body too: maybe the smaller, cheaper 500D?)
My interest is in getting the best performance possible within the parameters of reasonable cost, reasonable weight and and reasonable convenience of use. I'm not interested in sacrificing a noticeable and significant loss of image quality for the benefit of a noticeable and significant loss of weight. But I am interested in sacrificing a small and insignificant loss of image quality for the benefits of a substantial loss of weight.
Only when comparable test images and MTF charts are available can one make sensible choices regarding these matters. Fortunately, Photozone had tested the EF-S 17-55/2.8 and their results influenced my choice of this lens. I'm clearly not interested in saving a few grams of weight, and a few dollars, by getting a slightly lighter lens which is clearly not as sharp and useful in low light. Are you?
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Oh yeah, you are really going to be working the DOF hard with a 7mm lens..... I can't see where its going to make much difference if its f1.4 or f4, who is going to use a 7mm lens when they need shallow DOF? I don't think the sums are reflecting the real world, in which many people who use Olympus lenses have given up worrying if they are 'sufficiently sharp' to compete, because 'sharpness', or lack of it, is why they dumped Canon or Nikon in the first place.
Steve
You missed the point. I'm not arguing that the larger format has the benefit of a shallower DoF at any given aperture (although it does) because there's an equally strong argument that the smaller format has a greater, more extensive DoF at any given aperture. Such differences can be reduced to the principle of always using the best tool for the job. If shallow DoF is often a preference, then the larger format camera may be the best choice.
The 4/3rds format was designed to 'take on' the the 35mm format by capitalising on the superior quality of Zuiko lenses. I merely point out, if you want to get wide-angle performance from the 4/3rds format on a par with the D700/14-24/F2.8 combination, you need a Zuiko 7-12/F1.4 lens which is 50% sharper at F1.4, from corner to corner, than the Nikkor lens at F2.8, and 50% sharper at F2.8 than the Nikkor at F5.6.
These conditions are not only to enable equal DoF in all circumstances (except at the smallest apertures) but equal sharpness and low noise performance in low light. In other words, a 12mp 4/3rds camera with 7mm lens at F1.4 and ISO 1600 could produce results comparable to (and perhaps even better than) a D700 with 14mm lens at F2.8 and ISO 6400. Or if that's too extreme, F1.4 at ISO 800 compared with the D700 at F2.8 and ISO 3200.
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You missed the point.
I'm sorry Ray, but to some extent I think you have missed the point.
Not wanting to get into all your DOF calculations and combinations again because they are fundamentally sound in theory, the practical world bites back. For example, a top Olympus lens like the 7-14mm wide open at f4 is sharp, and sharp across to the corners. I don't know much about Nikon lenses, but the Canon 'L' lenses I have used are not as sharp at f2.8 (or f4 if thast is the faster aperture), and even more unsharp at the corners. So it isn't a practical starting point assuming the FF lens is everyday usable at f2.8 just because it has the facility to go one stop faster. Similarly I'd be happy to use an Olympus 12-60mm wide open at f2.8 for a landscape shot, but I wouldn't use a Canon 24-70mm at f2.8 . I'm just saying that 'like for like' is more complicated than the numbers on a page.
Further complicating the issue is the recent Amateur Photographer test that shows the G1 gives finer resolution just plonking a Sigma non-Four Thirds lens on it than a Nikon D3 gives using the same lens. This result was confirmed also using the G1 kit lens. So at the very least it implies that there is a choice for Nikon D3 user between taking advantage of shallower DOF, or wanting the image sharper and therefore needing to use an optimal aperture. So again, I'm just saying perhaps in the DOF calculations all the Nikon and Canon aperture ranges should have at least the widest aperture eliminated to get a truer 'like for like' overall performance both in DOF and overall resolution. Its about the camera settings people actually choose to use, and not those they would theoretically like to use.
Steve
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I'm sorry Ray, but to some extent I think you have missed the point.
Not wanting to get into all your DOF calculations and combinations again because they are fundamentally sound in theory, the practical world bites back. For example, a top Olympus lens like the 7-14mm wide open at f4 is sharp, and sharp across to the corners. I don't know much about Nikon lenses, but the Canon 'L' lenses I have used are not as sharp at f2.8 (or f4 if thast is the faster aperture), and even more unsharp at the corners. So it isn't a practical starting point assuming the FF lens is everyday usable at f2.8 just because it has the facility to go one stop faster. Similarly I'd be happy to use an Olympus 12-60mm wide open at f2.8 for a landscape shot, but I wouldn't use a Canon 24-70mm at f2.8 . I'm just saying that 'like for like' is more complicated than the numbers on a page.
Further complicating the issue is the recent Amateur Photographer test that shows the G1 gives finer resolution just plonking a Sigma non-Four Thirds lens on it than a Nikon D3 gives using the same lens. This result was confirmed also using the G1 kit lens. So at the very least it implies that there is a choice for Nikon D3 user between taking advantage of shallower DOF, or wanting the image sharper and therefore needing to use an optimal aperture. So again, I'm just saying perhaps in the DOF calculations all the Nikon and Canon aperture ranges should have at least the widest aperture eliminated to get a truer 'like for like' overall performance both in DOF and overall resolution. Its about the camera settings people actually choose to use, and not those they would theoretically like to use.
Steve
I'm talking about specific Canon and Nikkor lenses, the EF-S 17-55/2.8 and the Nikkor 14-24/2.8, the best in their category. They should be compared with the best equivalent Zuiko lenses in the same category.
Where are the comparisons? If I could get an E-620 with Zuiko 7-14/F4 lens which had nearly the performance of a D700 with 14-24/2.8 lens, I'd do it. I'll sacrifice a small amount of image quality, which might be noticeably only on really large prints (say 24"x32"), for the sake of the lighter weight.
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That is very misleading, because the image used from the 14mm lens in 4/3 is only half the width and height of that from the 14mm lens in 35mm format, so when printed at the same size, it must be enlarged twice as much. That extra enlargement doubles out of focus effects too, and so gives half as much DOF as 14mm in the larger format, and also a very different FOV, if comparing with equal f-stop.
But on the other hand, doubling focal length from 14mm to 28mm at equal f-stop reduces DOF by a factor of four (it goes with the square of focal length.) And doubling f-stop doubles DOF (with same focal length same degree of enlargement.)
So, doing the comparison sanely, viewing equal sized images of the same subject from the same distance:
- 14mm in 4/3 has half the DOF of 14mm in 35mm at the same f-stop
- 28mm in 35mm format has one quarter the DOF of 14mm in 35mm format at the same f-stop
- 28mm in 35mm format has twice the DOF of 28mm in 35mm format at half the f-stop
and thus
- 14mm in 4/3 has twice the DOF of 28mm in 35mm at the same f-stop
- 14mm in 4/3 has the same DOF of 28mm in 35mm at twice the f-stop. E.g 14mm f/4 in 4/3 vs 28mm f/8 in 35mm.
The last is my rule of thumb, doubling focal length and f-stop for equal FOV and equal DOF (and equal diffraction effects.)
Hopefully we will not now return to debating whether it is more reasonable to compare images with completely different field of view from the different formats, or to compare crops to equally sized portions of the differently sized sensors!
I think you misunderstood my meaning. All I meant was that, quite simply, regardless of format or field of view, a 14mm lens is a 14mm lens and will have the same dof at a given aperture as any other 14mm lens. Naturally, format and field of view affect how that relates to the actual image captured, but that basic understanding is quite helpful to most (it certainly was to me) rather than misleading. It's an awareness to build from.
Also, Ray, in your goal to compare to the BEST zuiko lenses in their category, the 7-14 is certainly appropriate, but the 14-35 f2, undisputedly the top normal zoom for 4/3, is curiously absent? And are either of these top-end lenses you mention stabilized for optimal low-light performance? It's something to take into account.
As for my stake in all this, I shoot Pentax, still have an old, beaten up Oly E-330, and know that I get better low-light performance but have to be more careful with dof with my Pentax than I did with my Oly, and if I were shooting with a FF model that would be true of it over my Pentax. Like 250swb, I think just a little too much is being made here of dof calculations and equivalence. The real question is, does it allow you to get the images you want?
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My interest is in getting the best performance possible within the parameters of reasonable cost, reasonable weight and and reasonable convenience of use. I'm not interested in sacrificing a noticeable and significant loss of image quality for the benefit of a noticeable and significant loss of weight.
Fine: and for some one like you who is willing to buy and use heavier, more expensive lenses and bodies, larger formats have a natural advantage; there is no need for fancy, detailed comparisons to show the well-known benefits of larger aperture diameters and such in some situations! And there is also no point to comparing those heavy, expensive larger format options to a Four Thirds body equipped with cheapest, lightest f/3.5-4.5 entry level 4/3 lens options either! (For example, my 4/3 lenses are f/2.8-3.5.)
But do not pretend that you are "not interested in sacrificing a noticeable and significant loss of image quality for the benefit of a noticeable and significant loss of weight", especially when cost is also acknowledged as a factor. Some of your gear choices clearly involve trade-offs on quality. For example, getting your 400mm focal length using a zoom lens that offers only f/5.6 at 400mm rather than say a Canon 400/4 or 400/2.8, and struggling to get longer focal lengths with TC's that kill AF. And on the cost limit there is the understandable fact that you do not augment your 35mm format gear with DMF for the higher resolution and such.
It is just matter of where we draw the line on size, weight and cost, not pretending such factors are "beneath us" in our gear choices. And since getting a lot of my favorite images involves hauling telephoto-capable gear on hikes, my trade-offs are different than yours.
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Also, Ray, in your goal to compare to the BEST zuiko lenses in their category, the 7-14 is certainly appropriate, but the 14-35 f2, undisputedly the top normal zoom for 4/3, is curiously absent? And are either of these top-end lenses you mention stabilized for optimal low-light performance? It's something to take into account.
I'm not familiar with all Zuiko lenses, but the 14-35/F2 would seem to be a good match for the EF-S 17-55/F2.8 IS, having just done a Google search. Trouble is, an E-620 with Zuiko 14-24/F2 is just as heavy as a 50D and EF-S 17-55/2.8 IS. It's also slightly more expensive than the Canon set-up. One would therefore expect image quality to be at least as good, on balance.
I wonder if it is.
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I think you misunderstood my meaning. All I meant was that, quite simply, regardless of format or field of view, a 14mm lens is a 14mm lens and will have the same dof at a given aperture as any other 14mm lens.
I understood perfectly: but that comparison only applies when one compares images with different angular FOV from the different lenses, and this is almost certainly not what people are asking about when they ask about how to compare DOF between different formats, which is why I called it "misleading" (not false). Especially since you did not mention the different FOV difference involved in that comparison.
DOF scales and tables are routinely compute using a "maximum acceptable circle of confusion" that increases roughly in proportion to format size, and for good reasons of allowing for the different degree of enlargement typically used with different formats. Without considering degree of enlargement in DOF reckoning, one is effectively debating the DOF to be seen on contact prints, or equivalently irrelevant stuff.
Your response is exactly what I was referring to in my final comment that
"Hopefully we will not now return to debating whether it is more reasonable to compare images with completely different field of view from the different formats ..."
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For me, the f/2 zooms are an irrelevant indulgence of the 4/3 system: larger formats are probably a better solution when one needs aperture diameters that large. Meaning 24x36mm, not the baby step up to EF-S.
P.S. Not that I am saying there is no good reason for anyone to buy and use them, just that they are not relevant to my approach to choosing a camera system and format, and not to the vast majority of Four Thirds users, I suspect.
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But do not pretend that you are "not interested in sacrificing a noticeable and significant loss of image quality for the benefit of a noticeable and significant loss of weight", especially when cost is also acknowledged as a factor. Some of your gear choices clearly involve trade-offs on quality. For example, getting your 400mm focal length using a zoom lens that offers only f/5.6 at 400mm rather than say a Canon 400/4 or 400/2.8, and struggling to get longer focal lengths with TC's that kill AF. And on the cost limit there is the understandable fact that you do not augment your 35mm format gear with DMF for the higher resolution and such.
BJL,
I'm not pretending. My attitude towards the 400mm problem is perfectly consistent with my previous statement, ie. "...best performance possible within the parameters of reasonable cost, reasonable weight and and reasonable convenience of use. I'm not interested in sacrificing a noticeable and significant loss of image quality for the benefit of a noticeable and significant loss of weight."
The 100-400/F5.6 IS is the only option avaialble that fits those parameters. There's simply no other lens available, whether Canon or Nikon. I might be prepared to accept the extra 1/2Kg weight of the 300/2.8 IS, but not the extra weight plus the extra cost (A$6,500 street price). The Canon 400/F4 DO IS is no heavier than the 100-400/F5.6 and would be an ideal replacement and upgrade, but the cost is ridiculous (A$8-9,000).
As regards 400mm options, I'm stuck.
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BJL,
My attitude towards the 400mm problem is perfectly consistent with my previous statement, ie. "...best performance possible within the parameters of reasonable cost, reasonable weight and and reasonable convenience of use.
...
As regards 400mm options, I'm stuck.
Right, so it comes down to different standards of reasonable, based on different standards of portability as well as cost. Which is why your insertion of the EF-S 17-55/2.8 into a comparison against far less expensive and lighter Four Thirds gear makes little sense: that is beyond the ``reasonable'' price limits of most DSLR users.
As to being stuck for 400m options: you need to think in terms of FOV, not focal lengths. Maybe a shorter, brighter[1] lens with a sensor of higher resolution[2] would be a better option! The sensor rather than the body might be your main barrier in telephoto performance.
Notes:
(1) "brighter" is the wonderful name used in parts of Europe for a lens of lower minimum f-stop: more accurate than "faster" when comparing different formats.
(2) resolution of the "electronic emulsion", in l/mm or pixels per mm or whatever.
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I understood perfectly: but that comparison only applies when one compares images with different angular FOV from the different lenses, and this is almost certainly not what people are asking about when they ask about how to compare DOF between different formats, which is why I called it "misleading" (not false). Especially since you did not mention the different FOV difference involved in that comparison.
DOF scales and tables are routinely compute using a "maximum acceptable circle of confusion" that increases roughly in proportion to format size, and for good reasons of allowing for the different degree of enlargement typically used with different formats. Without considering degree of enlargement in DOF reckoning, one is effectively debating the DOF to be seen on contact prints, or equivalently irrelevant stuff.
Your response is exactly what I was referring to in my final comment that
"Hopefully we will not now return to debating whether it is more reasonable to compare images with completely different field of view from the different formats ..."
That's the thing: I'm not talking about comparing between different fields of view and formats or not. I'm not talking about comparing anything. I'm talking about a law of optics. A 14mm lens is a 14mm lens and has a given dof for a given aperture at a given focussing distance and that's that. I think you would agree with that. Your points about fov and degree of enlargement are perfectly valid as far as I can tell, and I'm happy to agree with them. But that basic law is, as stated, constant between formats. Things like acceptable circle of confusion and degree of enlargement come after that basic fact. No comparisons needed.
It's easy to use it to make a comparison, if you wish: you say "well, my 50mm lens on my 35mm camera gives me a certain amount of dof at f2.8. Since I would use a 25mm lens on 4/3 to get the same angle of view, and 25mm lenses have more dof at f2.8 than 50mm lenses have at f2.8 due to their shorter focal length, I will have more dof using the 25mm lens at f2.8 on 4/3 than the 50mm at f2.8 on 35mm." It's that simple, and it's true, as I can attest having used both formats extensively and observed the results. If something in your arguments about degree of enlargement and "acceptable circle of confusion" applies to prints smaller than poster-size, I have yet to see it, having made great looking 11x14s from 4/3 with lenses at a variety of focal lengths and apertures, and having seen poster prints that look quite good as well. Hardly contact sheets.
It's also useful if you want to compare how much increase in dof you'd get by putting that 50mm lens on your 4/3 camera and shooting it at f2.8: the short answer is, at the same focusing distance, you wouldn't, since according to the simple law I described it's constant. Of course, given that you'd then have a much narrower fov, you'd have to back up to get a similar composition to what you had before, and therefore your focusing distance increases, resulting in greater dof. So there is no increase in dof if focusing distance is kept constant, but there is if the composition is kept approximately constant (obviously perspective will be altered).
I don't know how you're expecting your technical side-arguments to help the OP. The things I'm saying here are not misleading or hard to understand. They're quite simple and based on my direct experience in conjunction with a basic understanding of how optics work. I've never bothered with a dof calculator (I can see with my own eyes whether or not I have sufficient dof at a given aperture) but I have made plenty of prints.
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As to being stuck for 400m options: you need to think in terms of FOV, not focal lengths. Maybe a shorter, brighter[1] lens with a sensor of higher resolution[2] would be a better option! The sensor rather than the body might be your main barrier in telephoto performance.
I do think in terms of FoV. My current 100-400 has the FoV of a 640mm lens on FF 35mm, and my 50D is amongst the highest pixel densitiy DSLRs available, with the exception of the 12mp 4/3rds cameras.
I'm not aware of any Zuiko options that would either equal the performance of the 100-400/F5.6 with a substantial savings in weight, or exceed the performance of the 100-400 without a substantial increase in both weight and cost.
The Zuiko ED 90-250/2.8 certainly has the advantage with regard to speed, but it's doubful that a 12mp image from a 500mm (35mm equivalent) lens would be sharper than a 15mp image from a 640mm lens. Even if the Zuiko were marginally sharper, the additional weight and cost (compared with the 100-400) could not be justified. (3.2Kg and A$7-8,000 as opposed to 2Kg and A$2,000).
As I said, I'm stuck
Right, so it comes down to different standards of reasonable, based on different standards of portability as well as cost. Which is why your insertion of the EF-S 17-55/2.8 into a comparison against far less expensive and lighter Four Thirds gear makes little sense: that is beyond the ``reasonable'' price limits of most DSLR users.
The differences in price and weight between the EF-S 17-55/2.8 and the cheaper Zuiko zooms of equivalent focal length are trivial compared to the differences between the Zuiko 90-250/2.8 and the Canon 100-400 IS. I could be wrong, because there's a dearth of rigorously conducted comparisons on the internet, but I get a clear impression that the cheaper and lighter 4/3rds equivalents never quite match the image quality of the slightly heavier and more expensive Canon combinations. If you want to equal and, hopefully, even exceed the quality of the Canon equivalent, you end up with a 4/3rds system which is heavier and more expensive than the Canon equivalent. Right?
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That's the thing: I'm not talking about comparing between different fields of view and formats or not. I'm not talking about comparing anything. I'm talking about a law of optics. A 14mm lens is a 14mm lens and has a given dof for a given aperture at a given focussing distance and that's that. I think you would agree with that.
Your point is a point worth making for the sake of clarity, and it's a point that needs to be understood before embarking upon any DoF/FoV/FL comparisons. But the fact remains, for the practicing photographer, the resulting print or displayed image, is always, without exception, a specific composition which, of necessity, has a specific field of view.
Whether you acheive that FoV by selecting a lens of an appropriate focal length, or cropping during post-processing, is up to you. If maximum detail and sharpness is your priority, then maximising the 'real estate' of your sensor through use of the most appropriate FL, is the way to go; hence the popularity of zoom lenses.
Another point worth mentioning in relation to this, is that of image circle. Whilst a 14mm lens is a 14mm lens, the diameter of the usable image circle may vary considerably. If one were to fit the Canon EF-S 10-22mm to the Nikon D700 and take a shot at 14mm, then compare it with a shot of the same scene taken with the Nikkor 14-24 at 14mm (same aperture), you'd probably get a shock .
The images might appear to be about equally sharp in the centre of the frame (with equal DoF if you're lucky), but long before you'd reached the edge of the 35mm frame, the EF-S 10-22 would look like crap. DoF considerations in those areas close to the edge of the frame are irrelevant. Image quality is so poor.
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The differences in price and weight between the EF-S 17-55/2.8 and the cheaper Zuiko zooms of equivalent focal length are trivial compared to the differences between the Zuiko 90-250/2.8 and the Canon 100-400 IS. I could be wrong, because there's a dearth of rigorously conducted comparisons on the internet, but I get a clear impression that the cheaper and lighter 4/3rds equivalents never quite match the image quality of the slightly heavier and more expensive Canon combinations. If you want to equal and, hopefully, even exceed the quality of the Canon equivalent, you end up with a 4/3rds system which is heavier and more expensive than the Canon equivalent. Right?
Not on the budget end, you don't. The Olympus kit zooms (14-42 and 40-150) are easily some of the best kit zooms available, and they're tiny. I'd pit them against the current Canon kit zoom (admittedly pretty nice) any day, and there's really no comparison with the older non-IS 18-55. Then there's the Olympus 70-300, which is pretty competent even if not amazing, as opposed to the Canon 75-300, which I've only ever heard moaning and complaining about.
Another interesting comparison, at the other end of the price spectrum, might be the Zuiko 300mm f2.8 against the Canon 400mm 2.8.
Your point is a point worth making for the sake of clarity, and it's a point that needs to be understood before embarking upon any DoF/FoV/FL comparisons. But the fact remains, for the practicing photographer, the resulting print or displayed image, is always, without exception, a specific composition which, of necessity, has a specific field of view.
Whether you acheive that FoV by selecting a lens of an appropriate focal length, or cropping during post-processing, is up to you. If maximum detail and sharpness is your priority, then maximising the 'real estate' of your sensor through use of the most appropriate FL, is the way to go; hence the popularity of zoom lenses.
Another point worth mentioning in relation to this, is that of image circle. Whilst a 14mm lens is a 14mm lens, the diameter of the usable image circle may vary considerably. If one were to fit the Canon EF-S 10-22mm to the Nikon D700 and take a shot at 14mm, then compare it with a shot of the same scene taken with the Nikkor 14-24 at 14mm (same aperture), you'd probably get a shock .
The images might appear to be about equally sharp in the centre of the frame (with equal DoF if you're lucky), but long before you'd reached the edge of the 35mm frame, the EF-S 10-22 would look like crap. DoF considerations in those areas close to the edge of the frame are irrelevant. Image quality is so poor.
Have I ever said anything to the contrary? You could simply have added your point for further clarification. Making it sound like you're correcting something I said is unnecessary.
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Not on the budget end, you don't. The Olympus kit zooms (14-42 and 40-150) are easily some of the best kit zooms available, and they're tiny. I'd pit them against the current Canon kit zoom (admittedly pretty nice) any day, and there's really no comparison with the older non-IS 18-55. Then there's the Olympus 70-300, which is pretty competent even if not amazing, as opposed to the Canon 75-300, which I've only ever heard moaning and complaining about.
Another interesting comparison, at the other end of the price spectrum, might be the Zuiko 300mm f2.8 against the Canon 400mm 2.8.
It's very rare to see any comparisons between 4/3rds camera-and-lens combinations and the Canon equivalents. The Canon 70-300 is designed for full frame 35mm, isn't it? A better comparison might be between the Panasonic Lumix 45-200 for the G1 and the Canon EF-S 55-250 IS.
I'm sure it's possible to find a 4/3rds camera/lens combination which is not only lighter and cheaper than the nearest Canon equivalent, but delivers image quality on a par with the Canon and perhaps even slightly better. However, at this stage, the highest pixel density Canon, the 50D, has a slight resolution advantage. Photozone results show the EF-S 55-250 IS, tested on the 50D, as being sharper, in terms of LW/PH at 50% MTF, than the Lumix 45-200 on the G1, particularly at it's widest angle of 55mm, which is fairly close to 45mm on a 4/3rds sensor.
One should also bear in mind that 4/3rds DSLRs in general seem to have up to a stop worse performance at high ISO (than Canon APS-C). This can be a disadvantage with a long telephoto. I often find that I need to increase ISO to 1600, and even ISO 3200, when using my 100-400 IS at 400mm.
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A 14mm lens is a 14mm lens and has a given dof for a given aperture at a given focussing distance and that's that.
DOF is not a property of a lens alone, or of a focal length and f-stop combination alone. DOF is a property of final viewed images, like prints of a given size viewed at a given distance, and so varies with degree of enlargement and such. The same image enlarged to different degrees and then viewed from the same distance (which is quite likely if different crops are used and then enlarged by different degrees so as to get equal print sizes) will have different DOF. So when the the use of different format makes it likely that a different degree of enlargement will be made, that cannot be ignored in reckoning about DOF.
As an extreme case, have you ever tried to judge DOF from a contact sheet made from 35mm film? Usually, those tiny prints look to be in focus everywhere, but final prints look otherwise.
All that you know from focal length, f-stop and focus distance is how large the circle of confusion (OOF blurring) will be on the sensor or film for the part of the image coming from an object at a certain distance in front of or behind the plane of critical focus. How large that CoC on-sensor can be before it causes a perception of being OOF for the viewer of a print cannot be determined from that information alone; extra information like the degree of enlargement and viewing distance (or at least the ratio of those two) are essential.
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My current 100-400 ... The Zuiko ED 90-250/2.8 ...
We seem to have wandered very far indeed from the lenses relevant to the original comparison, which were small, inexpensive kit zooms for Four Thirds and Micro Four Thirds! I am glad though that you are following my advice of using a smaller, higher resolution sensor instead of a TC with a f/5.6 lens!
P. S. In my kit, my closest match for the 100-400/4-5.6 would be my 50-200/2.8-3.5 used with and without 1.4x TC, though effectively 2/3 stop slower. But if you are comparing super-telephoto options for Four Thirds, you might want to check out the Sigma options too. The Sigma 70-200/2.8 with and without 1.4x or 2x TC's offers similar speed/FOV options to the 100-400/4-5.6. There are also some extreme options like a 50-500/4-6.3 for about US$1100, or a 300-800/5.6 for the price of a small car. What would be more interesting for me though would be if the Sigma 100-300/4 (about US$1100) were offered in Four Thirds mount. For now that is available for Four Thirds bodies only in a clumsy manual focus form, via the Nikon mount version used with a lens mount adaptor. (Never mind the need for stop-down metering; I would probably not be stopping down often with that "600mm, f/8 equivalent"!) To be more ambitious, the Sigma 120-300/2.8 (US$2,900) would be tempting; it is supposedly as sharp as the Sigma 300/2.8 prime, and about the same price and weight.
I would expect that with the Four Thirds sensor using only the central 1/4 of the image area, IQ would be fairly good with these telephotos, except maybe the 50-500.
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We seem to have wandered very far indeed from the lenses relevant to the original comparison, which were small, inexpensive kit zooms for Four Thirds and Micro Four Thirds! I am glad though that you are following my advice of using a smaller, higher resolution sensor instead of a TC with a f/5.6 lens!
I've been through this exercise before. In the absence of direct and competently executed comparisons, I find it difficult to make any decision when it comes to opting for a different system, or going to the expense of adding yet another system to what I currently use. I also think it's reasonable to suppose that the true reason why there are no comparisons between 4/3rds camera/lens combinations and Canon APS-C and FF systems (apart from Dpreview comparisons using a standard lens), is because there's nothing to shout about regarding 4/3rds' performance. In other words, you get what you pay for. If a particular 4/3rds camera and lens is lighter and cheaper than the Canon equivalent, it probably produces at least slightly worse image quality, on balance. If the performance is noticeably better than the Canon equivalent, the 4/3rds' system is likely to be more expensive and heavier.
I notice that Photozone have tested the Panasonic 14-45 & 45-200 with the G1. There's a very close Canon equivalent in terms of price, focal length range, maximum aperture, price and weight. It's the Canon 500D with EF-S 18-55 IS and EF-S 55-250 IS. Photozone have tested both of these EF-S lenses using the 50D which has the same pixel count as the new 500D. Photozone advises against comparing systems because of issues of AA filter strength, pixel count and choice of RAW converter. However, I think it would be reasonable to assume that the image quality from the 500D will be very similar to that of the 50D.
The Australian price of the G1 with both kit lenses is slightly greater than the kit price for the 500D with the two EF-S lenses, about A$50-100 greater comparing a range of internet prices.
On the other hand, the G1 with both lenses is 115gms lighter than the 500D with its two kit lenses. Neither $100 nor 100gms either way, is likely to influence my buying decision by itself.
Comparing the Photozone results for these 2 lenses using the G1, with the two EF-S lenses using the 50D, the Canon lenses, on balance, produce better results. There are a few intances where the EF-S lenses are significantly sharper (the 55-250 at 55mm), and a couple of instances where the Panasonic lenses are significantly sharper (at full aperture at 14mm and 18mm, but only in the centre). The EF-S 55-250 is sharper at all apertures and focal lengths tested, although not always significantly sharper. Both EF-S lenses are sharper at the edges at all apertures and focal lengths tested. The Panasonic lenses seem to have a fairly severe vignetting problem. At 200mm, edge performance is abysmal on the Lumix G 45-200, at all apertures tested, including F11.
In my kit, my closest match for the 100-400/4-5.6 would be my 50-200/2.8-3.5 used with and without 1.4x TC, though effectively 2/3 stop slower.
You mean, the 50-200/2.8-3.5 with 2x converter, don't you?
But if you are comparing super-telephoto options for Four Thirds, you might want to check out the Sigma options too. The Sigma 70-200/2.8 with and without 1.4x or 2x TC's offers similar speed/FOV options to the 100-400/4-5.6. There are also some extreme options like a 50-500/4-6.3 for about US$1100, or a 300-800/5.6 for the price of a small car. What would be more interesting for me though would be if the Sigma 100-300/4 (about US$1100) were offered in Four Thirds mount. For now that is available for Four Thirds bodies only in a clumsy manual focus form, via the Nikon mount version used with a lens mount adaptor. (Never mind the need for stop-down metering; I would probably not be stopping down often with that "600mm, f/8 equivalent"!) To be more ambitious, the Sigma 120-300/2.8 (US$2,900) would be tempting; it is supposedly as sharp as the Sigma 300/2.8 prime, and about the same price and weight.
All comparisons I've seen between different lenses with and without converter, suggest that the shorter focal length with the converter is not as good as the longer focal length without converter. For example, the excellent and highly regarded Canon EF 70-200/F2.8 IS with 2x converter is not as good as the humble 100-400 IS at 400mm.
I've come across lots of glowing reports of the Canon 300/2.8 IS, supposedly one of the best lenses that Canon produce. Yet I've never come across a direct comparison between the 300/2.8 IS with 1.4x extender and the 100-400 at 400mm. Why is that? Have I not been searching hard enough? Again, it's a reasonable assumption that the reason there are no comparisons is because there's nothing to shout about. The 300/2.8 with 1.4x extender is probably very marginally sharper in the centre than the 100-400 IS, and very marginally less sharp at the edges. No big deal either way. If you already own a 300/2.8 IS, then it's probably not worth getting a 100-400. However, if one already owns a 100-400, then going to the expense of getting a 300/2.8 in order to improve upon the 100-400, doesn't make much sense.
I'm really only interested in significant leaps in quality, such as that offered by the D700/14-24/2.8 combination compared with the 5D/Sigma 15-30.
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You mean, the 50-200/2.8-3.5 with 2x converter, don't you?
For the rough equivalence I was talking about, either 1.4X or 2X, depending on how one adjusts for the difference in format and sensor size. If there were a 1.7x TC for 4/3, I would have mentioned that instead!
400mm on EF-S gives the FOV of 640mm in 35mm format while 200mm with 1.4x on 4/3 gives "560mm FOV" and with 2x it is "800mm FOV". Decide for yourself which is closer to equivalent.
And after all, we are "really only interested in significant leaps in quality", so the modest differences in pixel count and such should not matter!
As to the disadvantage of TC's; that is one reason why for telephoto work, I prefer using smaller pixels and cropping! Another is "loose framing" with moving subjects like birds in flight: deliberately choosing a focal length too short to fill the frame with the desired image of a moving subject, so that even if subject movement prevents me from positioning the subject as I want it in the frame, cropping can tidy that up.
Anyway, you have certainly dragged this discussion very far from the original question of
"will there be an inherent increase in depth of field for a given f-stop" and
"Would there be such things as 'f-stop equivalents' between micro four-thirds and APS-C sensors?"
onto the irrelevant and "well-worn to the point of thread-bare" subject of why you personally prefer Canon DSLR gear to Four Thirds, with the usual subject-changing segue of "let's us ignore the desire for adequate DOF and look instead at the low DOF and low light advantages of using bigger, heavier, and typically more expensive lenses", often accompanied by the misrepresenting these as effects of larger sensors rather of larger aperture diameters." I will try to say nothing more on that topic ... in this thread at least!
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DOF is not a property of a lens alone, or of a focal length and f-stop combination alone. DOF is a property of final viewed images, like prints of a given size viewed at a given distance, and so varies with degree of enlargement and such. The same image enlarged to different degrees and then viewed from the same distance (which is quite likely if different crops are used and then enlarged by different degrees so as to get equal print sizes) will have different DOF. So when the the use of different format makes it likely that a different degree of enlargement will be made, that cannot be ignored in reckoning about DOF.
As an extreme case, have you ever tried to judge DOF from a contact sheet made from 35mm film? Usually, those tiny prints look to be in focus everywhere, but final prints look otherwise.
All that you know from focal length, f-stop and focus distance is how large the circle of confusion (OOF blurring) will be on the sensor or film for the part of the image coming from an object at a certain distance in front of or behind the plane of critical focus. How large that CoC on-sensor can be before it causes a perception of being OOF for the viewer of a print cannot be determined from that information alone; extra information like the degree of enlargement and viewing distance (or at least the ratio of those two) are essential.
Is that not referred to as "apparent" depth of field? Given that we're not limited to printing at contact sheet size, or any other size for that matter, I'd say that that's less of an issue than the actual "circle of confusion" (I've never really bothered to learn the exact technical terms for any of these). So it's the "circle of confusion" and not the dof that will remain constant? Fine. That's still what I was talking about.
So what you seem to be saying is that 4/3 format has no dof advantage at equal angles of view and apertures, and enlarged to equal print sizes? Hmm... I guess that would also seem to throw the idea that you can't achieve sufficient subject isolation with 4/3 due to excessive dof...
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Is that not referred to as "apparent" depth of field? Given that we're not limited to printing at contact sheet size, or any other size for that matter, I'd say that that's less of an issue than the actual "circle of confusion" ...
It is the unique established meaning for "depth of field": look up "depth of field" up in any good reference work on photography, though the effect of degree of enlargement is sometimes hidden in the talk of adjusting the "maximum circle of confusion size deemed to be in focus" with format size. The sensor circle of confusion sizes tell us the degree of OOF effects at various parts of the image, but it does not give any dividing line between "in focus" and "out of focus"; DOF depends on print circle of sensor sizes.
One exception is those "digital DOF radicals" who deem an image to be OOF wherever the CoC is larger than the resolution scale of the sensor, so that OOF effects can be seen with sufficiently large prints or sufficiently close pixel peeping. But that is a very different criterion than the established one. For one thing, that radical version of DOF then varies if one uses films or sensors of different resolution with the same focal length and same aperture in the same format.
So what you seem to be saying is that 4/3 format has no dof advantage at equal angles of view and apertures, and enlarged to equal print sizes?
Not at all: reread my first post in this thread: http://luminous-landscape.com/forum/index....st&p=275028 (http://luminous-landscape.com/forum/index.php?showtopic=33678&view=findpost&p=275028)
At equal angle of view, focus distance, aperture ratio and print size, the DOF is greater in 4/3 than in APS-C formats by about 2/3 of a stop, and about two stops greater than in 35mm format. At equal aperture ratio, the shorter focal length used to get equal angle of view in a smaller format decreases CoC sizes at the focal plane by more than enough to offset the greater degree of enlargement. Approximately, sensor CoC varies inversely with the square of focal length and in inverse proportion to aperture ratio, and then print CoC grows in proportion to degree of enlargement, judged from equal print viewing distance. This adds up to print CoC being approximately in proportion to the effective aperture diameter (focal length divided by aperture ratio) for any combination of focal length and degree of enlargement used to get a print of the same size covering the same angle of view.
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.... with the usual subject-changing segue of "let's us ignore the desire for adequate DOF and look instead at the low DOF and low light advantages of using bigger, heavier, and typically more expensive lenses", often accompanied by the misrepresenting these as effects of larger sensors rather of larger aperture diameters."
I've never ignored the DoF implications in this thread or any other thread where DoF has been an issue. As a matter of fact, I usually prefer not to aim for the shallowest of DoFs where the larger format usually has the advantage. I use fast lenses mainly for low light situations and would prefer more DoF rather than less.
A point I didn't mention about the Photozone tests of the two comparable sets of lenses, is that the EF-S lenses at F8 and F11 always outperform the Panansonic lenses to some degree.
If one were to assume that the 4/3rds system would produce similar DoF at F8 to the EF-S lenses at F11 and therefore maybe slightly sharper results because F8 is usually a sharper aperture than F11, one would be wrong in the case of these examples. On balance the EF-S lenses at F11 are about as sharp in the centre as the Panasonic lenses are at F8 in the centre. That is partly due to the fact that we're comparing a 15mp sensor with a 12mp sensor. However, at F11 the EF-S lenses have significantly better edge performance than the Panasonic lenses have at F8.
If your goal is achieve the maximum DoF consistent with an acceptably sharp image from corner to corner, the 500D/EF-S 18-55/55-250 system will produce better results than the Micro 4/3rds G1/14-45/45-200 system, according to Photozone tests.
Just trying to get at the facts, BJL .
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A point I didn't mention about the Photozone tests of the two comparable sets of lenses, is that the EF-S lenses at F8 and F11 always outperform the Panansonic lenses to some degree.
Ray, this thread was not about the IQ of those entry level Panasonic Micro Four Thirds lenses; it was about DOF comparisons, and the fact for example that equal DOF is achieved at apertures about 2/3 stop lower in 4/3 than with EF-S. The Panasonic lenses are by all accounts the least good of all Four Thirds standard zooms, so not of much interest to me for performance comparisons.
And I do wonder why you choose those atypically small apertures for your comparisons. Remember the lower f-stops typically used with smaller formats: with Four Thirds, the old slogan translates as "f/4 and be there"!
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Ray, this thread was not about the IQ of those entry level Panasonic Micro Four Thirds lenses; it was about DOF comparisons, and the fact for example that equal DOF is achieved at apertures about 2/3 stop lower in 4/3 than with EF-S. The Panasonic lenses are by all accounts the least good of all Four Thirds standard zooms, so not of much interest to me for performance comparisons.
And I do wonder why you choose those atypically small apertures for your comparisons. Remember the lower f-stops typically used with smaller formats: with Four Thirds, the old slogan translates as "f/4 and be there"!
BJL,
Would you rather have endless discussion based upon unreliable and biased subjective opinion from people who are in love with their equipment, or a sound analysis of objective reports? Whether or not the Panasonic lenses designed for their micro-4/3rds system are typical of budget 4/3drs' lenses in general seems a matter of speculation. I've chosen to compare these Panasonic lenses with their EF-S equivalents because I can find no other objective comparisons on the internet. If you are in possession of other tests, on the same level as Photozone's, which allow for a meaningful comparison of equivalent 4/3rds and Canon APS-C systems, then let me know.
I have no particular allegiance to a specific brand of camera. I have an open mind and am always willing to use the best tool for the job, as evidenced by the fact that I bought a D700 because the reported tests and comparisons indicated that the Nikkor 14-24/2.8 zoom was better than, or at least as good as, 14mm primes and certainly better than any Canon wide-angle zoom. However, I would never make such a decision to purchase another system based upon hearsay and rumour. Show me some hard evidence.
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And I do wonder why you choose those atypically small apertures for your comparisons. Remember the lower f-stops typically used with smaller formats: with Four Thirds, the old slogan translates as "f/4 and be there"!
F11 with APS-C format and F16 with full frame 35mm are not atypical for me, and I suspect not atypical for many landscape shooters in circumstances where maximum DoF is sought without serious compromise of resolution.
F4 with 4/3rds simply does not get you to F8 with full frame, if we compare the latest prosumer cameras. A 12mp 4/3rds at any aperture can never provide the same resolution as a 21mp 5D2 at F8 (in terms of LW/PH of course. It's understood that resolution per mm has to be greater in 4/3rds lenses).
However, comparing 4/3rds with Canon APS-C is a different matter. We are then comparing F4 with F5. In the Photozone examples I quoted, there are a couple of instances where the Panasonic 14-45 produces sharper results in the centre, at approximately F4, than the EF-S 18-55 at approximately F5, but still not as sharp at the edges however.
I would not deny that there are a few advantages of the 4/3rds' system. It's just a pity we're so hazy about them.
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Whether or not the Panasonic lenses designed for their micro-4/3rds system are typical of budget 4/3drs' lenses in general seems a matter of speculation.
Try the SLRGear tests of the Oly kit zooms, perhaps? Excellent performers, both... and they will autofocus on the G1 (a little slower, however) with the 4/3 adapter.
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Try the SLRGear tests of the Oly kit zooms, perhaps? Excellent performers, both... and they will autofocus on the G1 (a little slower, however) with the 4/3 adapter.
Since I already have a number of Canon DSLRs, a number of Canon lenses, a D700 and a Nikkor lens, any performance advantage of a 4/3rds' system would have to relate to what I already have, otherwise it wouldn't be reliable or useful for me. The Photozone type of tests seems to lend themselves to direct comparisons of systems, and direct comparisons of lenses if they're tested with the same model of camera. I understand that Zuiko lenses only fit the Panasonic G1 via an adapter and that full functionality is not achieved. That's not an ideal situation. If the Nikkor 14-24 provided full functionality on the 5D, I would not have bought the D700.
SLRGear tests seem to be just standard reviews... the lens is quite sharp wide open...vignetting is quite good... performance drops off towards the long end etc etc. Direct comparisons involving standardised tests, such as MTF at 50% and lines per picture height for a wide range of lenses and equipment, is what's meaningful for me.
If a lens or system is really good, I want to see precisely how good compared with alternative systems. I've always been a bit suspicious of Olympus fanboy claims... 'the camera feels so good in the hands' ... 'the balance is just right'... 'as soon as I picked it up, I knew it was the camera for me'.. etc etc.
But thanks for the SLRGear link .
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BJL,
Would you rather have endless discussion based upon unreliable and biased subjective opinion from people who are in love with their equipment, or a sound analysis of objective reports?
Ray, are you not reading what I said at all? I am not disputing the accuracy of your carefully selected facts about Panasonic's entry level kit lenses for Micro Four Thirds (though as an aside, I am still puzzled by your choice not to quote any comparative data at the larger apertures where lens quality is more typically judged.)
I am disputing the relevance of any such discussion to the subject of this thread, which is DOF comparisons between formats. The discussion is also irrelevant to both your and my equipment choices, since neither of us has much reason to be interested in those lenses. I for example own several f/2.8-3.5 Four Thirds lenses of better quality than those Panasonic entry level models, and you have your far higher level Canon gear. On that topic:
I have no particular allegiance to a specific brand of camera.
No comment!
P. S. On another of your comments: a number of recent FourThirds lenses, the ones designed to work with the CDAF of Live View, apparently give full functionality when used on a Micro Four Thirds body with the adaptor. This is a "smart" adaptor supporting electronic lens-body communication, not merely a mechanical mounting ring that loses AF and aperture control. And no Four Thirds lens suffers the need for stop-down metering that most cross-format lens mount adaptors impose; at worst, AF is impeded.
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I would not deny that there are a few advantages of the 4/3rds' system. It's just a pity we're so hazy about them.
You may be hazy, but at least one is blindingly obvious: smaller size and weight of typical lens and body kits, in a trade-off against low-light performance and such, as is routinely the case with kits using smaller, lighter lenses. The size and weight advantage is clear with mainstream options like the E-420, E-450, E-520, E-620, and now the G1 and GH1, combined with standard grade zoom lenses of f/3.5-5.6 or thereabouts. I would even push this advantage to the Olympus 70-300/4-5.6 compared to any lens offering equal telephoto reach on a larger format. When the lower speed is acceptable (which it is more often with IS), some equal FOV comparisons are:
- Olympus 70-300/4-5.6, 620g, US$360
- Canon 100-300/4-5.6, 1380g, US$1429, effectively about 2/3 stop faster on an EF-S body.
- Canon 70-300/4-5.6 IS (630g US$549) with 1.4xTC (220g, US$290) ... but AF then fails on most Canon bodies, and it is still bulkier and more expensive.
- Canon 70-300/4-5.6 IS (630g US$549) and cropping, accepting the lower resolution: surprisingly this is still more expensive, apparently due to the higher cost in doing IS in-lens rather than in-body.
Far less expensive 70-300's area available for Canon mount, but they lack IS, so compare badly to any 4/3 kit with in-body IS, and still give a heaver and more expensive combination once the TC is added.
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You may be hazy, but at least one is blindingly obvious: smaller size and weight of typical lens and body kits, in a trade-off against low-light performance and such, as is routinely the case with kits using smaller, lighter lenses. The size and weight advantage is clear with mainstream options like the E-420, E-450, E-520, E-620, and now the G1 and GH1, combined with standard grade zoom lenses of f/3.5-5.6 or thereabouts. I would even push this advantage to the Olympus 70-300/4-5.6 compared to any lens offering equal telephoto reach on a larger format. When the lower speed is acceptable (which it is more often with IS), some equal FOV comparisons are:
- Olympus 70-300/4-5.6, 620g, US$360
- Canon 100-300/4-5.6, 1380g, US$1429, effectively about 2/3 stop faster on an EF-S body.
- Canon 70-300/4-5.6 IS (630g US$549) with 1.4xTC (220g, US$290) ... but AF then fails on most Canon bodies, and it is still bulkier and more expensive.
- Canon 70-300/4-5.6 IS (630g US$549) and cropping, accepting the lower resolution: surprisingly this is still more expensive, apparently due to the higher cost in doing IS in-lens rather than in-body.
Far less expensive 70-300's area available for Canon mount, but they lack IS, so compare badly to any 4/3 kit with in-body IS, and still give a heaver and more expensive combination once the TC is added.
BJL,
Are you a particularly frail person? I think everyone understands that smaller cameras are lighter than larger cameras. The hazy issue is the extent of the trade-off regarding image quality when one moves from a larger format to a smaller format. There's a claim from 4/3rds' enthusiasts that image quality is not compromised, compared with Canon APS-C. I've even seen claims on this forum that the E-3 is sharper than the Canon 5D.
What is very frustrating with this issue is that very few direct system comparisons are available on the internet. I found one comparison on the Photozone site, but it didn't include Zuiko lenses.
This is my point. I'm surprised you did not immediately understand this.
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I am disputing the relevance of any such discussion to the subject of this thread, which is DOF comparisons between formats. The discussion is also irrelevant to both your and my equipment choices, since neither of us has much reason to be interested in those lenses. I for example own several f/2.8-3.5 Four Thirds lenses of better quality than those Panasonic entry level models, and you have your far higher level Canon gear. On that topic:
It's very boring if comments on subject topics abide strictly to the original question. There are always ramifications. Anyone who asks questions about DoF differences between two different formats would surely be interested in the ramifications of such differences.
Getting back to the precise point of the topic, you never responded to my comment that your mathematically precise answer is probably wrong in practice. Canon cropped formats have a mathematical 1 & 1/3rd F stop DoF advantage over full frame. My own tests have confirmed that at close distances, this difference in DoF is actually 2 stops, using the same Zoom lens at different focal lengths.
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BJL,
Are you a particularly frail person?
No, but I am speaking on behalf of photographers who sometimes wish to carry their camera gear all day while hiking over possibly rough or steep terrain, or wandering in a city with something other than photography and load-bearing exercise as the primary goal.
Remember my goal was to answer your question about the existence of some advantages, not a futile effort to persuade you or anyone that 4/3 is superior in all ways to larger formats! I suggest rereading Michael's essay on street photography and the G1.
But there is really not much point in debating the manifest, widespread preference for lighter gear, or the century long and continuing trend in the direction of lighter kits and increased use of smaller formats when portability is an issue, or that in the telephoto realms of wild-life and macro photography, smaller formats offer a substantial and widely popular weight advantage over larger ones.
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... Canon cropped formats have a mathematical 1 & 1/3rd F stop DoF advantage over full frame. My own tests have confirmed that at close distances, this difference in DoF is actually 2 stops, using the same Zoom lens at different focal lengths.
That sounds like what one would see in comparisons at equal PPI (such as in 100% viewing on screen); I am talking instead about comparisons at equal print/display size. The higher pixel count of the larger format means that in an equal PPI comparison, the image from the larger format camera is enlarged more than it would be for an equal print size comparison, increasing the DOF difference.
For eaxmple for the 15MP 50D vs 22MP 5DMkII, the DOF ratio I get is
1.6^2/sqrt(22/15) = 2.1, satisfying close to your "2 stops".
And for the equal print size comparison, it is not just "my theory"; it also follows from the bog-standard DOF formulas as given in numerous texts on photography. All you have to remember is that for equal angle of view and equal print image size, the "circle of confusion" value to use in standard DOF formulas varies in direct proportion to linear format size, as does the focal length.
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That sounds like what one would see in comparisons at equal PPI (such as in 100% viewing on screen); I am talking instead about comparisons at equal print/display size. The higher pixel count of the larger format means that in an equal PPI comparison, the image from the larger format camera is enlarged more than it would be for an equal print size comparison, increasing the DOF difference.
For eaxmple for the 15MP 50D vs 22MP 5DMkII, the DOF ratio I get is
1.6^2/sqrt(22/15) = 2.1, satisfying close to your "2 stops".
And for the equal print size comparison, it is not just "my theory"; it also follows from the bog-standard DOF formulas as given in numerous texts on photography. All you have to remember is that for equal angle of view and equal print image size, the "circle of confusion" value to use in standard DOF formulas varies in direct proportion to linear format size, as does the focal length.
BJL,
How does this formula work? I don't have a 5D2. All my DoF comparisons are between the 5D and the 40D or 50D. If I apply this formula to the 40D vs the 5D, I get 2.56/sqrt(12.7/10.1)=2.56/1.12=2.28 stops. Is that right?
I always compare equal size images. Since I have a wide format printer and fairly low-pixel-count cameras, many of my prints require the image to be interpolated beyond its native resolution.
Here are some DoF comparisons between the 40D and 5D using my 100-400 zoom at 250mm and F8 (40D) and 400mm and F11 (5D). As you can see, there's only a 1 stop difference in DoF with this lens at the particular subject distance focussed upon.
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First, off, I think my previous formulas was wrong: it should have been DOF ratio 1.6*sqrt(22/15)=1.93, and for your 10MP vs 12.7MP case, 1.6*sqrt(12.7/10)=1.8, a difference of 1/7 stops. But now that I read your procedure involving up-ressing for very large prints, that traditional approach does not apply, so you have inspired me offer a new one. But the formulas comes out the same! So in your test with a one stop difference the ODF ratio is predicted to be 1.3, or 0.73 stops. Is that close enough to what you see?
Why my new calculation:
I always compare equal size images.
Good: with equal size images, ignore my formula, which was for equal PPI (before upressing).
Since I have a wide format printer and fairly low-pixel-count cameras, many of my prints require the image to be interpolated beyond its native resolution.
That probably makes the tradition DOF reckoning not applicable, as it is based on the assumption of the resolution being high enough that it is not a factor in perception of sharp vs OOF. That is, the resolution length scale on the print is assumed to be substantially smaller than the circle of confusion threshold at which OOF effects are noticeable. Remember that the traditional reference for DOF scales was 5"x7" prints viewed from 10". So to check that guideline of "4/3 stops from 35mm to EF-S", it would be better to use a print size not needing any up-ressing, maybe A4.
But the traditional DOF results that I described are giving the right answer to the wrong question for your situation! Instead you have raised an interesting new question:
When images are viewed at sizes so large that the resolution limits of the sensors are visible (roughly, when up-ressing is needed), how is DOF related to format size, focal length, aperture, degree or enlargement and the underlying resolution of the image?
The answer might be one advocated by Jonathan Weinke (sp.?): the parts of the image that are perceived as out of focus are those where the circles of confusion are noticeably larger than the resolution length scale of the sharpest, fully in-focus parts of the image. So in traditional DOF formulas, the CoC threshold value to use would be roughly the pixel spacing, or some suitable fixed multiple of that.
Computational Details
Assume focal length proportional to linear sensor size, for equal FOV, equal focus distance, equal aperture ratio.
Use numerical values LSS for linear sensor size, PC for pixel count.
The pixel spacing is roughly proportional to LSS/sqrt(PC), so we use a value CoC that is proportional to this. The traditional formula says that the DOF is proportional to
CoC/f^2
so in our case this is proportional to
1/(LSS*sqrt(P))
To compare formats that differ in linear sensor size by ratio LSSR and with pixel counts in ratio PCR, the DOF varies inversely with
LSSR*sqrt(PCR)
which is the formula I used above.
If the aperture ratio is also adjusted in ratio NR, the DOF varies in proportion to
NR/(LSSR*sqrt(PCR))
Example
Comparing the 10MP EF-S 40D to the 12.7MP 35mm 5D, we have LSSR=1.6 and PCR=12.7/10=1.27, so the suggested DOF ratio is
1.6*sqrt(1.27) = 1.8
Close enough to a factor or two, or two stops. To be precise, get stops by taking twice the log of this divided by the log of 2, getting 1.7 stops.
With your difference in aperture by a factor NR=1.4, the DOF is less for the 5D by factor
1.4/(1.6*sqrt(1.27)) = 0.77, or 0.73 stops. Doe that match your observation of "only one stop?"
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Example
Comparing the 10MP EF-S 40D to the 12.7MP 35mm 5D, we have LSSR=1.6 and PCR=12.7/10=1.27, so the suggested DOF ratio is
1.6*sqrt(1.27) = 1.8
Close enough to a factor or two, or two stops. To be precise, get stops by taking twice the log of this divided by the log of 2, getting 1.7 stops.
With your difference in aperture by a factor NR=1.4, the DOF is less for the 5D by factor
1.4/(1.6*sqrt(1.27)) = 0.77, or 0.73 stops. Doe that match your observation of "only one stop?"
Sounds to me, BJL, that you are massaging the maths to fit the observed results.
The impression I get from the relatively few tests I've made relating to this issue, is that the mathematical DoF calculations are merely a guide, possibly hardly more accurate than the 1/FL(35mm) rule for appropriate shutter speed for hand-held shots.
The 100-400 when focussed at a fair distance (about 30m) produces a 1 stop DoF difference between the 40D and 5D, with same FoV. The 50D when focussed at a close distance (about 2 metres) produces a 2 stop DoF difference compared with the 5D, same FoV, same method of comparison on monitor at 100%, same size images, different lens.
Why this should be, is a bit of a mystery to me. The obvious explanation is that I didn't focus accurately with the 5D. It's a possibility, but I did my best. The experiment with the 50D vs the 5D at close focussing distance was not actually made to observe DoF differences, but to observe noise differences. With all the talk about the 50D being a bit noisy, I wanted to test if I made DoF and shutter speed the reference points, which camera would be noisier. That is, how does 50D noise at ISO 100 and F4 compare with 5D noise at ISO 250 and F6.3.
I took several shots at different ISOs and apertures, working up to ISO 3200. The 50D appeared to be very slightly more noisy, although nothing to worry about. However, as a side effect I noticed that the 50D shots had a sharper background. The background was a bookcase with visible book titles. The 1 & 1/3rd F stop difference was not enough to equalise background blur.
In order to be certain about these results with regard to DoF, I would want to repeat the experiment under different conditions. It's a principle of science that results have to be repeatable, many times. I can't spare the time at the moment to do this. I'm building a house. (To help the Australian economy ).
However, in general it does seem to me that there are a number of variables that make a nonsense of the maths. It seems a possibility that different lens designs will affect these DoF differences based only upon format size and pixel count differences. We should also look at the accuracy of the F stop markings on lenses. There are certainly discrepancies in focal length marking on lenses, which are easier to see. F stop inaccuracy is perhaps more difficult to determine. I find it strange, for example, that DXOmark ISO ratings are significantly different from Dpreview's.
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Sounds to me, BJL, that you are massaging the maths to fit the observed results.
This is puzzling: theory should be tested against the facts, as a protection about errors like inaccurate approximtions or false assumptions, and should be revised when the facts point to an error or limitation of the applicability of the theory, like an unjustified assumption. So why are you so cynical when I revise the assumptions of my calculations to take account of the new facts that you presented me with, about viewing conditions that do not fit the assumptions of traditional DOF calculations?
It almost sounds to me as if you prefer you own experiments and observations over any theory, even theory that has been corroborated by many decades of experiments and experience by many competent photographers, so that the canard "mere theory" does not really apply.
Of course, the usual DOF formulas are not exact, for many reasons. Apart from applying to certain assumptions about adequate image resolution, image size, and viewing distance, they fail at very close distance ("macro"), at very large distances (hyper-focal), and they do not always apply to predicting the degree of blurring in highly out of focus backgrounds. The later is often what people are talking about when they talk of seeking very shallow DOF, but it is not quite the same as DOF.
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This is puzzling: theory should be tested against the facts, as a protection about errors like inaccurate approximtions or false assumptions, and should be revised when the facts point to an error or limitation of the applicability of the theory, like an unjustified assumption. So why are you so cynical when I revise the assumptions of my calculations to take account of the new facts that you presented me with, about viewing conditions that do not fit the assumptions of traditional DOF calculations?
It almost sounds to me as if you prefer you own experiments and observations over any theory, even theory that has been corroborated by many decades of experiments and experience by many competent photographers, so that the canard "mere theory" does not really apply.
Of course, the usual DOF formulas are not exact, for many reasons. Apart from applying to certain assumptions about adequate image resolution, image size, and viewing distance, they fail at very close distance ("macro"), at very large distances (hyper-focal), and they do not always apply to predicting the degree of blurring in highly out of focus backgrounds. The later is often what people are talking about when they talk of seeking very shallow DOF, but it is not quite the same as DOF.
I think I probably do prefer my own experiments and observations over a theory that seems less precise than my observations. A theory about DoF relativities amongst different formats should have practical value. I think it's likely that a simple and workable formula that covers all situations doesn't exist. There are probably too many variables to take into consideration. For example, how much variability is there between the accuracy of the F stops on one lens and supposedly the same F stops on another lens on another camera? F5.6 on one lens might actually be F5, and on the other lens F6. Perhaps differences can sometimes be even greater than this.
I imagine that a theory that attempts to predict the DoF differences amongst different formats would be a bit like the theoretical MTF charts of lenses that some manufacturers publish. In practice, the MTF measurements of different copies of the same model of lens can sometimes vary considerably, and none of them might be as good as the manufacturers published charts.
If or when I have the time, I might do some comparisons between the EF-S 10-22 with the 50D and the Nikkor 14-24 with the D700, in preparation for my next photographic trip. I'm curious how centre resolution will compare, although I have no doubt that the Nikkor will have superior edge resolution. Since both cameras have a high resolution Live View screen, there should be no possibility that misfocussing will skew the results.
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I think I probably do prefer my own experiments and observations over a theory that seems less precise than my observations.
As far as I can tell, the formula I offered for your case of "highly enlarged" images does fit with your experiment, so no need to defend your experiments, no matter how poorly designed! By " highly enlarged", I mean enlarged so much that the resolution limits of the camera are visible and even the parts of the image in the plane of critical focus are detectably un-sharp. In particular, situations like 100% pixel peeping, and prints so large that up-sampling ins needed to avoid visible jaggies.
By the way, let me suggest a better experiment, which will give a range of values, or an "error bar" for the result, as all good quantitative experiments should do. Vary the f-stop difference between the two formats and then in image comparisons, judge only whether one image has more DOF, less DOF or about the same DOF. (I.e. do not try to gauge the degree of the DOF difference directly.) This should give a range of f-stop differences over which there is a transition from more DOF to less DOF. Something like "at 2/3 stop difference, the 5D image has less DOF then the 50D image; at 4/3 stop difference it has more DOF, so DOF is equal at an f-stop difference of about one stop, plus or minus 1/3 stop".
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As far as I can tell, the formula I offered for your case of "highly enlarged" images does fit with your experiment, so no need to defend your experiments, no matter how poorly designed! By " highly enlarged", I mean enlarged so much that the resolution limits of the camera are visible and even the parts of the image in the plane of critical focus are detectably un-sharp. In particular, situations like 100% pixel peeping, and prints so large that up-sampling ins needed to avoid visible jaggies.
BJL,
I have assumed that anyone who enquires specifically about DoF differences between different size formats of cameras would want to know the results in an absolute sense. The fact that print or display size and viewing distance can affect the perception of DoF enormously, is a different issue. Answers relating to camera format DoF differences that assume a particular print or display size and/or viewing distance therefore cause confusion, in my opinion. In other words, at a particular print size and/or viewing distance, there may not any DoF differences at all between formats. You can get any result you want by varying print size and view distance.
It therefore only makes sense to pixel-peep such differences. This is one of the legitimate purposes of pixel peeping. If I want to go to the trouble of testing a number of copies of a particular lens before buying, or test different models of lenses with similar focal lengths in order to get the sharpest and best value lens on offer, it would be plain silly to restrict my self to comparisons at, say, A4 print size. If I were to do that, I might arrive at the conclusion that a $500 lens was as sharp as a $5,000 lens and therefore extremely good value.
The fact is, when comparing DoF issues at 100% on the monitor, the differences in sharpness between a 40D, 50D and 5D at the plane of focus are trivial compared with the differences in sharpness in areas of the image that are OoF to varying degrees.
By the way, let me suggest a better experiment, which will give a range of values, or an "error bar" for the result, as all good quantitative experiments should do. Vary the f-stop difference between the two formats and then in image comparisons, judge only whether one image has more DOF, less DOF or about the same DOF. (I.e. do not try to gauge the degree of the DOF difference directly.) This should give a range of f-stop differences over which there is a transition from more DOF to less DOF. Something like "at 2/3 stop difference, the 5D image has less DOF then the 50D image; at 4/3 stop difference it has more DOF, so DOF is equal at an f-stop difference of about one stop, plus or minus 1/3 stop".
This is more or less the procedure I follow and is what I have done in the limited number of tests I've carried out so far. What I have not done is test the DoF characteristics of the same lens (with different formats) when focussed at different distances. You've mentioned that DoF differences between formats break down with macro shots. I suspect they not only behave differently at very close distances, but also at moderately close distances compared with moderately far distances.
Supposing I outline some specific tests that I shall carry out in the next few days, time permitting, and you advise me beforehand what the DoF differences should be according to your formulas. I shall then be in a position to see just how accurate your formulas are .
I propose comparing the Canon EF-S 10-22 on the 15mp 50D, with the Nikkor 14-24 on the 12mp Nikon D700. I shall use Live View for absolutely accurate focussing and I shall compare the DoF of images at 100% on monitor taken at focussing distances of 1 metre, 5 metres and 10 metres, and at focal lengths of 16mm, 20mm and 24mm (35mm format equivalent).
Please post your predictions.
By the way, would you also explain what is happening in the following extract from your previous post; that is, the latter part in bold where you arrive at 0.77 stops. Maths is not my forte.
Example
Comparing the 10MP EF-S 40D to the 12.7MP 35mm 5D, we have LSSR=1.6 and PCR=12.7/10=1.27, so the suggested DOF ratio is
1.6*sqrt(1.27) = 1.8
Close enough to a factor or two, or two stops. To be precise, get stops by taking twice the log of this divided by the log of 2, getting 1.7 stops.
With your difference in aperture by a factor NR=1.4, the DOF is less for the 5D by factor
1.4/(1.6*sqrt(1.27)) = 0.77, or 0.73 stops. Doe that match your observation of "only one stop?"
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I have assumed that anyone who enquires specifically about DoF differences between different size formats of cameras would want to know the results in an absolute sense. ... Answers relating to camera format DoF differences that assume a particular print or display size and/or viewing distance therefore cause confusion, in my opinion.
Firstly, I kindly offered a formula for the different "absolute" terms of comparison that you prefer, and which gives a result that is consistent with your reported observation, so what exactly is your complaint?!
Secondly, it is futile to debate opinions, so I will only point out that your opinion about how people commonly wish to compare DOF is at odds with the opinions of every lens maker that has ever put a DOF scale on a lens, and of every photographic company and author on photography that has published a DOF table, as far as I know. Because more or less universally, those scales are based on describing the DOF at a fixed combination of print size and viewing distance, corresponding roughly to what is sometimes called "normal viewing": a viewing distance equal to print diagonal length. These DOF guides are also easily adaptable to other situations with rules like:
For each doubling of intended print area at equal viewing distance, close down one stop more than the DOF guide suggests, to compensate for the extra 1.4x degree of enlargement. (I believe that Michael discusses some such guideline somewhere on this site.)
or
For a print intended to be viewed at diagonal size greater than viewing distance by an "extra enlargement factor" E, increase the f-stop suggested by the DOF guide by that factor E.
By the way, would you also explain what is happening in the following extract from your previous post; that is, the latter part in bold where you arrive at 0.77 stops. Maths is not my forte.
Your are referring to
get stops by taking twice the log of this divided by the log of 2 ...
1.4/(1.6*sqrt(1.27)) = 0.77, or 0.73 stops. Does that match your observation of "only one stop?"
so I suppose you are asking how I got from the DOF ratoi of 0.77 to the value in stops of 0.73. That is explained in the previous line, as
each stop is a factor of sqrt(2), about 1.4 in aperture ratio and such. I realize now that a simpler formula is this
log(ratio of DOF values)/log(sqrt(2), and computing this time to four significant digits,
1.4/(1.6*sqrt(1.27)) = 0.7764 is the ratio of DOF, and
log(0.7764)/log(sqrt(2))= -0.7303 is the f-stop change corresponding to this DOF: the f-stop change that would equalize DOF.
(The minus sign means that 0.75 stops less DOF is expected, so the larger format would need to stop down by 3/4 stop.)
And since Maths (along with Optics and most of the science behind photography) is not your forte, let me suggest that rather than asking me, or considering this wrongly as debate between my theory and your experiment, you would benefit from studying some established references on photographic optics, whose conclusions and formulas have been experimentally validated on millions of occasions when they are used to predict the DOF that will be given by a given combination of aperture choice and such and such in technical photography, including much recent digital technical photography.
I suspect that if any solidly established and widely used optical formula were as wrong, inaccurate, or unreliable as you seem to suggest, many professional users of photography would have noticed it, and many would have complained publicly before you!
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so I suppose you are asking how I got from the DOF ratoi of 0.77 to the value in stops of 0.73. That is explained in the previous line, as
each stop is a factor of sqrt(2), about 1.4 in aperture ratio and such. I realize now that a simpler formula is this
log(ratio of DOF values)/log(sqrt(2), and computing this time to four significant digits,
1.4/(1.6*sqrt(1.27)) = 0.7764 is the ratio of DOF, and
log(0.7764)/log(sqrt(2))= -0.7303 is the f-stop change corresponding to this DOF: the f-stop change that would equalize DOF.
(The minus sign means that 0.75 stops less DOF is expected, so the larger format would need to stop down by 3/4 stop.)
BJL,
I understand the adjustment that takes into account the different pixel densities and pixel counts of the different formats under consideration, but I don't understand how you got from an initial 2 stop DoF difference to 0.78 or 0.75 DoF difference, which is why I think you are massaging the figures.
Secondly, it is futile to debate opinions, so I will only point out that your opinion about how people commonly wish to compare DOF is at odds with the opinions of every lens maker that has ever put a DOF scale on a lens, and of every photographic company and author on photography that has published a DOF table, as far as I know. Because more or less universally, those scales are based on describing the DOF at a fixed combination of print size and viewing distance, corresponding roughly to what is sometimes called "normal viewing": a viewing distance equal to print diagonal length. These DOF guides are also easily adaptable to other situations with rules like:
These views are now obsolete in relation to the new technology of DSLRs and inkjet printers. The ease and flexibility of producing large prints, or effectively large prints by cropping a small portion of the image and making, say, an A3 print from that small crop, which would effectively be like making a 6x9 Ft print from the whole image, makes a nonsense of the old-fashioned standard of 8x10". Surely we can move on from that standard.
And since Maths (along with Optics and most of the science behind photography) is not your forte, let me suggest that rather than asking me, or considering this wrongly as debate between my theory and your experiment, you would benefit from studying some established references on photographic optics, whose conclusions and formulas have been experimentally validated on millions of occasions when they are used to predict the DOF that will be given by a given combination of aperture choice and such and such in technical photography, including much recent digital technical photography.
You don't need a knowledge of maths or optical science in order to see the differences in sharpness and DoF at various apertures. I'm into photography for the purpose of taking pictures, not for the purpose of constructing grandiose theories in optical science.
I suspect that if any solidly established and widely used optical formula were as wrong, inaccurate, or unreliable as you seem to suggest, many professional users of photography would have noticed it, and many would have complained publicly before you!
They have. A number of MFDB users have noted on this forum that MFDBs seem to produce a shallower DoF compared with 35mm than the formulas would suggest. Others have suggested that it's impossible to get any precise DoF equivalent between formats, and that it's dependent upon focussing distance and lens design.
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... I don't understand how you got from an initial 2 stop DoF difference to 0.78 or 0.75 DoF difference, which is why I think you are massaging the figures.
I never proposed a 2 stop difference for the comparison that your are making between 40D and 5D. Let me summarize my calculations relevant to those cameras.
My first figure in post #3 of this thread was the traditional one relevant to "normal viewing" of images sufficient resolution, and equal aperture ratio, and that was a factor of 1.6 in DOF, or about 1 1/3 stops. That is, using aperture ratios that differ by 1 1/3 f-stop would give about equal DOF under those printing and viewing conditions.
The second calculation in post #52 was instead for equal PPI (better fitting you comparisons of highly enlarged images) and again equal f-stop, and this increased the DOF factor to about 1.8, or about 1.7 stops.
The third calculation also in post #52 was for your experiment with a one stop difference in apertures, which takes a factor of 1.4 off the DOF difference, and subtracts one from the f-stop difference: that is the 0.7764 DOF ratio and 0.73 f-stop difference.
This is simply computing for three different situations from the same well-established scientific basis. Your "massaging the figures" is my "taking account of different situations and data, instead of blindly applying a formula to a situation to which it is not directly applicable, due perhaps to not understanding the science behind the formula, and then declaring that the formula is wrong." A bit like that urban legend, enthusiastically quoted in these forums and many others, that "science has falsely proven that a bee cannot fly", typically used as an excuse for selectively disregarding scientific statements that people wish not to accept.
A number of MFDB users have noted on this forum that MFDBs seem to produce a shallower DoF compared with 35mm than the formulas would suggest.
That is not an error in the traditional formula, but a misunderstanding of when it applies, and of what it does and does not say, as I have already discussed in places like post #58.
To repeat yet again: the standard DOF scales, tables and formulas are for the reference case of comparing prints of equal (and modest) size at equal viewing distance: the traditional reference is 7"x10" prints viewed from 10" I believe. They do not include adjustments for factors like different intended print size, but those can easily be done by someone who makes the modest effort to understand the formula and the science behind it. (Can you tell that I teach science, and hate blind memorization of formulas as a path to misunderstanding and failure?)
When a high resolution image is instead "viewed larger" (larger print size and/or closer scrutiny), the DOF value from the standard formulas needs to be adjusted in inverse proportion to the "extra enlargement". For the case of viewing at enlargement sufficient for resolution differences to be detectable, my formula that allows for pixel count difference is one way to take this into account, and indeed gives lower DOF for higher pixel counts.
So it does not surprise me that when DOF comparisons are made that involve images of higher resolution from larger formats like DMF, the basic DOF formula understates the DOF difference; I doubt that these comparison are done with prints of equal, small size like 7"x10", but would guess that they are instead done at image sizes large enough to reveal the resolution advantage of the larger format.
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To repeat yet again: the standard DOF scales, tables and formulas are for the reference case of comparing prints of equal (and modest) size at equal viewing distance: the traditional reference is 7"x10" prints viewed from 10" I believe. They do not include adjustments for factors like different intended print size, but those can easily be done by someone who makes the modest effort to understand the formula and the science behind it. (Can you tell that I teach science, and hate blind memorization of formulas as a path to misunderstanding and failure?)
When a high resolution image is instead "viewed larger" (larger print size and/or closer scrutiny), the DOF value from the standard formulas needs to be adjusted in inverse proportion to the "extra enlargement". For the case of viewing at enlargement sufficient for resolution differences to be detectable, my formula that allows for pixel count difference is one way to take this into account, and indeed gives lower DOF for higher pixel counts.
So it does not surprise me that when DOF comparisons are made that involve images of higher resolution from larger formats like DMF, the basic DOF formula understates the DOF difference; I doubt that these comparison are done with prints of equal, small size like 7"x10", but would guess that they are instead done at image sizes large enough to reveal the resolution advantage of the larger format.
Dear me! What confusion! All the DoF comparisons I've made between FF 35mm and cropped format cameras have involved sensors of approximately the same resolving power. The resolution difference between the 40D and 5D is insignificant. The resolution difference between the 5D and the 50D is also insignificant. However, the resolution difference between the 40D and 50D is probably noticable at 100% on monitor or on very large prints, but such differences between these two sensors of the same format are not of course relevant to these DoF comparisons.
Likewise, most of the MFDB comparisons that have been hotly debated on this forum are between sensors of approximately equal pixel count, the 21mp 1D3 versus the 18mp and 22mp P21 and P25.
If the focal length and F stop number have been adjusted in relation to the differences in sensor dimension, then the diameter of the CoC on the sensor, at a particular distance from the focus point in the image, would presumably automatically be adjusted in proportion so that the DoF differences in the two images will remain constant whatever the size of the print.
To make the point clear with an example, if I shoot a scene using the 5D with 80mm lens at F13, and the circle of confusion is 0.03mm at a certain point in the image, say 2 metres from the point of focus, then the CoC on the 40D sensor at the same place in the image, 2 metres from the point of focus, should be 0.03/1.6=0.019mm, provided I use the appropriate lens (80/1.6=50mm) and appropriate F stop (13/1.6=F8).
If I make an 8x12" print from both images, the CoC in the 5D image becomes 8x0.03=0.24mm. If I make the same size print from the 40D image, the CoC, although smaller in proportion to the smaller sensor, is enlarged to a greater degree (1.6x8=12.8x) and ends up being the same size (12.8x0.019=0.24mm).
Whatever size prints I make, the CoC will be the same size on equal size prints from each camera, even if I examine images at 200% on the monitor. Is this not true?
If in my tests (and other comparisons with MFDBs) the results do not always conform with this F stop and FL multiplier for equal DoF, there must be some factor(s) other than image size going on.
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Ray, by my reckoning, the resolution difference between the 40D and 5D leads to about a 1/3 stop change in DOF if "compared at full resolution", shifting the difference from 1 1/3 stops predicted by the traditional formula (which is for conditions where image resolution differences are irrelevant) to 1 2/3 stops.
What are your observed values for the DOF difference between the 40D and 5D, and more important, what is the margin of error in your observed values? Is either 1 1/3 of 1 2/3 stops outside your margin of error? That is, do your observations with a one stop difference between the two cameras give a measured DOF difference that is inconsistent with either 1/3 or 2/3 stops?
Without knowing which MF camera was being compared to which 35mm camera, I can have no comment on the claim of MF revealing relatively less DOF than the formulas predict. And with different approaches to AA filers and different lenses, it is not clear that pixel size alone gives the resolution comparison needed there.
In short, I have not yet seen any quantitative evidence that there is a discrepancy between observation and the standard optical formulas.
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To make the point clear with an example ... Whatever size prints I make, the CoC will be the same size on equal size prints from each camera, even if I examine images at 200% on the monitor. Is this not true?
If in my tests ... the results do not always conform with this F stop and FL multiplier for equal DoF, there must be some factor(s) other than image size going on.
Yes, the circles of confusion at corresponding points on the prints will be the same size and so the perceived DOF would be the same when comparing equal sized images small enough that the resolution differences are not perceptible, as with the reference case of 5"x7" prints viewed from 10". But as we agree, and as I have been saying repeatedly, there is something else going on with sufficiently large prints viewed sufficiently closely[/i], like the ones that you say you have to up-sample in order to make. When the equal sized images are large enough that the resolution differences are perceptible, it is likely that certain parts of the scene which are visibly OOF in the higher resolution image (visibly less sharp than the sharpest parts of the image) may not be visibly OOF on the lower resolution image, because the loss of sharpness due to OOF focus effects is drowned by the overall lower sharpness.
That is, under sufficiently close scrutiny of sufficiently large prints, the perception of being in-focus or out-of-focus is probably influenced by comparing the sharpest at some part of the image to the sharpness of the sharpest part of the image. There, the difference of 1/3 stop between 10MP and 12.7MP is likely to be perceptible when you look closely enough.
Given your enthusiasm for experiment and observation, I do not think that you should dismiss the resolution differences between these cameras as insignificant without experimenting! Especially since my use of pixel count is only a rough measure of resolution, not accounting for example for lens resolution, which could tend to increase the resolution advantage of the larger format when used with the same zoom lens.
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What are your observed values for the DOF difference between the 40D and 5D, and more important, what is the margin of error in your observed values? Is either 1 1/3 of 1 2/3 stops outside your margin of error? That is, do your observations with a one stop difference between the two cameras give a measured DOF difference that is inconsistent with either 1/3 or 2/3 stops?
BJL,
As I showed in post #51, when the 100-400 is focussed at a fairly long distance, a 1 stop difference is sufficient to equalise DoF between the 40D and 5D (comparing 400mm at F11 (5D) with 250mm at F8 (40D). Other shots of the same scene taken on the same occasion show that a difference of 1 1/3 stops is equally satisfactory. I didn't take any shots separated by 1 2/3 stops on that occasion, but I wouldn't be surprised if 1 2/3 stop were also satisfactory and within the range of the margin of error. At print sizes of 30"x45", which a 100% view on the monitor represents, such differences are inconsequential. At smaller print sizes, invisible.
However, when focussing at close distances with a wider lens, such DoF differences seem more noticeable. I've found that a 2 stop difference is required to equalise DoF between the 50D and 5D, comparing 24mm at F4 with 40mm at F8. Do you want to see the images?
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Yes, the circles of confusion at corresponding points on the prints will be the same size and so the perceived DOF would be the same when comparing equal sized images small enough that the resolution differences are not perceptible, as with the reference case of 5"x7" prints viewed from 10". But as we agree, and as I have been saying repeatedly, there is something else going on with sufficiently large prints viewed sufficiently closely[/i], like the ones that you say you have to up-sample in order to make. When the equal sized images are large enough that the resolution differences are perceptible, it is likely that certain parts of the scene which are visibly OOF in the higher resolution image (visibly less sharp than the sharpest parts of the image) may not be visibly OOF on the lower resolution image, because the loss of sharpness due to OOF focus effects is drowned by the overall lower sharpness.
That is, under sufficiently close scrutiny of sufficiently large prints, the perception of being in-focus or out-of-focus is probably influenced by comparing the sharpest at some part of the image to the sharpness of the sharpest part of the image. There, the difference of 1/3 stop between 10MP and 12.7MP is likely to be perceptible when you look closely enough.
Given your enthusiasm for experiment and observation, I do not think that you should dismiss the resolution differences between these cameras as insignificant without experimenting! Especially since my use of pixel count is only a rough measure of resolution, not accounting for example for lens resolution, which could tend to increase the resolution advantage of the larger format when used with the same zoom lens.
BJL,
I agree. There's not much point in taking into consideration relatively small differences in pixel count without also taking into consideration the sometimes larger differences in lens resolution between the different f stops used to equalise DoF. As you know, lens resolution is typically sharpest at one or two stops down from maximum aperture and then begins to fall off below F8.
If we consider my comparison between the 40D at 250mm and F8, and the 5D at 400mm and F11 & F13, there can be little doubt that the 100-400 zoom is sharper at 250mm and F8 than at 400mm and F11 and F13. The slightly lower resolving power of the 40D, plus it's requirement for a sharper lens due to its higher pixel density, is at least partially met by the greater sharpness of the 250mm lens at F8. The fact is, the images from both cameras in these circumstances appear equally sharp at the plane of focus, so there should be no need to modify the formula.
If we take another example comparing the 50D with the 5D using the Canon 24-105 zoom at 24mm and F4 with the 50D, and at 40mm and F6.3 or F8 with the 5D, the process is reversed to produce a similar effect. The additional resolving power of the 50D is offset by the lower resolving power of the zoom lens at full aperture. Both images are therefore equally sharp at the plane of focus. The multiplier of 1.6 for F stop should therefore hold true, but in these circumstances it doesn't appear to.
On the other hand, there could be some minor difference in focussing responsible for this. The experiment was set up to compare noise between the two cameras, not the accuracy of the 1.6 multiplier. However, I can't detect any misfocussing. Both images appear equally sharp at the plane of focus, and there can be no doubt that the 50D was accurately focussed because I used Live View.
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As I showed in post #51, when the 100-400 is focussed at a fairly long distance, a 1 stop difference is sufficient to equalise DoF between the 40D and 5D (comparing 400mm at F11 (5D) with 250mm at F8 (40D). Other shots of the same scene taken on the same occasion show that a difference of 1 1/3 stops is equally satisfactory.
So far so good!: consistent with the traditional reckoning within the experimental margin of error (and the intended precision limits of the formulas).
However, when focussing at close distances with a wider lens, such DoF differences seem more noticeable. I've found that a 2 stop difference is required to equalise DoF between the 50D and 5D, comparing 24mm at F4 with 40mm at F8. Do you want to see the images?
The examples might be interesting. How much closer? The standard basic formulas break down as the magnification become significant, with texts typically limiting their utility to m<1/10 or even m<1/20, meaning subject distance should be at least about ten or twenty times the focal length. At closer range, lens extension means that both the effective focal length and effective aperture diameter shift, and more precise formulas are needed.
Another part of the approximation is that the formulas break down when the aperture is small so that the DOF is very large: large enough to be substantially greater behind the focal plane than in front of it. (The rule of thumb about 1/3 of DOF in front, 2/3 behind has no quantitative scientific basis: DOF is close to equally distributed fore and aft when the DOF is shallow enough, but grows more behind than in front as aperture size is reduced, eventually reaching infinity behind in the hyperfocal case.) The formulas are more oriented to choosing an aperture that ensures enough DOF in situations where DOF is potentially quite limited.
All this "fine print" is why one needs to understand the physics, mathematics, and applicability of the formulas, or otherwise use them cautiously, in the range of conditions for which they were intended. More detailed formulas are available in more advanced optics texts for the harder cases!
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The examples might be interesting. How much closer? The standard basic formulas break down as the magnification become significant, with texts typically limiting their utility to m<1/10 or even m<1/20, meaning subject distance should be at least about ten or twenty times the focal length. At closer range, lens extension means that both the effective focal length and effective aperture diameter shift, and more precise formulas are needed.
Another part of the approximation is that the formulas break down when the aperture is small so that the DOF is very large: large enough to be substantially greater behind the focal plane than in front of it. (The rule of thumb about 1/3 of DOF in front, 2/3 behind has no quantitative scientific basis: DOF is close to equally distributed fore and aft when the DOF is shallow enough, but grows more behind than in front as aperture size is reduced, eventually reaching infinity behind in the hyperfocal case.) The formulas are more oriented to choosing an aperture that ensures enough DOF in situations where DOF is potentially quite limited.
BJL,
In the comparisons below, the focussing distances, although close, are significantly greater than 20x the longest focal length used, which was 40mm. The distance to the focus point would have been about 2 metres, or 50x the longest focal length. In order to be pedantic, I've downsampled the 50D image to the 5D size. However, whether the 50D image is downsampled or the 5D image is upsampled makes no difference to the conclusion. In these samples, the 50D still retains a slightly greater DoF edge, even with a 2 stop difference, although I'm prepared to accept that such miniscule differences fall within the margin of experimental error.
As I mentioned before, my purpose in doing these tests, shortly after receiving my brand new 50D, was to check out the noise, comparing it with my 5D at equal shutter speeds and equal DoF, which involved comparing 50D noise at ISO 100 with 5D noise at ISO 320, and ISO 200 with ISO 500 etc. It was as a consequence of such tests that I discovered that the 1 1/3rd stop difference for equal DoF did not seem to apply in those circumstances and that nothing less than a 2 stop difference would produce the desired results.
Here's the over all scene: [attachment=13510:The_scene.jpg]
The general area of focus at 100%: [attachment=13511:General_...us_point.jpg]
The specific area of focus at 200% (the pale mauve, artificial flower): [attachment=13512:precise_..._at_200_.jpg]
The closest points in the foreground: [attachment=13513:Nearest_points.jpg]
The background, centre right: [attachment=13514:Centre_right.jpg]
The background centre left: [attachment=13515:Centre_left.jpg]
You'll notice that I should have used ISO 400 with the 5D instead of ISO 640. However this apparent advantage to the 5D (regarding noise) is at least partly offset by the slightly faster shutter speed (1/15th as opposed to 1/13th for the 50D) and is not as great as it might at first seem. I was simply trying to get a good ETTR. Checking out DXOmark figures later, I discover that at ISO 100, the sensitivies of both cameras is equal at ISO 93. However, at the nominal ISO of 400 the 5D is actually ISO 357, according to DXOmark, but it should be 4x93=372, so it does appear to be slightly understated. Nevertheless, according to EV compensation adjustments in ACR, the 5D has about a 1/3rd stop ISO advantage in these comparisons, that is, it requires -1 EV adjustment whereas the 50D image requires -0.67 EV adjustment.
The noise comparison images below were converted with zero black, zero contrast, linear tone curve, no sharpening, and no noise reduction of either luminance or color. Both images have been lightened to the same degree in 'levels'. The 5D comes out quite well. I was surprised that at ISO 640 the 5D would be on a par with the 50D at ISO 100. One should also bear in mind that the slight ISO advantage I've given the 5D does not translate to more photons per unit area of sensor, but a slightly greater analog amplification of the signal.
Noise comparison: [attachment=13516:Shadows_lightened.jpg]
All this "fine print" is why one needs to understand the physics, mathematics, and applicability of the formulas, or otherwise use them cautiously, in the range of conditions for which they were intended. More detailed formulas are available in more advanced optics texts for the harder cases!
The problem here is that, in the field where capturing the moment is often of the essense, we don't have time to engage in complex calculations. Outside of studio conditions, it's also very difficult to get precise measurements of distance to subject, so DoF calculations, however precise theoretically, can be no more precise in practice than the precision with which can one measure distances in the field.
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Ray,
thanks; I will look at the samples more carefully when I have the time. For now, on high precisision DOF formulas:
The problem here is that, in the field where capturing the moment is often of the essense, we don't have time to engage in complex calculations. Outside of studio conditions, it's also very difficult to get precise measurements of distance to subject, so DoF calculations, however precise theoretically, can be no more precise in practice than the precision with which can one measure distances in the field.
Agreed. My point about understanding the science behind the formulas is only to avoid misusing them, or expecting more precision of them that is justified. The main use for DOF formulas as far as I can tell is to ensure enough DOF in situations when one is facing trade-offs between DOF, shutter speed, diffraction and such. So probably all that is needed in the field is a suitably good approximation, used with sufficient caution. Very careful macro photographers (including the extreme macro case of microscopy) needs more care and have use for more precise formulas.
Then again, with a sufficiently large, sharp, accurate, and bright VF image, one could stop down and verify DOF directly. But no SLR optical VF is up to that task. Live View with zoom might be the coming solution.
But the original question of this thread is much easier, and does not need details of subject distance beyond avoiding the extremes of macro range and hyperfocal distance. Because that question was only about the DOF shift between different choices of format/focal length, under conditions of equal (if unknown!) subject distance and equal display size. I have not yet seen evidence that "equal DOF at equal effective aperture" is insufficiently accurate, but I will keep looking.
P. S. Modest downsampling of Bayer CFA raw data to a RGB format like JPEG or TIFF with about half or more the pixel count might have very little effect on resolution, due to the greater information in one three color RGB pixel than in one single color Bayer CFA pixel.
I would be interested in a careful comparison of 6MP and 12MP conversions from a 12MP raw file, given that
6MP RGB has 6 millions values for each of G, R and B,
12MP Bayer CFA raw has 6 million G values, 3 million each for R and B.
So it could even be that 6MP RGB can hold more detail in some situations than a 12MP Bayer CFA raw provides.
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But the original question of this thread is much easier, and does not need details of subject distance beyond avoiding the extremes of macro range and hyperfocal distance. Because that question was only about the DOF shift between different choices of format/focal length, under conditions of equal (if unknown!) subject distance and equal display size. I have not yet seen evidence that "equal DOF at equal effective aperture" is insufficiently accurate, but I will keep looking.
BJL,
I agree completely that taking the ratio of the diagonals of the different size formats as a multiplier for determining appropriate focal length and f stop #, in order to equalise FoV and DoF, is a good starting point. However, when the formats being compared also have a different aspect ratio, as the micro 4/3rds and Canon cropped formats have, then the formula becomes slightly more 'rule-of-thumb'. When one of the formats has a significantly different pixel count, then the formula becomes even more 'rule-of-thumb'. If one of the formats has the benefit of a better lens, then that may also change the rule-of-thumbness to a greater or lesser degree in either direction.
When the subject focussed upon is fairly close to the camera (as in studio conditions rather than macro conditions), that may also affect the rule-of-thumbness to a greater extent than all the other factors mentioned above (in my view; yet to be confirmed.)
As you know, I've often battled with MFDB users on this forum about their slack approach to these matters when comparing their expensive equipment with 35mm format. I was also surprised recently when Michael compared the G10 with a P45 without also taking these matters seriously. He got the focal lengths approximately right, but was miles out with the DoF. As a consequence, when experienced photographers were invited to compare his A3+ size prints from both cameras, they were (eventually) able to identify the P45 because of its shallower DoF.
In the comparison shots of the woods scene, Michael used the G10 at F3.5 and the P45 at F11. The diagonal of the G10 sensor is 9.5mm (info available from Dpreview), and the diagonal of the P45 is 60mm. The multiplier for DoF equivalence is therefore 60/9.5=6.3. F3.5x6.3=F22. Michael should have used F22 with his P45 in this comparison. By using F11, he gave the game away.
I'm surprised that no-one seems to have pursued this issue and repeated the comparison using images with equal DoF. We are left to speculate on what the results might have been. There's no doubt that the P45 image would be less sharp at F22 (than at F11). How much 'less sharp' and at what print size is the question. Would these experienced photographers whom Michael invited to view his A3+ prints have then confused the greater sharpness of the G10 with the P45? We don't know until someone repeats the comparison.
Out of interest, I downloaded Michael's G10 and P45 images and searched for the out-of-focus areas. They were easy to find. Consider the crop comparisons below, at two different magnifications. In the second image, the G10 crop has been upsampled to the P45 size.
[attachment=13563:G10_v_P45.jpg] [attachment=13564:G10_upsa...d_to_P45.jpg]
By the way, I understand it is not true that the origins of the expression 'rule of thumb' go back to a barbaric medieval law in England, which permitted a man to discipline his wife with a stick no thicker than his thumb. No record of such a law can be found. Just thought I'd mention it .