5x4 look on a MF chip?

[free1000]

One for the optical experts here.  I've been shooting work on 5x4 using a 150mm f5.6 Schneider Apo_Symmar.

Now I'm shooting with a Leaf Aptus I am wondering what focal length and aperture would be equivalent in order to create the same depth of field and look.

As 150 is about normal for 5x4, it must roughly correspond to an 80mm length on the MF chip.  So the question is, how wide would the aperture of the 80mm lens need to be to approximate a similar dof?

Most LF or digital lenses only open up to f5.6 so finding a lens which allows movements at a suitable aperture might be impossible.

If someone can provide a suitable equation I could plug it into a spreadsheet and play around a bit. There's no reward for providing this except for my admiration for your superior brain!

[Morgan_Moore]

2.8 ish I think

http://www.dofmaster.com/dofjs.html

BUt I dont think it is that simple because a longer lense kind of has a sharper cut off

 (think 400 2.8 football and grass - razor line of sharpness)

I dont think it is doable - hense the love by some of large chips , 67 and 54 cameras and my personal hatred of my D200 (which I was shootin at 1.4 today to try and replicate the look from my blad)

SMM

[BJL]

One for the optical experts here.  I've been shooting work on 5x4 using a 150mm f5.6 Schneider Apo_Symmar.

Now I'm shooting with a Leaf Aptus I am wondering what focal length and aperture would be equivalent in order to create the same depth of field and look.

As 150 is about normal for 5x4, it must roughly correspond to an 80mm length on the MF chip.  So the question is, how wide would the aperture of the 80mm lens need to be to approximate a similar dof?
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This is much discussed and disputed in these forums, so expect debate. You might also want to read what Charles Johnson had to say at this site on [a href=\"http://luminous-landscape.com/essays/Equivalent-Lenses.shtml]Lens Equivalents[/url] (the subsequent stuff by Nathan Myhrvold is probably less relevant to your question.)


You have already apparently decided on using a focal length that gives the same angular field of view, except that MF sensors are (at most) about 36x48mm, so 60mm on the diagonal, compared to about 150mm diagonal for 4x5, so the equivalent focal length might be more like 60mm; smaller by a factor of 2/5.

If you are interested in getting the same DOF when you make prints of the same size and view them from the same distance, what you probably want to do is adjust the aperture ratio in proportion to the focal length, here a factor of about 2/5. So for example from f=150, f/8 to f=60mm, f/3.2.

In other words, if you want to use view camera lenses limited to f/5.6, the DOF wide open will be like what you are used to at f/14 in 4x5.

Of course, you probably have to use a slightly different focal length, like 55mm or 80mm; then what happens depends on how you deal with the change: use the shorter focal length and crop? use the longer move further away?


My proposed foal length and f-stop equivalents are based based on the fact that at every point of the print, the circle of confusion due to out of focus effects will be the same size, along with the image being the same size. Some people will bring in other factors like the sharpness of the completely in-focus parts, and thus effects of sensor and film resolution, but I am doing it the traditional way, based on how far an object must be in front of or behind the focus distance before the OOF blur is visible. This approach works at least so long as your prints appear completely sharp except for OOF effects, due to sufficient film/senor resolution for the print size (and viewing distance) chosen.

[BJL]

a longer lense kind of has a sharper cut off

 (think 400 2.8 football and grass - razor line of sharpness)
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That is an effect of using a longer lens at a greater distance from the subject in the same format; an aspect of the perspective change in that situation. It does not apply when one stays at the same distance from the subject, using a longer lens in a larger format to cover the same FOV.

[Morgan_Moore]

That is an effect of using a longer lens at a greater distance from the subject in the same format; an aspect of the perspective change in that situation. It does not apply when one stays at the same distance from the subject, using a longer lens in a larger format to cover the same FOV.
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Well if you had a 400 2.8 that covered 10.8 film and shot a pic and then snipped a 35 mm bit out of the tranny that bit would be the same as if you had shot that bit with a 35mm camera

So in fact a 10.8 400 2.8 (the size of a dustbin??) would have that crisp cut too - amazing affect it would be

just like an 80 2.8 blad image cropped in half looks like a image off a 80 on a 35 chip

The crux of my argument is that while small chip may give shallow DOF (like the canon 85) it is my beleif that the same field of view taken with a larger format and therefore longer lense may have the same depth of field (ie acceptable COC over the same distance) the background will be more blurred and look cooler if that what floats your boat

I therefore believe that bigger chips look cooler and 54 even cooler IMO

I am however not 100% convinced that my thesis is true !!

I think that one needs data on how out of focus is an object 3 meters behind by focal plane when I have, say, a DOF onf one meter - such info is not available in my link above

S

[dobson]

The best way to chart lens equivalancy would be to make graphs of the CoC at a fixed focus point and aperture. You would be able to see how the CoC varies with distance out of focus. It looks like it aught to be a parabolic function. You just then need to solve for when one format equals the other.

It may be that there are no perfect equivalents, as Morgan suggested, and the curves are only approximations at best.

The next time I'm feeling bored, I'll see what I can do.

Phillip

[BJL]

Well if you had a 400 2.8 that covered 10.8 film and shot a pic and then snipped a 35 mm bit out of the tranny
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Maybe but working with such massive crops is not what the OP is asking about: he is asking about using the full frame size of each format. (Hence the adjustment of of focal length.)

What you propose is, as far as the final images look, working in 35mm format with a large amount of film wastage.


P. S. A f=400mm f/2.8 lens for 4x5 need to be particularly bigger than a f=400, f/2.8 lens for 35mm format. In either case irt is a relephot, so the big front lens elements can be of diameter fairly close to effective aperture diameter, 400mm/2.8 = 140mm.

[Morgan_Moore]

massive crops is not what the OP is asking about
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No I am demonstrating a well known exmple of the thin sharp field and wild blur of a long lense at a big aperture

With a large format camera you can get that look with with a larger field of view

with an un cropped 10.8 image you would get half of the staduim but still the thin focus

a look that is non replicable with a smaller format is my theory

P. S. A f=400mm f/2.8 lens for 4x5 need to be particularly bigger than a f=400, f/2.8 lens for 35mm format
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Yes this lense would be the size of a dustbin lid at least (!) as I said

S

[dobson]

I just did a bit of number crunching.

The size of the blur spot for a given object distance, focus distance, lens, effective aperture and so on, is also determined by lens design. This holds especially true in high magnification ratios. So while I can't give exact figures, I was able to do some calculations on ideal, symmetrical lenses. I'll post the results as soon as I finish checking them.

Phillip

[dobson]

Here's an equation that may help:

For a symmetrical lens; C=(d*f(v-a))/((a-f)(v-f)), where C is the blur-spot, d is the entrance pupil, f is the focal length, v is the focused distance, and a is the distance of the light from the focused distance. Enter values of equivalent focal lengths in different formats, (i.e. 100mm and 160mm for 35mm and APS sensors). Then enter an arbitrary d value for one of the other lenses and solve for d on the other.

You'll find that different focal lengths simply do not have the same DoF characteristics. If you assign v and a values you can solve it, but this result only holds true for that v and a value.

This math only correlates the actual size of the blur-spots on the sensors. It does not take into account the fact that a spot will be enlarged more from a small sensor than a large one. I suppose one could place a coefficent in front of the equation relating the area ratio of the two sensors. This should give you equvalencies based on prints enlarged to the same size.

Phillip

equation derived form information on http://www.vanwalree.com/optics/dofderivation.html

[BJL]

Here's an equation that may help:

For a symmetrical lens; C=(d*f(v-a))/((a-f)(v-f)) , where C is the blur-spot, d is the entrance pupil, f is the focal length, v is the focused distance, and a is the distance of the light from the focused distance.

You'll find that different focal lengths simply do not have the same DoF characteristics. ...

This math only correlates the actual size of the blur-spots on the sensors. It does not take into account the fact that a spot will be enlarged more from a small sensor than a large one
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Note: "entrance pupil" d here is I believe the at same as "aperture" or "effective aperture diameter": the ratio of focal length to aperture ratio.

That last comment raises a fatal flaw. As soon as one instead considers the case of making prints of the same size, the degree of enlargement is inversely proportional to the focal length, and for the same allowable blur spot size on the print, the acceptable value of C scales n proportion to f.

Other approximations are often safe, like v far larger than f, so that v-f can be replaced by v. In the end a common approximation for objects reasonably close to the focal plane is that
C is roughly d*f/a
so keeping entrance pupil d constant while adjusting focal length and degree of enlargement to get equal sized prints adjusts C in proportion to f, and gives similar DOF effects on the print for objects reasonably near to the focal plane.

For objects that are very far beyond the focal plane (very OOF), the approximation becomes
C approximately (d*f)/v
and this has the same consequence of getting similar OOF effects by holding d constant as one adjusts format size and f, and prints at the same size.

Either way, equal d, that is equal aperture size, gives similar OOF effects both near the focal plane (DOF) and far from it (extreme OOF effects), if one makes prints on which the main subject comes out the same size. That is, scaling aperture ratio in proportion to focal length.

[howiesmith]

The math involved is rather simply.  You might do the calculations yourself to avoid having to taking a stranger's opinion.

[BJL]

With a large format camera you can get that look with with a larger field of view

with an un cropped 10.8 image you would get half of the staduim but still the thin focus

a look that is non replicable with a smaller format is my theory
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That look is also non replicable in 8x10 format due to the non-existence of LF lenses with such huge aperture sizes (about 140mm). So it is not much of a claim of an additional capability of the larger format.

And there are fairly fundamental reasons why LF lenses never offer anything close to such large apertures. Apart from huge cost and weight and the overwhelming lack of interest amongst LF photographers in striving for even less DOF than they get at f/5.6 or f/8, there is the limitations of the between the lens leaf shutters used in LF: these could not open and close over a huge 140mm diameter fast enough.

So in fact the biggest aperture diameters and lowest DOF are achieved in systems with focal plane shutters, which means mostly 35mm format and smaller, plus Mamiya and Pentax 645 format systems, and the discontinued Hasselblad 200 series.

[Morgan_Moore]

So in fact the biggest aperture diameters and lowest DOF are achieved in systems with focal plane shutters,[a href=\"index.php?act=findpost&pid=99724\"][{POST_SNAPBACK}][/a]

I was of course making a ridiculous example.

While small camera may have the biggest apertures 50 1.2 etc I think in real terms once you have an aperture that gives a reasonable plane of focus lets say 5.6 which does exist the larger format will blur the OOF areas more given the same field of view

It not about what is in focus it is about how far out of focus the out of focus but are when the bits you want in focus are in focus

The widest aperture can be too wide for creating some images

It is hard to explain my point but the upshot is

My 645 80 at 2.8 has a creamier look than my 50 whos focus depth is often unaceptable at 1.2 (and virtually impossible to use) I think this effect is even more extreme with 54

SMM

[BJL]

While small camera may have the biggest apertures 50 1.2 etc I think in real terms once you have an aperture that gives a reasonable plane of focus lets say 5.6 ...
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You wish to compare at equal aperture ratio, which is to say, with the larger format using an aperture size ("entrance pupil") that is larger in proportion to the focal length. That is rather irrelevant to photographic practice, since usable aperture ratios do not stay constant across substantial changes in format size: there is a clear, strong trend to higher aperture ratios in larger formats.

In particular, taking f/5.6 as a "reasonable" common choice for the various formats being compared in unreasonable. Photographers seeking strong OOF effects in 35mm and medium format can and do use distinctly lower aperture ratios than that, while photographers using say 8"x10" LF will likely be forced to use higher aperture ratios than f/5.6, due to limitations on available lenses (including possibly quite poor wide open performance of LF lenses, which seem to be optimized for use stopped well down, with wide open intended more for ease of focusing and composition.)

[free1000]

You wish to compare at equal aperture ratio, which is to say, with the larger format using an aperture size ("entrance pupil") that is larger in proportion to the focal length. That is rather irrelevant to photographic practice, since usable aperture ratios do not stay constant across substantial changes in format size: there is a clear, strong trend to higher aperture ratios in larger formats.

In particular, taking f/5.6 as a "reasonable" common choice for the various formats being compared in unreasonable. Photographers seeking strong OOF effects in 35mm and medium format can and do use distinctly lower aperture ratios than that, while photographers using say 8"x10" LF will likely be forced to use higher aperture ratios than f/5.6, due to limitations on available lenses (including possibly quite poor wide open performance of LF lenses, which seem to be optimized for use stopped well down, with wide open intended more for ease of focusing and composition.)
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Yes, as was predicted, this did create quite a bit of debate.  I agree with the point about needing to compare different formats with different apertures.  I've currently been able to test and compare an 8" f4.5 lens with a 240mm f9 and a 150mm f5.6. While the numbers for the 8" f4.5 lens look most hopeful on 645 in terms of narrowness of dof...  the softness of the lens means that the overall look is completely different from the other two. Because the sharpest areas are very soft, the overall impression is one of softness rather than a sharp area with a very short cutoff.

There is a 150mm Schneider Xenotar which has an f2.8 aperture which might be better. However, if its anything like my 105 f2.8 it might be a bit too soft wide open to get the effect I was anticipating.

Overall I like the look of the 150 best, using a heavy degree of inverse swing as the DOF areas look nicest. Is this perhaps because bizarrely the DOF areas are less out of focus? Does it make sense to talk of an out of focus area being less out of focus when it was originated by a lens of greater quality?

Maybe what I should try next is the longest digital LF lens with a reasonably wide aperture.

Probably experimentation is more valuable than number crunching on this one.