Luminous Landscape Forum

Equipment & Techniques => Medium Format / Film / Digital Backs and Large Sensor Photography => Topic started by: BJL on October 04, 2005, 05:58:21 pm

Title: Leaf backs at 28MP, 35MP
Post by: BJL on October 04, 2005, 05:58:21 pm
I have not found anything at Leaf's site yet about those new 28MP and 35MP backs, but this seems to mean that Dalsa is joining Kodak with new "645" sensors of higher resolution, in the sense of closer pixel spacing.

Dalsa is my guess this time since Leaf is currently using Dalsa sensors, and the pixel counts are a bit different than for the forthcoming Phase One backs, which will use Kodak sensors. 35MP sounds like 7 micron spacing with Dalsa's current largest 36x48mm format.

Does anyone else wonder how well 645 format lenses will keep up with this reduced pixel spacing, given their historical design for 20lp/mm or 30lp/mm and generally lower measured MTF at 40lp/mm than 35mm format lenses? That 7 micron spacing corresponds to 50lp/mm or more. Maybe Fuji in particular anticipated this when designing a whole new series of lenses for the Hasselblad/Fuji H series?
Title: Leaf backs at 28MP, 35MP
Post by: dazzajl on October 05, 2005, 04:29:21 am
Quote
I have not found anything at Leaf's site yet about those new 28MP and 35MP backs

I was talking to someone at Leaf this week who told me they would be announcing some new products next week so perhaps some details will come out then.

However, Leaf are not great for getting info up on the web so it may be a little longer untill there is some web resource to look up.

I would certainly agree with your concerns about current lenses being able to "keep up' though.
Title: Leaf backs at 28MP, 35MP
Post by: izaack on October 05, 2005, 11:28:05 am
http://www.pdnonline.com/pdn....1221306 (http://www.pdnonline.com/pdn/prodtech/news/article_display.jsp?vnu_content_id=1001221306)
Title: Leaf backs at 28MP, 35MP
Post by: BJL on October 05, 2005, 01:25:16 pm
izaack,
    thanks for the Photo District News link. Those incorrigable medium format sensor makers keep forcing 4:3 shape on us!

dazzajl,
    I am actually not so much "concerned" (cannot vaguely afford a MF back!) as just curious to see where the lens-imposed resolution limits will fall. Currently I am betting on "no more resolution than a 20-40MP Bayer CFA sensor can give", except perhaps in some wide angle extremes. Pixel counts might get somewhat higher for other reasons, like avoiding moire by "oversampling".
Title: Leaf backs at 28MP, 35MP
Post by: michael on November 11, 2005, 10:30:13 am
The word on the street (what Kodak and Dalsa are saying privately) is that medium format digital backs will likely top-out at about 50-60MP some time in the next two years. That implies around 5 micron pixels, which is as small as current technology can go without serious noise issues.

The real problem is that most lenses aren't up to the task. I was stunned recently when I saw what a Schneider Digital lens can do compared to my Zeiss glass on the Contax. It is increasing becoming apparent to me that the limiting factor is no longer imagers, but lenses.

This applies to 35mm in spades. The 1Ds MKII at 16MP is pushing Canon glass to the limit. There are only a handful of Canon lenses that are a match for it. If Canon goes to 22MP next year (which some people are guessing they will) this is also likely to be the limit, due to pixel size, and also due to the inability of current glass to keep up with the sensors.

Michael
Title: Leaf backs at 28MP, 35MP
Post by: BJL on November 11, 2005, 12:29:29 pm
Michael,

   thanks for the industry inside comments. For Kodak, that 60MP fits with their chosen "digital 645" format of a bit over 36x48 and their current smallest FFT CCD pixels, the 5.3 microns in their 8MP FourThirds format sensor. So I can imagine they are already working on that roughly 60MP, 5.3 micron sensor design, and do not plan further pixel size reduction for the big format sensors.

Above all, thanks for the confirmation about lens limits on usable sensor resolution. Getting significantly more resolution on the final print than given by say 20MP seems solely the territory of high quality primes; nothing more than a return to the traditional situation of high resolution photography, be it in large, medium, or 35mm format. Zooms are only for the other 99% of us!

By the way "significantly more resolution on the final print" to me means something like going one step up the traditional print size scale, like 8x10 to 11x14 or 11x14 to 16x20. Or A4 to A3, etc. That is, about doubling the print size with the same lp/mm of print resolution so the bigger print sustains the same close scrutiny. And so needing roughly double the pixel count. Is there a significant visible resolution difference to be seen between 12.5MP and 16.5MP, or between 16.5MP and 22MP? I guess not, outside the realm of pixel peeping.
Title: Leaf backs at 28MP, 35MP
Post by: Ray on November 11, 2005, 11:51:40 pm
BJL,
We both know that close-up viewing of a large print can reveal fuzziness and/ or pixelation, yet photographs on the wall somehow invite us to get close to 'appreciate'  the detail.

Paintings that people hang on their walls, whether originals or prints, tend to be much larger than the everage photograph. We expect visible brush strokes and almost unrecognisable forms when we go close to a painting, especially an impressionistic painting. However, such close-up detail is not uniform and 'machine like'. There's great variety in those brush strokes.

When we approach a large photograph, say a billboard or advertisement  which looks pin-sharp from across the road, we see a uniform, evenly spaced quantity of precisely formed circular dots. It's obvious that the image has been produced by a machine. We are suddenly confronted by the impersonality and machine-like qualities of the process, and that's a bit off-putting.

As I see it, large format cameras simply allow us to make larger prints that can withstand that close scrutiny and still maintain a close representation of reality (or the photographer's concept). After all, when we get close to, and peer at a 'real' object, it doesn't suddenly become pixelated or appear to be composed of dots.
Title: Leaf backs at 28MP, 35MP
Post by: BlasR on November 12, 2005, 08:06:05 am
Hello to all. I have a question about a digital back in the rain.
Michael say about some one in the past got back to he's car because of the rain.
what about the p25 in the rain, will be ok to stand outside rainning and take photos with the back?
or the back is not for rainning days?


Thank You

BlasR
Title: Leaf backs at 28MP, 35MP
Post by: eleanorbrown on November 12, 2005, 10:41:05 am
Hi Blas, Recently i photographed in moderate rain using a Contax with a P25 back.  no problems. eleanor brown


Quote
Hello to all. I have a question about a digital back in the rain.
Michael say about some one in the past got back to he's car because of the rain.
what about the p25 in the rain, will be ok to stand outside rainning and take photos with the back?
or the back is not for rainning days?
Thank You

BlasR
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Title: Leaf backs at 28MP, 35MP
Post by: michael on November 12, 2005, 12:40:04 pm
Light to moderate rain and snow is not an issue for any camera gear. Photographers are far more paranoid about this than they need to be. If you can take it, it's likely that your camera can as well.

If I'm going shooting in the rain I just put a small hand towel in my back pocket to wipe off excess rain or snow, and a microfiber cloth to clean the UV filter (which I use when it's raining).

Michael
Title: Leaf backs at 28MP, 35MP
Post by: BlasR on November 12, 2005, 03:13:32 pm
Thank you...I ask because p25 have three opens space in the back, and canon don't . I was little concern about it.

BlasR
Title: Leaf backs at 28MP, 35MP
Post by: michael on November 12, 2005, 03:29:14 pm
I've been bugging Phase One for plugs for these sockets, but they have failed to respond.

What I do is simply put some black electrical tape over the holes when I'm shooting in bad weather.

Michael
Title: Leaf backs at 28MP, 35MP
Post by: BlasR on November 12, 2005, 06:18:21 pm
I plug the back with some part of my ipod   ..the  plug the firewire or USB it perfect for the back,
but I guess I will be using the black tape for the side...Thanks for the tips...
maybe you like to do your self  with the plug the come with the apple mouse to cover the USB cable
I used the one from my ipod but is the same


BlasR
Title: Leaf backs at 28MP, 35MP
Post by: BJL on November 14, 2005, 06:02:15 pm
Ray,

   I am not quite sure how your comment relates to mine above, but here are some observations of mine about the way the people view really large sharp prints, like 4'x5' prints (that's feet) made from 4"x5" format film, and how it relates to resolution needs.

Overwhelmingly, people do "view bigger" than with smaller print sizes, meaning close enough that the image has a larger apparent size --- but mostly to a limit of viewing distance not much less than the short dimension of the image, or about half of the traditional "normal" viewing distance of roughly image diagonal length. A minimum of 3' or so from those 4' by 5' prints seems almost universal, certainly not the ten inches to one foot envisioned by talk of the need for 300ppi printing regardless of print size.

I rather suspect that between diffraction limitations with smaller apertures and DOF limits with larger apertures, it would be very rare for sharpness to hold up under substantially closer viewing than "half normal", except for a few panoramas of large, distant glories. Format and pixel count have no effect on the balance of diffraction spot size with circle of confusion sizes; the same balance comes at equal aperture diameter and so at different aperture ratios with different formats.
Title: Leaf backs at 28MP, 35MP
Post by: Ray on December 21, 2005, 06:12:04 am
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Format and pixel count have no effect on the balance of diffraction spot size with circle of confusion sizes; the same balance comes at equal aperture diameter and so at different aperture ratios with different formats.
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BJL,
Been travelling in Nepal, Tailand and Cambodia for the past few weeks so a technical discussion on Airy discs from an internet cafe will help keep the grey matter active.

"The same balance comes at equal aperture diameter..."?? Okay! But supposing we ignore DoF for a moment and consider the balance between diffraction and all the other aberrations. At the plane of focus, the larger format, given sufficient pixel count, will always produce greater resolution, assuming we are using state-of-the-art lenses.

To put it another way, f64 with an 8x12" camera produces a similar DoF as f8 with 35mm, but the 35mm lens at f8 is about as sharp as you can get. There's a balance between diffration and the other lens aberrations. Very few 35mm lenses are sharper at smaller apertures than f8 but large format lenses continure to get sharper as the aperture opens up from f64. Of course, the DoF is reduced as it is with 35mm at apertures bigger (f stops smaller) than f8. However, if you want higher resolution, at least you can get it with the larger format although a tilt mechanism will be necessary to maintain good DoF.
Title: Leaf backs at 28MP, 35MP
Post by: BJL on December 22, 2005, 01:31:12 pm
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BJL,
Been travelling in Nepal, Tailand and Cambodia for the past few weeks ...
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Sounds like a good start to life with the 5D and 24-105 f/4! We both need to start posting some pictures, don't we?

Quote
"The same balance comes at equal aperture diameter..."?? Okay! But supposing we ignore DoF for a moment and consider the balance between diffraction and all the other aberrations.
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I agree that at low f-stops, aberrations are an important factor in determining how much "spatial detail" a camera can record. I think it is best to use the technical phrase "angular resolution of the subject", to avoid confusions when measures like lp/mm or pixel spacing are used in comparison between formats. I will shorten that to just "resolution".

Ignoring DOF makes no sense to me: the circles of confusion at every point not in the exact focal plane limit resolution just as much as diffraction spots and the smearing by aberrations. And view camera motions do not really increase DOF: they only convert the region of adequately sharp focus from being a thin slab perpendicular to the lens axis to being a thin wedge at some oblique angle to the axis. It is no panacea for inadequate DOF, only dealing with the situation where all the elements of which one desires a sharp image lie roughly in an inclined plane. (And to avoid this discussion becoming excessively theoretical, I note that in practice it is extremely uncommon for DLSR users to use view camera motions like tilt, and I doubt that tilt lenses will ever have much effect on mainstream choices of interchangeable lens camera systems.)

Without further study of  all I can see is the likelihood that optimal control of aberration limits one to apertures no larger than f/4 or even f/5.6, and thus diffraction limited resolution of about 150-200lp/mm at 50% MTF (formulas at Norm Koren's site). This is turn is about the resolution possible with the dominant Bayer CFA style sensors with pixel spacing of about 2 microns, or about 3 microns for X3 (Foveon style) sensors. Darn, no more than about 6000x8000 pixels for Four Thirds before I have to move to digital large format like 36x24mm or 48x36mm!
Title: Leaf backs at 28MP, 35MP
Post by: Ray on December 30, 2005, 07:06:30 am
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Ignoring DOF makes no sense to me: the circles of confusion at every point not in the exact focal plane limit resolution just as much as diffraction spots and the smearing by aberrations. And view camera motions do not really increase DOF: they only convert the region of adequately sharp focus from being a thin slab perpendicular to the lens axis to being a thin wedge at some oblique angle to the axis. It is no panacea for inadequate DOF, only dealing with the situation where all the elements of which one desires a sharp image lie roughly in an inclined plane. (And to avoid this discussion becoming excessively theoretical, I note that in practice it is extremely uncommon for DLSR users to use view camera motions like tilt, and I doubt that tilt lenses will ever have much effect on mainstream choices of interchangeable lens camera systems.)


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BJL,
Sorry for the long delay but you understand I'm travelling.

I can't speak with authority on large format usage but I'm very interested in the principles relating to any resolution advantage. You seem to be belittling any advantage whilst I'm under the delusion that there may be a real and substantail advantage, so bear with me while I try to work through the muddle.

Checking once again the Photodo results I see that the sterling performer is the Canon 200/1.8 with a rating of 90 at f4, followed by a Contax Planar T 50/1.7 with a rating of 88 at f8, Contax G Planar 45/2 with a rating of 88 at F4 and 87 at f8, and Canon 50/1.4 with a rating of 86 at f8.

I tend to think that the diffraction limited resolution of good 35mm lenses is closer to f11 than f8, which equates to f88 in an 8x12" format regarding DoF. In other words, if it were possible to produce a 16MP 8x12" sensor, then the resolution at f88 would be identical to a 1Ds2 at f11, but slightly greater at f64 than the 1Ds2 at f8.

Given appropriate technology, the DR of the 8x12" at f88 would be vastly superior.

The real point I'm making (assuming diffraction spot size is proportional to f stop) is that the large format at f32 produces double the resolution compared to f64, whereas one of the most expensive lenses that Canon produce (discontinued?) has only a marginal increase in resolution at f4 (compared with f8) but the same DoF as 8x12' at f32.

Furthermore, halve the f stop of the large format again to f16 and you've doubled again the resolution, whilst achieving the shallow DoF of 35mm F2. I know of no 35mm lens that increases in resolution by opening up to f2.

My conclusion is, if a DoF equivalent to 35mm F2 is required, then an 8x12" sensor with sufficient pixel count will deliver more than 4x the resolution. That's 4x horizontal and 4x vertical (assuming large format lenses can be truly diffraction limited at f16). Increasing the DoF through tilt, which I agree doesn't always produce the intended result, is a bonus.

If there's a flaw in my reasoning, please set me right   .
Title: Leaf backs at 28MP, 35MP
Post by: Jonathan Wienke on December 30, 2005, 07:55:05 am
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Given appropriate technology, the DR of the 8x12" at f88 would be vastly superior.
True. But it would come at the cost of the 8x12's exposure time needing to be slightly more than 89x as long as the 35mm camera, which most people would regard as somewhat of a tradeoff. Larger formats are certainly capable of greater resolution and DR than smaller ones. But all else equal, they require much longer exposure times to capitalize on these advantages, often to the point where the advantages are no longer relevant. Which is why people don't use 8x10 view cameras to cover sporting events. There is no free lunch.
Title: Leaf backs at 28MP, 35MP
Post by: Ray on December 30, 2005, 10:53:44 am
Quote
True. But it would come at the cost of the 8x12's exposure time needing to be slightly more than 89x as long as the 35mm camera, which most people would regard as somewhat of a tradeoff. Larger formats are certainly capable of greater resolution and DR than smaller ones. But all else equal, they require much longer exposure times to capitalize on these advantages, often to the point where the advantages are no longer relevant. Which is why people don't use 8x10 view cameras to cover sporting events. There is no free lunch.
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Hi! once again Jonathan,

Of course you're right there is a trade off but I'm not suggesting any free lunches. As always it's the right tool for the job. However, if we could conceive of an 8x10 digital camera, the difference between it and 35mm full frame is about the same order of magnitude as the difference between 35mm and the smallest digicam or mobile phone camera. The larger pixels compensate for the higher ISO's needed for faster shutter speeds to get equivalent DoFs. For example, the 5D is as noisless at ISO 800 as the avarage digicam at ISO 100. The lower noise and higher dynamic range of the larger format camera offsets the benefit of a smaller f stop number and corresponding faster shutter speed of the small digicam.

Given the appropriate noise reduction technology, if you wanted to use an 8x10 digital camera for a sporting event you would probably be using ISO 6400 at f16. Same DoF and shutter speed as f2 and ISO 100 with 35mm and theoretically just as low noise.

But to reinforce my point, 4x the resolution unless 35mm lenses can become truly diffraction limited at f2.

Perhaps the technological choice is this: Which is more feasible? (a) production of a diffraction limited lens at f2 for a 200MB 35mm sensor, or production of a 200MB 8x10" sensor? (I'm just guessing at the 200MB figure. I haven't got my calculator out.)
Title: Leaf backs at 28MP, 35MP
Post by: Ray on December 31, 2005, 01:17:53 am
I suppose the central point I'm making here, which I've made before, is that the advantage of being able to use a faster shutter speed with the smaller format (because small f stops provide the same DoF as larger f stops with a larger format camera) is actually illusory.

It's always more sensible to use the cheaper, lighter and smaller camera if it can provide the required image quality. If the shot requires 1/50th at f2.8 and ISO 100 with a small digicam (say in poor lighting), I might initially be fooled into thinking 'wow! this little camera can do something my 35mm can't. At f2.8 DoF would be much too shallow with my heavy, bulky, expensive 35mm DSLR.'

But the fact is, I can get the same shot with my 35mm DSLR. I just have to use different settings. Instead of F2.8 and ISO 100, I use f8 and ISO 800, or instead of 1/200th, f2.8 and ISO 400, I use 1/200th, f8 and ISO 3200. Experience tells me the 35mm DSLR will still provide better image quality in the above examples. There's nothing the smaller format camera can do that the larger format can't, except be cheaper, smaller and lighter.
Title: Leaf backs at 28MP, 35MP
Post by: Jonathan Wienke on December 31, 2005, 02:50:30 am
Quote
But the fact is, I can get the same shot with my 35mm DSLR. I just have to use different settings. Instead of F2.8 and ISO 100, I use f8 and ISO 800, or instead of 1/200th, f2.8 and ISO 400, I use 1/200th, f8 and ISO 3200. Experience tells me the 35mm DSLR will still provide better image quality in the above examples. There's nothing the smaller format camera can do that the larger format can't, except be cheaper, smaller and lighter.
That "fact" rather neatly sidesteps the fact that ISO is not infinitely increasable. Just because a 35mm sensor can be constructed to function well at ISO 1600 doesn't mean that an 8x12 sensor can just as easily be constructed to go up to ISO 142400 (89 X 1600) and deliver the same overall image quality and dynamic range. In fact, if identical technologies were involved in both sensors, the 35mm sensor would deliver a better overall image than the 8x12 sensor because the 8x12 sensor would have hugely higher levels of dark current noise than the 24x36mm sensor. Something like 89X the dark current noise, actually.

Larger-format sensors only offer image quality improvements when they are used to increase the number of photons imaged during exposure. Without a larger aperture, a longer exposure time, or increased ISO, that is not possible. All of these are tradeoffs that can negatively affect image quality, either by decreasing DOF, increasing motion blur, or increasing noise. To achieve the increased image quality, you must choose some combination of these three options. You cannot magically gain image quality by simply spreading out the photons collected during an exposure over a larger imaging area; all else being equal, doing so is actually counterproductive. Making apples-to-oranges comparisons between sensors of different formats with different designs and technologies doesn't change that. It's worth noting that the extremely expensive medium format sensors do not yet match the ISO range of the one found in the 1Ds-MkII. Nor do larger-format film stocks (645, 8x10, etc) come in a wider range of ISO ratings than 35mm film. There is no free lunch.
Title: Leaf backs at 28MP, 35MP
Post by: Ray on December 31, 2005, 11:42:23 am
Quote
That "fact" rather neatly sidesteps the fact that ISO is not infinitely increasable.

I think we're a long way from infinity making a jump from 35mm to 8x10 (12) which, as I said, is  about the same order of magnitude as going from the smallest digicam to 35mm (ie. 3x4.5mm to 24x36mm).

But you are right that in order to get the improved image quality and resolution from the same number of photons (which is what you're getting with an LF 400mm lens at f16 and ISO 6400 compared with a 50mm lens at f2 and ISO 100 on 35mm, ie. same shutter speed, same size aperture, same FoV, same DoF, same number of photons)) you would need to virtually eliminate dark noise. That would entail a lot of additional technology which would make the LF digital camera even heavier and more expensive.

I'm not suggesting such a camera is going to be a consumer product any time soon, but for all I know the US government might already have such a device.

If you lower the standards for the LF digicam, ie. given a static subject and long exposure it will always provide better image quality than a smaller format but never worse image quality using the same exposure as the smaller format, then the technological hurdles are reduced.

The basis for these apparently absurd statements I'm making is an observation that small digicams do not produce better image quality in poor light than the much larger format Canon DSLRs. I'm merely doing a bit of extrapolation.

I'm suggesting that the reason Leaf backs and medium format sensors in general do not boast a low noise 6400 or 12800 ISO setting are due to niche market factors and plain economics rather than an intrinsic technological handicap due to their greater size. But I could be wrong   .
Title: Leaf backs at 28MP, 35MP
Post by: Jonathan Wienke on December 31, 2005, 12:07:44 pm
Quote
The basis for these apparently absurd statements I'm making is an observation that small digicams do not produce better image quality in poor light than the much larger format Canon DSLRs. I'm merely doing a bit of extrapolation.
But not valid extrapolation, because if you took the number of photons involved in a well-executed ISO 800 24x36-format exposure, and dumped them on the digicam sensor, you'd still have blown highlights at ISO 100. The smaller sensor simply can't accept the increased photon load of the larger-format sensor. If you turned it around and dumped the photons involved in a perfectly-exposed ISO 100 digicam frame on to a 24x36 sensor, you'd have an underexposed mess which would at best be no better than the digicam shot, and would have a very good chance of being much worse. The Canon DSLRs deliver better image quality in low light because they process many more photons per exposure than the digicam, even at higher ISO setrtings. And that's why your comparisons are absurd.
Title: Leaf backs at 28MP, 35MP
Post by: Jonathan Wienke on December 31, 2005, 01:07:34 pm
Quote
I think we're a long way from infinity making a jump from 35mm to 8x10 (12) which, as I said, is  about the same order of magnitude as going from the smallest digicam to 35mm (ie. 3x4.5mm to 24x36mm).
To follow up on my previous post, let's conduct a thought experiment comparing an equal-photon exposure between the two formats you mentioned.

Let's start with an exposure optimized for the digicam. Assume the light level is such that a 4mm lens with a 1mm aperture (or f/4) yields perfect exposure for the digicam set at ISO 100, 1/100 second exposure. Let's translate that exposure to the 1Ds-MkII.

To get the same framing, the focal length needs to change from 4mm to 32mm. Keeping the 1mm physical aperture means we must shoot at f/32 to maintain equal DOF. To keep exposure at 1/100, the ISO would have to be raised to ISO 6400, which isn't even possible. If you raise the ISO to 1600 (the highest setting that is not based on firmware cheats manipulating the digital data after ADC conversion), you're faced with trying to recover a high-ISO image that is 2 stops underexposed, which is unlikely to be better overall than the perfectly-exposed digicam image.

Going the other way, a properly-exposed 1Ds-MkII ISO 1600 image is going to be overexposed by two stops given equal aperture diameter and exposure time, and ISO 100 on the digicam. The digicam simply can't handle the photon overload.

The best format for a given application (leaving lens limitations aside) is the one that is just large enough to handle the photon capacity of the desired exposure--sufficiently short shutter speed to minimize motion blur to acceptable levels, and sufficiently small aperture to achieve acceptable DOF--when the sensor is at its native ISO. No format is "best" in all situations.
Title: Leaf backs at 28MP, 35MP
Post by: Ray on December 31, 2005, 01:18:21 pm
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If you turned it around and dumped the photons involved in a perfectly-exposed ISO 100 digicam frame on to a 24x36 sensor, you'd have an underexposed mess which would at best be no better than the digicam shot, and would have a very good chance of being much worse. The Canon DSLRs deliver better image quality in low light because they process many more photons per exposure than the digicam, even at higher ISO setrtings. And that's why your comparisons are absurd.
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So basically you're saying my observation is wrong. That means I'll have to go back and check it. I've got a Sony T1 which I thought would be a great little camera to carry around everywhere in my shirt pocket. I no longer use it because ultimately image quality in any circumstance is compromised. It's only advantage is it's light and compact (although a little too dense for a shirt pocket).

I did a comparison with my Canon D60 at equivalent DoF and shutter speed but adjusted ISO to get the same shutter speed. Image quality was similar but the D60 was marginally better.

I've read reports on other forums of similar comparisons. I've never come across an example of a P&S digicam that can produce better image quality in poor lighting conditions (without flash of course) than a Canon DSLR at equivalent DoF.

However, because I haven't come acroos it means little. Put me straight and point me to such an example.
Title: Leaf backs at 28MP, 35MP
Post by: Ray on December 31, 2005, 01:41:27 pm
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To follow up on my previous post, let's conduct a thought experiment

No need to conduct a thought experiment. There are lots of practical examples.

If I was marketing a small digicam that could produce better image quality in poor lighting conditions than the heavier and much more expensive DSLR, I'd play it for all it was worth.
Title: Leaf backs at 28MP, 35MP
Post by: Jonathan Wienke on December 31, 2005, 01:45:13 pm
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I've read reports on other forums of similar comparisons. I've never come across an example of a P&S digicam that can produce better image quality in poor lighting conditions (without flash of course) than a Canon DSLR at equivalent DoF.

However, because I haven't come acroos it means little. Put me straight and point me to such an example.
Canon DSLRs are certainly capable of better low-light images sans flash, but such images are not obtained at digicam-equivalent near-infinite DOF. f/2 on a 1Ds typically involves a much larger physical aperture than f/2 on a digicam, so much so that even when shooting at ISO 1600, you're still imaging many more photons than you could with the digicam at ISO 100.
Title: Leaf backs at 28MP, 35MP
Post by: Ray on December 31, 2005, 03:15:52 pm
Quote
Canon DSLRs are certainly capable of better low-light images sans flash, but such images are not obtained at digicam-equivalent near-infinite DOF. f/2 on a 1Ds typically involves a much larger physical aperture than f/2 on a digicam, so much so that even when shooting at ISO 1600, you're still imaging many more photons than you could with the digicam at ISO 100.
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Jonathan,
Point me to some real world results. Small 2/3rds digicams have approximately 1/16th the area of FF 35mm. To get equivalent DoF on FF 35mm, the F stop has to be multiplied by 4. Ie., F2 on small digicams equates to F8 on FF 35mm.

To get the same exposure (shutter speed) on the 35mm DSLR, one has to bump up ISO from 100  t0 1600.

The question thus arises, how does a small digicam shot at ISO 100 compare with a FF 35mm shot (5D specifically) at ISO 1600.

Qujite favourably is my impression.
Title: Leaf backs at 28MP, 35MP
Post by: Jonathan Wienke on December 31, 2005, 04:19:58 pm
The example I gave was based on your earlier digicam example. If you compare to a different format, obviously the comparison parameters change. But I'd say that an ISO 100 image from a K-M A2 would compare fairly well to an equal-aperture/exposure ISO 1600 image from a 1D-MkII.

I stand by my assertion that a larger format is only advantageous if you can use it to image more photons than a smaller format. If so, the larger format is more suitable. If not, you're breaking even at best and run a significant risk of degrading image quality.
Title: Leaf backs at 28MP, 35MP
Post by: BJL on December 31, 2005, 08:19:04 pm
Jonathan has stated an idea that I than has great merit:

the dominant benefits of larger format sensors relate to gathering more photons and thus "more information" from the subject.

That requires longer exposure times and/or larger effective aperture diameters (e.g same f-stop with a longer focal length), and thus forces resolution trade-offs related to the effects of camera-subject motion and/or increased OOF blur for all parts of the scene not at the exact focus distance. Look at where MF and LF film cameras are and are not used and you should get the picture.

Dark noise can be reduced, but at most this will reduce, not eliminate, the advantage of smaller sensors when an equal amount of light is gathered in different formats. And dark current comes from some fairly fundamental physical sources, so reducing it much below current levels probably requires fairly drastic measures like cooling the sensor. Cooling is already done in some bulky high end equipment, but might never come in a conveniently hand-holdable camera.
Title: Leaf backs at 28MP, 35MP
Post by: Ray on January 01, 2006, 05:50:24 am
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The example I gave was based on your earlier digicam example. If you compare to a different format, obviously the comparison parameters change. But I'd say that an ISO 100 image from a K-M A2 would compare fairly well to an equal-aperture/exposure ISO 1600 image from a 1D-MkII.

I stand by my assertion that a larger format is only advantageous if you can use it to image more photons than a smaller format. If so, the larger format is more suitable. If not, you're breaking even at best and run a significant risk of degrading image quality.
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Perhaps I'm not doing a good job getting my point across so let me try another tack. Whatever the formats being compared, if the physical aperture is the same, the FoV the same, the shutter speed the same then the number of photons will be the same. In my example of 35mm format at f2 and ISO 100 (50mm lens) compared with 8x10 format at f16 and ISO 6400 (400mm lens), the total number of photons reaching the sensor is the same, right?

So what's different? Well, I'm making an assumption here that it's possible to optimise an LF lens so it's truly diffraction limited at f16. I've not heard of a 35mm lens being diffraction limited at f2. Although the number of photons are the same, their arrangement is different. The image from the 50mm lens at f2 contains lots of aberrations. Many of that total number of photons are wasted or counterproductive, whereas the photons that have passed through the LF lens are as good as they get. You can't get a better image than one that is limited only by lens diffraction.

But you are right that higher dark noise will degrade the sharper image, but by how much is complete guesswork. I have no access to the latest cutting edge technology that's being developed under great secrecy in the labs. All I can do is compare what's already out there and available, and when I do, I find that Canon DSLRs can do just as good a job with the same number of photons as the smaller digicam and I wouldn't be surprised if the 5D does a significantly better job than the latest small P&S digicams.

There's a lot of room in in an 8x10 format camera for a lot of sophisticated technology. Your assertion that what I'm proposing is absurd and impossible reminds me of those mathematicians who thought they could prove that heavier than air machines could not fly.
Title: Leaf backs at 28MP, 35MP
Post by: Jonathan Wienke on January 01, 2006, 10:22:23 am
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So what's different? Well, I'm making an assumption here that it's possible to optimise an LF lens so it's truly diffraction limited at f16. I've not heard of a 35mm lens being diffraction limited at f2. Although the number of photons are the same, their arrangement is different. The image from the 50mm lens at f2 contains lots of aberrations. Many of that total number of photons are wasted or counterproductive, whereas the photons that have passed through the LF lens are as good as they get. You can't get a better image than one that is limited only by lens diffraction.
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Your assertion that what I'm proposing is absurd and impossible reminds me of those mathematicians who thought they could prove that heavier than air machines could not fly.
You know what they say about assumptions...and again, you are being absurd. You've forgotten the practical reality that designing a lens to cover a smaller image circle makes it far easier to achieve a high MTF at high LP/mm. The cheapest digicam lenses maintain 50% MTF at much higher LP/mm values than the best 35mm lenses, and many LF lenses do not perform well when attached to a 1Ds for the same reason. As a result, doubling the linear dimensions of the format approximately doubles the usable resolution in practice, instead of the theoretically-possible squaring it. It's no easier to make a LF lens diffraction-limited at f/16 than it is to make a 35mm lens diffrraction-limited at f/2. I've not heard of either.
Title: Leaf backs at 28MP, 35MP
Post by: Ray on January 01, 2006, 12:22:13 pm
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You've forgotten the practical reality that designing a lens to cover a smaller image circle makes it far easier to achieve a high MTF at high LP/mm.


No, I haven't forgotten it. I recall BJL has been playing down this advantage for lenses of focal lengths greater than about 65mm. The  resolution advantages I  see for the larger format (ignoring dynamic range and dark noise considerations for a moment) result from the use of the LF lenses at apertures where diffraction is the main aberration. You simply can't get a sharper image, in combination with the DoF that the aperture allows, when a lens is diffraction limited at the aperture being used, whatever the format.

F64 on 8x10' format does not produce a sharper, more detailed image at the focal plane (as opposed to the recorded image) than f8 on 35mm if both lenses are diffraction limited at those apertures. I'm fairly sure that most 35mm lenses are not diffraction limited at f8. If they were, their performance at f8 would tend to be the same, which it clearly isn't according to the Photodo tests.

If LF lenses are nowhere near being diffraction limited at f16 then of course my argument is diminished. But the main point I've been making in these last few posts is that the smaller format has no advantage other than being small, light and cheap, and to prove it, when I next see my friend who owns a KM A2, I'll do some comparisons with my 5D at equal physical apertures and shutter speeds.
Title: Leaf backs at 28MP, 35MP
Post by: Jonathan Wienke on January 01, 2006, 02:32:57 pm
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F64 on 8x10' format does not produce a sharper, more detailed image at the focal plane (as opposed to the recorded image) than f8 on 35mm if both lenses are diffraction limited at those apertures. I'm fairly sure that most 35mm lenses are not diffraction limited at f8. If they were, their performance at f8 would tend to be the same, which it clearly isn't according to the Photodo tests.
For 35mm lenses, diffraction usually starts kicking in beyond about f/11 or so. f/8-f/11 is generally the "sweet spot" where the lens performs best, with better lenses generally having their sweet spot at larger apertures.

You're actually proving my point here, namely that given an equal-aperture, equal-photon exposure and diffraction-limited lenses, the larger format offers no resolution advantage whatsoever over the smaller one, and the constraints of practically achievable ISO and dark current noise dictate that the large-format image will actually be worse. The only way larger formats "win" is if they are allowed to image more photons, by either increasing exposure time or aperture size.
Title: Leaf backs at 28MP, 35MP
Post by: BJL on January 01, 2006, 10:41:26 pm
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No, I haven't forgotten it. I recall BJL has been playing down this advantage for lenses of focal lengths greater than about 65mm.
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I think you are misquoting me. My comments were about getting roughly the same absolute resolution (lp/mm) from lenses of the same focal length for different formats when the lenses compared are both of narrower than normal angular field of view.

The comparison being discussed now involve lenses of the same angular field of view for different formats, and thus with the larger format lens having a longer focal length. Here both evidence and theory suggest that the shorter focal length lens for the smaller format will typically have higher absolute resolution.

One source of experimental data is the MTF graphs provided at the website of Schneider.
First compare lenses in the same family at different focal lengths: as the focal length goes up, MTF at equal lp/mm values tends to go down.
Then compare their new Digitars, designed for smaller image circles and generally of shorter focal lengths, to any other Schneider view camera lenses: the smaller format Digitars have dramatically better MTF performance. (Compare at 20lp/mm, the lowest value used for the Digitars but the highest value used for any other lenses.)

In fact, judging from the MTF curves at 20, 40 and in most cases 60 lp/mm, the Digitars seem to have absolute resolution second only to the Olympus Zuiko Digital lenses for Four Thirds format (for which MTF curves also available at 20 and 60 lp/mm). But even some good Olympus zooms outperform the Digitar primes, so once again, smaller formats win out on absolute resolution.
Title: Leaf backs at 28MP, 35MP
Post by: Ray on January 02, 2006, 12:10:18 am
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For 35mm lenses, diffraction usually starts kicking in beyond about f/11 or so. f/8-f/11 is generally the "sweet spot" where the lens performs best, with better lenses generally having their sweet spot at larger apertures.

You're actually proving my point here, namely that given an equal-aperture, equal-photon exposure and diffraction-limited lenses, the larger format offers no resolution advantage whatsoever over the smaller one, [a href=\"index.php?act=findpost&pid=54942\"][{POST_SNAPBACK}][/a]

Yes, given equal physical apertures that are diffraction limited, equal FoV and equal photon count, there would be no resolution advantage to the larger format (assuming adequate sensors with more than sufficient pixels, reduced dark noise and no tilt to produce a DoF advantage).

However, in asserting that a diffraction limited LF lens at f16 would be just as difficult to make as a 35mm lens diffraction limited at f2, you are also making one big mother-of-all-stuffups' assumption. Where's your evidence for this? What facts or statements from LF experts are you using to deduce this?

I would agree that diffraction tends to dominate somwhere between f8 and f11 for 35mm, which is not necessarily the same as the sweet spot. The Canon 200/1.8 has a sweet spot at f4. It's marginally sharper at f4 than f8 but nowhere near diffraction limited at f4. If it was, its resolution in lp/mm would be double that at f8.

I think you've missed the point I'm making. With the exception of a few really expensive lenses such as the Canon 200/1.8, you are limited to a maximum resolution at around f8 to f11, which gives you the same image resolution and DoF as 8x10" at f64 to f90. With 35mm, I can sacrifice a bit of DoF and get an equally sharp image at f5.6, maybe. If a shallow DoF is desired, then of course it's no sacrifice.

Now according to statements from people such as Norman Koren, LF lenses used at f64 and f90 do not produce spectacularly detailed results because at such apertures the lenses are way beyond the diffraction threshold of the lenses. You have to open them up to f22 to get close to their full resolution potential. That's equivalent to 35mm f2.8. Show me the 35mm lens which can produce a dramatic increase in resolution by opening up to f2.8.

Add the tilt fator of LF cameras to the equation, then providing the subject lends itself to that process, you have both a dramtic increase in resolution whilst maintaining good DoF, but using just the same number of photons (provided you fit enough technology in that large box to dramatically reduce dark noise).
Title: Leaf backs at 28MP, 35MP
Post by: Ray on January 02, 2006, 12:44:13 am
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The comparison being discussed now involve lenses of the same angular field of view for different formats, and thus with the larger format lens having a longer focal length. Here both evidence and theory suggest that the shorter focal length lens for the smaller format will typically have higher absolute resolution.

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BJL,
Well now you've confused me. If the term 'absolute resolution' refers to line pairs per mm, then absolute resolution is not what we should be talking about. Surely it's total picture resolution that counts. As camera format increases in size, the absolute resolution falls off in inverse proportion to the increase in format size, provided the lenses are used at apertures where diffraction is the only limit to resolution, and assuming equal FoV and DoF for the different format lenses

Once again, if I can choose a format so that I will always be using the lens at diffraction limited apertures, whether or not a shallow or deep DoF is desired,. then I have a potential resolution advantage. As I see it, an 8x10" format camera is the most likely to provide that opportunity, followed by MF.

In other words, with LF I have the option to trade off DoF for an increase in resolution. There's no such option with 35mm. I'm stuck with the resolution it can deliver at f9 (say) and I just hope that resolution is not too bad at f2 or f1.8. (My Sigma 20/1.8 is pretty bad at F1.8, but even the much praised Canon 50/1.4 is not too hot at f1.8 and f2).)
Title: Leaf backs at 28MP, 35MP
Post by: Jonathan Wienke on January 02, 2006, 04:31:32 am
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However, in asserting that a diffraction limited LF lens at f16 would be just as difficult to make as a 35mm lens diffraction limited at f2, you are also making one big mother-of-all-stuffups' assumption. Where's your evidence for this? What facts or statements from LF experts are you using to deduce this?
Try re-reading BJL's post about Schneider lenses, for starters. It's exactly what you're asking for. And then do a bit of figuring with regard to the LP/mm and MTF achievable by cheap digicam lenses compared to the best 35mm and LF lenses and you'll find a pretty direct inverse correlation between image circle coverage and the LP/mm value where MTF falls below 50%. I'm not just pulling premises out of my butt here, all you have to do is go to any digicam review at DPReview and compare the sensor size and resolution, and convert that to LP/mm, then contrast that to LP/mm specs published for 35mm lenses or LF lenses. You'll find the digicam lenses are delivering pretty decent MTF percentages at LP/mm values that are far higher than 35mm or LF lenses can dream of. The only reason a cheap digicam lens can outperform an expensive LF lens so decisively is because it does not need to cover as large of an image circle as the LF lens.

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In other words, with LF I have the option to trade off DoF for an increase in resolution. There's no such option with 35mm. I'm stuck with the resolution it can deliver at f9 (say) and I just hope that resolution is not too bad at f2 or f1.8. (My Sigma 20/1.8 is pretty bad at F1.8, but even the much praised Canon 50/1.4 is not too hot at f1.8 and f2).)
Again, that proves my point that in order for LF to provide a usable advantage it must image more photons. And stating that 35mm does not offer any ability to trade off resolution for DOF is simply stupid. No lens in any format is perfect; all formats suffer from lens aberrations that are far from the diffraction when the lens is wide open. There's a disconnect between the diffraction limit and what the lens can actually deliver; this gap becomes wider as the imaging circle of the lens increases. Between that and the exposure time increases mandated by the fairly narrow range of available sensor/film ISO capabilites, and increased cost, weight, and bulk, larger formats become progressively less practical; the circumstances under which they can deliver a useful image become progressively more restrictive as size increases, to the point at which they become nearly useless. If larger is always better, why stop at 8x10? Why not 16x20, or 24x36, or something even larger?
Title: Leaf backs at 28MP, 35MP
Post by: Ray on January 02, 2006, 09:04:26 am
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do a bit of figuring with regard to the LP/mm and MTF achievable by cheap digicam lenses compared to the best 35mm and LF lenses and you'll find a pretty direct inverse correlation between image circle coverage and the LP/mm value where MTF falls below 50%.

I've done the figuring. That's why I'm able to make and understand statements that all lenses at equal physical aperture and equal FoV, regardless of format, will provide the same total image resolution (excluding degradation caused by film or sensor). That shorter focal length lenses with smaller image circles deliver higher spatial resolution (more lp/mm) is implicit in the above statement.

Were it not so, then 35mm at a diffraction limited f8 could not provide the same resolution as 8x10 at a diffraction limited f64. Absolute resolution at f8 has to be 8x as great as LF at f64. That's simple maths.

The point I'm making, which again seems to have escaped you, is that lp/mm at f4 with 35mm is not even nearly 8x as great as the equivalent 8x10 f32. Where's the problem in appreciating that fact? It seems quite clear to me, or are you perhaps refuting my claim that opening up from f64 on 8x10 format to f32 does not substantially increase resolution?

I admit there's not much reliable information available on the net regarding MTF tests of LF lenses, but following is an extract from a Schneider Optics FAQ on large format lenses.

 7. Why does the sharpness of my lens increase as I stop down, and then decrease as I stop down further?

You are experiencing the effects of two primary optical aberrations, spherical aberration and diffraction. As you stop the lens down, spherical aberration is reduced, and the effects of diffraction are increased. This generally results in a "sweet spot" around f11, where the image has benefited from reduced spherical aberration, but not yet been degraded severely by diffraction. At small apertures such as f64, diffraction effects are quite large and the image will be noticeably softer.

The interesting thing here is that Schneider Optics LF lenses have a sweet spot at f11. You'd almost think they were referring to 35mm. I assume it's the smaller LF lenses for 4x5 format they're referring to. Even so, a sweet spot at f11 on 4x5 format is equivalent to a 35mm lens with a sweet spot at f2.8.

The most thorough series of LF lens tests I can find on the net is by Perez and Talman. Their results can be viewed here (http://www.hevanet.com/cperez/testing.html)

Again, it's not clear which of the tested lenses would be suitable for 8x10 format, but I think it's likely that some of the 360mm and longer would be. I checked out some of the names and it seems some photographers are using some of these lenses with 8x10 format, such as the Fuji C-Series F12.5 for which there are 2 sets of results in the table, the first of which shows best resolution (and equal resolution) from f12.5 to f22. At f32, diffraction is already taking its toll. That would be equivalent to a 35mm lens having a sweet spot at f stops ranging from f1.6 to f2.8 with a progressive deterioration in resolution at larger fstop numbers.

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If larger is always better, why stop at 8x10? Why not 16x20, or 24x36, or something even larger?

Do you not remember a thread a while ago about an American who built his own very,very large format camera. He had the lens poking out of one side of a van, exposed something like a 4'x6' image on the other side of the van and made contact prints of apparently amazing resolution. He drove around visiting schools to demonstrate the principles of photography. Pretty stupid, eh?  

I just came across some MTF details of a wide angle lens with an image circle of 500mm designed for a 9x18" format camera. Usable resolution is 30lp/mm. Such a lens used with a cropped 8x10 format would deliver 30 lp/mm even into the corners at no less than 30% MTF. With a crop factor of 5/3, the 210mm wide angle lens becomes pretty close to a standard lens for 8x10. To capture that resolution you'd need at least a 180mp Foveon type sensor or perhaps better a 300MB Bayer type since sensitivity is an issue. . Do you think there's a snowball's chance in he*ll of anyone designing a 35mm lens that can make use of 180 megapixels. We're only up to 16mp with the 1ds2 and already people are complaining their lenses are not good enough.

Your arguments seem to be flying in the face of the facts, Jonathan. Details of this lens can be found here (http://www.gigapxl.org/technology-lens.htm) .
Title: Leaf backs at 28MP, 35MP
Post by: Jonathan Wienke on January 02, 2006, 02:51:36 pm
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Do you not remember a thread a while ago about an American who built his own very,very large format camera. He had the lens poking out of one side of a van, exposed something like a 4'x6' image on the other side of the van and made contact prints of apparently amazing resolution. He drove around visiting schools to demonstrate the principles of photography. Pretty stupid, eh? 
Not stupid, but not very practical, either. I doubt he was shooting surfing or weddings or fashion shows or car races or photojournalistic stuff with that rig. I think it's safe to say his exposures were measured in minutes or hours, not fractions of a second.

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I just came across some MTF details of a wide angle lens with an image circle of 500mm designed for a 9x18" format camera. Usable resolution is 30lp/mm. Such a lens used with a cropped 8x10 format would deliver 30 lp/mm even into the corners at no less than 30% MTF. With a crop factor of 5/3, the 210mm wide angle lens becomes pretty close to a standard lens for 8x10. To capture that resolution you'd need at least a 180mp Foveon type sensor or perhaps better a 300MB Bayer type since sensitivity is an issue. . Do you think there's a snowball's chance in he*ll of anyone designing a 35mm lens that can make use of 180 megapixels. We're only up to 16mp with the 1ds2 and already people are complaining their lenses are not good enough.

Your arguments seem to be flying in the face of the facts, Jonathan. Details of this lens can be found here (http://www.gigapxl.org/technology-lens.htm) .
You're deliberately mischaracterizing my remarks, and straying far from the equal-aperture/equal-photon exposure comparison we have been discussing. In any such comparison, the smaller-format camera will (all else being equal) deliver a better result until it is no longer capable of imaging all of the photons without overexposure/clipping. Once the quantity of photons in the exposure exceeds the imaging capacity of the smaller format (and clipping occurs), then the larger format will produce the better result, and will continue to do so in increasingly decisive fashion as the photon count is increased until it's imaging capacity is reached. I have never denied that larger formats are capable of greater resolution than smaller ones, even though large-format lenses are not capable of resolving as many lp/mm as smaller-format lenses. But in order to make use of this increased resolution potential, large-format cameras must image more photons per exposure than their small-format counterparts. And that means that their practicality decreases as format size increases.
Title: Leaf backs at 28MP, 35MP
Post by: BJL on January 02, 2006, 08:16:20 pm
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With the exception of a few really expensive lenses such as the Canon 200/1.8, you are limited to a maximum resolution at around f8 to f11
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I believe that many modern lenses have peak resolution at larger apertures than f/8 to f/11; f/4 seems a more reasonable figure for good primes, and even some good zooms (e.g. the Canon 70-200 f/2.8 IS L?) In fact the Canon 17-85 f/4-5.6 EF-S seems sharpest at apertures very close to wide open, and that is only a mid-priced, wide ranging zoom (for a dead-end, low level format!) FourThirds lenses in general seem to be sharp almost all the way to maximum aperture.

It is probably time to revise that old saw that "lenses are sharpest two stops down from wide open", to reflect progress like aspherical lens elements.
Title: Leaf backs at 28MP, 35MP
Post by: Ray on January 02, 2006, 08:57:07 pm
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You're deliberately mischaracterizing my remarks, and straying far from the equal-aperture/equal-photon exposure comparison we have been discussing. In any such comparison, the smaller-format camera will (all else being equal) deliver a better result until it is no longer capable of imaging all of the photons without overexposure/clipping. Once the quantity of photons in the exposure exceeds the imaging capacity of the smaller format (and clipping occurs), then the larger format will produce the better result, and will continue to do so in increasingly decisive fashion as the photon count is increased until it's imaging capacity is reached.
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Not really. I've always conceded that increased dark noise of the larger format is a technological barrier. The difference in our attitudes here is that I seem to be positive about the capacity of technology to solve problems and you seem to be negative, like those who were convinced that heavier-than-air machines could never fly.

I'll also concede that all else being equal the smaller format will do a better job imaging an equal number of photons. But all else is rarely equal, is it?

I've already compared my Canon D60 with the newer technology Sony T1 at equal physical apertures and found the D60 did a marginally better job. I'm fairly convinced the 5D with a sensor about 16x the area of the KM A2 will produce a better image than that camera with the same number of photons.

As I see it, you are making assertions with no concrete evidence to back them up, which is surprising considering how elegantly you espoused the scientific method recently in another thread.

Now if you'd like to provide some factual mathematical evidence along the lines that increased dark noise is not proportional to increased sensor size, but increases exponentially, then I'll eat my words and concede that the fact that current 35mm DSLRs can produce an equal or better image than the smaller sensor with the same number of photons is not relevant to the situation of very large format.
Title: Leaf backs at 28MP, 35MP
Post by: Ray on January 02, 2006, 09:41:43 pm
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I believe that many modern lenses have peak resolution at larger apertures than f/8 to f/11; f/4 seems a more reasonable figure for good primes, and even some good zooms (e.g. the Canon 70-200 f/2.8 IS L?) In fact the Canon 17-85 f/4-5.6 EF-S seems sharpest at apertures very close to wide open, and that is only a mid-priced, wide ranging zoom (for a dead-end, low level format!) FourThirds lenses in general seem to be sharp almost all the way to maximum aperture.

It is probably time to revise that old saw that "lenses are sharpest two stops down from wide open", to reflect progress like aspherical lens elements.
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A point worth making. However, good lenses often have a consistently good performance over a fairly wide range of apertures. That's one of the features you pay for. The Photodo ratings for the Canon 200/1.8 vary from 82 to 90 across the range of f stops from f1.8 to F8. That's roughly a 10% variation.

The fact is, when a lens is diffraction limited at the apertures being used, resolution increases inversely in proportion to the f stop number. With the 200/1.8 there's a sweet spot at f4. The lens is marginally sharper at f4 than at f8. If it was diffraction limited at f4, resolution would be double that at f8. This is the difference I'm talking about. Large format allows one to use the lens at diffraction limited apertures (or at least closer to the diffraction limit) whatever your DoF requirements are. Using a lens at a diffraction limit could be thought of as using that lens with 100% efficiency.

If we consider the performance of the wide angle lens designed by Paul Weissman for the Gigapxl project, a lens at f22 that is diffraction limited will have a maximum resolution of 66 lp/mm at 9% MTF. The MTF chart for this lens shows an MTF of 50% in the centre at 30 lp/mm, falling off to only 30% in the corners if the lens is used with the smaller format 8x10. I don't know what the resolution would be at 9%, but it seems a reasonable assumption it would be close to 66 lp/mm, at least in the centre. This lens seems pretty close to being diffraction limited at f22, wouldn't you say?
Title: Leaf backs at 28MP, 35MP
Post by: Ray on January 03, 2006, 08:57:35 pm
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But in order to make use of this increased resolution potential, large-format cameras must image more photons per exposure than their small-format counterparts. And that means that their practicality decreases as format size increases.
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Image more photons or use technology to remove dark/thermal noise?

The great fallacy in your argument, Jonathan, is this. Whilst it's true that the smaller camera with the smaller sensor has an inherent advantage imaging a small number of photons, to fully exploit and capitalize on this inherent advantage requires the application of state-of-the-art noise reduction technology, including microlenses to increase sensitivity, dark frame subtraction, on-sensor signal processing and super cooling with micro-miniature refrigeration devices to eliminate almost all dark noise.

Such a small format camera would have no peer amongst the larger formats when it came to taking reasonable resolution images in low light without flash and with short exposures. But such a camera would no longer be small, light and cheap. It would have a high ISO setting with remarkably low noise, but still only be capable of a small dynamic range because of its small pixels and relatively low resolution because of the small number of pixels. It would be a specialised camera suitable for certain scientific applications, and probably as big and heavy as a 1Ds.

People expect large format cameras to be big and heavy. I notice that Sony now has a notebook weighing only 1.2Kg which includes a 60GB HD and (I believe a first in this category) a built-in dual layer DVD recorder. (Ideal for photographers downloading and burning images in the field).

When a camera weighs say 4Kgs, an extra O.5Kg for a powerful computer to help reduce noise is acceptable. When a camera weighs 10oz it's over the top. The same applies to cooling systems.

A browse on the net leads me to believe there are a number of lightweight and efficient micro refrigeration systems currently available, not including those in the process of development such as the following;

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The devices, called "micro-channel heat sinks," circulate coolant through numerous channels about three times the width of a human hair. Such devices might be attached directly to electronic components in military lasers, microwave radar and weapons systems, as well as in future computers that will generate more heat than present computers, said Issam Mudawar, a professor of mechanical engineering who is leading the research.

The researchers are adapting refrigeration systems by using the micro-channel heat sinks to replace conventional "evaporators" components in household refrigerators that contain a labyrinth of tubing. As coolant circulates through the tubing, heat is removed from the refrigerator to cool the food inside.

"We are substituting these conventional evaporators which might be well over a meter long in the typical refrigerator with a heat sink that's only about 1 inch square," Mudawar said. "The challenge is how to unplug this large evaporator and put in its place this tiny heat sink and make the whole system work."

[a href=\"http://www.physorg.com/news3725.html]http://www.physorg.com/news3725.html[/url]


Again, a browse on the net leads me to believe that lowering the temperature of a sensor (and its environment presumably) by just 20 degrees C can result in as much as a 10 fold decrease in dark current noise. There are small, efficient cryogenic devices already available which can lower the temperature to around minus 200 degrees C in less than 15 minutes.

Imagine something the size of the average 8x10 field camera made of super lightweight carbon-fibre materials and containing inside a double vacuum thermal insulation. The refrigeration system could be initially powered from the car battery to bring the temperature down to say minus 50 degrees C (in about 15 minutes). From there on the gradual slight rising of temperature could be countered by use  a standard lithium battery back.

Taking an average of the lowest and highest rates of dark noise reduction I've seen on the net, I arrive at a figure of around 7x per 20 degree reduction in temperature. From +30 degrees (in Australia) to minus 50 should result in a dark noise reduction of over 2,000 fold. Do you think that would be sufficient?
Title: Leaf backs at 28MP, 35MP
Post by: Jonathan Wienke on January 03, 2006, 10:01:26 pm
Any thermal noise reduction technique usable on large-format sensors will work equally well on small-format ones, so the net result is a wash. If you can cool an 8x10, you can cool a 1Ds-MkII. A Peltier chip/heatsink for a 1Ds is going to be a lot smaller/lighter than one for an 8x10 sensor, so its weight will be increased much less. In both cases, the additional cost/bulk will be proportional to the imaging area, so the size/weight/cost/quality ratio between them will be relatively unchanged. The same goes for software noise reduction, which is better done in post with a real computer than in-camera anyway. Neat image can improve a 35mm image just as well as an 8x10 image. You've proved nothing here, except your propensity for wishful thinking.
Title: Leaf backs at 28MP, 35MP
Post by: Ray on January 03, 2006, 10:21:13 pm
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Any thermal noise reduction technique usable on large-format sensors will work equally well on small-format ones, so the net result is a wash. [a href=\"index.php?act=findpost&pid=55143\"][{POST_SNAPBACK}][/a]


Well that's essentially what I just said in my previous post.... except it's not a wash. The larger format sensor is capable of higher resolution and greater dynamic range. We have an instrument which is not so specialised and therefore more desirable for those wanting the ultimate in image quality. Ie. a camera that can deliver a stunningly detailed 8ft x 10ft print but also a remarkably sharp and noise free image in poor lighting conditions at high shutter speed.

Design a small format camera to produce a better image with the same number of photons, increases the weight, size and cost and leaves you with a relatively low resolution image with relatively poor dynamic range but superb signal-to noise at high ISO's. That's not a wash.

Did it occur to you that at certain sub zero temperatures there may be no further  noise reduction of practical consequence in the smaller format. The wash is in the potentially equal level of dark noise reduction, with the larger format requiring a greater reduction of temperature to achieve that. Having achieved it, the diffraction limited large format lenses provide the extra resolution with equal noise per pixel, but less noise per image because of the greater number of pixels.
Title: Leaf backs at 28MP, 35MP
Post by: Jonathan Wienke on January 03, 2006, 11:34:54 pm
Except that it is a wash at best. Given theoretically perfect, zero noise sensors, diffraction-limited lenses, equal aperture diameters, and equal-photon exposure, net image quality will be the same. Given any deviation from theoretical perfection in the sensor department, the smaller format wins. Larger formats can beat smaller ones, but only when they image more photons than the smaller format. Period.
Title: Leaf backs at 28MP, 35MP
Post by: Ray on January 04, 2006, 12:11:06 am
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Except that it is a wash at best. Given theoretically perfect, zero noise sensors, diffraction-limited lenses, equal aperture diameters, and equal-photon exposure, net image quality will be the same. [a href=\"index.php?act=findpost&pid=55150\"][{POST_SNAPBACK}][/a]

I'll go along with that. Except you seem to have already forgotten that diffraction limited lenses at really small f stops do not exist. If I recall, BJL has stated that around f5.6 is as wide as we can expect for diffraction limitation. Maybe f4. However, if you are talking about the small format, you've still got dynamic range limitations.

I'd agree in principle that if you were to apply all the noise reduction technology to the small sensor plus the 'still under research' frequent sampling and charge emtying of the photodiode as it fills, then there might be little point in developing a large format sensor.

However, you've still got the reducing photodiode efficiency factor as pixel sizes approach the dimenson of light waves, as you pointed out to me some years ago. You can't fit 100 million photo-diodes on a small 2/3rds sensor without each photo  site being too small and inefficient for optimal results.

I would still maintain that, after all the noise reduction technology has been applied, there is nothing the smaller format can do in respect of image quality that the larger format cannot, except be smaller, lighter and cheaper. But that of course is an advantage in its own right. If all you need is a 6mp image, say, under adverse lighting conditions, then you might as well use a relatively light and cheap camera that's been designed for the job (say a $20,000 3Kg camera as opposed to a $100,000  10Kg camera).

However, if you think you can use a $1000 P&S to capture images at fast shutter speeds that the large format camera with all its technology can't manage, then that's wishful thinking.

I'm prepared to let this rest now, having had my say.  
Title: Leaf backs at 28MP, 35MP
Post by: BJL on January 05, 2006, 01:51:30 pm
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If I recall, BJL has stated that around f5.6 is as wide as we can expect for diffraction limitation. Maybe f4.
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Actually I said rather the opposite; current good lenses can go to at least f/5.6 or f/4 before aberrations take over from diffraction as the main limitation on resolution. I am very open to the possibility than in the future, further development of technologies like two-sided aspherical lenses might achieve diffraction limited resolution down to f/2.8 or even f/2. Or at least, it is no less likely that your imaginings of 8"x10", 800MP sensors, which is about what would be required for diffraction to be the resolution limit at f/16.

You argument seems to be based an assuming vast progress in some areas (mostly do do with bigger sensors), while assuming that in other aspects, there is little room for further improvement (35mm format lens performance, small photodiodes). Oh, and pretending that, while diffraction spots are relevant to resolution, circles of confusion are not. Ignoring circle of confusion (DOF,OOF effects) at best makes sense only for purely planar subjects, like when copying documents.

By the way, "100 million photo-diodes on a small 2/3rds sensor" is a red-herring in a discussion that was, up to that point, all about DSLR's, not compact digicams. It is a fallacy to argue that the weaknesses of one extreme shows the superiority of an opposite extreme when the comparison at hand is to other intermediate options. (Like criticizing Stalinism to argue in favor of Fascism, or vice versa, both of which have been done of course.)
Title: Leaf backs at 28MP, 35MP
Post by: Ray on January 05, 2006, 10:06:33 pm
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I am very open to the possibility than in the future, further development of technologies like two-sided aspherical lenses might achieve diffraction limited resolution down to f/2.8 or even f/2.

So am I. When I wrote that you had said diffraction limitation at f5.6 to f4 is the most we can expect, I meant of course expect at the present time. Unless technological progress comes to an end, we can always expect future improvements in all areas.

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You argument seems to be based an assuming vast progress in some areas (mostly do do with bigger sensors), while assuming that in other aspects, there is little room for further improvement (35mm format lens performance, small photodiodes).

I deliberately side-stepped the issue of whether it would ever be practical to manufacture an 8x10" sensor. I simply don't know, but never is a long time. However, I can't help wondering what happens to all those rejected sensor chips that are supposed to keep the cost of full frame 35mm DSLRs so high. A flaw that makes a single sensor unsuitable in a 35mm camera does not necessarily make it unusable in a stitched array of around 50 or so. Also, a supercooled environment allows for the possibility of much more powerful computers using super conductors. Whatever seems impossible or impractical today can become achievable tomorrow with a jump in computer power.

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Oh, and pretending that, while diffraction spots are relevant to resolution, circles of confusion are not. Ignoring circle of confusion (DOF,OOF effects) at best makes sense only for purely planar subjects, like when copying documents.

I've pretended no such thing   . I've already addressed this issue but you seem to have forgotten. The whole idea of supercooling the large format sensor is so that it can provide at least the same quality image with the same number of photons as the smaller camera. If the smaller camera is not cooled, then I would maintain the larger format that is cooled would definitely deliver a better quality image with the same DoF.

To recap, 35mm f8 has equal DoF to 8x12" f64. Traditionally, f64 on a large format field camera requires a long exposure. However, if the LF sensor (and preferrably the whole interior of the camera) is super-cooled, then we can effectively use ISO 6400 which gives us the same shutter speed, same number of photons and same DoF as 35mm f8 at ISO 100.

The 'wash' that Jonathan was referring to seems to be based on an assumption that after all the techology has been applied to both the small and large format, virtually eliminating dark noise, significantly reducing read noise etc so all we are left with is photon noise, then the two systems will perform equally but only in that very narrow range where total photon count , equal shutter speed and DoF, is the same.  Increase the photon count and the larger format will have the advantage, admitted by Jonathan.

Maybe so, but I would maintain the larger format can contain more technology simply because it's larger. Is Jonathan trying to say that a notebook or laptop can ultimately be as powerful as a desk top computer? Imagine the possibilities for on-sensor processing with such a large 8x10" CMOS board.

Call me impractical if you like. I'm just trying to work out from basic principles where the limitations are.
Title: Leaf backs at 28MP, 35MP
Post by: Ray on January 05, 2006, 11:04:32 pm
I think I'd be prepared to accept that if you were to design a small format and large format camera incorporating equal amounts of computing power, cooling, radiation insulation etc, so that each camera was roughly equally heavy and bulky, (the smaller format being just a little lighter) then the small format would win in that narrow range of usage imaging an equal number of photons.

But who would want such a limited camera? As I said, it would only be bought for specialised scientific purposes.

To flesh out this concept a little more I'll have to refine my argument. I've used 35mm f8 and 8x10 f64 as being equivalent because of their popular usage. In fact they are not equivalent. There's no doubt at all that LF f64 is a diffraction limited aperture. That's not the case for 35mm f8 which is more of a sweet spot. Photodo have provided a reason for not testing 35mm lenses at f11. They're all equally bad at that aperture. There's no doubt there's a slight exaggeration in that statement. The really cheap lenses would probably still show some spherical and other aberration at f11, but there would be a sameness of performance amongst all good lenses.

I think a more accurate equivalence between 35mm and 8x12 would be f11 and f90, so let's start off from that point with our heavy, technology laden cameras.

The two super-cooled cameras are giving approximately the same image quality respectively at f11, ISO 100 and f90 ISO 6400. Let's say it's a wash in this respect. As I stop down with both cameras, DoF increases equally and image quality deteriorates equally due to increased diffraction.

But what happens when I stop up? With 35mm there's a sweet spot at f8, say an extra 10% in resolution, maybe less. If the lens is really expensive, like the Canon 200/1.8, there's another sweet spot at f4, say another 10% increase in resolution. At shallower DoFs than f4 there's a deterioration. So, by stopping up from diffraction limited f11, the maximum resolution increase I can get with 35mm is about 24%.

Now let's look at what happens when I stop up from diffraction limited f90 with 8x10" format. If we take the example of the Gigapxl wide-angle lens designed for 9x18" format, we see that such a lens is close to diffraction at f22 and almost certainly at its diffraction limit at f32. Stopping down from f90 to f45 doubles resolution. Stopping down from f45 to f32 (still in the domain of diffraction limitation) increase resolution by another 50%. Stopping down further to the sweet spot at f22 (not quite diffraction limited) gives us say another 20% increase.

I make that a total cumulative increase in resolution with the large format (and all at equivalent DoFs) of around 350%, as opposed to 24% for 35mm.

Now let's get into perspective what a 350% increase in resolution means.

The 5D delivers 100% more resolution than the D30 (ie. double the pixel count in each dimension or 4x the number of pixels). A future 24MP FF 35mm camera with double the pixels of the 5D would potentially give us a further 40% increase in resolution, provided the lenses were up to the job, which it seems clear they aren't. That's a cumulative increase from the D30 to a 24MP FF 35mm of 280%.

So, having demonstrated that current LF lenses are up to the job at the present time, the potential is already there for LF lenses to deliver spades more resolution than 35mm lenses. This not marginal stuff we're talking about. We're talking about a 300% increase in resolution over and above what the 1Ds2 can currently deliver at F4 with a good prime, but equal resolution at greater DoFs than f8 all the way to the smallest aperture the lens supports.

I hope my maths is correct. If it isn't I'm sure you'll correct me   .
Title: Leaf backs at 28MP, 35MP
Post by: Ray on January 06, 2006, 09:38:44 pm
Perhaps the confusion results because you think I'm saying that this dramatic increase in resolution as one stops up from f90 with the LF camera is also achievable at the same shutter speed as the 35mm format at equivalen apertures (same physical aperture).

No, not at all. Having designed the LF camera so that use of ISO 6400 produces about the same noise and resolution as the 35mm format at ISO 100, allowing use of equal shutter speeds for equal image quality in all respects, then these conditions apply across all equivalent f stops.

The dramatically higher resolution potential of the LF at f32 (compared with 35mm f4) can only be realised by increasing the photon count, ie lengthening the exposure. This of course not only results in a much higher resolution image, but much higher dynamic range. If a faster shutter speed is required at f32, to capture the same movement of subject that might necessitate the use of f4 with 35mm, then there is probably no advantage using the LF camera. On the other hand, there is no disadvantage, which is really all I've been trying to say in these last few hundred words.
Title: Leaf backs at 28MP, 35MP
Post by: BJL on January 16, 2006, 09:27:10 pm
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Increase the photon count and the larger format will have the advantage, admitted by Jonathan.
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And as I said before, getting as larger photon count with the larger sensor than is possible with the smaller sensor requires at least one of two things: (1) larger absolute aperture, meaning less DOF (2) longer exposure time.

If we are not ignoring the need for adequate DOF, this mostly means the longer exposure times idea that the main advantage of a larger formats like 8"x10" or even medium format is long exposures of stationary subjects.

Another thing I have said many times: you seem to assume that photosites of a given size will always have a maximum photon count that increases with size, whereas there are numerous technological possibilities for completely eliminating upper limits on photon counts. What substantial advantage would that leave for those far bigger, more expensive sensors requiring super-cooling?
Title: Leaf backs at 28MP, 35MP
Post by: Ray on January 16, 2006, 10:35:09 pm
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Another thing I have said many times: you seem to assume that photosites of a given size will always have a maximum photon count that increases with size, whereas there are numerous technological possibilities for completely eliminating upper limits on photon counts. What substantial advantage would that leave for those far bigger, more expensive sensors requiring super-cooling?
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Huge spades of extra resolution. The rapid filling and emptying of small sensors during one long exposure, increases the dynamic range but does nothing for absolute resolution.

In any case, my concession to the smaller format that it can perform at least as well as the larger format with equal photon count and equal DoF, is probably too generous.

Based on what I've observed with my own DSLRs, resolution does not fall off in inverse proportion to ISO. In fact it seems to be maintained pretty well up to ISO 1600, falling only marginally with increased noise.

Getting back to this hypothetical situation of an 8x12" format at f90 and ISO 6400 producing the same resolution, same DoF and same noise as 35mm at f11 and ISO 100, both employing the same shutter speed, I have assumed that the pixels of the larger format will be binned to reduce read noise, say in groups of 16, ie. the larger format is delivering just one quarter of the full resolution it was designed for.

As we stop up to f8 for 35mm and f64 for LF, keeping everything else the same except shutter speed which varies with f stop, the same conditions apply, ie, same DoF, same noise, same photon count, same resolution, EXCEPT there is the option of binning fewer pixels with the large format to achieve the significantly greater resolution that f64 provides over f90 (40% greater). This extra resolution may well come at the expenses of greater noise, but the option simply isn't there with the 35mm format. F8 can only deliver a very marginal increase in resolution compared with f11, with most if not all 35mm lenses.

I'm sorry BJL. I consider myself to be a reasonable bloke but I haven't seen any convincing arguments from you yet to support any innate technological advantage of the smaller format   . (I guess I'll have to add, innate technological advantage with respect to any aspect of image quality. There's no doubt that something lighter and cheaper has its own uses.)
Title: Leaf backs at 28MP, 35MP
Post by: BJL on January 17, 2006, 05:19:03 pm
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Huge spades of extra resolution.
...
I'm sorry BJL. I consider myself to be a reasonable bloke but I haven't seen any convincing arguments from you yet to support any innate technological advantage of the smaller format   . (I guess I'll have to add, innate technological advantage with respect to any aspect of image quality. There's no doubt that something lighter and cheaper has its own uses.)
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I'm sorry Ray, but as I have argues many times before, it seems quite clear that
1) sensor resolution can easily go to the point where overall resolution will soon enough be limited almost entirely by lens resolution
2) the main optical limitations relate to angular resolution (related lines per picture height) and this does not increase much with format size.

The obvious advantages of smaller formats in cost, size and weight are of value in themselves to all but those with infinite funds and infinite cargo capacity. Even Ansel Adams used medium format (Hasselblad) and miniature format (Contax) at times!. So the fundamental physical advantage of less total dark noise is icing on the cake; similar physics applies to film too, and is probably part of the reason for the long-standing preference for 35mm over larger formats in action photography. Given these advantages to a smaller format, the onus is surely on the advocates of a larger format to show if and when that larger format has sufficient compensating advantages.

And of course these advantages do exist in certain situations: for example, all current DSLR formats (4/3" and up) all have a clear advantage over current compact "digicam" format (2/3" and down) for high speed//low light/low noise, since what any DSLR can do at f/2 would require a lens faster than f/1 in any digicam format, probably resulting on quite noticably worse aberrations.

But such arguments have to be made in comparison of specific formats as applied to particular purposes; the desire to show that "bigger/smaller is always better" seems quixotically futile.
Title: Leaf backs at 28MP, 35MP
Post by: Ray on January 17, 2006, 07:41:57 pm
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But such arguments have to be made in comparison of specific formats as applied to particular purposes; the desire to show that "bigger/smaller is always better" seems quixotically futile.
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Agreed! But I think I'm covered on that account since I've already acknowledged earlier in the thread (somewhere) that one should always try to use the best tool for the job. This exercise for me has been an attempt to try and get a handle on the fundamental issues regarding image quality alone, as they apply to different formats.

Jonathan made the point that the only 'ultimate' advantage of the larger format is greater dynamic range as a result of the collection of a greater number of photons through longer exposures.

If that point is correct, then all advantages of the larger format will eventually be wiped out with the introduction of that new technology you've referred to, whereby small photodetectors are repeatedly filled and discharged during the course of one 'longer than usual' exposure.

I'm uneasy with such an explanation because; if we look at lens performance of the most popular (historically) of all formats, the 35mm format, we see that it's difficult to find a lens that's truly diffraction limited at f8, never mind f5.6 or f4.

If we go down the scale from large format to very small format at equivalent diffraction limited apertures, each potentially capable of producing the same resolution and DoF, provided the sensors in all cases have sufficient pixels, we get something like the following:

8x10.....f90;  4x5...f45;  6cmx7cm...f22;  35mm...f11;  APS-C and 4/3rds...f6.3;  2/3rds P&S....F3.

The above are of course approximate figures, but I don't believe they are far out. The essential principle is, as I understand it, each of those apertures will potentially provide the same 'picture' resolution and DoF provided the lenses are diffraction limited at those apertures.

Now the question I'm asking is this. Which of those formats currently have lenses available that are truly diffraction limited at those apertures? My guess is, only the first 4 (8x10 to 35mm).

Supposing we stop up by 2 stops in order to double resolution whilst still maintaining equivalent DoF across the formats. We get:

8x10... f45;  4x5...f22;  6cmx7cm...f11;  35mm...f5.6;  APS-C & 4/3rds...f3.2;  2/3rds P&S...f1.5.

Now I think already we've eliminated all the small formats from competing in terms of 'picture' resolution because there aren't any lenses for those formats that are diffraction limited at those apertures. We are left with just large and medium format.
Title: Leaf backs at 28MP, 35MP
Post by: BJL on January 19, 2006, 10:40:59 pm
Ray, if you are trying to assess the image detail limits of imagined future cameras, with sensors far beyond what is currently possible (like 8"x10"!), it does not make sense to me to assume that the lenses will have roughly the performance limits of current 35mm format lenses designed within the far more modest resolution needs of keeping up with film. Especially when your estimate of those performance limits seem rather pessimistic, or at least are not based on the very best quality prime lenses, as would presumably be used in this pursuit of ultimate image detail.

So at very least, I suggest that you allow that future 35mm format lenses could avoid significant aberration limitation of resolution down to somewhere between f/2 and f/4, not f/11. And even f/4 gets one to the point that DOF would be inadequate for almost all extreme high resolution images, given the high degree of enlargement (or extremely close viewing) needed to show the great detail provided by that high resolution.
Title: Leaf backs at 28MP, 35MP
Post by: Ray on January 20, 2006, 12:01:27 am
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So at very least, I suggest that you allow that future 35mm format lenses could avoid significant aberration limitation of resolution down to somewhere between f/2 and f/4, not f/11. And even f/4 gets one to the point that DOF would be inadequate for almost all extreme high resolution images, given the high degree of enlargement (or extremely close viewing) needed to show the great detail provided by that high resolution.
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BJL,
F4 is a very usable f stop on 35mm. I can't of course predict the nature of future developments in lens design. It would seem a reasonable assumption that 8x10 and 4x5 is likely to become increasingly irrelevant in the digital age, but maybe a full frame 6x7cm sensor is a possibility. In fact, it might well be more easily technologically feasible to produce say a 100MB 6x7cm sensor with a 90mm lens truly diffraction limited at f8, than a 100MB 35mm sensor with 50mm lens truly diffraction limited at f4.

I mean, if a 50mm lens for 35mm format were diffraction limited at f4, we'd be looking at an MTF response of around 70% at 80 lp/mm, would we not? Is such performance really feasible?
Title: Leaf backs at 28MP, 35MP
Post by: BJL on January 20, 2006, 07:45:37 pm
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F4 is a very usable f stop on 35mm.
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With normal print size/viewing combinations yes, but if we for example quadruple the linear resolution (16 times the pixel count) and so enlarge four times more so as to be able see that extra detail, the perceived DOF is reduced four-fold, so it looks like f/1. I would think that very, very few of such highly detailed images would work at "f/1 equivalent" DOF. Most such "high detail" work is already done at f/8, f/11 and beyond even with poor old 35mm film.

Anyway, I will try to sign of discussing hypotheticals far beyond any current or forseeable technological progress. My expectation though is that lenses will be the dominant limit or resolution and such, far more than sensor capabilities.
Title: Leaf backs at 28MP, 35MP
Post by: Ray on January 21, 2006, 03:31:43 am
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With normal print size/viewing combinations yes, but if we for example quadruple the linear resolution (16 times the pixel count) and so enlarge four times more so as to be able see that extra detail, the perceived DOF is reduced four-fold, so it looks like f/1. I would think that very, very few of such highly detailed images would work at "f/1 equivalent" DOF. Most such "high detail" work is already done at f/8, f/11 and beyond even with poor old 35mm film.
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BJL,
That's a cop out. Okay! So you're getting tired of this thread because of the hypotheticals. Let's bring it back to your assertion that current f1 DoF would look like f4 Dof if we had sufficient resolution (on 35mm).

My gut feeling is, this is not true. There's a tendency in that direction, but it's not linear or proportional.

Perhaps you'd like to start another thread and share your insights with us   .