Theoretical digital sensor equivalent to 8x10?

[BetterSense]

If you're curious about equivalence, read this white paper very carefully.

You'll see why it's actually quite easy to equal 8x10 in situations where you need a lot of depth of field, and almost impossible to do so in situations where you don't.

This theory is born out precisely in tests like the one discussed here.

The test shown actually disproves your point. They used a different aperture on the large-format camera, and then said that the large-format camera had less DOF.

So here are the aperture settings that should have been.

f/11 on IQ180 should be f/53 (or f/45⅔)
f/16 on IQ180 should be f/77 (or f/64⅔)

But we actually used f/32 on the 8×10 and so this has a large impact on depth of field.

Depth of field is only different for different formats if you open the lens more (which is commonly done, because bigger formats are slower).

Of course, in practical photography, speed is an issue. But instead of saying "smaller formats have more DOF" you should really say "smaller formats are faster".

Your other link gets it right

For this reason, it is impossible to tell the images apart. Which in turn means that sensor size is not an image property...

A camera setting is fully described by either of the following parameter sets (including exposure time t):

t, d, FoV, #MP (4 independent parameters)

[Bruce Watson]

I am curious to calculate how large an array of sensors would be needed to be able to record as much information as there is on a well-made and properly processed 8x10 negative.

It would have to be... 10x8 inches, now wouldn't it? There's a lot more to an image than simple resolution. If you want to capture the tonality, the DOF, all that stuff that makes a 10x8 image a 10x8 image, then you're going to have to have a 10x8 sensor. I would have thought that was painfully obvious. Maybe that's just me doing LF for so long, IDK.

[Terry Christian]

A "pixel" has no direct analog equivalent. What we think of as a "grain" of silver is actually a cluster of silver molecules that can vary in size and particular sensitivity. The "1 pixel = 1 silver grain" idea doesn't quite hold up.

Comparing digital to analog media is like comparing apples to oranges. How big does a digital 8x10 equivalent sensor have to be? As big as possible. ;-). Possibly of the same importance is the question of digital achieving the same dynamic range as analog. As it is today, digital is most like slide film in its narrow range.

[rdenney]

I suspect the tonal smoothness is more the cause of the contact-print effect than resolving power--though the usual assumptions about the sharpest thing people can see are generalities that don't encompass all the subtleties. Ctein insists that people can see the effects of high printer dot density without a microscope when comparing prints side by side, but I suspect that if they were separated by more than a few inches that would be less the case.

It's a false choice, though. All digital files have to be printed by a digital printer (or a laser lambda) which is subject to its own resolution limits, while a contact print is only limited by the resolution of the paper emulsion itself. Thus, it may be impossible to compare that digital file with a contact print meaningfully.

I find it interesting that other tests have shown that differences in actual prints do not vary linearly with size. The explanation that the orderly array of pixels has resonances that differ in the frequency domain from the random array of silver grains is something that seems obvious now but I hadn't thought about it before.

Rick "suspecting nobody designing digital equipment will ever define requirements necessary to match a contact print" Denney

[BetterSense]

If you want to capture the tonality, the DOF, all that stuff that makes a 10x8 image a 10x8 image, then you're going to have to have a 10x8 sensor.

This is actually incorrect, but you are free to think what you will.

[Andrew Clearfield]

A "pixel" has no direct analog equivalent. What we think of as a "grain" of silver is actually a cluster of silver molecules that can vary in size and particular sensitivity. The "1 pixel = 1 silver grain" idea doesn't quite hold up.

Duh. Anyone who has ever worked with silver images at significant degrees of enlargement knows that all too well. The question is, under specified conditions, what average size the actual grain of silver would be, and how that would compare to the unmodified pixel as captured by the sensor. Because in both cases these will be the absolute limit of resolution.

Possibly of the same importance is the question of digital achieving the same dynamic range as analog. As it is today, digital is most like slide film in its narrow range.

Now this is indeed important. However, I'm not sure that high-quality digital is as limited as you state: I seem to remember slide films having dynamic ranges more in the 5 to 7-stop range at the maximum (the sharper, more contrasty slower films are less, which is why they have so little exposure latitude) while the manufacturers of top-of-the-line sensors claim they have a range of up to 12 3/4 stops. As we all know from learning the Zone System (?? I hope!) b&w film has a total usable range of about 14 - 15 stops (pyrocatechin, anyone?) but as a practical matter, no more than nine stops in the final print. (Zone 0 means that no density was recorded).

[Andrew Clearfield]

Thus a color pixel is more like an 18 to 20 µm pixel, with B&W possibly less, depending on the specific algorithm used. This bayer demosaicing then reduces the effective sensor resolving capability by up to a factor of 10 for color and somewhat less for B&W. . . .

Fine grain film would typically have silver halide grains of about 0.8 µm diameter with a range of say 0.5 to maybe even 1.5µm. When irradiated by photons say as few as 1 or as many as 100s' the latent image increases in area by several times . . . Under low light conditions the latent image may still be close to the silver halide dimensions - obviously very high resolution . . . At the other end of the density range, heavy illumination from the scene highlights, the larger latent image grows even larger upon development forming silver clumps up to say 20 µm in diameter. So the resolving power of film is a sliding scale depending on the amount of original exposure and modulated by the development sequence.

Does this mean we can take the typical granularity of fine-grain film as ranging from, say 1/8 the size of a pixel (four silver halide molecules of 0.8μm) to 20μm, which is the same size as a color pixel, or slightly larger than a b&w one? Wouldn't this be the theoretical limit?

Of course, then the magic of computer algorithms intervenes, and we end up with something which looks considerably sharper than the grainiest part of a silver image. But it sounds like it is still nowhere near the maximum resolution obtainable in shadow detail—which would explain the much-vaunted ability of the very large negative (especially when contact printed or scanned at very high resolution) to "see into the shadows."

[paulr]

Does this mean we can take the typical granularity of fine-grain film as ranging from, say 1/8 the size of a pixel (four silver halide molecules of 0.8μm) to 20μm, which is the same size as a color pixel, or slightly larger than a b&w one? Wouldn't this be the theoretical limit?

To understand the diferences you'd have to compare both MTF curves and S/N ratios between the film and sensor in question. What you commonly find is that the finest grained, highest resolving films have extremely high extinction resolutions, whcih can be difined as the finest detail the film can visibly resolve before its contrast drops below the noise floor. This is what you attempt to measure with old fashioned resolution charts. The trouble is that detail this fine, or anywhere close to it, looks so bad that it's not photographically relevant, unless you're operating a spy satelite. A good digital sensor has a lower extinction resolution, but extremely high contrast and s/n ratio right up to its limit.

This is why it's possible in some cases for a digital sensor to make a better looking medium sized print than a piece of film, but a worse looking mural size print.

The other issue you'll see addressed in the links I posted is diffraction. An 8x10 camera with a good lens can resolve a stupefying amount of detail at high MTF if the lens is used near its optimum aperture (typically around f8 or f11). But it will have extremely shallow depth of field compared with a much smaller format that covers the same field of view. If you stop down to equal the depth of field of a medium format digital camera (with a lens set to its own optimum aperture) you'll be introducing enough difraction to level the playing field.

There are parallel situations where a top end full frame dslr can have advantages over medium format digital.

[Martin Courtenay-Blake]

Getting away from the science and math of this thread a similar type of argument/discussion has broken out in the 35mm arena since the arrival of the full frame sensor Nikon D800/800E. Advocates of the digital form of image making are stating that this camera not only produces superior images than traditional film (including 50ASA velvia), but challenges the superiority of medium and even large format film. Interestingly most of the wags supporting this view have never actually taken a picture with a film camera but are very sure that what the marketing men are saying must be true. Personally I would like to see a direct comparison between a virtually identicle image produced on the D800 and a Velvia (or better still Tech. Pan.) image scanned at the very highest possible resolution (i.e. a resolution theoretically higher than the grain structure of the film), with the same amount of post scan processing, before making a decision as to which is best. My gut feeling is that the digital image would run things pretty close on the detail front whilst there would be subjective differences which would cause one to fall into one or other camp.

The image quality from the highest resolution Hassy backs, 200MP I believe, do make remarkable images and may well be as good or superior to film. I would like to see some direct comparisons. But it is clear that it would take a hell of a lot of pixels to challenge film even on 5X4 let alone 10X8, the suggestion of gigapixels probably being right.

But, is it really just a matter of resolution for resolutions sake. A digital image is going to be different in many, possibly subtle, ways from that produced by film. Everyone has their favourite film (and developer in the case of monochrome) and it's these personal decisions we make when producing an image that makes them different and, in many cases, identifiable to a particular photographer. My concern with camera to print digital photography is that we may end up with vast numbers of extremely high resolution images that simply look the same.

[Leigh]

If you make this assumption and that assumption,

and use this fudge factor and that fudge factor,

and this equivalence and that equivalence,

you can make the numbers come out however you want.

That doesn't make them valid.

Remember... All of these supposed comparisons were developed by folks interested in selling digital imaging.

- Leigh