Luminous Landscape Forum

Equipment & Techniques => Computers & Peripherals => Topic started by: stevegust on May 16, 2006, 08:19:02 pm

Title: MP Equiv to Film Sq Inches: Why so Non-Linear?
Post by: stevegust on May 16, 2006, 08:19:02 pm
Why is it that 39 MP roughly equals 4x5 sheet film (roughly 20 square inches), yet 16.7MP only equals 645 film (roughly 3.87 square inches).  The relative difference in film area is over 5X, whereas the megapixel differences isn't even 2.5X.  Larger format lenses resolve slightly less lines per mm than smaller format lenses, but with color film, I thought the final difference in resolving power for film systems was quite similar....taken linearly, at 2MP per square inch of 4x5 film, 3MP would equal 35 mm film, but that isn't quite true by most people's results....

by extrapolation, will 80 MP equal 8x10 color sheet film if the digital sensor is large enough (i.e. 3x4 or 4x5)?
Title: MP Equiv to Film Sq Inches: Why so Non-Linear?
Post by: normkoren on May 16, 2006, 10:58:47 pm
Although the measurements in this report are not extremely precise (in terms of MTF, resolving power, etc.) the general trend you noted is quite correct. The issue is that real-world photography is not the same as ideal photography. Most large format lenses are sharpest around f/11. Sharpness is lost to diffraction as smaller apertures (larger f-numbers). As you go to larger formats, depth of field at f/11 tends to become hideously narrow, so most of the time (at least if you want DOF) you need to stop down well beyond f/11, which puts you into the diffraction-limited realm. It seems quite remarkable, but if you need extreme DOF, you become highly diffraction limited, and it almost doesn't matter what format you use. I explain this on

http://www.normankoren.com/Tutorials/MTF6....DOF_diffraction (http://www.normankoren.com/Tutorials/MTF6.html#DOF_diffraction)

Warning: This page his highly mathemtical. There are some other reasons why total resolution for film cameras doesn't scale linearly with film size. One is film flatness. It's not perfect for large formats; it can very with temperature and humidity. It's another reason that most large format photographers stop down beyond f/11. Another factor is atmospheric disturbances, especially for scenes at a distance.

I have seen a very few huge enlargements from 8x10 film, evidently taken under ideal conditions at optimum aperture, that are truly stunning, well beyond what you could do with any digital back. It's very hard to achive such quality under real-world everyday conditions.
Title: MP Equiv to Film Sq Inches: Why so Non-Linear?
Post by: Anon E. Mouse on May 17, 2006, 12:30:36 am
It is not linear because it does not need to be. To make an 8x10 print, you are not magnifiying a 35mm negative the same amount you are a 4x5 negative. The 4x5 negative will give you a heck of a better print even though in absolute terms it is not "performing" at the level of 35mm. Since sharpness is a relative term defined in relation to the human visual system, 4x5 cameras can be stopped down to very small apertures and still provide sharp images.

And this is something I notice about the amateur community. They speak in absolute terms. To them everything is black and white. Professionals speak in relative terms and things are shades of grey. And here is the rub. While Micheal's test is a very good attempt for amateurs, it falls short on actually making any definate statements on which is "best" or even "better." Micheal alluded to the problem which is basically how an image looks - an extremely high-resolution imaging system does not always produce visually pleasing pictures. Imaging is really a systemic issue which is not dealt with at all. So while I found it interesting, I also found it hard to make any definate conclusions about the results because there were too many variables and unknowns.

But having worked 5 years in the production of digital cameras for a major Japanese manufacturer, I take great exception to Micheal's prejudice against optical and imaging theory. If it is good enough to produce the toys he likes using, then it is good enough to describe them. The problem again is a systemic approach. Just because he does not understand it nor do many people who use it in the silly film/digital debates, does not mean it does not work.
Title: MP Equiv to Film Sq Inches: Why so Non-Linear?
Post by: Anon E. Mouse on May 17, 2006, 03:24:24 am
BTW, I looked at the same pictures as you and I thought the medium-format film resolved more than the 16 MP DSLR. Check the little loops on the right of the frame around the 1. The DSLR had better contrast, but where that comes from cannot be determined. But Micheal's test is really not very good at showing resolving power. It really is more about sharpness which is a much trickier affair to judge.
Title: MP Equiv to Film Sq Inches: Why so Non-Linear?
Post by: michael on May 17, 2006, 05:28:11 am
"I take great exception to Micheal's prejudice against optical and imaging theory"

Well, there's an interesting assumption. A totally unfounded one, but interesting nevertheless.

A couple of comments, if I may.

I am a photographer. Not a scientist. I know that's no excuse. Bill Atkinson is both a photographer and a scientist.

But speaking for myself only, I have found remarkably little correlation in photography between theory, test results, and real world image quality. Our own little experiment reported on in Measuring Megabytes shows the pitfalls of even an attempt by three experienced photographers (one of whom applied scientific rigor to the process) can encounter.

On another note; I was a consultant to DXO Labs in the development of their DXO Analyser system. This is now in use by Chasseur D'Image, Popular Photography and a number of camera makers. I published camera tests here for a year or so using the system, but in the end stopped, because I found that difference in cameras reported by the tests didn't bear a whole lot of relationship to real world images. The graphs and charts made the whole thing look impressive, but I lost faith in them and couldn't share them with readers when my photographs from the field showed that what sometimes appeared like marked differences were not, while problems that I saw in image quality wern't reported by the test adequately.

And, with all due respect to my friend Norman Koren, whom I mention because he is in this thread, I think that while he offers with Imatest probably the finest testing system that I've yet seen outside of an optical lab, again, test results don't always coorelate to what is seen in practical use.

I'm not a Luddite when it comes to the scientific method. (I have some 7-8 US and international patents in my name, so I do have some experience in this area). I'm simply an unrepentant emperisist though. By this I mean that after doing photography, writing about it and teaching it professionally for some 30 years, I trust my eyes above anything else.

MichaeL
Title: MP Equiv to Film Sq Inches: Why so Non-Linear?
Post by: paulbk on May 17, 2006, 07:23:27 am
“..an unrepentant emperisist"

Hear hear! All art is empirical. Scientific deconstruction of a image, while it may be valid, says little about the photograph. A human being deconstructed is a bucket of mud. The whole is greater than the sum of its parts.
Title: MP Equiv to Film Sq Inches: Why so Non-Linear?
Post by: Kenneth Sky on May 17, 2006, 08:38:22 am
The proof is in the pudding - in this case the prints. What this forum needs to set up is a thread that can only be contributed to by those who have received the data disc, processed  and printed the pictures and judged them. The rest of us can only be voyeurs because talk is cheap (especially on the internet). But seriously, we need to await the distribution and evaluation of the data before making critical comments.
Title: MP Equiv to Film Sq Inches: Why so Non-Linear?
Post by: Anon E. Mouse on May 17, 2006, 10:21:46 am
"Well, there's an interesting assumption. A totally unfounded one, but interesting nevertheless."

Well Micheal, you said at the end of your essay not to trust the theory. And this is not the first time you have made the comment. If the science and the results contradict each other there must be a problem in understanding the science (or the result). I also have a long career in photography and am well versed in the science. The science works. The problem is folks don't understand the complexity. They will take a single number and hold it up as some kind of truth rather than one piece of a puzzle that comes to form the final image. You actually recognized some of these problem in your essay.

Having just retired from the camera manufacturing industry, I find it ironic that folks think the science used to make the cameras is faulty, but demand perfection from their gear. That means the cameras, lenses, and other gadgets work coz of dumb luck - we are not talking about a new industry or science here. You will find the industry has many dedicated individuals working hard on this complex problem and doing it with more than a hit or miss approach. That is why your test does show how good cameras actually are. I think one thing we can agree on is all those cameras (and scanner) work very well. And inspite the range of manufacturers of cameras, lenses, and sensors, they, at least from what I saw in your essay, perform remarkably similarly. I certainly am not surprised the lenses test very close. MTF is great and VERY sensitive, but it is not a pass or fail test. Actually it is more of a diognostic test to make sure everything is tickey-boo. You may be surprised at how bad an MTF curve can be and still get good images from a lens. But I digress.

And yes, manufacturers do test their cameras in "real-world" situations at the end to make sure the thing works. Number tell so much and ultimately photography is subjective. (Lemons are rare and usually traced to a human error.) And the science is used to understand what is right or wrong with the final product and (hopefully) fix it.

Whether you take a good picture with the camera is up to the photographer. What constitutes a good picture is much harder. I know of one made with a bad lens (by modern standards), underexposed, on a bad emulsion, and not that sharp, but "behind the Gare St-Lazare" by Cartier-Bresson is still a good picture.

Now as far as the normal technical debates that rage on the internet, well lets just say a little information can be more dangerous than none at all.

But I have a feeling we will not agree on this topic.
Title: MP Equiv to Film Sq Inches: Why so Non-Linear?
Post by: Ben Rubinstein on May 17, 2006, 04:04:40 pm
That is an interesting point actually, maybe you could write an article explaining how the science and real world can and do differ?
Title: MP Equiv to Film Sq Inches: Why so Non-Linear?
Post by: michael on May 17, 2006, 04:28:38 pm
If the science and the results contradict each other there must be a problem in understanding the science (or the result).

I'll make a single observation in response.

Just as with high-end audio, where measurements do not necessarily correlate with what is heard, so too in high-end imaging.

The answer may be as simple as that we are either measuring the wrong things, or we do not know which things to measure, or how, to accurately represent the differences that we are seeing.

Michael
Title: MP Equiv to Film Sq Inches: Why so Non-Linear?
Post by: normkoren on May 18, 2006, 10:22:16 am
Since I'm about as deeply involved in actual measurements as anybody, it's time to pipe in.

Scientific measurements are indeed valid and correlate well with visual image quality. But that said, there are a number of caveats.

First of all, image quality is the result of several factors, including MTF (sharpness, which is expressed as a curve, not a simple number), noise (which has spectral properties), tonal response curve, dynamic range, and color accuracy (pleasing colors are not necessarily accurate). These factors are summarized on
http://www.imatest.com/docs/iqf.html (http://www.imatest.com/docs/iqf.html)
And the image quality you perceive in a print is strongly dependent on post-processing. Imatest attempts to measure the quality of the raw material you have to work with, though it is affected by processing in the raw converter.

I've resisted the temptation to reduce Imatest results to a simple number. (I make an imperfect attempt to do so with Shannon information capacity, but signal processing (noise reduction and sharpening) makes it less than reliable.) Instead I provide users with tools they can use to arrive at their own conclusions. I expect that as time goes on, readers will refine their understanding of what constitutes excellent image quality.

I'm very familiar with the situation in high-end audio. Put simply, total harmonic distortion (which generated a marketing race in the 1970s) was a BAD measurement-- it didn't correlate with sound quality. I'll spare you the details here, but I've written about it, somewhat technically, in
http://www.normankoren.com/Audio/FeedbackFidelity.html (http://www.normankoren.com/Audio/FeedbackFidelity.html)

The audio issue correlates in a curious way with highlight burnout in (linear) image sensors. Long story, but the bottom line is that photographic measurements work a lot better than audio measuremets, but you can get in trouble when you try to reduce complex results (like MTF curves, noise spectra, and tonal response) to one or two simple numbers (even MTF50, which I use). As we become familiar with photographic measurements, which are new to many photographers, we should start to have a better idea how to interpret the numbers.

And by the way, if you don't plan to print larger than letter-size or A4, all the cameras tested are totally superb. They are superb at 13x19 inches as well. My EOS-20D, which is below the level of the cameras in this test, produces gorgeous 13x19 prints, far beyond anything I've ever seen with 35mm. The results in this test don't really apply to prints under about 16x24 inches.
Title: MP Equiv to Film Sq Inches: Why so Non-Linear?
Post by: Gary Ferguson on May 18, 2006, 11:54:50 am
Quote
And by the way, if you don't plan to print larger than letter-size or A4, all the cameras tested are totally superb. They are superb at 13x19 inches as well.... The results in this test don't really apply to prints under about 16x24 inches.


Good point, and one that deserves repeating. But let me ask you a question.

In the days of film I used 35mm, medium format, and 4x5. Up to about a 10x8 print I couldn't normally see significant quality differences between these different formats. The key word being "significant". Because, using the very best lenses and most careful technique, I could still see some difference. However with digital capture and ink jet printing this relationship no longer seems to apply.

I now use a Canon 5D, a Canon 1Ds MkII, and a Phase One P25. Furthermore, I'll often use the P25 on a sliding carriage and stitch two frames together, giving a massive 40MP image. I agree with your point that for A4 or A3 all the cameras tested are superb, but I'm not sure your statement goes far enough. If I print to A4, or in some cases A3, using my range of cameras, say from 10-40MP, then I no longer see "no significant difference", I now see "absolutely no difference at all".

In other words, in the days of film a photographer printing to say 10x8 may have been satisfied with a 35mm negative, but could still have harboured a regret that they weren't using medium format for that extra fraction of quality. But in the digital world, with inkjets that simply discard pixels above a certain resolution limit, is there any point at all in having more pixels unless you're printing bigger and bigger?
Title: MP Equiv to Film Sq Inches: Why so Non-Linear?
Post by: normkoren on May 19, 2006, 02:55:19 am
Quote
But in the digital world, with inkjets that simply discard pixels above a certain resolution limit, is there any point at all in having more pixels unless you're printing bigger and bigger?
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Hi Gary,

Since I'm using an 8.3 megapixel EOS-20D, which has fewer pixels and a smaller sensor than any of the cameras in the test, I couldn't make that statement myself. But now that you've made it, I'm happy to concur. 8x11 prints from the 20D are incredibly fine; it's hard to imagine better. So yes, there's no point at all in having more pixels (read, higher cost) unless you plan to print considerably larger. I suspect all the participants have Epson 7800 or 9800 printers. By the way, a friend from HP tells me they're coming out with some large format printers later this year that will give Epson a real run for it's money. I can hardly wait. I love big, fine prints.
Title: MP Equiv to Film Sq Inches: Why so Non-Linear?
Post by: mtomalty on May 19, 2006, 12:15:09 pm
Quote
I can hardly wait. I love big, fine prints.


I guess,then,  you'll be looking for a new camera   :>))

Mark
Title: MP Equiv to Film Sq Inches: Why so Non-Linear?
Post by: Jack Flesher on May 20, 2006, 10:53:22 am
Quote
The results in this test don't really apply to prints under about 16x24 inches.

Amen!

And IMO this points to the core of the problem -- you have hoards of people commenting on the files that have never printed larger than A3.  After you have printed large for a bit, you develop an "eye" for what qualities will matter and what won't in a larger print.  I continue to be amazed when I find things in my large prints I never noticed onscreen, yet on careful review they were in the file all along.
Title: MP Equiv to Film Sq Inches: Why so Non-Linear?
Post by: rmaes on May 23, 2006, 01:13:02 pm
And then there is the whole (scientific) territory of RGB to CMYK transformation, and the representation of all these 10-40MP pixels through a stochastic dittering process. Many megabytes can be lost in this process.

If i want Big, Fine prints and get ultimate print quality out of the captured image. Shouldn't i rather opt for an RGB printing process (e.g. Lambda Durst) ?
Title: MP Equiv to Film Sq Inches: Why so Non-Linear?
Post by: BJL on May 23, 2006, 05:25:21 pm
Quote
Why is it that 39 MP roughly equals 4x5 sheet film (roughly 20 square inches), yet 16.7MP only equals 645 film (roughly 3.87 square inches).  The relative difference in film area is over 5X, whereas the megapixel differences isn't even 2.5X.
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Norm Koren and others have offered fine answers, but let me throw up one point: decreasing absolute len resolution (lp/mm).

As you move up in format size and focal length, lens resolution in lp/mm typically decreases, so doubling linear format size (quadrupling image area) probably gives significantly less than double the "line pairs per picture height" of resolution, or in the new digital currency, it less than doubles "pixels per picture height", meaning significantly less than a quadrupling of the "pixels worth of detail".

Photodo made a similar observation in a resolution comparison of 35mm, MF and LF systems using Velvia, concluding that in 35mm resolution was largely film limited, while in LF resolution was largely lens limited.


P. S. Another possible factor is scanning rsolution: Michael mentions in another thread that the 645 was scanned at about 4500dpi while the 4x5 was scanned at 2450dpi, so that is a potential factor reducing the "lp/mm" of the larger format scans. However, 2450dpi is close to the 50% MTF of the film (Velvia), so this might not make much difference.
Title: MP Equiv to Film Sq Inches: Why so Non-Linear?
Post by: Ray on May 24, 2006, 11:29:33 pm
Quote
As you move up in format size and focal length, lens resolution in lp/mm typically decreases, so doubling linear format size (quadrupling image area) probably gives significantly less than double the "line pairs per picture height" of resolution, or in the new digital currency, it less than doubles "pixels per picture height", meaning significantly less than a quadrupling of the "pixels worth of detail".


That's a good point, JBL, which could be summarised as the 'law of diminishing returns' at work. We now have cameras that have 4x the pixel count of Canon's first DSLR, the D30. I checked the dpreview site for a comparison of lines per picture height for the D30 and the 5D. The table below is not exactly analagous to the situation you refer to above. The 5D has 4x the pixel count of the D30 but only 2.5x the area. Nevertheless, I am surprised  the 5D really does seem to deliver twice the 'lines per picture height' of the D30. However, I wonder if the 5D  resolution per picture height is an extrapolation of resolution at the centre of the lens and would only apply in practice using a lens with an unusually flat MTF response.

[attachment=608:attachment]
Title: MP Equiv to Film Sq Inches: Why so Non-Linear?
Post by: bob mccarthy on May 25, 2006, 10:04:40 am
Quote
As you move up in format size and focal length, lens resolution in lp/mm typically decreases, so doubling linear format size (quadrupling image area) probably gives significantly less than double the "line pairs per picture height" of resolution, or in the new digital currency, it less than doubles "pixels per picture height", meaning significantly less than a quadrupling of the "pixels worth of detail".

I don't know if that holds water anymore. The modern LF lens is darn good today. I'm seeing resolutions of 60-80 LP-MM with the newest generation and the resolution holds up quite wel, nearly to the edge of the image circle in the Super Symmars.

http://www.hevanet.com/cperez/testing.html (http://www.hevanet.com/cperez/testing.html)

The reduction in image magnification is what makes the LF film camera interesting. Much greater apparent DOF before defraction kicks in.

(wishful thinking) a 4x5 chip with big wells would be the ultimate capture device. Only a government could afford it though.

Bob
Title: MP Equiv to Film Sq Inches: Why so Non-Linear?
Post by: BJL on May 25, 2006, 11:41:49 am
Quote
I don't know if that holds water anymore. The modern LF lens is darn good today. I'm seeing resolutions of 60-80 LP-MM with the newest generation and the resolution holds up quite wel, nearly to the edge of the image circle in the Super Symmars.

The reduction in image magnification is what makes the LF film camera interesting. Much greater apparent DOF before defraction kicks in.
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I disagree on both points: smaller format lenses maintain a very big resolution advantage over even the latest lenses for 4"x5" format, measured by MTF at equal lp/mm, and the trade-offs possible between DOF and diffraction are the same for any format. Only the use of view camera motions given any advantage to a larger format on apparent DOF when diffraction effects are equal, and view camera motions are coming to 35mm format digital now.


I) The Super-Symars you cite are still not even close to good 35mm format lenses for "absolute resolution", MTF at equal lp/mm. (They probably are sharper in line pairs per pictuer height, and thus for lp/mm on prints of equal size.)

Compare the MTF curves for two normal primes, the Super-Symmar XL 210mm f/5.6 at
[a href=\"http://www.schneideroptics.com/photography/large_format_lenses/super-symmar_xl/pdf/super-symmar_xl_56_210.pdf]http://www.schneideroptics.com/photography...r_xl_56_210.pdf[/url]
and the Canon 50/1.8 II at
http://www.usa.canon.com/consumer/controll...52&modelid=7306 (http://www.usa.canon.com/consumer/controller?act=ModelDetailAct&fcategoryid=152&modelid=7306)
I see the Canon having better MTF at 30lp/mm than the Super-Symar at the lower 20lp/mm, and the Canon at 10lp/mm is way ahead of the Super-Symar at 10lp/mm or even at 5lp/mm. And that is comparing to a very inexpensive non-"L" lens! Comparing instead to the Canon 50/1.4 (still not an "L" lens, but pricier) gives similar results.

Going to an even smaller format, the inexpensive Olympus 4/3 format 35mm f/3.5 macro lens http://www.olympusamerica.com/e1/sys_lens_35mm.asp (http://www.olympusamerica.com/e1/sys_lens_35mm.asp)
does even better fr lp/mm of resolution. Its MTF at 60lp/mm and wide open f/3.5 is far better than the Super-Symmr at 20lp/mm and any aperture, and the 35/3.5 has MTF at 20lp/mm as good or better than the Super-Symar at even 5lp/mm.
Even a mid-priced small format 4x zoom lens like the Olympus 14-54/2.8-3.5
http://www.olympusamerica.com/e1/sys_lens_14mm.asp (http://www.olympusamerica.com/e1/sys_lens_14mm.asp)
has better MTF at 60lp/mm (wide open or f/8) than the Super-Symar at 20lp/mm, and the 14-54 at 20lp/mm trounces the Super-Symar at 20lp/mm and 10lp/mm, and outdoes even the 5lp/mm Super-Symar performance.

At the risk of being "too theoretical", any resolution improvement in a larger format can carry over to a smaller format, and smaller format makers like Canon have a lot more money and resources, so are certainly capable of making such improvements if they choose. Downsizing a LF lens design in all dimensions by a factor of four shrinks the focal length by the right factor to give the same angular FOV, and shrinks the size of all "design" abberrations by the same factor, essentially giving four times the resolution (same MTF ast fout times the lp/mm). This downsizing  gives equal aperture ratio, as was used in the tests (f/11 for all). Arguably (see below) the smaller format woud mor often use a lower apertrure ratio, worsenign abberrations.


II) On the second point about DOF and diffraction: the possible balances of DOF and diffraction effects on print sharpness are independent of format, once you level the playing field by viewing prints of the same size from the same distance. In fact, they are each determined solely by the effective aperture diameter (focal length divided by aperture ratio), so you get the same DOF and diffraction results in different formats by adjusting aperture ratio in proportion to focal length.

Why? Famously, if a larger format and longer focal length are used with the same aperture ratio, the larger format gives less DOF. In detail, the sizes of the circles of confusion on the film or sensor increase with the square of focal length, but then degree of enlargement is reduced in proportion to focal length, so the CoC sizes on prints are larger in proportion to focal length.
To get equal perceived DOF, this must be compensated for by increasing the aperture ratio in proportion to the focal length (that is, using the same effective aperture diameter).
Then the diffraction spot size on the film/sensor is determined by aperture ratio alone, independent of focal length, so once you choose apertures to get equal DOF, the diffraction spot size on film/sensor is larger in proportion to focal length.
The smaller degree of enlargement needed with the larger format just cancels this out, so the diffraction spot sizes (and circles of confusion) are the same size on same sized prints, from any format.


P. S. Large format enthusiasts should probably stick mostly to the legitimate claims of
1) greater print resolution in lp/mm on equal sized prints, after the lower degree of enlargment needed
and
2) finer tonal gradations/greater dynamic range
to explain this preference. Those two have always been and probably always will be the main real reasons to sometimes choose a larger format than most others photographers use.
Title: MP Equiv to Film Sq Inches: Why so Non-Linear?
Post by: Jack Flesher on May 25, 2006, 01:51:16 pm
Quote
P. S. Large format enthusiasts should probably stick mostly to the legitimate claims of
1) greater print resolution in lp/mm on equal sized prints, after the lower degree of enlargment needed
and
2) finer tonal gradations/greater dynamic range
to explain this preference. Those two have always been and probably always will be the main real reasons to sometimes choose a larger format than most others photographers use.
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And 3) Easier scheimpflug adjustments due to the longer focal lengths used at any given magnification ratio; 3a) And thus in many (but not all) compositions the appearance of greater DoF compared to smaller formats.
Title: MP Equiv to Film Sq Inches: Why so Non-Linear?
Post by: Mark D Segal on May 25, 2006, 04:09:21 pm
Quote
Hi Gary,

Since I'm using an 8.3 megapixel EOS-20D, which has fewer pixels and a smaller sensor than any of the cameras in the test, I couldn't make that statement myself. But now that you've made it, I'm happy to concur. 8x11 prints from the 20D are incredibly fine; it's hard to imagine better. So yes, there's no point at all in having more pixels (read, higher cost) unless you plan to print considerably larger. I suspect all the participants have Epson 7800 or 9800 printers. By the way, a friend from HP tells me they're coming out with some large format printers later this year that will give Epson a real run for it's money. I can hardly wait. I love big, fine prints.
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Norm, the point of having higher MP count whatever your print size is that the more MP you have, the more cropping you can do while preserving high quality in large prints of cropped images. It just gives added flexibility for all those who may see the need to improve composition by cropping their images in post-processing. How much that is worth varies of course from one photographer to another.
Title: MP Equiv to Film Sq Inches: Why so Non-Linear?
Post by: Gary Ferguson on May 25, 2006, 04:19:08 pm
I'd agree that larger image circles generally come at the cost of reduced resolution. But in the real world of available optics there's some notable examples that manage to depart from a smooth linear relationship.

Rodenstock's Apo Sironar Digital HR lenses, with image circles of about 70mm, manage to deliver the kind of performance I'd normally associate with excellent 35mm lenses with their typical image circles of about 45mm. And there's others, Hasselblad's V system 40mm IF, or the Contax 645 120mm Macro, or the new Sinar/Zeiss optics, or the Canon 300mm 2.8L compared with the equivalent optic for a smaller format than 35mm.

So even though I accept the general thesis of the trade off between image circle and resolution, there's sufficient spectacular exceptions to the general rule so that individual lenses still need weighing on their own merits.

As for camera movements coming to the smaller formats, yes that's self evidently so. However, in my experience of using a 37x49mm digital back on a Linhof, and also of using Canon's tilt and shift lens range, I'm not completely convinced that movements are quite such a happy marriage as with the more traditional formats such as 4x5.

The problem IMO is achieving the increasingly exacting movement precision required as sensor or film formats shrink. One simple example is loupe magnification. The x4 loupe I used with 4x5 was consistent with my typical print enlargement, but if I try and use a x7 or x10 loupe on a 37x49mm sensor then the image is simply lost in the grain of the ground glass.
Title: MP Equiv to Film Sq Inches: Why so Non-Linear?
Post by: BJL on May 25, 2006, 04:49:22 pm
Quote
And 3) Easier scheimpflug adjustments due to the longer focal lengths used at any given magnification ratio; 3a) And thus in many (but not all) compositions the appearance of greater DoF compared to smaller formats.
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Ah yes, I did mention that earlier in my post. Though strictly speaking that is an advantage of a view camera, regardless of format size itself.

As Gary mentions, using smaller format sensors with view cameras seems to bit of a hack at least for now. I wonder if anyone will produce a view camera system designed from the ground up for use with smaller sensors, say via digital backs with 24x36mm or 36x48mm sensors. I understand that "medium format" style sensors without microlenses are best for this, so strapping a DSLR onto the back of a view camera might not be the ideal solution.
Title: MP Equiv to Film Sq Inches: Why so Non-Linear?
Post by: BJL on May 25, 2006, 05:26:54 pm
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I'd agree that larger image circles generally come at the cost of reduced resolution. But in the real world of available optics there's some notable examples that manage to depart from a smooth linear relationship.

Rodenstock's Apo Sironar Digital HR lenses, with image circles of about 70mm, manage to deliver the kind of performance I'd normally associate with excellent 35mm lenses with their typical image circles of about 45mm.
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The new digitally oriented Rodenstock and Schneider Digitar lenses do seem to push resolution forward in "medium format" sizes, and a rough comparison of MTF for the Digitar's at 40l/mm to data for Canon lenses at 30lp/mm does suggest that these new "digital large format" lenses have comparable or better resolution than good Canon primes.

But perhaps the more interesting comparison is to equally new high resolution lenses for smaller digital formats. Canon has talked about producing new sharper lenses for the needs of high resolution 35mm format digital, and hopefully will publish MTF data for them at higher thn 30lp/mm. But for now the best comparison available to me is 60lp/mm MTF data for Olympus Digital Zuiko lenses and for Schneider Digitars. (Are MTF graphs availablefor those Rodenstocks?)

Again, all four of the Zuiko Digital non fish-eye primes have 60lp/mm MTF far higher than any Digitar, and similar to or higher than the 40lp/mm of any Digitar. If you look towards the corners, the 60lp/mm MTF of the Zuiko Digital primes is similar to even the 20lp/mm of most or all Digitars.
Title: MP Equiv to Film Sq Inches: Why so Non-Linear?
Post by: neal shields on May 26, 2006, 03:04:48 pm
One suggestion that I would have to make the tests more defendable and easier to compair would be to either use a test target that had deminishing resolution or simply back away progressively by doubling the distance each time.

Then if two lines on a bill could be resolved with all systems at 10 feet but only selective system at 20' this gives a quantifiable difference that isn't dependent on opinions.

The FBI spent about a year compairing systems and concluded that 35mm film at 200 asa is about 16 meg.  I can't understand why there is so much difference between their test results and some others unless it is method.

http://www.fbi.gov/hq/lab/fsc/backissu/apr...swgitfield1.htm (http://www.fbi.gov/hq/lab/fsc/backissu/april2002/swgitfield1.htm)

It seems to me that unless you are developing quantifiable objective numbers with you testing that are independent of subjective opinions you are simply compairing initial outputs of one system to another.

Film will always lose as it is orange and reversed in colors.

I have also found in my own testing, using charts and microscopes to read the negatives that fill captures about 130% the detail of a 9 meg camera.  That comes close to agreeing with the FBI.

I might add that in my tests, I can get way more detail onto film than can be seen with less than a good 8000 dpi scan.  So some people also fall into the trap of compairing direct capture to scans, not to film.

For many people the work flow is the most important thing.  Which camera will get me where I want to go quickest and easiest.  Digital usually wins.  However that is a different question than: "which camera captures the most information?"

The reason I feel the second question is the most important one is that with modern computers and programs I can synthise almost any "look" I want.  I can certainly make a low res picture "look" "sharper" than a high res one.  

About the only thing I can't do is create information that the camera didn't capture.
Title: MP Equiv to Film Sq Inches: Why so Non-Linear?
Post by: Jack Flesher on May 26, 2006, 03:58:21 pm
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The FBI spent about a year compairing systems and concluded that 35mm film at 200 asa is about 16 meg.  I can't understand why there is so much difference between their test results and some others unless it is method.

http://www.fbi.gov/hq/lab/fsc/backissu/apr...swgitfield1.htm (http://www.fbi.gov/hq/lab/fsc/backissu/april2002/swgitfield1.htm)

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Maybe because they did that test about 5 years ago and there have been significant improvements in digital sensors, camera firmware and raw converters since then?

Title: MP Equiv to Film Sq Inches: Why so Non-Linear?
Post by: Gary Ferguson on May 26, 2006, 05:30:54 pm
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The FBI spent about a year compairing systems and concluded that 35mm film at 200 asa is about 16 meg.

Neal, a few points.

It wasn't "the FBI" that conducted the test, it was an individual within a department of the FBI, so we shouldn't give the results more prestige than they warrant. If the same individual had been working for the Kazakstan Dental Association would we be quite so respectful of the results?  

There was a debate recently on the Leica forum at Photo Net regarding photographs as evidence. It wasn't conclusive but there were clearly experienced professionals using photographs around the world in courts of law who believed film was the better law enforcement choice. Not becuase of resolution but because a negative is more likely to be accepted as untampered and authentic than a digital file.

And finally, as has been pointed out, that report is ancient history. If I remember correctly (and I'm sure you'll bring me to book if I'm wrong) the 16MP conclusion was extrapolated, they didn't actually look at a 16MP file, they just guessed.

Now none of this makes their conclusions wrong in itself, but we should see it as just another data point in a rich and complicated debate.

But really, who cares? I use both film and digital and I rarely choose one rather than another because of quality. With a bit of application I can usually get the quality I require from either medium at the print sizes I commonly use. The choice is more governed by look and application than lppm.
Title: MP Equiv to Film Sq Inches: Why so Non-Linear?
Post by: neal shields on May 27, 2006, 10:23:17 am
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Neal, a few points.

It wasn't "the FBI" that conducted the test, it was an individual within a department of the FBI, so we shouldn't give the results more prestige than they warrant. If the same individual had been working for the Kazakstan Dental Association would we be quite so respectful of the results? 

There was a debate recently on the Leica forum at Photo Net regarding photographs as evidence. It wasn't conclusive but there were clearly experienced professionals using photographs around the world in courts of law who believed film was the better law enforcement choice. Not becuase of resolution but because a negative is more likely to be accepted as untampered and authentic than a digital file.

And finally, as has been pointed out, that report is ancient history. If I remember correctly (and I'm sure you'll bring me to book if I'm wrong) the 16MP conclusion was extrapolated, they didn't actually look at a 16MP file, they just guessed.

Now none of this makes their conclusions wrong in itself, but we should see it as just another data point in a rich and complicated debate.

But really, who cares? I use both film and digital and I rarely choose one rather than another because of quality. With a bit of application I can usually get the quality I require from either medium at the print sizes I commonly use. The choice is more governed by look and application than lppm.
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Title: MP Equiv to Film Sq Inches: Why so Non-Linear?
Post by: neal shields on May 27, 2006, 10:42:53 am
I thought he had done the tests as part of his work, but in any case it is published on the FBI's web site and looks like an official recomendation to me.

Also, I don't think that there are many people saying that a 2006 pixel has more resolution than a 2000 pixel.  Larger pixels have more dynimic range than small ones but pixels are getting smaller not larger in most new cameras.

Beyond that this gets into a debate about what is "science".  In the book by the Nobel prize winner who basically made gene maping possiable, (Dancing Nakid in the Mine Field) he talks about the fact that science is: coming up with a theory, runing experiements to prove the theory and publishing the results in a manor that other people can check, by running the same experiements and seeing if they get the same results.

Yes I can order the disks and get the raw files to see which image I like better but that doesn't tell me much about absolute resolution limits.  To make judgements about resolution I need to have some deminishing detail so that I can say that I can read this line but not that line, for example.

To do that you have to quantify something.  The title of the article is "measuring megapixels".  Normally if you "measure" something you get numbers, not opinions.

People have been testing resolution for over a hundred years.  Why not use the proven techniques?  (You can download a resolution test chart off the web.)  

Yes I know, people will say, "I don't photograph resolution test charts".  Point is, if you are trying to decide what you like best for your work, the test is a great test.  Just don't advertise it as a resolution test.

As to who cares, I assumed that was the purpose of the article.  If resolution and absolute information capture isn't important to someone's efforts or art then that is fine.  I suspect that for 99% of the world's photography (a vast amount better than mine) resolution isn't a factor.

One of the reasons that I believe the FBI article is that it tracks my own tests.  However, I collect microscopes so I am checking my negatives under the microscope, not by using low res scans.  With very carefully made 4x5 negatives, I found that I had to have an 8000 dpi drum scan (wet) to get all the information off of a velva transparancy.

The easiest resolution test that I can come up with is to photograph a newspaper and keep increasing the distance.  Different camera systems will drop out as you try to read the paper from the file or negative.  However, you will have to have some very high resolution way of checking your negatives. (A 40 power loupe, a microscope or a very high res scanner.)
Title: MP Equiv to Film Sq Inches: Why so Non-Linear?
Post by: BJL on May 30, 2006, 10:38:17 am
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The easiest resolution test that I can come up with is to photograph a newspaper and keep increasing the distance.  Different camera systems will drop out as you try to read the paper from the file or negative.
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That would measure about the same thing as high contrast test pattern images, still rather removed from the more important issues of photographic fidelity relating to reproducing detail at boudaries of far lower local contrast, and reproducing contrast levels in the final image that are reaasonbaly close to the original subject matter. This is very different from turning a "black and white" subject into a "49% gray and 51% gray" image on the print, even if you or the FBI can still just barely read the writing on the "gray and gray" print.

Referring again to Fuji's datasheet for Velvia: it cites 160lp/mm for an extremely high contrast (1000:1) test pattern, but only 80 lp/mm for a low contrast test pattern, and I have read skeptical comments from film reiewers about even the latter lower figure. No film reviews I read put much weight on the high contrast test pattern number, but of course it was always the one that got most prominance in film advertsing, with some film makers publishing only that number, and of course it is still the favorite of the film rear-guard.

The difference between those two numbers (160, 80) already gives a factor of four difference in "pixel count equivalent", showing how much room there is for fudging the answers by choosing a measurement that favors the result one wants to get.


My preferred style of test: take some real photographs of interesting, finely detailed subjects, and view them (not images of newspapers or test patterns) from various distances.