Comparison of 4 film formats and 2 digital cameras

[Brian Ellis]

I too applaud Bert for taking the time to do this and for sharing the results but I don't think this is an "experiment on image quality and real life resolution." What Bert has done is similar to taking six negatives made with six different films and six different cameras to six different labs and then using the resulting prints as the basis for comparing the quality of the films. I think we all would say "wait a minute, that's no way to compare films, things have to remain more constant than that from one film to the other if you're going to validly compare them." There are a huge number of variables here that affect the results including the equipment and methodology used to scan the negatives, the software and methodology used to convert the RAW digital files, the quality of the various lenses, Bert's ability to identically focus six different cameras six different times, etc. etc. almost ad infinitum.

This isn't intended as a criticism of Bert at all, like others have said I think it's great that he's doing his own "testing" and has taken the time to share the results. I just don't think this "test" should be taken as saying anything more than that these happen to be the results Bert obtained when he used the various cameras, lenses, scanners, software, films, chips, computer, monitor, etc. and that changing anything in the chain could and al ost certainly would change the results. I do know for a fact that the differences in the prints I make from my 6x7, 4x5, 8x10 and digital cameras are far far less than the differences shown here among these same formats.

[Bert Otten]

Thanks Brian for your response. Let me set one thing straight: I developed all 4 formats films myself, they were all Provia 100F and they were developed with a computerized machine, the Jobo ATL 2000 with very tight temperature and timing tolerance. So there are a few things constant here. The focus of the two large format cameras has been checked carefully on reproducebility. The focus of the Plaubel Makina has been checked by photographing a ruler, using the rangefinder, and has been corrected until precise. The focus of the Leica was very accurate, besides at the aperture used there is quite some tolerance. As I have explained on the site, I have done all I could to get the maximum resolution out of the RAW files of the digital cameras, and I have shown that the lens of the 300D was not limiting.

If you find that the difference between the prints from various formats is much smaller than the results I show, that can easily be explained by the limits in the printing process. You really have to produce very large prints to get everything out of an 8x10 transparency. So your statement is correct for prints of 40 cm wide and smaller, but not for larger prints.

Now here's my statement, and I'm very interested if you can falsify it by something stronger than impressions: The differences in image content I show are very robust as long as the quality of the optics is high, something like Provia is used and the focussing is correct. If you can show that you can get twice the resolution out of a 6.3 Mpixel camera as I did, I would already be convinced. Now to mess up a large format print so that you get much less resolution than I did is easy ofcourse, so that would not convince me.

My original transparencies are very close to the maximal resolution given by Fuji in their data sheet of Provia 100F. In fact I get close to that resolution in all film formats (75, 71, 63 and 61 linepairs/mm for the formats 35mm, 6x7, 4x5 and 8x10 respectively). As I have indicated, concerning the scans you look at on my site, the scanner was the weakest link. The optics and focussing were not limiting.

If you doubt my tests because your experience tells you something else, that's understandable, but only convincing if you have experimental results yourself!

Perhaps this is a good moment to ask if anyone on this forum is willing to repeat my experiment on any of the formats (including the digital ones) I have used. In science this is done very often: to try to repeat other ones experiments, to see whether they hold. Let us know.

Once again Brian, thanks for your reply,

[Brian Ellis]

Hi Bert - Thanks for your reply. I don't want to get into an argument, especially since I do (as I said before) admire you for doing the testing and posting the results. Just a couple points of clarification. When I mentioned focus as a variable I didn't mean the ability of the various cameras to focus accurately, I meant the ability of any human being to focus consistently and accurately. I seem to remember somewhere seeing the results of focusing tests showing that even the best photographers could only focus on the same point something like five out of ten tries or something like that.

With respect to print sizes, you're absolutely correct. I didn't mean that just because I see relatively little difference in my prints (which usually are no larger than 11x14) among the four different formats we both use, no differences ever exist in any prints of any size. I just meant that in my "real world" of making prints (as opposed to enlarging to the point you did in your tests) I don't see the kinds of differences your tests show.

[Bert Otten]

Good Brian, thanks for replying to the issue of printsize.

Concerning the issue of focussing: my standard deviation of focus position of the lens over a series of 20 times focussing on the 4x5 camera is 0.1 mm. Even if we use an extremely critical circle of confusion of 0.01 mm, the depth of focus is 0.33 mm for the used lens of 150 mm and f16 and the object distance used of 4 meter. That means that focussing was not limiting, since my accuracy of focussing was well within the depth of focus.

The only issue that could have infuenced sharpness of the testshots in the large format cameras is shift of focus due to spherical aberration of the lens, since I focus at f5.6 and shoot at f16. So I did a number of focus experiments with various apertures using the Rodenstock Sironar N lens. It appears that the standard deviation of focus position of the lens increases proportionally to the f number, but the average position of focus does not change (statistical t-test used). Hopefully these data gives you peace of mind concerning the accuracy of focussing in my experiments.

[Bert Otten]

A small clarification of the data I gave:

The standard deviation of focussing of 150 mm focal length at f16 is 0.1 mm The standard deviation of focussing of 150 mm focal length at f5.6 is 0.03 mm The difference in average of focussing of 150 mm at f16 and f5.6 was 0.065 mm

The focal length for f16 was 0.065 longer than at f5.6, but t-test showed it not to be significant because of the scatter of the data. Problems of film flatness are more important here.

Film flatness I have studied also in a fidelty hoder (4x5) and in a Sinar holder with pressure plate. The flatness was within 0.3 mm in the fidelity holder and within 0.1 mm in the Sinar holder. Both are within the 0.33 depth of focus at f16 of the 150mm lens at the extreme demand of a circle of confusion of 0.01 mm. (Normally a circle of confusion for 4x5 of 0.1 mm is used, which is too tolerant in the light of modern optics I think)

Hope this is of use.

[Stan. Laurenson-Batten]

My thanks to all contibutors for a very well conducted informative discussion on a oft delicate subject.

[grepmat]

The tests and commentary are interesting, but all I can say is... I want an 8x10!

Cheers.

[Phillip Liebowitz]

I don't understand why no one on here is pointing an obvious glaring problem with this study. I'll start by pointing out that the lense used on the Digital Rebel is an $80 consumer zoom that wouldn't compare to a $2500 Leica lense under ANY condition. This whole study is a complete farce: comparing $5000 film setups to $700 digital cameras is totally absurd. I hope that you all enjoyed this pointless exercise in self-justification which seems to be the hallmark of every high-end electronics purchaser discussion: I spent $10,000 on it, so it MUST be awesome. Give me a break.

[Michael Chmilar]

The issue of lens quality on the Digital Rebel was asked:

Ellis Vener: [...] with the dslr the problem is the lens [...] and [...] with the DSLR he uses a lens that isn't equal to the quality of the lenses used on the film camera,

Darin Cozine: The LF equipment was tested with top-of-the line optics. Meanwhile the digital cameras and lenses were entry-level.

and answered:

Bert Otten: Today I have looked with a microscope at the air image of the plastic lens of the Canon (18-55) at the same focal length setting as in the test and seen that on axis the image of the USAF chart is resolved with the finest detail blocks at full opening of the lens. This implies that the lens has a resolution of a factor of at least 2.5 times higher than the test result of the whole camera. The lens was not limiting.

[Phillip Liebowitz]

So according to Bert's microscope, there's no difference between the plastic zoom and a 50mm prime lense. I don't need a microscope to tell me that is totally absurd. ABSURD! A joke!