Harald_E_Brandt

Hi again! I am the original poster, i.e the creator of this thread, where I first posted an article about my own camera scanning setup, and then an article about optimising the aperture. The camera I used was a Canon EOS 7D and a Canon EF-S 60/2.8 macro lens. I wrote that if I buy new equipment, I would post a new article. Now I own a Canon EOS 80D, and a Sigma 70 mm f/2.8 DG Macro Art, now mounted on a rail. I have written a long article again, comparing the previous equipment with the new one, using the same slides for comparison regarding color, sharpness, shadow performance etc. It's pretty long, pretty deep, pretty technical, but I am pretty certain that many people will find useful information there. I have also included a fair amount of my conclusions and my personal recommendations. Here is the article on the new camera scanning equipment: http://photo.bragit.com/CameraScan/80D_CameraScan.shtml Best Regards

Well, yes, in principle. But in the case of copying a piece of film, where the film bulges only a small fraction of a millimeter, I am pretty sure the effect is much smaller than you would be able to detect, no matter how hard you look. The big problem is DoF. PS: The example you gave does actually not give rise to distortion, but a difference in perspective. Portraiture close-up with a rectilinear wide angle lens gives rise to a strange perspective that we may perceive as distorted, but technically it is actually not distortion.

I know, and it is good to know that you only deal with neg. 99% of what I have are slides. In some future I might dive into my fathers 6x6 and the odd format of 4x4 cm. Yes I am sure! I tested the lens years ago on a ISO 12233 chart and saw the problem also there. In my present camera scan setup I have been careful to measure both sides of the setup to within about 1/10 mm. That's hard! I have tested my other lenses with 12233 chart, and think all of the lenses are more or less unsymmetrical, also Canon L-glass! There is always some corner that is worse than the other corners. I am not convinced that I can demand perfectly symmetrical lenses from Canon. In any case, my macro is many many years old, so it is probably not worth sending in for (expensive) adjustments. I have had some weak thinking of trying an enlarger lens, but it appears cumbersome, requiring various adapters that I do not even know how to get hold of in Sweden... I think my biggest problem is not really resolution, but my oldest slides are glass mounted, and I must detach and remove the film since glass causes terrible results. So I have to re-mount them glassless, which is a nightmare and a "waste of time", or use some other method.

Another thing that is worth mentioning: If the lens use internal focus (probably all modern macro lenses) the focal length may actually change as you focus, so you cannot be 100% certain that the marked f-number is the real f-number. Theory shows and explains a lot, but cannot tell us everything. Your macro lens and your Rodigon are probably different in this respect. You say your film is held flat. Does that mean it is "only" film without it be mounted in a frame? And is that with any glass towards the film? Maybe you have negative film, but for slides they are usually mounted in frames, and it is really a lot of terrible work to take the frames apart and try to position a little flimsy 35 mm film bit in some holder – next to impossible... What I wonder is this: concerning curvature of field, is there any known or systematic differences between a modern macro lens and an old repro/enlarger lens? I also suspect that any use of extension rings makes the lens be used in an area that it was not optimized for. My lens is very sharp, does not need extension rings, but I have had problems with the lens being not as good at the left side as it is on the right side. However, that is a common problem with lenses. I have no idea whatsoever if my lens, EF-S 60/2.8 USM Macro, has more or less curvature than other macro lenses. Does anyone know?

The f-numbers that are mentioned are always the marked f-numbers. But of course the calculations take the magnification into account, thereby with the same effect as using Neffective as N(1+M/p) where M is magnification and p is pupil size. I strongly encourage you to look att Jeff's paper that I referred to for mathematical details and explanations. I have to apology that my post has three duplicate graphs at the end. I made a mistake, discovered that, then edited the post to delete them, tried to save the edit, whereupon I get the following stupid response from the stupid photo.net system: "Your content can not be submitted. This is likely because your content is spam-like or contains inappropriate elements. Please change your content or try again later. If you still have problems, please contact an administrator." That's absurd! It refused me to save! After 15 minutes it even refused me to go into edit mode! It's embarrassing with several duplicate images in the post! I have messaged both an admin and a moderator for help, but no one has responded. Actually, I think I should not have posted it at all in this thread – rather I should have referred to the article I just published on that subject. Also because I got some small comments from Jeff, which I used to update the article with a couple of language issues and a couple of references plus some small clarifications. The updated article can be read here: What is the optimal aperture for camera scanning?

Concerning optimizations of the aperture for APS-C and FF, I had some detailed mathematical discussions with Jeff Conrad who sent me some graphs. (Jeff is the author of Depth of Field in Depth at https://www.largeformatphotography.info/articles/DoFinDepth.pdf and Optimal Aperture: Balancing Defocus and Diffraction (not on the web)). I'll make a post here of our findings. The background material is very theoretical, but the results are interesting and illustrative since they show what theory predicts in nice graphs. However, you always need carry out practical testing to see what is best with your camera and your lens and your (bulging) slides that you intend to copy with your camera scan setup. The following graphs show the theoretical results of the combined effect of diffraction and depth-of-field at two distances: (1) at the Plane of Focus — PoF. (2) at the planes of the Depth of Field — DoF — as a result of defocus. The total focus spread at the sensor plane is ∆v as indicated in the graphs. The theory assumes a perfect lens with no aberrations, and no considerations to the limitations of sampling (i.e assuming a perfect anti-alias filter according to the Nyquist theorem, or assuming it is an analog recording). The object size, i.e the film we shall take a picture of, is 24x36 mm. The focal length is irrelevant. For both of the following two graphs, the total focus spread ∆v at the sensor, 0.164 mm for APS-C and 0.368 mm for FF, corresponds to 0.368 mm at the film we are photographing. In other words, 0.368 mm is the total depth of field we are studying (0.368 mm is the difference between the near and far object distances). That value was chosen quite arbitrarily based on that it results in a Circle of Confusion—CoC, the blur spot size—of 2 pixels on a 20 Mpx sensor if we use f/5.6 on APS-C or f/7 on FF. This is arbitrary, but is chosen for the purpose of comparing APS-C and full frame. The y-axis shows the MTF, i.e the modulation transfer function that indicates how much contrast there is: 1.0 is perfect contrast, 0.0 is no contrast at all (gray). The 'm' in the graphs is the magnification, which is 1.0 for FF and 0.667 for APS-C. The f-number is the aperture (f-stop). The interesting and illustrative thing that these graphs show is that there is an optimum aperture! This optimum aperture appears to be about f/5.6 for APS-C and f/7 on FF. At those apertures, the depth of field is exactly the same for APS-C and FF, namely 0.368 mm when the CoC is 2 pixels on a 20 Mpx sensor. One can show that, at these magnifications, the DoF for APS-C and FF are exactly the same if FF uses an f-number that is 1.25 times the f-number for APS-C. The highest spatial frequency in these graphs, the yellow ones, corresponds to one cycle being about 2.4 pixels on a 20 Mpx sensor, which is a very high frequency. The Nyquist frequency (the ultimate theoretical limit) is one cycle being 2 pixels, and no sensor can resolve that because it would require infinite ideal filters. (If you see any pattern there on a test chart it is guaranteed to be only alias, i.e spurious.) In practice, you cannot get as much modulation as these graphs show at the indicated frequencies, but at the frequency of the yellow line you should just barely be able to see at least some weak resolution with a 20 Mpx sensor. More megapixels would be better since we would come further away from the theoretical Nyquist limit, but you would also have to accept that the circle of confusion for DoF would have to be more than 2 pixels. One can argue that the DoF is too narrow. Let's see what happens if we increase the DoF so that the CoC becomes 2.5 or 3 pixels on a 20 Mpx sensor when using the same aperture as above, i.e f/5.6 on APS-C. And let's study at different frequencies so that the highest frequency corresponds to the theoretical limit of one cycle being 2 pixels. This is shown below, and the graph is expanded so that it is easier to read the f-numbers on the x-axis. The graph for ∆V = 0.205 mm corresponds to 0.460 mm DoF, i.e the depth at the slide/film. The graph for ∆V = 0.245 mm corresponds to 0.552 mm DoF, i.e the depth at the slide/film. As ∆v increases, i.e targeting a wider DoF, the optimal f-number increases. The highest spatial frequency in these graphs, the yellow ones, corresponds to one cycle being only 2 pixels on a 20 Mpx sensor, which is the theoretical Nyquist limit, which no real 20 Mpx sensor can resolve. The gray, red and blue lines correspond to one cycle being 2.5, 3 and 4 pixels respectively on a 20 Mpx sensor, which are all sensible frequencies to study for any sensor with at least 20 Mpx. In summary: For all these graphs, the theoretically optimal aperture for APS-C 1.5 crop sensor should be somewhere between f/5 and f/7, most probably f/5.6 or f/6.3. The more the film bulges, the higher is the optimal f-number. For FF, the optimal f-number should be 1.25 times higher, i.e somewhere between about f/6.3 and f/9. Optimal aperture in Practice: To find out the optimum aperture in practice, I made detailed tests with my equipment, which is an oldish 18 Mpx Canon EOS 7D (crop factor 1.6) and an EF-S 60/2.8 USM Macro. The optimal aperture is not only dependent on how much the film bulges, it also depends on how accurate the slide is positioned, i.e how parallell it is to the sensor. It also depends on how much the lens has to be stopped down to get good resolution in the corners, and it also depends on how much field curvature the lens has. I used various glassless mounted slides: Kodachrome in Kodak paper frames, Kodak plastic frames, and manually mounted Gepe frames with metal masks; Fuji Sensia in plastic machine mounted frames, and manually mounted Gepe frames with metal masks. I found that bulging slides should always be inserted so that they bulge outward from the camera. The reason is of course that the lens is not perfectly flat—there is some field curvature, and since we are dealing with extremely short DoF, it is critical. In addition, the left hand side is not as good as the right hand side (which I knew from before). Normally, the emulsion side is concave, but some slides (most notably some in manually mounted frames with metal masks) could actually bulge in the opposite direction, or be doubly bulging. Slides that are scanned mirrored will of course have to be flipped in the program (such as Lightroom). Scrutinizing the entire image, middle, sides and corners, I found that the optimum sharpness was obtained at f/6.3 (provided that the slide bulges outward from the camera). If you use a camera with many more pixels in the hope of getting higher resolution, I am afraid you will have to place the film between absolutely clean glass or plastic plates. But with such plates, you increase the number of transitions between air and materials with a different refractive index, and you have many sides to clean from dust, and you risk newton rings. The optimum way is to use a wet method with a suitable solution that drives away the air between the surfaces, and if the solution has a refractive index close to 1.5, alla scratches will disappear, and transparent dust virtually disappears. For me, however, I guess the method is too cumbersome to be worthwhile to use. I haven't used it myself, but a friend of mine got fantastic results. /Harald PS. An updated version of the above can be found at: What is the optimal aperture for camera scanning?

I also elaborated a bit further, now including diffraction, and I came to the same conclusion that both DoF and Diffraction are exactly the same for FF and APS-C! Regardless of focal lengths! As for diffraction I used the equation in the Lens Tutorial on OTF but replaced N with N(1+M). I just today discussed this issue with Jeff Conrad who agreed, and it is the same equation (after som algebra) as his equation 115 in the super detailed Depth of Field in Depth at https://www.largeformatphotography.info/articles/DoFinDepth.pdf (I really recommend that – it is fantastic, as a complement to Lens Tutorial). As for DoF, equation 24 in the above reference is the same as the one I am using. The diffraction formula may not be fully exact since light is not entering parallel to the lens axis at 1:1, but I don't think it makes a big difference for the principal arguments on frame format. Some numerical details: If you stop down the FF camera 2/3 stops relative to the 1.5 crop camera (from say f/5.6 to f/7), you get exactly the same DoF (up to 6 decimals). Moreover, the OTF for diffraction also becomes exactly the same! As for CoC, I assumed both sensors to be 20 Mpx, and the confusion disc to be 2 pixels. With this criteria, DoF becomes 0.37 mm using f/5.6 for the APS or f/7 on FF. As for diffraction, I assumed the spatial frequency to be so that one cycle is 2 confusion discs, i.e 4 pixels (thereby making defocus and diffraction at least somewhat similar, just for a principal discussion). At this frequency, the OTF becomes 0.63 for f/5.6 on the APS. I don't think we need to delve into this any further, except that in practice, I think it is safest to experiment what f-stop gives you the best results as studied over the entire frame of a real slide with some bulging (glassless or using single-glass or using double-glass).

You always need to scale the aperture according to the format if you want to compare apples to apples! Otherwise both DoF and diffraction will be off. With normal photography, i.e far away from macro, a 4/3 system is useless beyond f/11 because that corresponds to f/22 on FF. APS and FF differ by just over one stop. Large format cameras may very well need f/32 for an adequate DoF. If you scale the f-stop number, DoF will be the same, and diffraction will be the same as measured by the total number of line pairs that can be resolved (i.e not line pairs per mm). The accepted circle of confusion (CoC) must of course also be scaled. I do note that the famous tutorial no longer resides at photo.net, but is found at numerous other places: • Photographic Lenses Tutorial (1995 version) • Photographic Lenses Tutorial (1996 version) • Photographic Lenses FAQ (1997 version, basically the last one) • https://www.largeformatphotography.info/archives/JacobsonLensTutorial.pdf (1998, but info is from the 1997 version. Absolutely the best one since it is typeset PDF.) Jacobson is fantastic! We communicated on DoF matters back in 1993. In summary, the exact formula I used for total DoF (front+rear) is: 2Nc(1+M/p)/(M^2 - (Nc/f)^2), where N is f-stop c is circle of confusion M is magnification p is pupil magnification (which for normal focus lengths is about 1) f is focal length Be sure to scale c with sensor format for the same degree of sharpness relative to the format. I think it is convenient to assume a constant number of Mpx regardless of format, and then express the c in number of pixels. This is easy to do in a spreadsheet. I believe you, but I had problems at edges with DoF. If your film is very very flat, I am sure f/5.6 is better than f/8. That is basically also my conclusion. For really capturing the grains, however, I am afraid it is not sufficient. Drum scanners did 8000 ppi if my memory serves me right. Personally, I am not a fan of sculpturing grains, so if they get soft, so be it. In B&W, I remember how much I hated when grains were sharp in the center and completely fuzzy at the corners! My copying lens was not good enough.

I am sorry to say that this is most probably not really true. Theoretically, given ideal lenses and ideal sensors, APS-C and full-frame have identical performance at long distances if you adjust the aperture accordingly – it all scales. This means you need to stop down the full frame lens with a factor of the focal length multiplier (just over one f-stop) to obtain identical depth of field and diffraction and resolution. At 1:1, however, things get more complicated. If I enter values into the exact equations for depth of field (as derived by David Jacobson at photo.net long ago), I get: With APS-C (your Nikon sized 24 mm sensor width, i.e multiplier 1.5), using your suggested f/5.6 aperture, 36 mm objekt width, and assuming an acceptable circle of confusion that would correspond to 2 pixels on a hypothetical 20 Mp camera, I get a depth of field of 0.37 mm. If I do the same thing on a full frame camera, using f/8, I get depth of field of 0.42 mm! Quite surprising that it is microscopically larger, but that is what the equations tell me (assuming a pupil magnification of 1). Focal length does surprisingly not matter in the first 5 decimals of the DoF. At longer distances, above 220 mm object width, the full frame gets shorter DoF, and at long distances you need to stop down to f/8.5 to get the same DoF (which is expected). Diffraction, however, seems to be more complicated, since I think the formulas I have are only valid at long distances. I have a feeling that full frame may be at a slight disadvantage here for 1:1, about 20%, but I cannot prove it. All-in-all, however, there is basically no significant difference between an APS-C and a full frame as regards DoF and diffraction, provided you stop down the full frame about one f-stop. I personally think f/5.6 is too wide on APS-C unless the slide is glass mounted – there is substantial risk that the frame edges become unsharp. I suggest f/8, which means f/11 on full-frame (just over one half mm in DoF). There are still a few advantages with APS-C: Since 1:1 on APS-C is a much smaller object than on a full frame, I can easily do a factor 1.6 crop of a 36 mm slide with the macro lens I have! That's nice! And the whole setup is relatively small and stable, and the lens is considerably cheaper and lighter than the corresponding quality for full frame.

If you have questions about my setup, as shown in the article, or questions about the images I posted, just ask here.

I wrote a long article that compares two ways to scan slides, using two types of equipment I had: - An ArtixScan 4000tf film scanner - An EOS 7D with a macro lens plus a slide duplicator attachment I actually elaborated the camera scan set up and many of the comparisons and findings 5 years ago (May 2013). At that time, it was only privately documented, but after several requests I now decided to write a full in-depth public article about it all, including detailed conclusions. The crucial question to be answered is: Will a camera scan setup be good enough for high contrast slides? With this post I simply want to share this with you. Here is the article: Camera Scan vs Film Scanner