Camera Scan vs Film Scanner – A Detailed Comparison

[AlanKlein]

FF have larger sensor elements. Don't they absorb light better than APS sensors?

[Ed_Ingold]

And yet many people engage in macro photography with full frame cameras. Are they all misguided? Would they be better off using the cameras in their phones?

There are several functional advantages to copying 35 mm slides to a cropping sensor. The most important is the ease with which you can focus the lens when the magnification is less than 1:1. At unity magnification. the distance from subject to the film plane is at a minimum, so the only way to focus is by adjusting the film to lens distance. Using a sensor with a crop factor of 1.5, the magnification is less than unity, and you can use the focusing helix or auto focus to full advantage.

 

I use a full frame camera (Sony) to copy slides. I adjust the distance by sliding the tube as best as possible, then extend it a little more (1-2 mm), then use the lens for fine tuning. The net magnification is about 1.1:1, which is no big loss.

[Harald_E_Brandt]

Well of course you get more depth-of-field at f/8 than you do at f/5.6.

 

I was comparing like-for-like, not apples to oranges.

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'm not familiar with Mr. Jacobson's formulae for depth-of-field, only the ones I've formulated myself, which take careful account of physical aperture size and tangential half-angle. The 'accepted' circle-of-confusion is, of course, fairly useless for this purpose, but it scales to the pixel level quite readily - simple geometry of similar triangles.

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 can easily see the difference in sharpness due to diffraction when stopping the copying lens down from f/5.6 to f/8 (marked aperture) on a APS camera. However, with an APS sensor the f/5.6 aperture is fully useable, with enough depth-of-field to take care of some degree of bowing in the film.

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.

I've also shown to my own satisfaction that increasing the copying 'resolution' beyond 4000 ppi doesn't get any more detail from the 'average' negative. Well, actually from a carefully focussed and exposed negative shot on T-max 100.

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.

[rodeo_joe1]

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.

 

- No. That's only if you want to replicate results between formats. I'm suggesting that better results can be got from a smaller format, by using a wider aperture.

 

What would be the point of deliberately throwing away the advantage of increased depth-of-field for the same aperture number?

 

And I've already shown that DoF and diffraction scale slightly differently. So it's impossible to exactly replicate both of their effects between formats simply by altering the aperture.

 

I'm not out to create an argument here. Just suggesting that those people with access to both full-frame and APS cameras do the experiment and see which gives the better result.

 

"Drum scanners did 8000ppi"

- Drum scanners outputted 8000 ppi. The evidence of the eye suggests the optical resolution fell well below that figure. Getting a true resolution of 8000 ppi would require a scanning spot diameter of 3 microns, which is a bit unbelievable using white light.

 

And yes, in general those people using a larger format for any task that requires magnification, are misguided. That's why you don't see many rollfilm or 5"x4" cameras being used to copy 35mm slides!

Edited December 15, 2018 by rodeo_joe|1

[rodeo_joe1]

OK. I spent a couple of hours with my 'does everything optical' spreadsheet, and it appears that this is a no-win situation.

 

The killer is diffraction. In order to keep the Airy disk size at, or below the circle-of-confusion diameter, the aperture has to be opened enough to give the same depth-of-field, regardless of sensor size.

 

Example: For 24 Mp sensors, the 2x pixel diameter is 12 microns for full-frame, and 8 microns for APS-C. If we plug these numbers into the circle-of-confusion, and also put these limits on the Airy disk diameter, we find that we get the exact same depth-of-field after adjusting the respective lens apertures to meet those criteria.

 

The full-frame sensor requires an aperture of f/4.5, and the DX sensor needs an aperture of f/3.6. Both give a DoF of 0.216mm. The lens focal length turns out to be irrelevant and the effective apertures scale exactly with (linear) sensor size; being f/9 and f/6 respectively.

 

In summary; it appears that sensor size makes no odds, but that we should aim to use the widest aperture possible compatible with whatever film-flatness we can achieve. And since focal length doesn't really matter as far as depth-of-field is concerned, we might want to use a longer focal length for the sake of field flatness.

 

Also, the increased pixel numbers available with some FF sensors may be entirely wasted unless a very wide aperture is used to overcome the diffraction effect.

 

Of course, all this is based purely on thin-lens theory. In practise there may be considerations of convenience or compactness; not to mention the real-world quality of the lenses we have available.

 

I'm not sure whether this complicates or simplifies things. What it should do is put to rest any full-frame snobbery or DX inferiority complexes.

 

BTW Harald. My DoF formula completely agreed with that of Jacobson's. Despite apparently approaching the calculation from different directions - yours based on CoC and magnification, while mine used the geometry of similar triangles scaled by a factor of (physical aperture/CoC) to find delta-v.

[Harald_E_Brandt]

OK. I spent a couple of hours with my 'does everything optical' spreadsheet, and it appears that this is a no-win situation.

<snip>

I'm not sure whether this complicates or simplifies things. What it should do is put to rest any full-frame snobbery or DX inferiority complexes.

 

BTW Harald. My DoF formula completely agreed with that of Jacobson's. Despite apparently approaching the calculation from different directions - yours based on CoC and magnification, while mine used the geometry of similar triangles scaled by a factor of (physical aperture/CoC) to find delta-v.

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).

[rodeo_joe1]

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).

 

- Agreed.

If I may just add one more thought on the subject of film-flatness.

 

The usual remedy is to use anti-Newton glass, which brings its own issue of having a microscopically dimpled surface. Instead, I would suggest using multi-coated anti-reflection glass. Since Newton's rings are caused by reflection between a glass surface and the shiny surface of the film, using AR glass should eliminate or greatly attenuate the offending rings without affecting image sharpness in any way.

 

Some years ago I came across some 5" square AR (green) coated optical plates that I assume had come from a high-end printer or enlarger. I never got round to testing their efficacy at reducing Newton's rings, and have now misplaced them. However, the glass from a multi-coated UV filter should suffice to test the theory.

 

MC glass might well provide a 'perfect' way to keep film flat during copying.

[Ed_Ingold]

Glass carriers for the Nikon LS-8000 have a coated piece nearest the lens, and an etched piece opposite. That way the film is seen through a transparent surface. The scanner easily resolves the stippled pattern in the AN glass if the film is omitted. I get the best results placing the emulsion side down. Since it is dull, and generally cupped upward in the center, Newton's Rings are unlikely to form. The back is relatively shiny, but the etched AN glass forms only faint rings, or none at all.

 

The glass in a flatbed does not appear to be coated, but placing the emulsion side down is unlikely to cause Newton's Rings. I make a spacer from thin black matting board and cover the film and mask with an inexpensive piece of anti-reflective framing glass.

 

Using a coated, clear filter to hold the film flat is an interesting idea. I have one lens (Sony PZ 28-135) which takes a 95 mm filter. That would cover 6x6 negatives, possibly 6x7, and the ring would serve as a spacer. Schneider makes rectangular, coated filters for video matte boxes, which is another possibility.

Edited December 16, 2018 by Ed_Ingold

[John Crowe]

I have had excellent results "scanning" 35mm, 6x6, and 4x5 using my Canon 5D II, Canon FD 50mm Macro with extension tubes all mounted on a converted enlarger stand and using a lightbox with special daylight bulbs as the light source.

 

 

The enlarger stand is ideal for fast and accurate adjustments of the sensor to film distance.

 

 

I actually go larger than 1:1 to varying degrees for each film format. I use the 36mm side of the sensor to photograph the 24mm side of the 35mm film. I shift the slide/neg on a jig I made for the lightbox and take 3 images of the slide/neg and stitch them together in one final copy. I did this to maximize the final resolution since the 5D II has only 21 MP. A higher resolution body would likely be fine at 1:1.

 

 

For 6x6, I stitch 6 images to get the final copy. 4x5 is done essentially at 1:1 using 18 images to construct the final copy. For 4x5 the final image is in the range of 1 to 1.5 GB. I have done a dozen 4x5 copies and printed a few at 16x20. I need to improve my light source for the 4x5 images to help eliminate light fall off on each individual frame. For the copies that I created and printed I was able to overcome light falloff as I built the final file. I can now tell that I can print much larger than 16x20 with no problems. Fortunately I only have a few dozen 4x5 images that I wish to copy to digital. I have done hundreds of 35mm copies and will likely wait for a higher resolution body before I continue. I am still processing the 6x6 images but again there are probably only a hundred of these that I wish to do.

 

 

What amazed me across all film formats is how much colour I could pull out of those slides/negs and how the 5D II was able to capture them. I get deeper richer colour out of the film, using the 5d II, than I get when photographing live scenes with the camera itself! Makes absolutely no sense at all to me, but for a few minutes I actually considered going back to film photography for the purpose of "scanning" with my camera.

 

 

The results that I have gotten are far superior to the late 90's 35mm film scanner that I used originally. Obviously the Coolscan 8000 and 9000's would be superior to the scanner that I used but I doubt they could do significantly better than my camera scanning process and of course they cannot do 4x5 or larger medium format either. My entire macro setup including enlarger, light source, lens, and lens accessories and jigs was purchased for less than $150. Making this an extremely affordable option.

[John Crowe]

Here is a crop from a copy of a 4x5 transparency.

[AlanKlein]

So when I'm out shooting my P&S digital 1" camera, the DOF is usually through the range I'm shooting for most scenes. What would I set to get the same DOF from a FF and APS?

[rodeo_joe1]

So when I'm out shooting my P&S digital 1" camera, the DOF is usually through the range I'm shooting for most scenes. What would I set to get the same DOF from a FF and APS?

 

- Sensors quoted as 'one-inch' are nothing like 1" in actual size. (For some unknown reason, camera makers like to use the obsolete vidicon tube diameters.)

 

To get a true depth-of-field comparison you need to know the size - in mm - of the sensor.

 

The f-number approximately scales in proportion to the sensor size. So if, for example, f/4 gets you sufficient DoF on an APS-C sensor, you'd need f/5.6 on full-frame to get the equivalent DoF.

 

Anyway, it's all explained in this Wikipedia article, along with depth-of-field.

 

"4x5 is done essentially at 1:1 using 18 images to construct the final copy. For 4x5 the final image is in the range of 1 to 1.5 GB."

 

-Wow! That's cumbersome John. 5x4 is one instance where I'd definitely dust off my old flatbed scanner - a Canoscan 9950F. Even at a modest 2400 ppi the flatbed makes a terrific job of sheet-film scans. And I see that Canon's latest model - the Canoscan 9000F - is at a rock-bottom price now.

Edited December 17, 2018 by rodeo_joe|1

[Robin Smith]

My repro lens is a 75mm f4, and although f5.6 is apparently the stop for best resolution across the plane at 1:1, I usually stop down to f8, as this provides slightly better depth of field and helps to deal with slide curvature. I don't glass mount the slides as the dust issue is multiplied and because it takes extra time, quite apart from anti-newton glass issues that ensue. I mount them in the steel edged GePe slide mounts, which holds them quite flat. I find the final quality is excellent. I have yet to embark on any of my MF shots, but was thinking of either making do with a single 30MP shot or indeed doing as John is doing combining 1 or two 35mm shots to make the whole.

[Harald_E_Brandt]

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?

Edited January 31, 2019 by Sandy Vongries

[rodeo_joe1]

Thanks Harald. That just confirms what I've found through trial and error.

 

I'm using either a Nikon 55mm f/3.5 Micro-Nikkor with a front-of-lens filmholder attachment, or an 80mm f/4 Rodagon P enlarging lens with a Bowens Illumitran dedicated film copier device. Both lenses appear to give close to diffraction-limited resolution.

 

The Micro-Nikkor gives its best resolution at f/4, but needs f/5.6 to give adequate edge-to-edge sharpness to account for lack of film flatness. The Rodagon also works best at f/5.6. This is using a 24 megapixel Sony APS-C digital camera.

 

I've yet to use my 36Mp D800 on the Bowens Illumitran copier since its bellows are lacking a Nikon adapter. However, there seems to be little gain in the sharpness of the 'scan' when using the front-of-lens copier attachment, regardless of whether full-frame at 36Mp or APS-C at 24Mp is used.

 

I put this down to the extra magnification needed for full-frame use, with concomitant decrease in effective aperture and increase in diffraction loss.

 

The Illumitran also has a better filmholder - a weighty chromed steel negative carrier that crops the image area slightly, and presses the film flatter. Despite this, the best edge-to-edge sharpness still requires a marked aperture of f/5.6 to be used.

 

However; most film shows no more or less macro detail regardless of whether the optimum copying lens aperture is used or not. Only apparent graininess is affected.

 

Incidentally: Has the marked or effective aperture been used in the above diffraction calculation? The increased distance between aperture and focal-plane increases magnification of the Airy disc over the infinity case. Therefore the effective aperture number should be used in diffraction calculations.

 

Oh, you might also want to look at the photomicrographs of film dye-clouds that I posted at the end of this long and rather pointless thread.

Edited January 19, 2019 by rodeo_joe|1

[Harald_E_Brandt]

Incidentally: Has the marked or effective aperture been used in the above diffraction calculation? The increased distance between aperture and focal-plane increases magnification of the Airy disc over the infinity case. Therefore the effective aperture number should be used in diffraction calculations.

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?

[Harald_E_Brandt]

Incidentally: Has the marked or effective aperture been used in the above diffraction calculation?

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?

[rodeo_joe1]

You say your film is held flat. Does that mean it is "only" film without it be mounted in a frame?

 

- Yes, it's bare strips of negative film, both colour and B&W. I had little interest in slide film, since it was expensive to make decent prints from.

 

The other advantage of colour negative is that you can interpret the colour in much the same way as interpreting the tonal range in B&W. Many people find this a disadvantage, in that there's no immediate reference for the colour. Fortunately I have a good memory for colour, and like to print or scan how I'd prefer the colour to be, and not how Kodak/Fuji/Agfa or whoever's chemists wanted it to look. The exceptional dynamic range of colour negative appeals also.

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.

- Infernal Focus is an increasing 'problem', especially if trying to calculate effective aperture or the subject distance required for a given magnification.

 

Lenses should always be symmetrical in sharpness however. Any one-sidedness usually indicates decentring, and shouldn't be accepted. It seems less of an issue with old unit-focussing designs. Plus, are you sure it's not due to a slight angle between the lens and film-holder? It only takes an imperceptible tilt to prevent the focus being off on one side or the other.

 

FWIW, I have a preference for using enlarging lenses for macro work on a bellows. They're cheap, they nearly all have a standard M39 fitting, they're computed for short distances, and they have a very flat field. And I've yet to find one that's noticeably decentred or faulty in any way. Yes, there are some horrors out there, but at today's used prices you can be picky and stick to top-end 6 element lenses from the likes of Schneider, Rodenstock or Nikon.

[Harald_E_Brandt]

The exceptional dynamic range of colour negative appeals also.

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.

Lenses should always be symmetrical in sharpness however. Any one-sidedness usually indicates decentring, and shouldn't be accepted. It seems less of an issue with old unit-focussing designs. Plus, are you sure it's not due to a slight angle between the lens and film-holder? It only takes an imperceptible tilt to prevent the focus being off on one side or the other.

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.

[mike_halliwell]

Is it right that the longer the focal length of the copying lens, the less the distortion effects of film curvature are?

 

In the same way that if you photograph a curved page of a tightly bound book plate for example, the further away you are, the less the plate becomes distorted in the image, so a 200mm gives better results than a 35mm.

 

....or indeed full-face portraiture with a 24mm or a 150mm lens....;)

[Ed_Ingold]

Is it right that the longer the focal length of the copying lens, the less the distortion effects of film curvature are?

Yes, because the further from the subject, the less the effect of perspective (convergence). The DOF is the same for the same absolute magnification on film, independent of the format or focal length. Doubling the focal length means you have to be twice as far away, which becomes a practical issue in keeping the setup centered and parallel if you can't use a copy stand or fixture.

[Harald_E_Brandt]

Is it right that the longer the focal length of the copying lens, the less the distortion effects of film curvature are?

 

In the same way that if you photograph a curved page of a tightly bound book plate for example, the further away you are, the less the plate becomes distorted in the image, so a 200mm gives better results than a 35mm.

 

....or indeed full-face portraiture with a 24mm or a 150mm lens....;)

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.

Edited January 22, 2019 by Harald_E_Brandt

[mike_halliwell]

Indeed, it's 'true' name is Perspective Distortion. Perspective distortion (photography) - Wikipedia

 

According to my DoF calculator, 150mm macro at 1:1 gives ~ 0.5mm @ f5.6.

 

Anyone actually measured 35mm slide total 'deviation' from the centreline? So maybe focused plane +/- 0.75mm?

 

Guess I need to stack 4 frames?

[mike_halliwell]

Late EDIT.

Just found a macro DoF calculator and it give a total of 0.132mm for the same parameters as above!

[Glenn McCreery]

When I look up depth of field on Wikipedia, they give an approximate equation for depth of field (DOF) for close up photography (image distance << hyperfocal distance)

 

DOF approx.= 2Nc((m+1)/m^2)

where, for Mike's example,

N = f number = 5.6

c = circle of confusion = 0.03mm (for full-frame 35mm)

m = magnification = 1

DOF = 4*5.6*1 = 0.67mm

 

If c = 0.02mm, then DOF = 0.448mm, which is consistent with Mike's value of 0.5mm

 

If I use Harald's more exact equation,

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

 

with p = 1, the results agree almost exactly with the approximate equation (since (Nc/f)^2 is only about 10^-6)

Edited January 23, 2019 by Glenn McCreery