Camera Scan vs Film Scanner – A Detailed Comparison

Discussion in 'Digital Darkroom' started by Harald_E_Brandt, Dec 3, 2018.

  1. 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?
     
  2. 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?
     
  3. - 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.
    - 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.
     
  4. 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.
    [/QUOTE]
     
  5. 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....;)
     
  6. 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.
     
  7. 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.
     
    Last edited: Jan 22, 2019
  8. 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?
     
  9. Late EDIT.
    Just found a macro DoF calculator and it give a total of 0.132mm for the same parameters as above!
     
  10. 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)
     
    Last edited: Jan 23, 2019
    mike_halliwell likes this.
  11. - There should be no difference between a 'macro' DoF calculator and an accurate DoF calculator.

    Optical theory states that there's no such thing as a lens with a perfectly flat field. The field is always a section of a spherical surface, which may be convex or concave toward the camera. So, as Harald said earlier, you may get better sharpness across the frame by making sure that the films bows, or dishes, in the same direction as the field curvature. However, there's no guarantee that every macro lens 'curves' in the same direction.

    I tried this with my 55mm f/3.5 Micro-Nikkor, and the difference is almost negligibly slight, but just noticeable.

    Therefore the curvature of field with this lens must be less than the curvature of the film, and in turn the film curvature outstrips the DoF at f/5.6, which is the aperture for best resolution.

    (I am going somewhere with this. Bear with!)

    Theoretical DoF @ f/5.6 is a total of approximately 0.34 mm, which means the film must bow more than that. So perhaps we can estimate glassless film bowing at ~ 0.5mm for a 35mm frame in a plastic clip-type filmstrip holder.

    I also have a heavy chromed-steel enlarger negative carrier that crops the frame slightly and definitely holds the film flatter. However this needs a more cumbersome setup than a simple horizontal front-of-lens attachment - needing gravity to let it do its work of pressing the film flat.

    Having said that; how often is the absolute best edge-to-edge sharpness needed in a digital copy?
     
    mike_halliwell likes this.
  12. Photographic flat earthers? What a pompous, ignorant comment.
     
  13. ???? enlarger lens? I'm comparing to scanners
     
  14. Scanners also use a lens, and usually a not-very-costly or wide-aperture lens at that.
    Do you think the image of the film gets transferred to the scanner sensor by magic?
     
  15. But compare the product scan from even a flatbed scanner to a camera lens...

    And apparently it is "magic" Jeez, so much heat and so little light
     
  16. I have. The camera wins hands down.
     
  17. Dave: Ed already apologized, sort of, for the "flat earthers" comment. I rather enjoy the slight. I do disagree however, that it was not 15 years ago, it only occurred in 2012, when Nikon introduced the first 24 MP crop body and the first 36 MP full frame body. I almost exclusively shot K25, and Velvia 50 from a tripod, so it took digital a little longer to catch up for me.


    I had no idea how technical this thread had gotten. I got by just fine with f5.6 for all of my 35mm, 6x6, and 4x5 scanning that I described earlier. If there was a real problem it should have showed up with the 4x5 since I only used a 4x5 enlarger film holder in an attempt to keep it flat, and then proceeded to take 18 shots of it! I only chose f5.6 because that was the best rated aperture for my Canon FD 50mm f3.5 Macro, and it gave me a shutter speed that I was comfortable with.


    I hope soon to continue my "scanning" project with my new-to-me 5DS R, but first I will invest in a better light source, and then perhaps I could try f8.


    As for the "flat earther" thing I am very much planning to return to flat earth sometime this year when I will start shooting, on a very limited basis, 6x6 Velvia 50. As I mentioned in my post this film produces colour to me, that surpasses what a DSLR and ACR and Photoshop can do. I would not make the return if not for a very unique lens/camera combo that cannot be duplicated on my 5DS R.
     
    Last edited: Feb 25, 2019
  18. Silverfast (Lasersoft) now has a USAF style resolution target in card form for use on any flatbed. Previously, they had only transparency targets, which required flatbed scanners with backlight, and only as close as the thickness of the mount.

    Optimum Sharpness: the brand-new SilverFast Resolution Target for Flatbed Scanners

    "Flat Earther" was intended to poke at those who think film is coming back, with all the accouterments, including dedicated film scanners. There are still a few outrageously priced film scanners, Hasselblad and Scitex to name a couple, but it's time to look forward to new methods which will be with us for the foreseeable future, at a price we can afford.

    The official FE's had a convention recently, which included globes which looked rather like a vegan pizza. The continent of Antarctica served as the crust. Their "globe" does not explain why one cannot traverse the continent, rather only travel Antarctica by coastline (iceline), and the South Pole does not exist, in their view. The fact that stars appear to rotate around Polaris is explained by a rotating firmament, like a planetarium light show. At the South Pole, a similar rotation occurs around Sigma Octantis at zenith, rather than at the horizon in the FE model.

    It's easier to believe in a new Kodachrome.
     
    mrjallen and John Crowe like this.
  19. Sorry Ed....I misinterpreted what you meant.
     
  20. No, you were correct to say something if I came up short. My mind runs faster than my fingers, which leaves gaps in my logic.
     

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