Shooting at f/64

Discussion in 'Beginner Questions' started by Ricochetrider, Mar 28, 2020.

  1. You probably wouldn't be able to see it unless you compare to a similar shot at a "better" aperture. The effect is very much like a small focusing error. See my post #9 with respect to the extent of the effect in terms of "resolving power."

    As a note the limit is based on the idea that there is a limit to how small of a point that light can be focused down to. This smallest "spot" is called the Airy disk after astronomer George Airy, who worked out the mathematical treatment.

    The concept of resolving power, in terms of line pairs per mm, can be seen as the application of the idea of two Airy disks next to each other - how close to each other can they be before they merge into a single blob of light? In order to "resolve" a difference, meaning to see two distinct points, they must be separated by some distance; a guy known as Lord Rayleigh made some rules known as the Rayleigh criteria. The names should allow you to look things up should you desire.
     
    Ricochetrider likes this.
  2. Go it, Bill. Thanks so much for your super detailed posts. Really appreciate it. I will look around at some of this stuff but I have a basic understanding of resolution, line count etc, and thanks very much.
     
  3. When we use tiny lens openings like f/22 or f/32 or f/64, the length of the zone we call depth-of-field is expanded. These tiny aperture diameters increase depth-of-field however there is a cost.

    Well studied by Lord John Rayleigh 1842 ~ 1919 British Nobel prize physics 1904, his findings remain true today. The Rayleigh criterion for theoretical resolving power tells us that the twin demons of diffraction and interference take their toll as we stop down.

    A table, lines resolved -- thus at f/4 the best a lens can do is resove 320 septerate lines per milimeter. This table is computed using Rayleigh equation for wavelength 589 millimicrons, This is the center color of our visual scale.

    f/1 1392 lines per mm

    f/2 696 lines per mm

    f/2.8 487 lines per mm

    f/4 320 lines per mm

    f/5.6 249 lines per mm

    f/8 184 lines per mm

    f/11 127 line per mm

    f/16 87 lines per mm

    f/22 63 lines per mm

    f/32 44 lines per mm

    f/64 22 lines per mm
     
    Ricochetrider likes this.
  4. Pictures are worth a thousand words. So here are some examples shot at mid and small apertures.

    First a full frame of the subject:
    Whol-frame.jpg
    Not a real tiger, but a quality half-tone calendar picture of one!
    Here's a crop of the nose area at f/5.6, where you can clearly see the half-tone ink dots resolved:
    F5-6_1.jpg

    The definition starts to deteriorate at f/16:
    F16_1.jpg

    At f/22 it's a bit worse:
    F22_1.jpg

    And you can't see any dots at all at f/32:
    F32_1.jpg

    Tech data: The printed dot pitch was 6/40ths of a millimetre (0.15mm or about 6 thou") according to my weirdly-scaled measuring loupe. However, there are 4 ink screens used at angles to each other, so the overall dot pitch will vary with the colour and density of the print.

    I used a sturdy tripod and flash lighting to eliminate any vibration effect.

    The image was manually focused using magnified Live View.

    Lens was a Tamron 90mm f/2.8 macro that stops down to f/32, and camera was a 24Mp Nikon D7200.

    It should also be noted that at close or macro distances, the effective aperture of the lens should be used to determine the degree of diffraction.

    FWIW. The diffraction effect might actually be useful if you're copying half-tone pictures and moire patterning is an issue. Stop your lens right down and let diffraction work for you as a low-pass spatial filter.
     
    Last edited: Apr 1, 2020
  5. Good examples to demonstrate the practical effect of the lens apertures.

    But since this is a "beginner" forum, it's probably worth explaining this paragraph:
    Strictly speaking the f-number of a lens is only correct at, or near, infinity focus. When the camera is focused closer, a conventional sort of lens setup has the lens being moved farther out from the camera. When this happens the lens aperture "seems" smaller from the viewpoint of the film/sensor, and consequently the diffraction becomes more significant. In the case of a 1:1 (same size) macro, a conventional lens has to be extended by one "focal length," meaning twice the infinity-focus distance. In this case, the "effective aperture" would be double the actual setting. For example, if a lens is set to f/32, but then racked out another focal length, then the effective f-number becomes f/64. The diffraction effect is that of an f/64 setting, and the exposure must also be treated as an f/64 setting.

    Anyway, that is what the "effective aperture" means. It might be significant in rodeo_joe's example. But generally speaking, unless you are doing significant close-up shots, you don't have to worry about it.
     
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  6. Thanks for expanding on that Bill.

    I know my posts can get a bit wordy, and I didn't want to stretch anyone's attention span!
     
    Ricochetrider likes this.
  7. So in a week or so I will have a 135mm F/2.8 lens that allows me to shoot at F/64 on 35mm. My SLR's are currently being serviced so I have been using my legacy glass on my Olympus EM1 MkII.

    Clearly the diffraction is going to be 'off the charts' but if you were going to shoot with this lens at that aperture, what kind of shots would you be considering?
     
    Ricochetrider likes this.
  8. [​IMG]
    Snow Gum Dance, Charlotte Pass
    Gelatin-silver photograph on Ultrafine Silver Eagle VC FB photographic paper, image size 24.6cm X 19.5cm, from a 8x10 Fomapan 100 negative exposed in a Tachihara 810HD triple extension field view camera fitted with an Apo-Nikkor 610mm f9 lens working at f128.
    This is an extreme example of the capacity of large format photography to work at very small relative apertures and still deliver sharp images. Yes, diffraction is present but because this picture is not enlarged but rather contact printed it still contains detail finer than the eye can see.
     
  9. James G. Dainis

    James G. Dainis Moderator

    When I told a friend that i usually shot my 8x10 negatives at f/64 he said that I must get tremendous depth of field. Not so, The depth of field on 8x10 at f/64 is about the same as f/16 on35mm film.
     
    morrisbagnall likes this.
  10. James G. Dainis

    James G. Dainis Moderator

    I don't know about diffraction with a large format lens. On a "normal" 300mm large format lens, at f/64 the aperture opening is over 3/16 inch about the same opening as 50mm lens set a f/8.

    lens_aptr.jpg

    This all may not be pertinent to the discussion but is a bit interesting.
     
  11. It is both pertinent and interesting, i think.
     
    morrisbagnall likes this.
  12. I enjoy ultrawide angle photography with objects in the foreground within inches of the lens. Through 35mm, 6x6, 4x5, and DSLRs I have been using the smallest apertures for maximum depth of field out to infinity. Trading loss in resolution for sharpness throughout the frame is definitely worth it. More recently I have started using medium apertures with focus stacking when I can. Many of my images also have the sun in them and depending on the lens I get much better sunstars and reduced flare at the tiniest apertures.

    I like to think that Ansel Adams has influenced my photography and I have always strived to achieve the results of the f64 group, and will continue to do so.
     
    ajkocu likes this.
  13. Doesn't refraction also depend on the size of the film - as in 35mm vs 4x5 and the enlargement of the print? Contact printing an 8x10 shot at f64 is different than shooting 4x5 at f/64 and than enlarging it to let's say 16x20"
     
  14. When I got my 8mm fisheye lens for my D500 I played around with it some:

    [​IMG]

    You won't see much effect of having used it at f/22 here because the shot is not enlarged that much. I went for that f/stop because I wanted to bring the DOF to within the MFD (minimum focusing distance) to create a more dramatic perspective. Getting closer actually magnifies the detail more and compensates for what is lost from diffraction, so it's a balancing act for close-up photography and the overall DOF is part of the equation too.
     
    morrisbagnall likes this.
  15. I love that shot, Tony. Very Image Bank!
    It goes to show that even experienced photographers have to recalibrate their expectations when dealing with, or talking about, large format. I do, anyway. Cameras are not all the same, and the myth that they are does not help in our understanding of how they work.
     
    tonybeach_1961 likes this.
  16. If your objects are flat, that is a good question.

    But in most cases, you need some depth of field, and so stopped down will be sharper,
    over the depth of the actual subject.

    For pinhole cameras, there is an optimal size for the pinhole, depending on the focal length
    (funny to call it that). You minimize the size of the pinhole plus the amount of diffraction.

    Otherwise, for actual lenses, and given the resolution of film and such, in most
    cases f/22 wasn't bad. Now with the highest resolution digital sensors, you can see it.
    But then again, they are removing the optical low-pass filter, as sensors get
    better than lenses. Most cheaper cameras never had the LPF, as the lenses
    weren't good enough to need one.
     
  17. When I look at some of my old P&S 4MB and 8MB photos, they look pretty good. Sharp, colorful, etc. OK, I couldn't blow them up to 20". But if kept small, they're great. Plus, the DOF is outstanding.
     
  18. Yes, for ordinary use f/22 is fine. I have never thought I needed to worry about it in ordinary use.

    Just a few days ago (before I saw this) I got out my Nikon AI 55/2.8 that I haven't had out in years.
    (So long that the focus ring is very stiff to turn.) I had forgotten until then that it goes to f/32.

    When I was young (Nikon F days, not yet F2), my father borrowed a Nikon F and,
    I presume, 55/3.5, and extension tube. As well as I remember (maybe 50 years ago),
    it goes to f/32, but the extension tube had numbers down to f/45. I will have to look
    for a picture.

    In any case, if you need the depth of field, that is usually more important than diffraction.

    Years ago, I was TA for an optics lab, which had as one lab that tested lens resolution with
    the usual USAF resolution targets. I only remember one group doing it, but not the results
    that they got. I had to hand spool TP2415 for them to use.

    I suspect that getting focus close enough is more of a limit than anything else.
     
  19. The thing with small sensors of course, is that you get huge DOF with landscapes without a need for small apertures. When I shoot even my 1" sensor camera, I mainly leave it on P mode and let the camera do the work. Only when I shoot MF film do I worry about DOF.
     
  20. AJG

    AJG

    I had a generally excellent 50 mm f/4 Pentax macro lens that produced results that looked like they hd been shot with a pinhole at the minimum f/32 that could be set. At wider f/stops it performed extremely well.
     

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