Page 1 of 2 12 LastLast
Results 1 to 10 of 14

Thread: stopping down, how much is too much?

  1. #1

    Join Date
    Dec 2004
    Location
    Pennsylvania
    Posts
    275

    stopping down, how much is too much?

    I have two lenses, one that stops to f45 and the other stops to f64. Alot of times I want to maximaize my depth of field without diffraction. What exaclty is diffraction? How far is too far to stop down? And in what curcumstances will I see the effect of diffraction more? Ansel Adams and others believed in f64. I'm just curious. Thanks!!

  2. #2

    Join Date
    Aug 2001
    Location
    San Francisco
    Posts
    357

    stopping down, how much is too much?

    http://www.largeformatphotography.info/fstop.html
    http://www.largeformatphotography.in...ic/500779.html

    In general, the advice that I've been given is use the aperture that's necessary to get the proper DOF and don't worry about diffraction. I was told that for contact prints, you can't notice diffraction until you get smaller than f/128 or f/256. Could you tell us what format you shoot and how you print (ie. enlargements vs contact prints)?

  3. #3

    Join Date
    Dec 2004
    Location
    Pennsylvania
    Posts
    275

    stopping down, how much is too much?

    I'm shooting 4x5 Tmax 100, mainly 11x14's on 16x20 paper. I do conatct prints as reference, never to be a finished print though..

  4. #4

    Join Date
    Jan 2004
    Location
    Halifax, Nova Scotia
    Posts
    440

    stopping down, how much is too much?

    If you want no effect, stop at f/32. If you stop down more it would be up to you whether the final results are acceptable. As to Adams and f/64, he was shooting 8X10 so the level of magnification is lower. Also he prized full depth of field over minimal loss of sharpness.

  5. #5
    Robert A. Zeichner's Avatar
    Join Date
    Feb 1999
    Location
    Southfield, Michigan
    Posts
    1,094

    stopping down, how much is too much?

    The rule of thumb I've repeatedly heard is to avoid apertures smaller than f32 for 4x5, f45 for 5x7 and f64 for 8x10. When diffraction starts to become a factor, the visible result is a softening of fine detail. In certain situations where the need for depth of field is the difference between making the image you want or not, I have closed down to f45 or even a half stop smaller in 4x5 without regret in most cases. I suppose in situations where there is a tremendous amount of fine detail in the negative, the softening effect may be more obvious and objectionable.

  6. #6
    Donald Qualls's Avatar
    Join Date
    Oct 2004
    Location
    North Carolina
    Posts
    1,034

    stopping down, how much is too much?

    Diffraction is unlikely to be noticeable on prints at around 3x enlargement (like yours) at f/64. Depending on the focal length of the lens and amount of magnification, f/90 may produce unacceptable diffraction, or you might be able (if your lens supports it, or if you were to make Waterhouse stops and install them in the shutter over the existing diaphragm) to go to 1/128 or f/180.

    Worthy of note, however, is that pinhole photography has diffraction as a limiter on pinhole size, where the increased sharpness of a smaller circle of confusion starts to be overwhelmed by the decreased sharpness due to diffraction; for a pinhole distance (equivalent to focal length) comparable to focal lengths we use in large format, say 150 mm, the "optimum" pinhole size, the one with the best compromise (for sharpness) between circle of confusion and diffraction, is 0.49 mm (or about .019"), which corresponds to about f/300; this will give effectively infinite DOF with everything in field equally "semi-sharp". Any aperture similar to this (f/256, surely, but probably f/180 and possibly even f/128) will show some of the same characteristics as a pinhole -- extreme depth of field, but coupled with a visible loss of sharpness (which becomes more noticeable with any magnification) in all parts of the image.

    There are mathematical formulae that suggest a minimum aperture to avoid unacceptable diffraction effects, but like DOF calculation, they're a little slippery because of the subjective definition of "unacceptable". How much image degradation you're willing to accept from a particular source (whether defocus, camera motion, diffraction, or lens aberrations) depends on how much (if any) you'll enlarge the negative in printing, what level of sharpness or fuzziness you find comfortable in the final print, and what other sources of unsharpness may be present (for instance, I've found that with a pinhole body cap on my 35 mm SLR, I can easily hand-hold at 1/4 second, because the fuzziness from the pinhole overshadows motion blur in most shots) -- all of which, in turn, may depend on the subject being photographed and the type of image sought.

    No, I know that's not a clear answer -- but there *isn't* a clear answer on this one.
    If a contact print at arm's length is too small to see, you need a bigger camera. :D

  7. #7

    Join Date
    Mar 1999
    Posts
    674

    stopping down, how much is too much?

    What exactly is diffraction?

    When a beam of light passes an edge, it bends or spreads around it - this phenomenon is referred to as diffraction. Incidentally, diffraction occurs with all kinds of sound waves - sound, water etc. It can be understood utilizing the wave nature of light - an intuitive way to understand it is to think of ripples (i.e., waves) on the surface of a pond if you toss a stone into it. Think of what happens when these ripples reach an edge such as a wall with a slit in it through which they can pass. On the other side of the wall, you see these ripples spreading out as though the slit was the source of the waves (i.e., as though you had dropped a stone into the water exactly at the slit). In other words, you do not see the wave continuing in a straight line past the slit but it sort of propogates in all directions around the slit (i.e., it bends around the slit). The reason for this bending/spreading is the fact that the wave consists of a whole lot os waves in sync with each other. So each wave sort of pulses up and down but exactly in sync with the waves next to it, so that it is a stable wavefront. Now think of what happens if some obstruction cuts off the wavefront next to another wavefront. All of a sudden, this wavefront does not have another wavefront in sync next to it as it pulses. As a result, it spreads out.

    How far is too far?

    In photography, diffraction is only a function of f-stop (an oversimplification - it also depends upon the wavelength of light etc but its the only thing we have control over). The smaller the aperture, the higher the diffraction. However, diffraction is only one of the things we have concerns about. Two main reasons why we stop down. One, most lenses have aberrations that are large wide open and become progressively smaller as you stop down. So, there is some optimal point when you stop down where you have benefited from these reductions in aberrations but not suffered too much loss from diffraction. Two, depth of field. Balancing DOF and diffraction can be tricky. Diffraction results in the gradual softening of everything across the whole image. DOF is a selective softening - somethings are in crisp focus and some things are very much out of focus. You decide which one you can live with - generally, I find lack of DOF more troubling than a slight softening of the whole image. I think the reason for this is that the eye-brain system makes sharpness judgments by comparison. As long as things are not terribly and obviously unsharp, it looks to see if one part is sharper than the other.

    In practical terms, you can approximate the diffrcation limited resolution with mathematical formulae (something like 1500/aperture). This means that at f/64, you would get about 24 lpmm, at f/45 you'd have about 34 lpmm, f/32 you'd have 47 lpmm etc). The figure usually quoted for the eye is the ability to resolve about 5-10 lpmm on the print (under specific viewing distances etc). So, if you are contact printing, you can stop down to f/90 and still have adequate resolution. If you are making a 3X enlargment from 4x5, at f/64, you'd have 24 lpmm on the negative and about 8 lpmm on the print (making the unrealistic assumption of no losses during the print making process), which would probably still be adequate. Some may want to play it safe and leave some more resolution for losses during print making etc. Although, from a visual perspective, I think a more logical approach is to get the DOF your visual concept needs and settle for the largest size print that gives you adequate resolution. Lack of DOF means you can't make any print at all, whereas diffraction might mean you can make only an 8x10 print instead of a 16x20 print.

    Under what circumstances can I see diffraction?

    If you want to see what diffraction looks like, the easiest way is under an enlarger. Place a negative in the enlarger and using a high quality focussing aid, focus on the grain in the negative. Now, stop down the enlarging lens and watch the grain turn to mush. In the field, it is hard to see diffraction. At the kinds of f-stops where you could see it (f/128 and above), the image on the ground glass is terribly dim. You can use a loupe but that also magnifies the image (the loupe may be useful to try and estimate what diffraction would be like at a particular enlargement, though). So, you are probably better served with using rules of thumb. Try using movements to reduce the amount of stopping down. Try to stay with as large an aperture as permitted by other demands such as DOF etc. Although, as the above figures have indicated, you should be fine with f/45 and probably even f/64 if you are making 11x14s from a 4x5 negative, and are a careful worker.

    Cheers, DJ

  8. #8

    Join Date
    Feb 2001
    Location
    Los Angeles
    Posts
    1,771

    stopping down, how much is too much?

    Brian: I would list "don't be afraid of small stops" as a lesson I wished I had learned a long time ago. I recently made a mental math error in the field converting the shown stops on my shutter for what they should have been for the lens elements I had just moved over to it. (Moved a 305 Repro Claron into a Compur 2 marked for a 240 mm lens). I ended up shooting at f:64 when I didn't intend to on 5X7 film. The print at 16X20 looks very sharp at any reasonable viewing distance and people often remark on how "sharp and clear" that print, in particular, looks. So try it, f:45 will look fine in prints this size with 4X5 film. Sometimes it is just the only way you can get what you want in focus, and I agree with DJ, you'll probably be quite satisfied with it. If I made larger prints (which I can't really do with my present sink) then I'd have to reevaluate, but within these limits, you should be fine.

  9. #9

    Join Date
    Jul 2004
    Location
    Tucson, Arizona
    Posts
    4,143

    stopping down, how much is too much?

    When I got a 480mm Apo Ronar for my 8x10, the first thing I did was shoot a negative at the smallest f/stop, f/256, just because I could. The negative is very sharp under a 4x loupe. As I tend towards contact prints for the smoother grey-scale, I now disregard the diffraction issue.

    One exception is in macro work: The effective f/stop is actually determined by aperture size and the distance from the lens to the film, NOT what is marked on the aperture scale, (which is for infinity only). We compensate for this with a "bellows extension factor," but it could more accurately be called a "diminished f/stop factor."

    In other words, if you have your 215mm lens cranked out to 600mm, you're shooting with a 600mm lens that just happens to be focused a whole lot closer. And f/64 on a 600mm lens is bigger that f/64 on a 215, so if you shut down to the scale-indicated f/64, you're actually way smaller than that.

    But don't make me do the math... I save that for real photographs.
    "I love my Verito lens, but I always have to sharpen everything in Photoshop..."

  10. #10

    Join Date
    Dec 1997
    Location
    Baraboo, Wisconsin
    Posts
    7,742

    stopping down, how much is too much?

    Lots of excellent answers. I'd only add that IMHO diffraction isn't a significant problem and shouldn't be a concern with 4x5 negatives until prints are larger than 16x20. I think that insuffcient depth of field will almost always be more objectionable than whatever minimal loss of sharpness results from diffraction so I use whatever aperture is needed for the desired depth of field without being concerned about diffraction.
    Brian Ellis
    Before you criticize someone, walk a mile in their shoes. That way when you do criticize them you'll be
    a mile away and you'll have their shoes.

Similar Threads

  1. Replies: 54
    Last Post: 26-Mar-2007, 11:36
  2. Focus shift when stopping down Goerz lenses
    By John Kasaian in forum Lenses & Lens Accessories
    Replies: 13
    Last Post: 7-Nov-2005, 11:00
  3. Stopping Posting
    By Gene Crumpler in forum Announcements
    Replies: 16
    Last Post: 10-Aug-2005, 20:15
  4. Fuzzy edges-- does stopping down help?
    By chris jordan in forum Lenses & Lens Accessories
    Replies: 4
    Last Post: 4-Mar-2005, 13:45
  5. stopping down - coverage?
    By sammy_5100 in forum Lenses & Lens Accessories
    Replies: 13
    Last Post: 24-Jan-2005, 07:19

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •