How to determine sharpness at f/22 - f/32

Discussion in 'Canon EOS' started by gunjankv, Feb 2, 2010.

  1. Most of the MTF charts shows sharpness values till f/11. If I am to buy a lens for landscape photography, I would be interested in performance at f/22 or f/32. How to determine which lens would be sharpest there?
    I tried to take photos using Canon EF-S 18-55mm IS at f/22.. but I am not at all happy with results.
     
  2. Once you get past f/11 or f/16 in most DSLR rigs, you'll be losing sharpness to diffraction. It can be very noticeable on certain subjects/scenes.
     
  3. All lenses will be pretty much the same at f32 because diffraction will be the primary factor affecting resolution, not lens design. They will all be soft when used on a small sensor camera and prints are made.
    This article http://www.bobatkins.com/photography/technical/diffraction.html deals with the issue of sharpness, aperture and diffraction. For an APS-C crop sensor, I wouldn't stop down past f16. After that you will significantly reduce sharpness. For full frame DSLRs, f22 would be my limit.
     
  4. If you are shooting a cropped sensor camera at f/22 you are giving up a lot of sharpness to diffraction blur, as mentioned above. If sharpness is your goal, don't shoot at f/22 on this camera. In general, if you want to maximize sharpness you will not want to stop down a cropped sensor camera beyond f/8 - you might occasionally go to f/11, but only in a shot where you are willing to give up some maximum resolution in exchange for slightly more DOF or a bit slower shutter speed.
    Diffraction blur at such small apertures affects all lenses essentially the same way. It is an optical property that doesn't respect the price of the lens. Whether you use a cheap lens or the best L prime, both will lose sharpness to diffraction at f/22 and f/32, especially on your cropped sensor body.
     
  5. The only reason to go down to f22 is if depth of field is all important, and therefore you're willing to tolerate loss of sharpness from diffraction.
     
  6. I concur with everyone else.
    I'm also not sure why you would use f/22 or f/32 on a 35mm body much less a crop sensor as your DOF is already going to be quite large around f/11. At 18mm and infinity (I guess a typical landscape photo) your near focus is ~5 feet at f/11 and ~2.5 feet at f/22. I'm sure that sometimes the extra DOF may be critical but f/22 is hardly a typical working aperture on APS-C. 4x5 sure, 35mm maybe, APS-C... not really.
     
  7. any reason you need to shoot at that aperture? even when i shoot landscape i don't go that high.. the only time i shot at f/32 was to see if i had dust in my sensor/lens
     
  8. For close-up/macro work it is sometimes worth sacrificing some sharpness to diffraction in order to increase DoF. But even then, going beyond f/16 on 1.6-factor or f/22 on FF is seldom a good idea. For landscape work, the answer may be to use the tilt movement of a tilt/shift lens.
     
  9. I agree with Robin, except that I sometimes go to f/20 or so for some macro shots where the extra DOF is worth the diffraction. I would not do that for landscapes. If you need to reduce light further, you can use an ND filter rather than stopping down so much.
     
  10. It is fun to stop down to F22 with a sunset, or pinpoint light sources (street lights at night, etc) to get the star effect in the image. Yes, you begin to see diffraction but not that much loss in IQ.
     
  11. [[. In general, if you want to maximize sharpness you will not want to stop down a cropped sensor camera beyond f/8 - you might occasionally go to f/11,]]
    This broad-sweeping generalization does a real disservice to this thread. The practical loss of detail in moving from f/8 to f/16 for anything but extremely large prints is almost zero.
     
  12. Most of the time when I see any landscape / nature photographs they are all taken with f/16 to f/22 or even f/32. That was the trigger for me to try out that on my own lens.. and that raise all these questions.
    The major difference as I can realize might be, I use APS-C and those excellent nature photographs might be taken with 4x5
    I am always happy with the results between f/5.6 and f/8 which is a natural sweetspot for many lenses.
    I sincerely thank you all contributors.
     
  13. ansel adams usually shot at f22+. are you looking at his stuff, or work of photogs of that era? they were shooting 8x10 and could more easily afford the diffraction.
     
  14. There's a good reason that most digicams won't let you stop down past about f8. It's diffraction combined with a 5x7mm sensor.
     
  15. [[. In general, if you want to maximize sharpness you will not want to stop down a cropped sensor camera beyond f/8 - you might occasionally go to f/11,]]
    This broad-sweeping generalization does a real disservice to this thread. The practical loss of detail in moving from f/8 to f/16 for anything but extremely large prints is almost zero.
    Disservice? Oh, come off it.
    That's why I included the words "in general" and "if you want to maximize sharpness" and then went on to write "you might occasionally go to f/11, but only in a shot where you are willing to give up some maximum resolution in exchange for slightly more DOF or a bit slower shutter speed."
    This is actually a very useful generalization for shooting with a cropped sensor camera. In this case it would have helped our OP considerably.
    Back to the OP, you are correct when you point out that many "nature" and landscape photographs are made at smaller apertures. But, as you note, quite a few of them are not made on cropped sensor cameras. For those who shoot DSLRs and make high quality prints, there are good reasons to choose a full frame body over a cropped sensor body. (To head off the angry responses... it is quite possible to make fine landscape photographs on a cropped sensor camera.) On full-frame it is common to shoot at apertures such as f/11 or f/16 where the effect of diffraction relative to the frame width is reduced at a given aperture. In fact, it is necessary to use the smaller apertures to get the desired DOF for many images. On MF it is common to stop down even more.
    Dan
     
  16. By the way, it is simple and useful make a quick set of test images with one or more of your lenses at different apertures to determine (among other things) how you feel about the resolution at various apertures for your own photography.
     
  17. On a crop sensor you never need f/22 for DoF in a wide angle landscape.
    At 18mm, f/11, and a focus of 5.1 feet, everything from 2.53 feet to infinity will be in focus. At f/16 and 3.56 feet, everything from 1.78 feet to infinity will be in focus. The shots where people are 'on top of' foreground rocks and the landscape sweeps out to the sky are typically made at 10mm or 11mm (crop body). 11mm, f/11, and a 2 foot focus point will cover everything from 0.97 feet to infinity.
    In reality you are almost never that close to the foreground object. You might think you're close, but take a measuring tape and you'll realize you're actually 5 feet away or more. (If you were 1 or 2 feet away you would feel like one wrong move might cause you to hit the object with the lens.) So you would focus out a little further and possibly use an even wider aperture. Outside of macro, you don't need f/22.
    Play with this calculator until you have a feel for close distances and apertures for your wide angle focal lengths. http://www.dofmaster.com/dofjs.html Write down common focus points, apertures, and distances covered on a note card and keep it with you. Use LiveView plus DoF preview, if you have it, to judge critical sharpness in a scene and nail the optimum focus distance / aperture.
    But do not sacrifice fine detail to f/22 unless the scene doesn't demand it and you're looking for a dreamy look (i.e. long exposure to blur water, star points on lights, etc.).
     
  18. Her you test yourself by using diffraction limit calculator.
    (....) The form below calculates the size of the airy disk and assesses whether the system has become diffraction limited. Sections in dark grey are optional and have the ability to define a custom circle of confusion (CoC). (....)
    http://www.cambridgeincolour.com/tutorials/diffraction-photography.htm
    BR.
    Esa Kivivuori
    Finland
     
  19. Esa, that term "diffraction limited" is misunderstood and misapplied by many people who presume that one shouldn't use a diffraction limited aperture. After all, who wants limits!?
    I still say the best and simplest thing that photographers can do is put their camera on a tripod and make series of test shots and then look at them closely. You may find that so-called "limited" apertures are quite fine for your photography.
    Dan
     
  20. Very useful thread for me. I ruined most of my photos last week by shooting @ f/16 on 28-135mm and Sigma 12-24mm.
     
  21. [[Disservice? Oh, come off it.]]
    Yes, a disservice. "an act intended to help that turns out badly."
    Claiming that you should not shoot beyond f/8 on a crop camera is not good advice, nor is it a good generalization, and it does not help new photographers in the least. It limits them, in fact, to a very narrow aperture range.
    The drop in resolution from f/8 to f/16 is so minimal that it does not have any affect on anyone not creating extremely large prints. Maximum resolution is simply not realized in anything but those large prints. Any net effect from diffraction is not visible except in those limited situations where large prints are desired.
    Claiming f/8 is the limit of a crop-sensor camera is measurbation gone wild.
     
  22. Rob
    I'm uncomfortable with the term "disservice" even when used in its precise form. I've learned considerably as a result of reading this thread and I'm extrememly appreciative of the time and experience that G. Dan so generously shares with us all.
    I would also add that I also read your contributions with great care. I doubt that guys like yourselves comprehend how much value you add for interested amateurs like me.
    Apologies to the O.P. .... FWIW, I shoot landscapes no further down than f/11 on a 40D/17-40 combination and reckon that's the best compromise for me. Having said that, I've not printed large. The DOF available at that aperture always surprises me.
     

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