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  1. #1

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    Using Small Apertures

    I have seen a difference in centre sharpness between using some lenses at full aperture and stopping down to, say, f5.6 but how about small apertures? Between F11 and F22 I can't see any difference in a 10x 8 print. I am talking centre sharpness rather than depth of field. Is it just with very large prints that this is a worry? I suppose it is to do with refraction. I use 35mm and medium format.
    thanks
    Dave

  2. #2

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    this is diffraction-limited f/stops

    http://www.cambridgeincolour.com/tut...hotography.htm
    Bill

  3. #3
    ic-racer's Avatar
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    Ralph Gibson (early 35mm work) and Joel Meyrowitz (Cape Light) both used an aperture around 3mm. A little fuzzy for me, but certainly an 'artist intented' effect.

  4. #4

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    Thanks for those replies. Diffraction is what I meant! Just curious if anyone had noticed this phenomenon.
    Dave

  5. #5

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    Because lens design is a compromise between several optical effects, lenses have an optimal resolution at only a single aperture. This information can be obtained from the maker. Resolution will fall off on either side of the optimal stop. The further you differ from this stop the poorer the resolution.
    A rock pile ceases to be a rock pile the moment a single man contemplates it, bearing within him the image of a cathedral.

    ~Antoine de Saint-Exupery

  6. #6
    ic-racer's Avatar
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    Quote Originally Posted by Sirius Glass View Post
    Most if not all lens manufactures do not put apertures that show strong diffraction.
    I think nearly every lens I own with an adjustable aperture will stop down to fuzz. Most notable, a 5mm Bolex lens with a minimum aperture of f22!

  7. #7

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    The rule of thumb is that best resolution is two stops down from wide open. Consider, however, that on an f/1.4 50mm lens on a 35mm camera, your sharpest aperture would be f/2.8. If you go by the rule of thumb, you have a whole lot of stops left over that would give poorer quality images. Hogwash. Use the aperture you need to get the depth-of-field and exposure you need. Just be aware that f/16 or f/22 may give you the depth of focus you need at the expense of some sharpness in some circumstances.

    I've really noticed diffraction effects only on extreme close-up photographs. A photographer in a studio I used to work in was having trouble getting a good, sharp image of an ornate ring. He was using an RZ67 with a macro lens stopped down as far as it would go, bellows racked way out. I suggested he open the aperture a stop or so to reduce diffraction and that did the trick. Use what you need to get what you want. Also, the more you enlarge an image, the more any defects, including diffraction effects, will show.

    Peter Gomena

  8. #8
    ic-racer's Avatar
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    Quote Originally Posted by Sirius Glass View Post
    The minimum aperture for maximum DOF and low diffusion varies with the format.
    35mm ~ f/11
    120 ~ f/16
    4x5 ~ f/22

    This is a rule of thumb, YMMV as some lenses are better than others. You can use this as a starting point, test it if you want or ignore it. This is not an invitation to start a religious flame war. Please note the use of "~" before you start to blather.

    Steve
    Agreement and simplification:
    linear aperture around 4 to 5mm for all formats

  9. #9
    bobwysiwyg's Avatar
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    Newbie here. I've been following these threads and they may go a long way to explaining some of my less than desired results on some shots as far as sharpness goes. I'm a bit of sucker for flowing water shot at 1 sec. or so. Using ISO 100 film I can sometimes get this by stopping way down. Now I see it would be better to use a more optimal f-stop and ND filters. Now to my question, if, for example f22 is optimal for 4x5, why are there additional f-stops way beyond f22?? Is it simply a matter of making fuzziness available for those who like it?
    WYSIWYG - At least that's my goal.

    Portfolio-http://apug.org/forums/portfolios.php?u=25518

  10. #10
    RalphLambrecht's Avatar
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    Quote Originally Posted by Sirius Glass View Post
    The minimum aperture for maximum DOF and low diffusion varies with the format.
    35mm ~ f/11
    120 ~ f/16
    4x5 ~ f/22

    This is a rule of thumb, YMMV as some lenses are better than others. You can use this as a starting point, test it if you want or ignore it. This is not an invitation to start a religious flame war. Please note the use of "~" before you start to blather.

    Steve
    Open up a stop for each, and it matches my tests.
    Attached Thumbnails Attached Thumbnails LensResolution.jpg  
    Regards

    Ralph W. Lambrecht
    www.darkroomagic.comrorrlambrec@ymail.com[/URL]
    www.waybeyondmonochrome.com

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