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Thread: apperture f22 ?

  1. #1

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    apperture f22 ?

    LF lens are, I have been told (numerous times) are optimised at f22, what I do not understand is, where a lens has a max speed of f5.6 or f 9 then f22 differs % wise in the f stop range for the specific lens, with this in mind are all LF lens optimised at f22 regardless of their speed?

    Thanks for some guidance on this question

    peter

  2. #2

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    Re: apperture f22 ?

    No, for instance, the Rodenstock Apo-Grandagon 35mm, 45mm and 55mm wide angle lenses are 4.5 lenses and are optimized at f11.

  3. #3

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    Re: apperture f22 ?

    I suspect it would be better to think of it as that f22 is where many lenses reach their maximum useable coverage spec, and where things really start to fall apart from diffraction. Probably most lenses reach their optimum resolution a couple of steps before that.

  4. #4
    ic-racer's Avatar
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    Re: apperture f22 ?

    F22 is a good compromise between diffraction and depth of field for many situations in 4x5" photography. Do not equate that with any lens being 'optimized' for f22.

    F22 is frequently not a good compromise between DoF and diffraction for 35mm or 11x14".

  5. #5
    Jac@stafford.net's Avatar
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    Re: apperture f22 ?

    There is a congruence relation between focal length and aperture. What makes f/22 less significant in terms of diffraction-effect is the lesser enlargement ratio of LF compared to the same-sized sized print from a miniature camera. (given a a nominal standard viewing distance). No?
    .

  6. #6
    hacker extraordinaire
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    Re: apperture f22 ?

    What matters for diffraction is aperture diameter and final print magnification. F22 on a 240mm lens is about 10mm aperture. The equivalent on 35mm would be something like a 90mm lens at F8. If you think diffraction is an issue in this regime you are much more confident in the rest of your process than I am. Hope you are using a vacuum back.

    For pictorial purposes diffraction does not begin to enter until you get down to apertures of more like 3mm and below (e.g. f22 on a 50mm lens of 35mm camera or F64 on 150mm lens of 4x5)
    Science is what we understand well enough to explain to a computer. Art is everything else we do.
    --A=B by Petkovšek et. al.

  7. #7

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    Re: apperture f22 ?

    I don't think diffraction is any where near as exotic as you make it out to be! I can definitely see the effects of diffraction in my Nikon lenses starting at f8. For instance my micro-Nikkor, the lens I use most for critical work, visibly tops out at about f7.1. Likewise with most enlarging lenses I've used. In the darkroom I was always carefully working around this; not so much in the camera, but I was at least aware of the consequences of what I was doing. Maybe you LF folks are used to being sloppy, but if you work with 35mm, you start to watch these things. :-)

  8. #8
    Jim Jones's Avatar
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    Re: apperture f22 ?

    My experience agrees with mdarnton's. This can be observed in enlarging by observing the grain pattern with a high power focusing aid.

  9. #9

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    Re: aperture f/22 ?

    Regarding the difference in behavior between F/11 and f/22 for a given view camera lens, you may have a look at the official FTM charts for the Rodenstock Grandagon-N 6.8 / 75 mm

    https://www.flickr.com/photos/43175600@N00/456327448/

    at f//11 the image qualty is slightly better on-axis than at f/22, but the homogenity of the image is better at f/22.
    I often use this lens in combination with a 6x9 rollfilm back, so I do not have to stop down to f/22 all the time, f/11 or f/16 will be OK.
    In 4x5" if you wish to use all the available image circle of this wide-angle lens (102°) you'd better stop down to f/22.
    But this is specfic to this wide-angle lens designed for the 4x5" format.

    If you use a standard 300 or 360 mm lens for the 8x10" format you can stop down to f/32 or f/45; and if you only make contact prints, f/64 like Saint Ansel at some point of his career, will deliver very good 8x10" images, provided that you do not look a them through a loupe.

  10. #10
    Jac@stafford.net's Avatar
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    Re: apperture f22 ?

    Mr. Bigler's experience echoes my own. One lens I keep in the cabinet is Rodenstock's 35mm for 6x12. Rodenstock's literature is right up-front by stating the lens's performance begins at f/16 or greater (numerically). I never thought I would find a MF lens too wide until I got this one.

    If I had to choose one manufacturer for lenses it would be Rodenstock.

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