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Thread: Achieving adequate DOF in 8x10

  1. #21

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    Re: 8x10 DOF examples

    Quote Originally Posted by BetterSense View Post
    If you use the same aperture diameter (d), DOF is the same on all formats. It's that simple although it is annoying that lenses are not marked in mm.
    Yes: at the same aperture, a 300mm lens has the same depth of field on 8x10 as it does on a 35mm film: it's very shallow.

    We don't mind it on a small camera because on 35mm the lens is acting as a telescope, but on 8x10 where we're using it as a normal lens, the modest depth of field can be troublesome.

    As DJ pointed out, with 8x10 on a tripod, we can stop down the lens to get adequate depth of field, but our exposures will be commensurately longer. The sample photo taken inside a railroad car was an appropriate subject for f/128: the photographer probably used his hat for a shutter
    Last edited by Ken Lee; 31-Mar-2017 at 03:42.

  2. #22

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    Re: Achieving adequate DOF in 8x10

    Remember when comparing formats, DoF is also a function of the enlargement factor, since the required CoC for a negative is a function of how much it must be enlarged.

  3. #23

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    Re: Achieving adequate DOF in 8x10

    Quote Originally Posted by Michael R View Post
    Remember when comparing formats, DoF is also a function of the enlargement factor, since the required CoC for a negative is a function of how much it must be enlarged.
    I realize that we have 2 interesting CoC values:

    > one is what we need for the future enlargement factor, and if we want to see a big print at near reading distance or not.

    > the second CoC is related to the practical film+lens performance, meaning that a better focusing won't improve resolving power. This has a particularity, as at same point if we stop more to get better focus it happens we lose resolving power because difraction.

  4. #24

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    Re: Achieving adequate DOF in 8x10

    You can get an idea of the DOF Edward Weston would get at his normal f64, but he only contact printed his negs...

    At wider apertures, even at great distances you can see/roll the focus "windows" of DOF with long lenses, even my telescope with 600mm/f6 requires slight refocusing if I view the moon, planets, or deep space objects...

    It's the physics of optics...

    Steve K

  5. #25

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    Re: Achieving adequate DOF in 8x10

    Quote Originally Posted by Michael R View Post
    Remember when comparing formats, DoF is also a function of the enlargement factor, since the required CoC for a negative is a function of how much it must be enlarged.
    And the third part of this compromise is how much Scheimpflug derived distortion you are willing to put up with to hold an adequate depth of focus at the smallest possible aperture that will not limit the resolution of the largest print you wish to make...

  6. #26

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    Re: Achieving adequate DOF in 8x10

    Quote Originally Posted by LabRat View Post
    You can get an idea of the DOF Edward Weston would get at his normal f64, but he only contact printed his negs...

    At wider apertures, even at great distances you can see/roll the focus "windows" of DOF with long lenses, even my telescope with 600mm/f6 requires slight refocusing if I view the moon, planets, or deep space objects...

    It's the physics of optics...

    Steve K
    Well, at f/64 no more than 25 Lp/mm can be resolved, and still a large format 8x10 sheet would be enlarged to 40" without any flaw visible at reading distance.

  7. #27

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    Re: Achieving adequate DOF in 8x10

    Quote Originally Posted by Pere Casals View Post
    Well, at f/64 no more than 25 Lp/mm can be resolved, and still a large format 8x10 sheet would be enlarged to 40" without any flaw visible at reading distance.
    That's making a heck of a lot of assumptions about the taking lens, the enlarging lens/ scanner optics, the film flatness at various stages etc, etc, etc.

  8. #28

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    Re: Achieving adequate DOF in 8x10

    And has not much to do with Depth of Field issues in question.

  9. #29

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    Re: Achieving adequate DOF in 8x10

    Quote Originally Posted by cowanw View Post
    And has not much to do with Depth of Field issues in question.
    More than you'd think - if you're limited to using f22 owing to attempting to minimise diffraction, but want to make a 7x enlargement with no schiempflug derived distortion, how would you do it in 8x10 while holding OK depth of focus?

  10. #30

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    Re: Achieving adequate DOF in 8x10

    subject magnification being constant, there is only one depth of field at f22; no more, no less.

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