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  1. #11
    RalphLambrecht's Avatar
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    As with taking lenses, stopping down an enlarging lens will improve image quality and cut down on lens aberrations. This is especially true and visible in the image the further you get away from the image center.

    I find it easier to use the grain focuser with a wide open enlarger lens, because I can more easily see the 'snap' in and out of focus.

    Depth of field (at the baseboard) and depth of focus (at the negative stage) are in a geometrical relationship with each other (see attached illustration).
    Attached Thumbnails Attached Thumbnails DoFieldFocus.jpg  
    Regards

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

  2. #12
    ic-racer's Avatar
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    The optimal aperture for any lens is not some nebulous guess at how many stops down to go. The published MTF curves and light fall off curves tell all.
    The DOF is related to aperture size and magnification and acceptable size of circles of confusion. It is independent of lens design or construction or focal length.

  3. #13
    RalphLambrecht's Avatar
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    I've never seen any EL-Nikkor MTF graphs. Does anybody know where to find them?
    Regards

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

  4. #14
    Bob Carnie's Avatar
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    On a very practical level. Visually looking at prints

    With all good things in place , like I suggested above.

    Focus on grain with paper under grain scope.

    make a print wide open , make a print two stop downs adjust time.

    Do not re focus between.

    Look at the prints.. If someone here can honestly say they say the one print is sharper than the other I will eat my shorts.

  5. #15
    RalphLambrecht's Avatar
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    Quote Originally Posted by Bob Carnie View Post
    On a very practical level. Visually looking at prints

    With all good things in place , like I suggested above.

    Focus on grain with paper under grain scope.

    make a print wide open , make a print two stop downs adjust time.

    Do not re focus between.

    Look at the prints.. If someone here can honestly say they say the one print is sharper than the other I will eat my shorts.
    Bob

    You should be able to see at least a difference in edge sharpness from wide-open to a couple of stops down. If you can't, you must have some wonderful lenses. Try the test with a picture of a resolution target and you should see it.

    I don't have a lot of enlarging-lens MTFs, but I have attached one for a Rodenstock Rogonar-S. One can clearly see the performance difference between f/2.8 and f/5.6.

    Regardless of this evidence, I'm not holding you to your promise. I don't think it's healthy.
    Attached Thumbnails Attached Thumbnails EnlargingLensMTF.jpg  
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    Ralph W. Lambrecht
    www.darkroomagic.comrorrlambrec@ymail.com[/URL]
    www.waybeyondmonochrome.com

  6. #16
    Bob Carnie's Avatar
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    I shop at Victoria Secrets

    Quote Originally Posted by RalphLambrecht View Post
    Bob

    You should be able to see at least a difference in edge sharpness from wide-open to a couple of stops down. If you can't, you must have some wonderful lenses. Try the test with a picture of a resolution target and you should see it.

    I don't have a lot of enlarging-lens MTFs, but I have attached one for a Rodenstock Rogonar-S. One can clearly see the performance difference between f/2.8 and f/5.6.

    Regardless of this evidence, I'm not holding you to your promise. I don't think it's healthy.

  7. #17
    RalphLambrecht's Avatar
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    Quote Originally Posted by Bob Carnie View Post
    I shop at Victoria Secrets
    That's different. Go for it then, I like to see you eating your shorts in that case.
    Regards

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

  8. #18

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    I might add an additional advantage when stopping the lens down a few stops - uniformity of illumination. This of course all depends on the design and focal length (particularly in relation to negative format) of the lens, but generally light falloff is greatest wide open.

    Regards.

  9. #19
    Bob Carnie's Avatar
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    I should add that for each format I am using a longer lens.
    ie

    35 - 80mm
    6x6 ,6x7 - 90mm
    6x9 - 105mm
    4x5 -150 and 180mm

    I am still convinced that sharp grain at wide open will not be sharper grain at 2 stops down.

    There are a lot of factors that contribute to edge defects, but if you do all the good things your edges are sharp wide open. At least in my darkroom
    Quote Originally Posted by Michael R 1974 View Post
    I might add an additional advantage when stopping the lens down a few stops - uniformity of illumination. This of course all depends on the design and focal length (particularly in relation to negative format) of the lens, but generally light falloff is greatest wide open.

    Regards.

  10. #20
    RalphLambrecht's Avatar
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    Quote Originally Posted by Bob Carnie View Post
    ... I am still convinced that sharp grain at wide open will not be sharper grain at 2 stops down.

    There are a lot of factors that contribute to edge defects, but if you do all the good things your edges are sharp wide open. At least in my darkroom
    Bob

    I already provided evidence to the contrary. All lenses suffer from aberrations to some extend. Enlarging lenses not excluded. Some of these aberration effects are reduced when the lens is stopped down.

    Maybe your lenses suffer from a focus shift when stopping them down, offsetting the effect?
    Regards

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

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