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  1. #41

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    Some types of film grain just seems to bounce more light at larger apertures. Then there are cases where one wants to be certain what they are focussing upon is the emulsion side of the film itself and
    not the grain of an attached mask. Then different kinds of Newton ring glass bounce incident rays a
    little differently with different lenses and diffusers. Sounds complicated in theory, but is pretty simple
    if you just examine the image at more than one f-stop. I like to print color with a very shallow depth of field for all the above reasons, so want the widest aperture which bags the result. B&W printing is less
    fussy unless an unsharp mask is also employed. And like I already indicated, one simply can't assume
    a lens is devoid of focus shift - there are a lot of cheap lenses in use out there, and I sure as heck don't
    intend to purchase and test a bunch of them. Gimme Apo Nikkors and Apo Rodagon N's and Rodagons
    and Nikkor EL, whatever... just nuthin old or cheap (I do sometimes use a wretched old Carl Meyer process lens because it wonderfully complements certain soft portrait images, but that's a deliberate
    tweak into oldie land).

  2. #42

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    Cliveh, Bob is not clouding the water. He's saying he focuses wide open and then closes down two stops to make the exposure.

    It depends on the lens. Most modern high quality enlarging lenses from Nikon, Rodenstock and Schneider should be free of focus shifting. Stopping down a stop (usually recommended for highly corrected top line lenses) or two, is really only to help minimize aberrations and falloff. It also slightly increases depth of focus (at the film plane) and depth of field (at the paper plane) which can help reduce the effects of incorrect focus, enlarger misalignment, and lack of negative flatness (assuming you don't use a glass carrier).

    With older and/or lower quality lenses there can indeed be focus shifts when stopping down. You can sometimes see this in the grain focuser.

    Try this: Focus wide open. Then stop down to the working aperture. Make slight/fine adjustments to focus and see if you can get the grain any sharper than it was. Once it is as good as you can get it, open up to maximum aperture again and check the grain focuser. You may or may not see fuzzier grain than when you originally focused wide open.
    Last edited by Michael R 1974; 04-02-2013 at 04:09 PM. Click to view previous post history. Reason: typo

  3. #43
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    Quote Originally Posted by Michael R 1974 View Post
    Cliveh, Bob is not clouding the water. He's saying he focuses wide open and then closes down two stops to make the exposure.

    It depends on the lens. Most modern high quality enlarging lenses from Nikon, Rodenstock and Schneider should be free of focus shifting. Stopping down a stop (usually recommended for highly corrected top line lenses) or two, is really only to help minimize aberrations and falloff. It also slightly increases depth of focus (at the film plane) and depth of field (at the paper plane) which can help reduce the effects of incorrect focus, enlarger misalignment, and lack of negative flatness (assuming you don't use a glass carrier).

    With older and/or lower quality lenses there can indeed be focus shifts when stopping down. You can sometimes see this in the grain focuser.

    Try this: Focus wide open. Then stop down to the working aperture. Make slight/fine adjustments to focus and see if you can get the grain any sharper than it was. Once it is as good as you can get it, open up to maximum aperture again and check the grain focuser. You may or may not see fuzzier grain than when you originally focused wide open.
    Perhaps you don't understand my point, as I am all for stopping down to print, but not to focus.

    “The contemplation of things as they are, without error or confusion, without substitution or imposture, is in itself a nobler thing than a whole harvest of invention”

    Francis Bacon

  4. #44

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    Your point was you don't want to focus at the working aperture. I'm simply explaining why it might make a difference, and giving you a quick way to check to see if it matters with your lens.

  5. #45
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    Quote Originally Posted by Michael R 1974 View Post
    Your point was you don't want to focus at the working aperture. I'm simply explaining why it might make a difference, and giving you a quick way to check to see if it matters with your lens.
    Can someone help me out here?

    “The contemplation of things as they are, without error or confusion, without substitution or imposture, is in itself a nobler thing than a whole harvest of invention”

    Francis Bacon

  6. #46
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    You are joking right.

    Quote Originally Posted by cliveh View Post
    Please don't cloud the water here, as I appreciate the value of stopping down, but not checking focus at one stop down.

  7. #47
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    Quote Originally Posted by cliveh View Post
    Can someone help me out here?
    Some lenses do suffer from focus shift, but most don't.

    So Michael described a method of checking whether your lens is one of the problem ones.

    Perform the suggested test. If you observe focus shift, you will need to build a "focus at working aperture" step into your workflow.

    If the test doesn't reveal any shift, you can confidently focus at maximum aperture for all your work.
    Matt

    “Photography is a complex and fluid medium, and its many factors are not applied in simple sequence. Rather, the process may be likened to the art of the juggler in keeping many balls in the air at one time!”

    Ansel Adams, from the introduction to The Negative - The New Ansel Adams Photography Series / Book 2

  8. #48
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    Quote Originally Posted by MattKing View Post
    Some lenses do suffer from focus shift, but most don't.

    So Michael described a method of checking whether your lens is one of the problem ones.

    Perform the suggested test. If you observe focus shift, you will need to build a "focus at working aperture" step into your workflow.

    If the test doesn't reveal any shift, you can confidently focus at maximum aperture for all your work.
    But how can you judge when you are viewing with an increase in depth of focus?

    “The contemplation of things as they are, without error or confusion, without substitution or imposture, is in itself a nobler thing than a whole harvest of invention”

    Francis Bacon

  9. #49

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    Relevant question, but generally a non-issue in practice. This is because enlarging lenses are typically fast and used fairly wide open. So adjusting down just one stop won't make a radical difference in depth of field as far as viewing grain is concerned. But even with slower process lenses any such issues can be detected using a high-quality magnifier.

  10. #50
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    Quote Originally Posted by DREW WILEY View Post
    Relevant question, but generally a non-issue in practice. This is because enlarging lenses are typically fast and used fairly wide open. So adjusting down just one stop won't make a radical difference in depth of field as far as viewing grain is concerned. But even with slower process lenses any such issues can be detected using a high-quality magnifier.
    I take it you mean depth of focus and not depth of field, but it still means you are still trying to judge focus in a wider depth of focus.

    “The contemplation of things as they are, without error or confusion, without substitution or imposture, is in itself a nobler thing than a whole harvest of invention”

    Francis Bacon

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