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  1. #21
    Steve Smith's Avatar
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    Quote Originally Posted by declark View Post
    So if a 1/2" one way or the other doesn't make a difference why even bother with a grain focuser? I can easily guess within a 1/2" head height?
    Because you still have to get it in focus. It's just that the depth of focus is greater than you might think it is.

    And that depth of focus can change quite a bit with a very small lens to negative movement.

    Most people focus by moving the focusing knob both directions so you find the two points at which the image starts to go out of focus and then you end up with it in a middle position (hopefully). In this position the paper is in the middle of the depth of focus and a bit of movement up or down will not be noticeable.


    Steve.

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    What ever it is you are not alone, hpulley. I would have sworn the same thing.
    "There are a great many things I am in doubt about at the moment, and I should consider myself favoured if you would kindly enlighten me. Signed, Doubtful, off to Canada." (BJP 1914).

    Regards
    Bill

  3. #23
    declark's Avatar
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    Thanks for clearing that up Steve. It's been a few months since I printed anything and now I see what you are saying. Once it is in focus, a slight change in the head height probably doesn't alter sharpness much, just the projected image size.

  4. #24
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    The enlarger is really a macro camera with huge magnification. The negative is the subject and the paper takes the place of the film. As anyone who has done any macro work will know, there is hardly any depth of field on the subject especially when you go to magnification greater than 1:1. With an enlarger this translates to depth of field around the negative which is why negative flatness is important and why some people use glass negative holders despite the extra surfaces which need to be kept clean.


    Steve.

  5. #25
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    OK so I tried it with and without my glasses and I think it is my glasses that are causing the problem. This is a bit odd however as I often use glasses with my telescope and I would have thought the small exit pupil would give similar problems but I guess the objects near infinity are very different from this case where the object is at minimum focus distance.
    Harry Pulley - Visit the BLIND PRINT EXCHANGE FORUM

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