How to focus to infinity?

Discussion in 'Large Format Cameras and Accessories' started by pawlowski6132, Feb 28, 2011.

  1. pawlowski6132

    pawlowski6132 Member

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    I guess I never thought of this before but, how does one focus a view camera to infinity??

    Although I'm sure the answer will be painfully obvious and I'll be embarrassed I asked, I have to ask.

    Do you need to know the focal length of your lens?
     
  2. jbbooks

    jbbooks Member

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    Actually, this is a quick and dirty way to find the focal length of a lens. Just pick a distant object that is small and easy to determine that it is in focus; like hardwood tree branches in winter or lights, wires, fences, etc. and focus it on the ground glass. When in focus, the camera is focused at infinity for that lens. The distance from the face of the lens board to the plane of the ground glass will be the approximate focal length of the lens.
     
  3. ntenny

    ntenny Member

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    It'll be the exact focal length of the lens, won't it? Modulo the fact that "infinity" isn't really infinity, which should make a microscopic difference if you picked a nice distant object, and any slop in choosing your points of measurement. Am I missing something that makes it only an approximation?

    -NT
     
  4. lxdude

    lxdude Member

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    Nathan-
    The rear nodal point of the lens, the distance from which to the film plane is the focal length, is not necessarily on the same plane as the face of the lens board.
     
    Last edited by a moderator: Feb 28, 2011
  5. ic-racer

    ic-racer Member

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    Some folding view cameras have infinity stops. Once set, they allow you to rapidly pull the front standard out to a specific point after unfolding the camera. Some people set them just past infinity, so you can find tune the focus, if it needs to be at infinity, after you get the camera set up.
     
  6. lxdude

    lxdude Member

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    View cameras are focused by observing the image on a ground glass at the film plane, which is then removed and the holder containing the film or plate is put in its place.