(Probably) Stupid T-Dimension Question

Discussion in 'Camera Building, Repairs & Modification' started by Steve Goldstein, Jul 9, 2008.

  1. Steve Goldstein

    Steve Goldstein Subscriber

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    When discussing the T-dimension for LF holders, is the measurement made with or without film in the holder? I would think a film-independent value would be more universal, but since most LF film seems to be 0.007" (0.178mm for you metric speakers), at least these days, it could be done either way.

    Thanks!
     
  2. Steve Goldstein

    Steve Goldstein Subscriber

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    I forgot to mention that for ground-glass frames with no fresnel (or the fresnel on the user side of the gg) the dimension can only be from the frame face to the surface of the glass. So if the spec is applied to the gg frame, the film holders must be slightly deeper to allow for the film thickness, thus keeping the plane of focus the same.

    I've searched around for this info but could not find a simple definitive statement answering the question in my first post.
     
  3. barryjyoung

    barryjyoung Member

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    I measure T dimension with film in place when making film holders. The distance to the groundglass from the groundglass frame needs to be the same as the distance from the frame on the holder to the emulsion. If it were otherwise the image on the emulsion would not be the same as the image on the groundglass. Depth of focus (not depth of field) will almost certainly accomodate some latitude in T dimension. Hope this helps.