Originally Posted by
Doremus Scudder
Stephen,
You describe a classic ground-glass positioning problem. It may have to do with the fact that you have after-market Bosscreens installed. If, for example, your Cambo originally came with a Fresnel/ground-glass sandwich with the Fresnel on the lens side of the assembly, then your Bosscreen will be too close to the lens (closer than the film) by 1/3 the thickness of the original Fresnel (this latter fact might give you a starting point for determining shim thickness). The fact that you see the error more with shorter-focal-length lenses is that the shorter the focal length, the less Depth of Focus you have at the film plane (as opposed to Depth of Field in front of the lens, which is greater with shorter-focal-length lenses). Lens design plays a role here too I would expect. The point here is that if you position your ground glass correctly using the most sensitive lens, i.e., your 72mm, it will be right on for the rest.
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