After having some eradict focussing issues, I decided to investigate the issue o f ground glass / film alignment. I read the last thread, however it did not add ress some of the issues I thought of. For consistent critical focus I realize the film must sit in the exact sam e plane as the ground glass, i.e. so the film sees exactly what I see in the gro und glass. However, when studying how to test this, I came up with a good syste m, but many questions. Using a depth micrometer with a large straight milled me tal bar, I can measure from the rear standard plane down to the glass. Comparin g that distance to the film holder in place with film would make sense. However this raised several questions which I could not find answers to.
1) Since the ground glass and film are different thicknesses, where do you meas ure the micrometer to for proper comparison? How about fresnel lenses, how do t hey affect the measurement?
2) Is the actual focus point on the ground glass on the back where your eye is, or in the front towards the lens?
3) Once it is determined what you should be measuring to, then what would be a reasonable tolerance between film holders, quick loads, polaroids, roll film bac ks, etc? The micrometer for $30 reads to .001 inch.
This seems like such a critical issue, I find it hard to beleive this is n ot tested more often and a micrometer kit is not sold for 4x5 and 8x10's with in structions. Anybody have experience at this? It will save me a lot of headache s, thanks in advance...
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