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[Rollei] True focal length

Has anybody successfully tried to find out the true focal length of a lens
by measuring object size, object distance and image size on the film and
calculate from there? At first sight, even if I take into account
considerable misreading I would still arrive at the true value plus or minus
one millimeter. Am I missing something? I AM missing an Autocollimator,

I have some lenses where I doubt what the engraving says is true. I always
thought this would be marginal, but now I have a 85 mm lens that is actually
'longer' than a 90...



End of Rollei Users list digest V12 #106