navmannz Offline Upload & Sell: On
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artur5 wrote:
After reading the last pages of this thread, specially Candreyo, Fred and Guy findings with the shims ( thanks guys), it seems clear that lenses with floating elements, like the ZM35, are much more complex to fix/correct for infinity adjust with a front filter than old style glass which moves back and forth the whole optical block to achieve focus.
For one thing, adding a front filter modifies the focal length of the combo, so the optimal placement of the floating elements to the focal plane possibly changes with respect to a ‘naked’ lens. What I have no idea is if this (possible) change requires moving back or forth the floating element. Hence, if removing shims helps or it’s detrimental.
Anyway, if finding the correct front filter/infinity adjust for normal focusing lenses is already tedious, requiring trial and error, lenses with internal focus/floating elements are worse still. Until somebody with advanced knowledge in optics chimes in here (Candreyo, Haruhiko ..? ) we’re like a blind man trying to find his way out of a maze.
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I agree that there's some complexity in here that we're not necessarily on top of, but is your assessment perhaps a little pessimistic, given the marked improvement in the tests that Fred showed a couple of pages back? For me, the fact that Zeiss even uses shims at the rear to allow adjustment of infinity focus indicates that removing one or two of them is probably fine - like you, I'd be much more wary of touching the internal ones. In particular, Fred's post on this page where he describes the gains in flat field infinity performance at more open apertures highlights the gains I would want to exploit, i.e., use of a front filter for night sky photos, and I'm currently investigating ways to purchase one in NZ. As for understanding exactly what's going on, it would be brilliant if we could get an optics engineer (ideally Zeiss) to comment, even if off the record. Perhaps one of us should write a brief summary, send it to them, and see if they will engage?
-John (NZ)
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