john robison , Dec 19, 2005; 11:52 p.m.
Well Philippe, the problem is, the flange to film distance of the OM is 46mm. The M42 distance is 45.5mm. Thus you only have .5mm to work with in designing an adapter, that is if you want the M42 lenses to be able to focus to infinity. I have seen an adapter, but it was thicker than .5mm and employed a single weak negative element to allow inf. focus. It was poorly designed and the M42 threaded front was not deep enough to allow any of the lenses I tried to be seated all the way. At any rate, the element would have acted as a weak telenegative effect and also degraded the quality somewhat. As an option, if you have several nice M42 mount lenses that you don't want to part with, why not just purchase a suitable body? An average condition Spotmatic body should not be more than $65 to $85 on ebay. A Fujica ST605 or ST701 would be even less & offer brighter focusing screens, but are not as well made.