On 8 Dec 2004 at 1:16, Peter Spiro wrote: > I would have thought focussing is a pretty simple matter of one object > turning against the threads of another. I thought perhaps the parts had > gotten misaligned, and it would be a matter of snapping it back into place. > However, I can't see anything like that here. Does anybody know what the > moving part is supposed to be for focussing this lens? > > I don't have another 50 f/2, so I don't know if the rear element is supposed > to > move when it focusses. Does it? Any tips would be appreciated.
Hi Peter, Wow you sure did take it apart :-) The you really don't need to separate the lens groups from the body/aperture mech of the lens, the whole assembly simply moves in and out to focus. The free focus ring is likely the fine focus thread which turns with the heavy pitch aluminium helicoid tread. On part of the focus helicoid is cut into the barrel of the lens (the other side of the aperture mech) and the other one is under the focus ring. It seems the case you describe it appears that the helicoid has bound, a drop or corrosion will do it, but most likely a drop. Brute force may be the only way to separate them and there is no guarantee that the threads will ever mate again as they are so soft. You may be able to repair them using a very fine file them lube it up with some heavy lens lube. Good luck. Cheers, Rob Studdert HURSTVILLE AUSTRALIA Tel +61-2-9554-4110 UTC(GMT) +10 Hours [EMAIL PROTECTED] http://members.ozemail.com.au/~distudio/publications/ Pentax user since 1986, PDMLer since 1998
