I have a Pentax P50 (newly acquired) which seems to have a focus problem.

Every shot is slightly out of focus and the focus alignment seems off -- i.e. if I focus through the mirror at something at infinity, when I look at the lens scale it reads 10 or 20m.

Now I presume this means the mirror isn't sitting in quite the right place.

However, I'm not sure how to adjust this. There seems to be a 'stop' that the mirror comes to rest against. Would I be right in assuming that I need to move this somehow (it looks like it may have a socket for a hex key in the middle)?

or do I need to add something to the stop e.g. a fine piece of rubber to slightly 'thicken' it?

Any suggestions?

thanks in advance.