[lotech]

The title may sounds strange to you, but I wonder if anyone had problem with focusing on SLR/DSLR due to mis-aligned mirror ? I got an used LX and the focus is very slightly off I can't get infinity focus even in the eye piece, I got it fixed in a repair shop, I don't know the actual cause of the problem, I believe it was the mirror or the prism gone out of place after long time use. Unlike mirrorless on SLR/DSLR we rely on the mirror/prism to focus, and we will not know when it messed up until we do long tele shots and serious macro works, of course live view can fix that but not in every situation.

[pschlute]

Misaligned mirror will cause exactly that problem

The LX is a likely culprit for this reason: the rubber bumpers have a habit of decaying and go sticky. The bumpers get replaced but without original parts they can be out of alignment. Hence a problem like yours

[lotech]

IC, it won't be LX alone then !

[Ishpuini]

On a DSLR there would always be the workaround to use LiveView for focus, but unfortunately on a SLR that's not possible...

[MikeMcE]

I repaired SLRs for years, the only cameras that needed mirror alignment were Hassleblads, when replacing the wind key. I had a factory fixture for that . Most 35mm SLRs have a mirror stop that could move if impacted, simple adjustment. Focus screen/fresnel would commonly get pushed by people trying to clean it.
The mirror bumpers have nothing to do with the mirror angle, so they aren’t the culprit. And I can’t remember when a prism didn’t sit flat.

Don’t forget zone focus with DOF can save your shots , how sports action shots used to be done before AF

Hang up and DRIVE!