I recently got hold of a near-mint Pentax SV body. Being a big Spotmatic fan, I was curious to see what its predecessor looked and felt like. I was quite impressed with the mechanical smoothness of the SV, although I found the focusing screen inferior to that of the Spotmatic. While playing with it, I encountered a strange occurrence: The mirror tends to remain stuck in the up position, esp. at 1/30 and 1/60s speeds. This happens every 5-6 out of 10 times the shutter fires at those speeds, it happens only occasionally at slower speeds and almost never at higher speeds. I know this is not uncommon for Spotmatics, in fact I have a SPII which has the same problem at 1/15s and lower, but it tends to correct with a little gun oil applied over the shutter gears under the base plate and it is not real problem since I never go below 1/30s. Now, what is REALLY strange is that this happens ONLY WHEN A LENS IS ATTACHED! When it happens, the tab that pushes the lens aperture pin stays in the forward position keeping the lens stopped down and preventing it from unmounting. Advancing the film and firing the shutter sometimes (but not always) lowers the mirror, otherwise turning the speed dial to another speed and firing is required. At first, I thought that the aperture pin of the lens might somehow go over the tab blocking its return and thus keeping the lens up, but the same thing happens (although less often) when a Helios 44-2 which is a preset lens without an aperture pin is attached to the camera. The lack of a pin allows that lens to be removed without problem and this sometimes (but not always) allows the mirror to fall back into place. Without a lens attached, everything works OK, no matter how many times the shutter fires at all speeds, the lens always returns to its position. Any ideas on what may be wrong and how to fix it?