Hi, mirror's lower edge at an angle doesn't indicate a maladjustment of the stop but a problem with the hinge mechanism at the top of the mirror or a twisted mirror carrier frame. With the mirror up and the shutter open you may be able to see the cause of the problem in good light with a magnifier. Hold the shutter open with a locked cable release to avoid damaging it.
Looking at the underside of the mirror through the lens mount and the gate it should be possible to tell if it's horizontal and central, or is skewed in any way.
If the mirror carrier or hinge mechanism needs straightening remove the mirror first for safety.
Sorry to repeat myself but don't do anything until you're certain you know the exact cause of the problem.
Thanks.
Looking into the chamber with a flash light and wiggling the MIRROR_UP knob, it is clear to me that the whole mirror assembly goes up and rests down crocked. Here's something else. As I said earlier, on right side, there is a mirror stop. Also, the right side has the mirror-up assembly. The whole thing depends on right side to move it up and down.
On left, there is a lever attached to this to move the aperture-close lever on lens. (so that the aperture will close when I release the shutter) I can tell, if I hold this lever by my finger to rel eave the pressure on left side, the whole mirror goes up and down leveled. Looks to me, the design depends on this assembly to keep its shape - and it apparently didn't.
I've taken this camera apart before and I know for certain, there is no internal linkage going from left to right. (I was careful not to disturb anything else)
From this, I am thinking, over years of use and uneven mechanical stress has caused this mirror assembly to twist and possibly worn linkage or pivot point.
Can you help me with few things?
A lot of alignment procedure depends on lens going to infinity focus. On this lens, it's all the way to right until it stops. How do I know this is actually calibrated correctly? Can it drift? I know, some of modern lens doesn't do this mechanical stop anymore. My Nikon lens actually goes to infinity few degrees before it's mechanical stop. On Mamiya, it's one and the same.
Another thing is... how do I obtain suitable material so that I can use it to check focus at the film plane?? I do not have spare focusing screen. Are there any commonly available material that's suitable?