Backfocus on Mamiya 645 Pro 80mm 2.8

Hi all,

I'm trying to make sure the focus on my Mamiya 645 Pro Tl 80mm 2.8 Lens is good. I believe it might be a little off. I can't find the focus calibration screw anywhere on the net. Any help would be appreciated

I have the service manual for the *old* M645 (from suaudeau.eu ). Like a lot of manuals, it's not crystal clear.

On that camera, infinity focus is adjusted by three screws which position the focusing screen (so you raise or lower the screen to match the actual infinity focus). They show a collimator being used for this.

The manual has this adustment *after* first checking and adjusting the correct position of the lens mount flange (adjusted by fitting shim washers on its mounting screws), and checking and adjusting the mirror angle of 45 degrees (requires a special stand).

If you trust your camera to be right in those two places, you could look for adjusting screws for the focus screen. If you're thinking of doing this, I guess you can rig up something to do instead of a dedicated collimator.

The focussing screen in the ProTL is completely different from the old metal 645s. It's a thin plastic single unit fresnel that has no adjustment. It just clips in and out from underneath, through the lens throat IIRC.

If the focus is off, then the first thing I'd suspect is the plastic mirror rest. Infamous for cracking. It's located on the lower RH side of the body as you look into the lens mount with the mirror raised. A little plastic thing with a spring wrapped around it. Give it a wiggle. If it moves easily, it's cracked, and practically your whole camera is a write off because the part is no longer obtainable.

If it isn't cracked, you're very lucky, and need to look elsewhere for any focussing error.

This could be sloppiness between the magazine and camera body, an incorrectly seated film insert, a displaced focussing screen or a mis-adjusted mirror rest.

Without a thorough inspection of the camera, it's almost impossible to diagnose at a distance, but as I said, the first place I'd look is the flimsy little plastic mirror-brake/rest.