Mamiya m645 inconsistent frame spacing & frames cut in half

Hi there,

I was wondering if anyone would have some advice for me on how to fix my Mamiya m645 - I'd really like to avoid sending it out for repair. I bought it used recently and shot about 40 rolls on it with no issues. However, in my last batch of film I found that some of the exposures had been cut in half. There has always been a bit of inconsistent spacing between frames on the negative but never anything too dramatic.

For some reason when I load this camera, the exposure counter only goes back to 7 instead of S, so I have to wind the little gear back by hand before putting a new roll in. Before loading this roll, I forgot to wind the counter back by hand and didn't realize til I'd advanced the film one exposure. I opened the camera again, took the film out, wound the counter back to S, and put the film back in. Could this be the reason for the half frames?

My other theories are a sticky mirror, or some kind of discrepancy between the two shutter speed knobs (one goes to 1/1000, the other only to 1/500 - if they were set to different speeds could it cause the frame to be cut off?)

I still have half a roll in the camera so I haven't been able to open it up and take a look yet, but even when I do I'm not sure what to look for. Any advice appreciated!

Caterina

Some questions:
Is this a plain Mamiya M645 with the insert, or a Pro or Super with the interchangeable back?
When you say the exposures were cut in half, do you mean the frames overlapped but a 6x4.5 area was exposed, or that you only got half of the 6x4.5 area exposed onto film and the other half was blank?

I think that taking the insert / back out and rewinding the counter might mess up the frame spacing (also, unless you have the interchangeable backs, didn't you lose some frames to being light struck when you did this?) However, I would expect that the full 6x4.5 area should have been exposed regardless of counter problems.

You can test whether the camera is exposing the full area by opening the back, setting the camera to Multi, winding, and firing the shutter on say the 1/2 or 1 sec exposure, so you can see what is going on and if the shutter is opening fully. (You need to set Multi so that it will fire the shutter even though there is no film to advance.)

There are a lot of different bodies and prisms, but on the M645, I think that you need to set the body shutter dial to the red dot for the prism shutter speed knob to take effect. Otherwise you get whatever the body is set at.

Excuse the question, but: were you using flash? The M645 has a focal plane shutter and max sync speed of 1/60, so if you use flash and set a speed higher than 1/60, only part of the frame will be exposed due to the way a focal plane shutter curtain works.

I had a M645 1000s that developed an issue with one or more of the winding gears and started overlapping frames and/or missing frames. It started with inconsistent spacing and got worse. The bodies are so cheap I just bought another one from Roberts Camera that was in near mint condition and put the old one on a shelf.