Sample of a problem

perhaps the first shutter curtain is slow? What camera is it?

The camera is a Mamiya M645. The shutter moves up in the same direction as the light stripes at the edges. It occurred to me that it might be from the mirror. I was using a 55mm lens, F22 and long exposures. I raised the mirror before triggering the shutter to avoid the extra shake. I noted during use that the mirror sometimes failed to drop again after the shot. Yesterday while inspecting the camera to see about that issue I saw that about half the time when I raise the mirror it only goes halfway up. The mirror is a trapezoid, narrower at the bottom, I suppose to save weight. When only halfway up there are gaps between it and the chamber side walls. I know the lens will expose the film with only a partial opening because all parts of the image come from all parts of the lens, but then probably at a reduced exposure, especially at the top of the backplane. Add additional exposure to the sides from the slots and also from the view finder and that might cause it. The extra puzzle is that dark strip just inside of the right hand side light strip. My film rolls top to bottom. That is why I considered a light leak at the back cover, but when I checked all the frames there seemed to be full detail...not "fogged", even in the light areas.

What happens if you make a similar exposure with the lens cap on? That might tell if you have a light leak.