Hi,
I have a Mamiya 7 with an 80mm lens, bought second-hand from Japan in great condition. It's been with me for about a year and I must have put about 70 rolls through it so far -- I love this camera, and it's very unlikely that I'll be able to afford to replace it anytime soon (which is why I'm so desperate to find out what's going on!)
I took it with me on a trip to China in March and shot about 10 rolls. When the film came back, I noticed a distinctive fog shape on the bottom-left corner on maybe 4 shots on every roll. These were spread inconsistently throughout the roll, and never occurred at the start/end (which rules out mishandling while loading and unloading). The mark is always the same size/shape, and always at the same position on the frame, which also eliminates x-ray machines. Most of the photos were taken in daylight.
I'm based in Singapore at the moment and there is a dearth of good repair resources here -- I've brought it to three shops and no one would take it. Instead I was told to check everything from my scanner to my negatives. (I did. . .and it's still definitely a camera issue.) I also tried to rent another Mamiya lens to rule out a faulty lens or lens glare, but to no avail, since no one trades film equipment here anymore. Finally, I gave the lens a thorough clean, put another roll in it, and when it came back, 9 out of 10 frames were okay (I'd shot mostly in shade. . .not sure if this has anything to do with it). . .but ONE shot still had the distinctive mark in the left corner, and it looks much more prominent (whiter) than before. Examples are attached, with CH2.jpg being the latest/worst of it.
There are no visible holes or gaps in the camera body. The Mamiya 7 doesn't have a shutter curtain either. It's a complete mystery to me, and I'm desperate as I was hoping to take the camera with me on another long trip next month. Has anyone experienced something similar? Would appreciate any advice on this at all!