I'm the experimental type. So, I designed a test to find the leak. Fresh film. Shoot a couple of frame. Then run past four blank frames to put unexposed film in all the areas of interest. Then leave the camera in bright light for a day. Click off four more blank frames to avoid exposing over any further leaks, and inspect the whole negative strip.
Here's the film strip:
And, here's some explanation:
- Right hand side is the film leader. It's bulk loaded so Kodak's frame numbers are meaningless.
- A couple of correctly exposed frames of test targets. These look fine.
- Note light leaks at the edges. I've determined that these are from my bulk-loaded film and appear with all my cameras. I'll worry about these later.
- For the full-day test in bright light, Frame 7 is in postion behind the lens.
- I believe A is the primary leak, onto the take-up spool. Looking at the camera geometry, it's from the film-door hinge. GSN winds film on the take-up spool with emulsion out. Nice broad light leak.
- B is print-through of sproket holes at A onto the film one layer down on the take-up spool.
- C is confusing, especially the distinct line. This is on film at or near the advance sproket. Is this light through the anti-halation backing? Why the line? Electro owners, please have a look inside your cameras and see if you can figure out what creates this pattern.
- In this test strip, everything beyond Frame 7 is clear, so there's no further light leak.
Solution: Added a second piece of light seal at the film-door hinge. This solved the problem.