Mamiya 7: Light Leaks from Loose Film Spool Fit
Originally posted on Instagram. Notes from the repair bench, kept here as a searchable archive. View the original on Instagram
Something that comes up from time to time is light leaks on Mamiya 7 bodies. Since Mamiya did not use conventional foam light seals on the Mamiya 7, worn seals are not something to suspect of causing a problem. But I do see light leaks on the negatives of clients that indicate the film is not being rolled up tightly.
I believe that these are the two issues that will cause this: 1.) film spools that are out of spec and 2.) spool pin holders on the Mamiya 7 that are slightly too small. Either of these issues will cause backlash on the film spool. Combine these two and you may have a problem.
Photo two shows two film spools taken from a random box here in the shop. It may be hard to see, but the one on the right has a slightly large keyway and hole in the center. Measuring the keyway, photo three shows the spool on the left at 2.65mm and photo four shows the right hand spool at 3.24mm. Since ISO specs are 2.2mm to 2.8mm, I am going to call the spool on the right out of spec.
The video shows the result of this out of spec spool on a Mamiya 7: backlash of around 1.5mm. Yes, this can cause a winding issue and a roll that is not tightly wound.
Mamiya realized this issue because in 2000, about one year after introduction of the Mamiya 7II, they changed the shape of the spool holder and spool shaft. Photo six shows the spool holder from April 1999- July 2000. Beginning in August of 2000, the new style as shown in photo seven was produced for a better fit on the film spool. Also, the lower spool pins were enlarged by 0.2mm for a better film spool fit. When Mamiya was still in business, they would replace all of these parts with the new style when a camera was sent for service so they obviously thought it was an important change in design.
My suggestion is to make sure that the film is rolled tight after exposing and before removing from the camera and if possible, change film in subdued light.
