Mamiya 645 Pro: Finding a Tiny Light Leak with a Pico-Ammeter
Originally posted on Instagram. Notes from the repair bench, kept here as a searchable archive. View the original on Instagram
This Mamiya 645 PRO came into the shop with a difficult to locate light leak. I first checked body for impact damage suspecting that the back was not mounting properly. Then, using a sensitive photo detector and a pico-ammeter, a very tiny light leak was noticed by the dark slide opening. Shining a bright light into and out from the back did not disclose this with a visual test initially.
For the technical minded: dark current was approximately .0026 nanoamps and when a bright light was directed at the top of the dark slide opening, current peaked to around .0189 nanoamps indicating that light was entering the back through the opening and hitting the photo detector mounted at the lens opening. I would normally use an oscilloscope for this test but the signal was too small to show on the scope.
