Mamiya 645 80mm f/2.8: Sticking Diaphragm from Oily Blades
Originally posted on Instagram. Notes from the repair bench, kept here as a searchable archive. View the original on Instagram
This Mamiya 80mm f/2.8 lens arrived with a sticking diaphragm. As seen in the photos, lots of oil present on the diaphragm blades. And, a lot of grease on the focus helicals and surrounding areas.
What happens is that the focus helical grease will sublimate and now you have oil on the blades. While cleaning the oil will solve the problem, what the lens really needs in these cases is a complete disassembly to remove all lubricant from the focus helicals and replace with new lubricant. If this is not done, the blades will get oily again in the future. So, a lot more labor but a much longer term repair.
Also, with cleaning and lubricating the focus helicals, the focus will be much smoother. When lubrication changes composition the focus may be stiff or erratic.
