Mamiya 645 80mm f/1.9: Stiff Focus and Focus Ring Setscrews
Originally posted on Instagram. Notes from the repair bench, kept here as a searchable archive. View the original on Instagram
This has been a week of servicing Mamiya 645 80mm f/1.9 lenses. Most common issue is stiff focus and this is caused by dried or sublimated focus helical grease.
While the solution is straightforward and involves a disassembly of the lens and the focus helix to remove old grease and install new, reassembly requires proper fitting of the focus ring setscrews. Mamiya used three setscrews to hold the focus ring to the outer helical. Since the barrel of this lens is a bit large, these three setscrews have a lot of energy put upon them when the focus ring is turned. Especially when the focus is stiff.
The setscrews have a conical surface that contacts the edge of the helical and there really is not a lot of surface contact. The complaint often is that the focus ring will be slipping. The solution that Mamiya proposed in the technical manual is what I do: after focus is set, each setscrew is removed in turn and a 1.3mm drill bit is hand drilled into the threaded opening. This gives the setscrew more surface area to grab.
Photo two shows hand drilling of the threaded hole. Photo three is of the setscrew shown installed before drilling the hole. After removing the screw, photo four shows what it looks like drilled and the final photo is of the screw installed.
Together with a clean and lubricated helix, this lens should be good for a long time.
