Mamiya 645 80mm f/1.9: Lens Separated into Two Pieces
Originally posted on Instagram. Notes from the repair bench, kept here as a searchable archive. View the original on Instagram
This lens, a Mamiya 80mm f/1.9 for the Mamiya 645 series, came into the shop in two pieces as shown in the second photo. This is not unusual for this lens. What happens is that the focus helicals get stiff from dried lubrication and cause the focus ring to slip. This slipping will cause the focus ring to move to a point were now you will be able to unscrew the lens past its stop point and then you have separation.
After the lens separates, it can not be put back together without a disassembly because the helix needs to fit into the guides on each side for proper reassembly. And, of course, the helicals need a complete cleaning of old grease and installation of a new lubricant (for this lens I use a Lithium and PTFE grease). Photo four shows the four helix and thread surfaces that need to be cleaned. Photo five shows the final stage were the focus is adjusted on the autocollimator and lens fixture.
For several reasons, this particular lens, the 80mm f/1.9 seems to have the most issues with stiff focus and loose focus rings. This is likely because 1.) the lens has three small 1.7mm setscrews holding the focus ring to the body and 2.) the helicals are larger than most lenses as this is a f/1.9 lens and when the grease dries out, it takes a bit of force to focus.
If you have one of these lenses and the focus is stiff or slipping, I would recommend having it taken care of before you end up with a two piece lens.
