Mamiya 645 80mm f/1.9 Lens: Why It Comes Apart in Two Pieces
Originally posted on Instagram. Notes from the repair bench, kept here as a searchable archive. View the original on Instagram
Servicing a Mamiya 80mm f/1.9 lens for the 645. This is the third 80mm f/1.9 to come into the shop this month in two pieces. Here is why: the lens has a fairly large focus helix because of the lens size (f/1.9). When the focus helix lubrication gets dry, the extra force needed to turn the focus ring can cause it it slip (the focus ring is only held on by three small 1.4mm setscrews) and then it has lost the infinity stop and next time it is focused, it can extend the helix out too far and then the lens ends up in two pieces. The solution to that issue is to disassemble the focus helix, remove all old lubrication and put a very small amount of focus grease on the threads. Photo three shows the helix shiny clean after an ultrasonic bath in a 1% Alconox solution.
Final step of course, is to reset infinity focus on the lens. The video at the end of the photos shows the image being focused on the autocollimator. Might be hard to judge from the video, but wide open, the lens performs very well.
