Mamiya 645 80mm f/1.9 Cine Lens: Loose Focus Ring Setscrews
Originally posted on Instagram. Notes from the repair bench, kept here as a searchable archive. View the original on Instagram
This Mamiya 80mm f/1.9 cinema modified lens came into the shop with a loose focus ring. Not an uncommon issue with this lens as the focus ring is held to the inner helix ring by three small 1.7mm setscrews. These days, with the focus grease getting stiff, it does not take much for the ring to begin to slip. By 1979, Mamiya realized that the setscrews were not making good enough contact so they advised drilling a 1.3mm hole after adjustment was made and the setscrew installed. This gives the screw more surface area to grab.
Photo two shows the end of the setscrew from inside the lens and photo three shows the angled and ribbed area where the setscrew makes contact. If a 1.3mm hole is not drilled for the setscrew, it increases the possibility of the focus ring loosening again.
While not all lenses require this drilling of the contact surface, the f/1.9 is a larger barrel lens and a bit of force is applied to the focus ring during normal operation.
The last photo shows the lens installed on the flange back adjusting fixture. Using this tool, I can adjust the flange back (specification is 63mm +0.05 and -0.03mm) to within 0.01mm quite easily.
