Mamiya 645 80mm f/1.9: Lens Out of Focus Tolerance
Originally posted on Instagram. Notes from the repair bench, kept here as a searchable archive. View the original on Instagram
This Mamiya 645 w/80mm f/1.9 lens came into the shop with a complaint of poor focus. In checking the lens, I found it to be plus 0.16mm out of tolerance as you can see in the second photo. Even though this is quite out of specs (it went through infinity), you might not notice this if you were stopping down your lens. But in this case, at some point in the past, the body focus screen was adjusted for this error. Problem was that the image reaching the film plane was not matching the finder! Of course, with a f/1.9 lens shooting wide open sometimes becomes an interesting option.
The procedure that I use for checking/adjusting focus is, in this order:
1.) check film to flange distance
2.) check/adjust lens focus off the body
3.) adjust focus screen if necessary
Also, on looking at the adjustment screws for the lens focus I noticed that one of them had only half of the slot intact as shown in photo three. With Mamiya cameras and lenses, most adjustment screws are held in with sealer. If you attempt to turn the screw without releasing the seal, you will very likely damage the thin screw head. Mamiya technical manuals say to use a “cigarette lighter” to loosen the sealer on the screws. That’s not what I do. A hot soldering pencil tip, MEK solvent or a hot air rework gun with 5mm tip is my preference depending on the location of the set screw.
