RB67 350mm f/5.6 APO K/L: Inconsistent Slow Shutter Speeds
Originally posted on Instagram. Notes from the repair bench, kept here as a searchable archive. View the original on Instagram
Servicing a Mamiya RB67 350mm f/5.6 APO K/L lens. No too common of a lens, image quality and lens glass build is outstanding. This particular example had problems with the shutter speeds, specifically the slow speeds (although all were effected, slow speeds were more obvious). After a disassembly of the shutter and removal of the speeds escapement gears and other related parts, these were all cleaned and re-assembled. While this slightly resolved the issue, there were still issues with the speeds being consistent. Close examination showed excess play on some of the pivots. These are part of the mechanism plate so at this point I replaced the complete shutter and problem solved. The third photo shows the lens with the new shutter ready to be installed.
A little info on the shutters used in these lenses: Since 1978 Mamiya used this new style Seiko 791 shutter in all their lenses. The last photo shows the gear train used in the shutter and as you can see, all the gears and the pallet are plastic (Delrin?). Quite a departure from other shutters at the time. But these parts seem to be holding up well and I do have a large supply of replacements for at least the next five years.
