RB67 90mm Lens: Replacing a Missing Index Stop
Originally posted on Instagram. Notes from the repair bench, kept here as a searchable archive. View the original on Instagram
This Mamiya RB67 90mm came into the shop with a complaint that it would not lock on the body. A quick inspection showed that the rear lens index stop was missing. This particular lens is a very early style and was the last to use the type of index stop shown in photo two. This type was only used from 1970-1972. After 1972, Mamiya changed to a different stop with two screws holding it in place as seen in photo three.
After installing the new index stop, it needs to be calibrated so that the shutter will cock and release at the proper angles. The video at the end of the post shows the lens installed on the R4 cocking angle jig. To fully cock the shutter, the angle needs to be 107 degrees and it should release at 70 degrees. If these angles are not set properly, you can have issues with the shutter not cocking or not releasing.
While you can go back and forth and adjust these angles using a camera body, it is best to calibrate lenses (for any camera) separate from a camera body so that it will work with all bodies. If you calibrate it using a body, you are also getting any wear or other issues with the body involved in the calibration process.
