RB67 Lenses on RZ67: Why Use Post-1978 791 Shutter Lenses
Originally posted on Instagram. Notes from the repair bench, kept here as a searchable archive. View the original on Instagram
I often receive questions regarding the use of Mamiya RB67 lenses on RZ67 bodies. Hopefully this post will answer these questions.
While you can certainly use the RB lenses on the RZ bodies, there is a caveat: Due to the higher torque needed for the earlier RB lenses, I’d recommend using only post 1978 RB lenses that use the 791 shutter (please see my previous post on shutter types). The earlier shutters from 1970-1977/78 used the 653 shutter and these take more energy to cock, resulting in more pressure on the RZ cocking system. I feel this is an important point because Mamiya had several issues with the cocking system and made many changes to the mechanism over the course of production.
High torque was not a problem on the original RB because moving the cocking lever only had to charge the mirror and shutter. On the RZ, the cocking lever also had to wind the film. As seen in the second photo of the RZ innards, the cocking lever needed to move every gear seen in this photo. The shafts at right angle went out to the film back and to other parts that needed winding.
I have done a simple, rather crude test of the torque needed using a force gauge. Video one shows torque needed to cock the early RB lens, a little less than 3 foot pound. Video two shows torque needed for RB K/L lens, a little more than 1 foot pound. Video three show torque needed for RZ lens, slightly more than 1 foot pound.
I think the extra force required with the early lenses may hasten wear/damage to the wind system, especially with the early, non-updated RZ production. Also, the adapter ring should be used with any RB lenses used on the RZ. My next post will be on the significance of the RB67 lens adapter ring.
