RB67 Lenses on RZ67: Cocking Torque of C vs K/L Lenses
Originally posted on Instagram. Notes from the repair bench, kept here as a searchable archive. View the original on Instagram
Mamiya made it so that the RB lenses would work (in full mechanical mode) on the RZ bodies. However, there is a caveat: Mamiya recommended that RB lenses used on the RZ bodies should be either K/L lenses or late model C lenses. This has to do with torque compatibility.
The early C lenses required more energy to cock the shutter. As seen in my test in video one of a 65mm C lens, about three pounds of force is required to arm the shutter.
The second video shows a 127mm K/L lens and it requires a little less than two pounds of force.
This might not seem like a big difference but keep in mind that the RZ bodies failure point is often in the winding mechanism. Over time, this little bit of energy needed for cocking the shutter might make a difference in camera operation. At least Mamiya felt that it did.
The other item that was recommended was to have the interchanges mounting ring (photo 3) installed on the C lenses. The K/L lenses all came with this ring although it may have been removed at some point to use the lens on an early RB body (Non PRO SD).
All K/L lenses have the improved shutter and some late model C lenses also do. You can tell by looking at the shutter blades from the front of the lens: the early blades are shiny and flat, the later model blades are a dull color with one blade tip turned upward
