RB67 Lenses on RZ67: Lens Throat Diameter and Adapter Ring
Originally posted on Instagram. Notes from the repair bench, kept here as a searchable archive. View the original on Instagram
This post is a bit of a continuation of my previous one regarding using Mamiya RB67 lenses on the RZ67.
The first photo shows the RB67 Pro S body in the upper left, RB67 Pro SD upper right and RZ67 lower middle. It’s obvious that Mamiya increased the diameter of the lens throat opening on the Pro SD and the RZ. The original Mamiya lens opening was approximately 53mm in diameter and this was increased to approximately 60mm in the Pro SD and RZ. This was to allow for higher spec K/L lens use.
While the older non K/L lenses will fit the Pro SD and the RZ, Mamiya recommended using a special adapter ring with the older lenses to make up for the extra diameter of the body lens throat. This was to keep the lens stabilized and centered in the body. All K/L lenses came with this adapter ring which needed to be removed in order to use the lens on the older bodies. The second and third photos show the ring (with its inner rubber o ring to keep it tight on the lens) being installed on a K/L lens.
The first video shows the result of using an older non K/L lens on an RZ67 without using the adapter ring. If you look carefully you can see the lens shift in position when cocking and releasing. This can be a few degrees of movement and cause a misfire.
The second video shows a K/L lens being used without the adapter and again the movement of the lens is visible.
The final photo shows a K/L lens with the adapter ring installed and no movement of the lens when cocked or released.
While installing the lens mounting ring very tight can eliminate some of the movement, it still will not be centered and I have seen many of these lenses stuck on the body from over tightening.
