These adapter rings are required to allow M39-Mount lenses to be fitted on M-Bajonett-Mount camera bodies.

We have three types of this adapter to change its frame lines correctly:
35 / 135mm, 50 / 75mm, 28 / 90mm

For Bessa cameras whichever is fine. Due to the enormous depth of sharpness of the 12, 15- and 25mm lenses each adapter ring is fine.