RB67 90mm f/3.8 Lens: 791 vs 653 Shutter Differences
Originally posted on Instagram. Notes from the repair bench, kept here as a searchable archive. View the original on Instagram
Servicing a Mamiya 90mm f/3.8 lens for RB67. Mamiya made three different generations of shutters for the RB lenses. The last two are the most common that I see. The lens shown here has the later model 791 shutter. Mamiya claimed that the new style shutter had “high quality and excellent performance”. The shutter mechanism was totally changed in relation to the the earlier shutter.
The third photo shows the later model 791 on the right and the earlier 653 shutter on the left.The 791 was introduced in October 1978 production and featured shutter blades with “drilube graphite with mat black” while the 653 had blades of “oxidizing coating with blue luster”. I will say that the earlier 653 shutter blades seem to be more susceptible to oil contamination.
The 791 shutter had a quite different speeds escapement. It used several gears that were plastic. While the earlier 653 shutter had an all metal geared escapement, it was only sold as a complete assembly but the later model 791 escapement was made up of different parts that were sold separately. In the fourth photo, you can see the two different escapements in the foreground of each shutter.
