RB67 Lens Shutters: 653 vs 791 and Plastic in K/L Lenses
Originally posted on Instagram. Notes from the repair bench, kept here as a searchable archive. View the original on Instagram
get a lot of questions regarding the use of plastics in RB K/L shutters. Usually, it is someone deciding on making a purchase.
Keep in mind that Mamiya changed shutters in all RB lenses long before the K/L lenses were introduced. While the K/L lenses came out around 1990, Mamiya had been using the 791 shutter (used in the K/L lenses) in all RB lenses in 1978.
The first photo shows the evolution of the speeds controller in the 1 Seiko shutters:
1.) Upper left, the 653 shutter used in RB lenses from 1974-1978. All metal speeds escapement seen in the photo at top of shutter. Note the shiny shutter blades, these “oxidizing coating with blue luster” blades are often found these days with oil contamination on the surface.
2.) Upper right, the 791 shutter used in RB lenses from October of 1978 to end of production. The dull finish shutter blades “Drilube graphite with mat black” are almost never found with oil contamination. The speeds escapement shown at the top of the shutter uses plastic gears.
3.) Bottom of photo shows the RZ Seiko 1ES shutter for comparison. At the top of the shutter is the single electromagnet that opens the shutter blades since the controlling circuit is in the camera body. These electromagnets rarely fail.
Yes, there were plastics used in the new shutters, mostly in the speeds escapement. But, where previously the complete (all metal) speeds escapement needed to be replaced in case of failure, the individual plastic parts could be replaced in the new style escapement. Testament that these escapements needed replacement is the second photo which shows a box weighing over one pound full of speeds escapements that were removed for replacement on shutters. The third photo shows the plastic parts in the new style shutters (1978 and onward) and the escapement is able to be disassembled when needed to replace these parts unlike earlier designs that needed the complete controller to be replaced.
