RB67 Lenses: Overexposure from Slow Closing Shutter Blades
Originally posted on Instagram. Notes from the repair bench, kept here as a searchable archive. View the original on Instagram
I constantly see RB67 lenses with this complaint: overexposure in bright light. In almost every case, this is caused by the shutter blades not closing down in the first part of the blade closing cycle. I will illustrate a way to check this on your lens.
The first video shows an RB lens mounted on a test fixture. Fully cocked, the fixture should indicate 107 degrees (the degrees are calculated based on the index pin located on the rear of the mount, seen at around two o’clock in the video). When the cocking pins are slowly moved counter-clockwise, the shutter blades should start to close and by 95 degrees should be totally closed. Continuing to turn the cocking pins counter-clockwise, at 70 degrees the shutter should release and time out with the chosen speed.
To do a test on your own, the second video shows how you can slowly turn the cocking pins clockwise to insure that the shutter blades close at 95 degrees and then fire at the correct speed by 70 degrees (you will have to press in the small chrome release button located to the left of the locating pin to release the cocking pins).
If the shutter blades don’t close when you reach 95 degrees, then in almost all cases, they are contaminated with oil. No simple solution in this case as the shutter needs a complete disassembly to remove the blades and clean the mechanism plates of oil.
