How do long exposures work on a Mamiya RB67 ProS, and what does a dual cable release actually do?

Question

I’m learning to use a Mamiya RB67 ProS with a 90mm f/3.8 Sekor C lens and want to make exposures longer than 1 second. On most cameras I’d use Bulb with a locking cable release, but this lens only has a T setting above 1 second, not B. On my camera, T opens the shutter and then the release locks; the shutter seems to close only if I recock the body or turn the shutter-speed ring off T.

I’ve seen claims that a dual cable release is needed for long exposures on the RB67, especially with mirror lock-up, but I can’t find a clear explanation of what the dual release actually does or whether it changes how T mode closes. Can someone explain the practical long-exposure workflow on an RB67 ProS, including whether T mode can be closed remotely, and whether some lenses also support a true B mode?

user83099 · Accepted Answer

I've had my RB67 Pro for a few years now, and have occasionally done long exposures using two separate cable releases. Mamiya's double cable release is no different, as it is virtually a 2-in-1 cable release. You may as well use a hairpin to set off the shutter when the lens is in mirror up mode.

So, unfortunately, the only way to close the shutter in T mode is to either turn the shutter speed ring, or by advancing the cocking lever on the side of the body. This is regardless of whether you are or are not using two cable releases. If you're afraid of moving the camera doing this, I recommend covering the lens with a lens cap to prevent any motion blur from you touching the camera.

How do long exposures work on a Mamiya RB67 ProS, and what does a dual cable release actually do?

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