Used my RB67 for moonlight landscape exposure -- used Ilford FP4 and exposed for 1 hour at f11. It came out very underexposed -- so disappointing. Don't know what went wrong -- has anybody experienced a failure using the time or 'T' function with an RB lens? The moon was full -- nice and bright.
I have a 65mm lens that "t" doesn't work on if "t" works you should hear the shutter close when you press the winder lever forward,1hour seems very long for full moon light don't use fp4 much but still 10 mins or so for acros
from the manual "Mamiya lenses for mamiya rb" *" Time Operation When releasing teh shutter by setting the shutter speed scale on T (time) the shutter will remain open for effecting an extended time exposure. to close the shutter, turn the shutter speed ring toward the 1 second marking or press down the shutter cocking lever about 30 [degrees]; however, do not move the shutter cocking lever until just before closing the shutter."
In case you only have a single cable release for long exposures, is switch the turn the switch up to M (for mirror up photography ) and attach you cable release to the lens... then press the shutter release on the camera, which will only allow the mirror to go up... you should allow a couple of seconds to pass for the 'vibrations' to dissipate... then press the cable release... OF course you will still have to turn the knob to the 1 second mark... some people carry around cardboard to cover the lens quickly before they turn to the 1 second mark...
Obviously there was a problem with your time exposure. You didn't mention the conditions or the phase of the moon, which would affect your exposure. For reference, a night scene, away from city lights, under full moon, has an exposure value of -3; under half moon, exposure value -4; and under crescent moon, exposure value -5. At f/11, an EV of -3 would call for an exposure time of 16 mins; EV -4, 32 mins and EV -5, 64 mins. So at f/11 for an hour you should have had a perfectly exposed to 2 stops overexposed image.
Perhaps try replicating a time exposure while looking into the lens at a wide aperture and see what the shutter is doing?
Although it won't help with your current lens, KL lenses have a "Bulb" fitting to close the shutter in time exposure mode. So with these lenses, you can attach three release cables - one to the shutter button to flip the mirror up, one to the mirror up fitting to open the shutter and one to the bulb fitting to close the shutter.