Posted 22 March 2011 - 07:05 AM
If you've got a reflex model, don't forget you need to compensate for light loss in the beam splitting prism. If you move the turret out of the way (or remove the taking lens) you can see it behind the filter holder. The prism sits between the lens and the film plane and diverts about 1/4 of the light to the viewfinder, allowing you to see through the lens even when filming.
The first reflexes still had the 144 degree shutter angle, giving about 1/60 sec exposure time at 24 fps as you calculated, but taking into account the prism light loss the 'adapted' exposure time is about 1/75 sec, not far off the 1/80 sec 'adapted' exposure time of later reflex models.
If you look through the archives of cinematography.com in the Bolex forum you'll find plenty of discussions about how people work out their exposures for reflex Bolexes. Some use the 'adapted' exposure time, some prefer to offset the ISO setting on their meter, others just open the lens 2/3 of a stop more than their meter indicates (using a meter with frame rates and an assumed shutter angle of 180 degrees).
None of this explains your problem though. Given that you calculated for 1/48 sec exposure time, your footage should be about 2/3 of a stop underexposed, not over. Even if your camera was running extremely slow, say 18 fps when the speed dial indicated 24, the footage would still not be overexposed. Did you check the iris of the lens as Bernie suggested? Or your meter? Could you have made a mistake with the film stock speed?