Does anyone know the aperture size of the pinhole that is part of the Beseler make-your-own 120 pinhole camera? Knowing would help me better calculate exposures. Thanks.
Take some test shots at varies shutter times and develop the film. Do this at high noon on a sunny day. lets say your hand held meter reads f16 at 125th of a second and your best shot was at four seconds when you viewed the developed film. That is your base now all you have to do is double the exposure time for every stop below the base. One stop under = 8 seconds two stops under equal 16 seconds etc.
Terry is right. Then write yourself a exposure chart, keep it with your camera, and refer to it every time. Mr. Pinhole also can give you an exposure chart: http://www.mrpinhole.com/exposure.php