P-Sharan STD-35 and exposure
I built myself a P-Sharan STD-35 pinhole camera for a bit of fun http://www.sharan-camera.com/ but I can't quite figure out the suggested exposure times. The pinhole is stated as being 0.16mm to give F/130 for 20mm focal length which seems about right, but the suggested exposure time for ISO 100 film is 2-3 seconds for sunny conditions and 3-4 seconds for cloudy. Using the sunny F/16 rule, I would guess that F/130 should be about a half a second, so the recommended time should be about 2 stops over-exposed. The funny thing is, when I stick to the recommended times, they negatives are well exposed, but if I meter the scene and use F/130 shutter speeds (around 1/2 a second for bright sun) the negatives are underexposed. Any idea what might be going on?