To get the actual number (not a decimal), divide the focal length by the pinhole diameter. As for exposure, my method is to meter the scene at say f/16 and use equivilant exposure to determine the exposure for the pinhole. Double the time for each stop. Say it's a sunny day with 100asa film, the scene meters at 1/125 at f/16 and your pinhole is somewhere around f/180. You count 22, 32, 45, 64, 90, 128, 180, that's 7 stops, so you double the shutter speed 7 times. 1/125 * 2 = 1/60 * 2 = 1/30 * 2 = 1/15 * 2 = 1/8 * 2 = 1/4 * 2 = 1/2 * 2 = 1 second.
John ----- Original Message ----- From: Renovica To: pinhole-discussion@p at ??????? Sent: Tuesday, March 13, 2001 2:38 PM Subject: [pinhole-discussion] f-number I made a pinhole with a pinhole diameter of 0.1mm. What formula do I use to calculate the f-number? How do I determine the exposure time. Please reply to this email address. Many thanks. Gorana Renovica
