You can use the formula for similar triangles: (the distance from the lamp to the slide) divided by (the distance from the lamp to the wall) EQUALS (the size of the pinhole on the slide) divided by (the size of the pinhole on the wall) You should be able to increase the accuracy by removing the projector lens and forming the largest image possible on the wall. Jim K www.paintcancamera.com
----- Original Message ----- From: "Rune Tallaksen" <[email protected]> To: <pinhole-discussion@p at ???????> Sent: Saturday, April 07, 2001 10:04 AM Subject: [pinhole-discussion] Calculating f-stop for pinhole camera > When making a pinhole by means of a needle one usually know the pinholesize > by the needle size used. > I seem to recall that there is another way to do get to know the exact > pinholesize but cannot remember the formula used. The method was described > as follows. > Mount the pinhole sheet in a slideframe, place it in a slideprojector. > Then by measuring the distance from the pinhole in the slideframe and to the > projector screen and the diameter of the projected pinhole on the screen, by > means of a formula it was possible to find the exact pinhole size. Anybody > out there that know which formula (s) to use?? > > Rune Tallaksen > Norway > > > _______________________________________________ > Pinhole-Discussion mailing list > Pinhole-Discussion@p at ??????? > unsubscribe or change your account at > http://www.p at ???????/discussion/ >
