pen hole for 810greenspun.com : LUSENET : Large format photography : One Thread
does someone out there happen to have the pin hole diameter for an 8x10 at 300mm exstension? I assume that would be more or less "normal." and could you give me the f stop for that, so I could use my light meter with it. thanks.
-- david clark (firstname.lastname@example.org), March 10, 1999
Formulae for optimum pinhole diameters are of the form: d = sqrt(v) * k, where d is the diameter, v is the extension, and k is a magic number that people disagree about. If d and v are in mm, then k=0.04 works.
So for v=300, d=sqrt(300)*0.04 = 0.7mm.
The f-number is 300/0.7 = 428, which is about 5.5 stops slower than f/64.
-- Alan Gibson (Alan.Gibson@technologist.com), March 11, 1999.
Calumet sells a nice set of "laser drilled" whatever that means aluminum sheets of various apertures for about 30 bucks.
-- Erik Ryberg (email@example.com), March 11, 1999.
David, as the world is full of magicians, my books suggest another magic number, i.e. k = 0.036 So the "perfect" diameter comes out to be O.62 mm. And the coresponding f value is f/483 about 10 stops slower than f/16. Regards, Franco
-- Franco Rallo (firstname.lastname@example.org), March 12, 1999.
calumet is selling premade precision pinholed aluminum sheets as well as comple cameras and info books as well if you are still interested.
-- Ellis (email@example.com), March 17, 1999.