View Full Version : pen hole for 810

11-Mar-1999, 00:17
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.

Alan Gibson
11-Mar-1999, 10:05
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.

Erik Ryberg
11-Mar-1999, 12:40

Calumet sells a nice set of "laser drilled" whatever that means aluminum sheets of various apertures for about 30 bucks.

Franco Rallo
12-Mar-1999, 05:25
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

Ellis Vener
17-Mar-1999, 15:53
calumet is selling premade precision pinholed aluminum sheets as well as comple cameras and info books as well if you are still interested.