### pen hole for 810

greenspun.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 (doc@ellensburg.com), 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.

David,

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

-- Erik Ryberg (ryberg@seanet.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 (f.rallo@ele.uniroma3.it), 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 (evphoto@insync.net), March 17, 1999.