Pinhole Question

[John Kasaian]

I'm need to make a pinhole post haste for a demo (Cub Scouts) I've got a 1 gallon metal paint can on hand, so I thought I'd make a "Merlin" wannabe ( I've run out of frozen turkeys a' la "The Turkey Cam" and the ULF made from the box my 'puter came in, the "Holstien Cam" has long since given up the ghost. The "winebarrel cam" is alas, still in the development stages) and shoot for 5x7 paper negatives.

Heres my question: What size pin hole do I need to make?

Thanks!

[Tom Westbrook]

I couldn't tell you, but this may be of some help: http://www.pinholeday.org/support/faq.php#BM4

[Capocheny]

Hello John,

Here's a number of sites that you might find useful:

http://jerryo.com/formula/pinhole.htm

http://www.pinhole.cz/en/index.php

http://users.rcn.com/stewoody/

http://unblinkingeye.com/Articles/Pinhole/pinhole.html

http://www.pinholeresource.com/

I think there's one site here that describes the sizes of pinholes...

Good luck and... have fun! :)

Cheers

[John Kasaian]

Thanks for all the tips!

I'll check them all out. I just found one recommendation----from Kodak no less---for 1/75" as optimum for focal lengths from 3"-6"

I'll be interested in what the other resources have to say (Kodak's example looked a little blurry to me---not what I was expecting from a pin hole!)

Thanks!

[Donald Qualls]

I'm used to working in millimeters for this stuff -- but Kodak is wrong anyway; there should be a 40% variation in optimum pinhole size for the range from 3" to 6" focal length.

For a gallon paint can, with 6" or so to the farthest part of the negative, I'd usually use square root of focal length, then divide by 25, though I've recently started thinking up to 1/3 smaller than this can still gain something (especially with paper negatives, which are almost insensitive to wavelengths longer than green). For 6" (152 mm), that would give SQRT(152)/25 = 0.49 mm, or up to 1/3 smaller (down to about 0.33 mm) -- in inches, that'd be .013" to .018".

Do you know the method of using a scanner to measure the pinhole size?