Re: IR pinhole problems

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From: Eric Kees (eskees@internetcds.com)
Date: 06/03/01-04:56:12 PM Z

See http://www.stanford.edu/~cpatton/pinholemath.htm for Pinhole math
primer.

The IR constant listed is for 750nm... if you are using 820nm film you might
want to try a slightly smaller #. Make a few pinholes... test until you find
the image you like.

In the example they give the focal length for visable light is 82.24mm.
Recalculating with an IR constant of 384 gives a focal length of 61.44mm.

If your camera has a focal length of 75mm an IR pinhole would be 0.44-0.46
for IR film (750-820nm range.)

*******************************************************************
Focal length of lens = (size of pinhole) X (size of pinhole) X 514

if we have a pinhole of 0.4mm then

82.24mm = 0.4mm X 0.4mm X 514

or an ideal focal length of 82mm is found.

Constants for other types and colors of light:

Daylight (560nm) 514
Blue (450nm) 640
Green (550nm) 523
Red (650nm) [also used for tungsten] 443
Infrared (750nm) 384

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