IR Exposure meter

[kenneth.r.rockwell@xxxxxxxxxxxxxxxx]

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Original Text
>From tom@xxxxxxxxxxxxxxxxxxxxxx (Tom Benedict), on 7/19/96 3:25 PM:
To: <kenneth.r.rockwell@xxxxxxxxxxxxxxxx>

So has anyone gone out and made an IR light meter?  Most silicon photo
diodes that have been optimized for IR performance usually cut off
just past 9500A anyway, so it seems like it would be pretty well suited
for most of the IR films.  So long as you metered through the same filter
that's on the camera, and calibrated the meter through careful bracketing,
it seems like it would save on film in the long-run.

Tom
Tom and all - 
                 I was just thinking about an IR light meter just last 
night.  Designing and making one would be as simple as designing any other 
light meter.  Since IR is such a teeny market no has bothered to introduce 
one comercially.

Even better, some conventional light meters based on silicon photo diodes 
(which are more sensitive to IR than visible light) actually have IR CUT 
filters in them to optimize them to conventional film.  A real great thing 
is for someone to find a meter like that and pull out that filter!

Almost all CCD imagers for video have IR cut filters for exactly that 
reason; the colors would really look bad if that filter wasn't there.  That 
is the first part to crack if a video camera is left pointed at the sun to 
long, obviously.

Has anybody tried the obvious of taping an 87 filter over a conventional 
meter and changing the ASA accordingly?

I'd suggest interested people try to get hold of an optical company who 
specialize in these sorts of filters and ask them for reccomendations.  
They just may make a filter especially designed to "trim" a "detector" to 
optimize it for IR work.  Try to get a hold of OCLI, who last were at 2789 
Northpoint Parkway, Box 1599, Santa Rosa, CA 95402-1599  (707) 545-6440 and 
try to get hold of an applications engineer.


Ken Rockwell
kenneth.r.rockwell@xxxxxxx

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Topic No. 19