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Re: IR measurement trick...ery?
In a message dated 3/30/00 3:32:08 PM Eastern Standard Time,
earthsoda@yahoo.com writes:
> Do ordinary light meters have the ability, even
> weakly, to sense IR?
Hi Ray,
I don't do IR myself, but your questions raised my curiosity, so I checked
"Photographic Materials and Processes" by Stroebel, et. al. It has the
spectral sensitivity curves for selenium, cadmium sulfide, and silicon cells
used in light meter.
According to the curves, selenium almost has no sensitivity in the IR region.
CdS has some sensitivity (looks like usable), and Si cells have *high*
sensitivity in the IR region. In fact, in normal use, the Si cell must be
covered by a blue filter so that its sensitivity matches closer to
panchromatic film. I suppose if one can replace this blue with IR filter, one
should be able to calibrate it for IR use.
My Stroebel's book is 1st edition, and the curves are on p. 114.
Dave Soemarko