On Aug 4, 1:30 am, Unclaimed Mysteries
theletter_k_andthenumeral_4_...@unclaimedmysterie s.net wrote:
Wayne J. Cosshall wrote:
Hi All,

I've been experimenting with using a circular polarizing filter when
shooting digital infrared images:
http://www.dimagemaker.com/article.php?articleID=1053

Can Digital HDRIR be far behind?

Ever tried using a pair of crossed linear polarizers? As you approach 90
degrees, the spectrum of light that makes it through apparently gets
weighted toward the red and IR. Not an appealing prospect to add these
to a filter stack, and the pair didn't substitute well for the IR pass
filter, but I was amused anyway.

Observed with unmodded Sony F828 in "nightshot" mode. Crossed linear
polarizers stacked with IR pass filter, in an attempt to reduce the need
for additional ND filters. (Yeah I know, I should just go get the thing
modded)

Imagine my surprise when I saw the IR target scene not fade at all as I
approached 90 degrees.

Several filters have unexpected effects when used outside their intended
spectra. A Hoya X1 *green* filter is more effective at attenuating IR
than yer basic 2 or 3 stop ND filter.

Why use any of that junk when you can buy interference filters that
have almost dead-stop cutoffs at any wavelength you'd like? You can
get cutoff filters, narrow band filters or even notch filters, all
with steep attenuation and throughput.


YMMV. HTH. HAND.
C.

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