(meteorobs) OT -Test on CCD IR & Fireball bloom.
stange
stange34 at sbcglobal.net
Wed Nov 26 05:37:19 EST 2008
Since the daylight camera is down for retro-fit, I ran some repeat testing
on it in regards to the excessive meteor & fireball bloom from near to the
far INFRA-RED. The results are a disaster, but there is an easy solution for
non-AllSky camera's.
The purpose of this test is to see to what extent CCD cameras +& their
pictures distort the appearance of a fireball as compared to what the eye
would see during the same event.
This test also included a black IR dome transparency test as normally found
in casino's or in surveilance use. To sum this particular test quickly,
those IR domes are just super dark sunglasses with little transparency in
visible light. It takes a low light camera to have any chance on seeing
through them at all. But as far as infra-red goes, they are completely
transparent, like nothing was there at all! --Rather useless for meteor work
except in special applications. Now back to the main IR test....
This main test was conducted on a typical 1/3 CCD HAD camera with two
lenses. One lens is an auto iris, the other is a fixed iris. Both were about
8mm focal length. One purpose of this test was to determine if excessive IR
bloom would cause an iris to automatically reduce aperature during a bloom
thus diminishing background detail or fireball detail. A reference LED light
was used which had little IR transmission as a control. Throughout the
testing the reference light diameter & intensity did not change which means
no background detail will be diminished from most bright fireballs.
A Baader IR blocking camera filter is used in this test for image comparison
of a hot object to that same object without an IR blocking filter. Our
individual eyes can expect to see a fireball or hot object the same as would
be seen by a camera with an IR blocking filter.
This link to my website contains several graphs and a summing photo of the
test.
http://www.geocities.com/stange34@sbcglobal.net/CCD_IR
Graph (A) depicts the eye response to color wavelengths in nanometers.
Graph (B) depicts where the visual colors are in a broad spectrum UV thru
IR.
Graph (C) depicts the typical bandpass response of a CCD camera compared to
colors.
(Notice how far into the infra-red the CCD camera can see. Far beyond what
we see.)
Graph (D) is the IR blocking filters response. Nearly perfect in the visible
spectrum with excellent blocking of most IR.
Photo (E) is pictures taken in a totally dark enviornment with a burning
cigarette as the IR source with and without an IR filter in front of the
camara lens and using both lenses. Focus was not perfect on the fixed iris
lens, but that is not the issue. Detail WITHIN this infra-red source
IS. --Notice dark ash is clearly outlined within the heated areas with a
filter.
Are we missing something important in our fireball pictures taken with a
CCD?....
YCSentinel
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