🚀 go-pugleaf

In <1992Nov12.235528.2939@elroy.jpl.nasa.gov> jack@robotics (Jack Morrison) writes:

>>The second CCD camera question deals with the CCD's response to IR.
>>What is the response curve of a CCD camera?  How quickly does the CCD's
>>sensitivity taper off as the frequency of the light drops below visible
>>and into IR?   And how come I can see the IR on my monitor/view-finder?
>>(try pointing your TV remote at the cam-corder).  My potential application
>>is a pseudo-night-vision device.

>It depends on the CCD used, and the optical filters in front of it that
>make specific CCD elements sensitive to red, green, or blue. But as you've
>observed, they do see some IR. Your monitor displays this signal as
>visible image (TV remote IR LED's are actually pretty bright).

>As far as night-vision, all you can do is experiment. Find a bright non-visible
>IR light source (no, LED's aren't *that* bright!) and see what the camcorder
>can see. Good luck!

CCDs are reasonably sensitive to near IR at room temperature. Get them
cold (liquid nitrogen), and they're even more so; I have an astronomer
friend who uses cooled CCDs as his IR image sensors.

Camcorders have a filter (either a separate one or as a side-effect of 
the color filters used in color camcorders) which cuts out a lot of the IR.
Trivia note: of the three color filters, the blue one seems to be most
transparent, as an IR LED shows up as a bluish color (at least on my
camcorder). Not exactly what one would expect...

I have a Fisher Price PXL2000 kiddie camcorder (b&w) from which I've 
removed the IR filter, which was a tiny square of very light blue-green 
glass/plastic. It's now pretty sensitive to IR; I can go into a dark
room with an IR source and I can see my way around.

The IR source? I use a flashlight with one piece each of red, green, and
blue filter plastic on top of each other. That cuts out almost all of
the visible light, but it's almost transparent to IR (again, not what
you'd expect!), so you can barely see the flashlight with the naked
eye, but the CCD picks it up great! It's also surprising what you can
see with a TV remote control. I haven't yet tried it with an array of
LEDs.

My suggestion: find yourself a cheap b&w camera - I have a 3.5x2.5x1.0
inch camera I got at a hamfest for $125 - and see if it has an IR filter
you can remove. Hook it up to a camcorder video monitor, and you have an
IR viewer you can use with the above-mentioned flashlight setup.

Happy viewing,
Rick

-- 

Rick McTeague
Electrical Engineering Department, Speed Scientific School
University of Louisville, Louisville, KY 40292
(502) 588-7020

Internet: sysrick@starbase.spd.louisville.edu

Disclaimer: I'm a stand-up comedian; if anyone takes me seriously, I'm
            doing something wrong!