Re: IR filters

[Steve Patriquen <patriquen@yahoo.com>]

Hmmm...

There are a couple of ways of referencing filters. Lay-speak would
call a red-colored filter a "red filter" when it actually "filters out
cyan light" (the complement of red).

An IR filter would probably filter OUT IR (often used in photo
projectors/enlargers). What we want is an IR-only *pass* filter -
correct? Something that will reduce the visble light but pass all the
IR to blind the Laser.

These filters typically appear almost black to the eye in color (both
reflected and transmitted light).

I would also guess that we'd want to run high-wattage bulbs behind
these filters. Since the filter would have to absorb about 1/3 the
radiation from a tungsten bulb (handy for us, the other 2/3 is IR) - I
would guess they would get pretty darn hot - way more than 100C -
unless spaced a distance from the bulb/reflector (with resulting light
leak perhaps). I would look for glass filters to avoid meltdown.

A more elegant solution (any geniuses out there?) would be a dichroic
mirror that would reflect only IR. The rest of the bulb's energy could
be directed into an air-cooled baffle box. The mirror would not have
the fading problems a filter will sufer from.

Seems to me a company like PIAA could make a nice killing by offering
an IR accessory light. Really quite simple for a company light that.
The reflector could be the dichroic mirror and the lens the IR pass
filter. 

Do I have to do everything myself?

Steve P - 98.5 A4TQMS - 97 Passat GLX - 94 Kawa ZG1000
==
Steve Patriquen - Training consultant - UNUM America - Portland, ME - (207) 770-7187
Work e-mail (mainframe, no attachments) <patriquen@e-mail.com> 
Personal/travel e-mail <SPatriquen@aol.com>
Large files (cable modem) <spatric1@maine.rr.com>

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