Brett,
as you know, one advantage/disadvantage of CCD sensors is
they are sensitive to all visible bandwidths and quite deep into the
IR as well as UV.
This is great for astro work because of the Hydrogen Alpha being
up in that IR. But it's downside for daylight cameras and handicams is
that the lenses have trouble focusing all of that at once on the chip.
Webcams for example will focus the RGB well but the IR still coming
through if you remove the IR filter will make the IR component of a star's
light blurred on the chip. It has a different focus point.
I pulled a few handicams and webcams apart years ago to test their
IR filters. Not all IR filters work the same. Depends on whether they
are interference types or not. One type is a greenish glass/plastic and
the other are a red tint.
About halfway down this page is a comparison of filters using a cheap,
rough webcam spectroscope.
http://jfbo.webs.com/cdspectroscope.htm
Also attached is a star image with and without the IR filter.
Note the IR unfocused halo. This is from an M type star, one with a
lot of red and IR light. Note the tighter focus on most stars
also with a filter. I took this through a modded webcam.
Steve