From: "Duane" <macastronomer@mac.com>
Date: April 12, 2008 11:20:09 PM MDT
To: Astro_IIDC@yahoogroups.com
Subject: Re: IR filter with a DMK color .AS camera?
Yea, that's really the first and foremost reason to use one. I can color correct with the best
of them. Show me an off color photo and I'll set it right. A fuzzy photo is a completely
different puzzle. Anything you do to fix fuzz always has a drawback. Better to do
everything possible to avoid it in the first place.
--- In Astro_IIDC@yahoogroups.com, "larry.towers" <larry.towers@...> wrote:
The IR filter isn't just for color correction. The focal length of
lenses depends on the wavelength. Lens manufacturers compensate for
this with achromatic lenses but these only work within the visible
light spectrum. A lens focused in visible light will be somewhat
off-focus in infrared, If your ccd picks up infrared it will be out of
focus with respect to visible light. This will be especially true if
focus on the object is very critical. There will seem to be a
"glowing" aspect to the images you capture. The only reason Not to use
an IR blocking filter is when you specifically want IR capture, or you
want that subtle softening effect.