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.