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DSLR camera for astronomy?

Has Canon or any other maker come out with a replacement for its 20Da camera, which was modified for astronomical imaging?

--Gerry Ziemann, Oconomowoc, Wisc.

Unfortunately, there is no direct replacement for the Canon 20Da. It was a regular 20D with a wider passband infrared filter and other features added (S&T: November 2005, page 84). Digital cameras normally have an infrared-blocking filter built in, to provide a natural color balance for ordinary photography. But for deep-sky astronomy you want all the very-far-red light you can get, especially to catch the deep red hydrogen-alpha emission from nebulae. Typical filters built into digital cameras cut off the red end of the spectrum before this wavelength (656.2 nanometers), because the human eye isn't very sensitive to it.

I suspect that Canon dropped the 20Da because the astronomy market was too small. However a few companies, such as Astro Hutech ( and Hap Griffin (, will modify your mainstream DSLR to increase its IR transmission at reasonable cost.



Also, Astronomik ( offers clip-in filters for most Canon DSLR cameras with a variety of passbands to suit your needs. See last month's issue, page 43.

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Title Annotation:Astro Q&A
Author:Walker, Sean
Publication:Sky & Telescope
Article Type:Brief article
Geographic Code:1USA
Date:Feb 1, 2009
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