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A useful DSLR camera modification.

Having decided to begin digital imaging of stellar spectra with a DSLR camera and after initially obtaining disappointing results, I wondered if removing the infrared blocking filter would improve the blue as well as the red end sensitivity of the CCD sensor? In theory it should, so I purchased a Canon Rebel 300D with the IR blocking filter removed, and took comparison spectra of Vega through this and a Canon EOS 400D (unmodified). I used a Rainbow Optics Star Spectroscope, 200 lines/mm, at the prime focus of my 0.3m Newtonian reflector, a drift time of 20sec across the field of view at ISO400, RAW image setting for each camera, on 2010 Nov 15.

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The answer to the question is yes; removing the infrared blocking filter does improve the spectral sensitivity of the CCD sensor at both the blue and red end, as seen from the results. This has interesting implications for deep sky astrophotography and I encourage people to have a go.

Jack Martin

[jackmartin78l@googlemail.com]

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Title Annotation:Observers' Forum
Author:Martin, Jack
Publication:Journal of the British Astronomical Association
Article Type:Brief article
Geographic Code:4EUUK
Date:Apr 1, 2011
Words:171
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