SaratogaSkies Jim Solomon's Astropics


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M51 (Whirlpool Galaxy)

[Hα+R G B]

Mouse-over to see annotations. (Requires Javascript) Click to see high-res version.

Image Details:

Camera: Mofidied Canon Rebel XT (350D): Hutech Type I Filter Replacement
Mount: Celestron AS-GT
Scope: Celestron C8-N (8" f/5 Newtonian)
Configuration: Prime Focus
Additional Optics: Celestron/Baader Multi Purpose Coma Corrector (MPCC)
Filter: Hutech Hα Front Filter (HA-FF)
Effective Focal Length: 1000mm
Effective Focal Ratio: f/5
Exposure: 31 x 4min @ ISO 400 (RGB), 23 x 8min @ ISO 1600 (Hα)
Total Exposure: 5hrs, 8min
Date: 5/11/2005 11:28:24 PM PDT (RGB); 6/16/2006 10:11:42 PM PDT (Hα)
Location: Saratoga, CA, USA
Acquisition: DSLRfocus
Focus: DSLRFocus
Dithering: GADFly 1.0.5
Guiding: GuideDog via Philips ToUcam Pro II (840k) through Orion ST80 w/ Celestron 2x "Kit" Barlow


  • IRIS: Dark subtraction, registration, gradient removal
  • JimP: Flat field, Kappa-Sigma Stacking, HαRGB Combination, White balance, ASINH stretching
  • Photoshop: Sharpening, Levels, cropping, JPG conversion
  • Neat Image: Noise reduction

Image Description:

This is M51, aka the Whirlpool Galaxy in the constellation of Ursa Major. This is Third Light <smile> for my Hutech Hα Front Filter (HA-FF). For RGB data, I used my M51 image from last year, taken with an unmodified 300D. The image above is that same image with ~3hrs of Hα taken with the modified 350D. The Hα regions are the small, cherry-red regions in the spiral arms of M51. Note that mousing-over the above image, in addition to displaying the object labels, will switch back-n-forth between the HαRGB image and the standard RGB image, very clearly showing the effect of the additional Hα data. See the full-resolution image for a better view of these regions. North is up.