SaratogaSkies Jim Solomon's Astropics


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NGC 6960 (Cirrus Nebula)

[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: 30 x 8min @ ISO 400 (RGB), 30 x 8min @ ISO 1600 (Hα)
Total Exposure: 8hrs, 0min
Date: 9/17/2006 (RGB); 9/19/2006 (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, White balance, HαRGB combination, ASINH stretching
  • Photoshop: Levels, cropping, sharpening, JPG conversion
  • Neat Image: Noise reduction

Image Description:

This is NGC 6960, aka the Cirrus/Filamentary/Lace-work Nebula and the Western portion of the Veil Nebula, a supernova remnant in the constellation of Cygnus. This image consists of 4hrs of RGB exposure and 4hrs of Hα exposure over two nights.

Unlike my previous Hα+R G B images, in this one I used Hα for Luminance, and the RGB data for color after first blending a smidgeon of Hα into the Red channel. I suppose that makes this technically an Hα:Hα+R:G:B image. Using Hα for Luminance gives a very high contrast result, with added benefit of attenuating the star field which otherwise tends to overwhelm the rather faint nebula. And blending a bit of Hα into the Red channel prevents the salmon-i-zation (salmonella!? <g>) — i.e., the washout — of the red region that results from simple luminance layering in Photoshop. Robert Gendler has an explanation of this technique at his web site. Mousing-over the image shows the RGB stack, without any of the Hα data. Notice how the Veil tends to get lost in the Milky Way star field in that RGB-only image.

A higher-resolution image is also available. North is left.