SaratogaSkies Jim Solomon's Astropics


Latest news

December: Test shots with new scopes/mounts

Dec 21: TMB 80/480 Arrives!

Dec 3: AP1200 Arrives!

Nov 30: TMB 152/1200 Arrives!


B33 (Horsehead 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: Orion ED80 (80mm f/7.5 APO Refractor)
Configuration: Focal Reduced
Additional Optics: William Optics 2" APO 0.8x Reducer/Field Flattener
Filter: Hutech Hα Front Filter (HA-FF)
Effective Focal Length: 480mm
Effective Focal Ratio: f/6
Exposure: 21 x 8min @ ISO 800 (RGB), 29 x 8min @ ISO 1600 (Hα)
Total Exposure: 6hrs, 40min
Date: 2/21/2006 (RGB); 12/28/2006 (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, reflection removal, JPG conversion
  • Neat Image: Noise reduction

Image Description:

This is an update of my previous Horsehead Nebula image, with nearly 4hrs of Hα exposure added to the existing RGB data. The Hα really helps bring out many of the features in this busy field.

To create the HαRGB composite, I first added some Hα into the red channel of the original RGB data, which was then converted to Hue, Saturation, Luminance. Then I used a process similar to Photoshop's “Screen” blending mode to combine the luminance of the original RGB data with the (grayscale) Hα data. This Screen-blended Luminance, along with the Hue and Saturation of the Hα-enhanced RGB image, was then converted back to RGB. This method seemed to preserve details in the non-Hα-emitting regions, provide excellent detail in the Hα regions, and preserve the colors.

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