NGC 1893 and SH 2-236

The open galactic cluster NGC 1893 is located in the star constellation Auriga. NGC 1893 is a nice cluster of stars forming a few elliptic chains of stars. It looks as if the star chains are aligned along a virtual swirl. The cluster is embedded in the nice but very faint H II region SH 2-236. Larger exposure times and a dark night usually are needed to obtain such a pretty image.

The collection of images has been taken in twilight. Therefore most images have a certain offset of bright sky, that has been subtracted to obtain an image with "dark sky". Seeing conditions were bad. Half of the images collected have been rejected due to strong artefacts of the star images. The average seeing blur is estimated between 3" and 5" (arcseconds). The procedure of rejection of images with bad seeing sometimes is called lucky imaging. In this case the images have been manually selected by visual inspection. A noise reduction was applied to correct a certain line bias noise found typical with any DSLR. Color processing done with Photoshop CS3.


Telescope:Vixen VC200L, focal reducer f/6.4, Sphinx SXD
Camera:Canon EOS 60D, clear glass modification (internal filter removed), 400 ASA
Filter:Astronomik UV/IR EOS block filter
Exposure:20 x 30s
Calibration:Dark (100 images), Sky-Flat (50 images)
Image Processing:Shift & add with correction of subpixel movement, improved noise reduction
Date of exposure:06 March 2011
Software:ArgusPro SE, color saturation enhanced with Photoshop CS3


Seeing was larger than 4" (average)

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