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Thursday, March 31, 2016
I have published a photo of the Lower's Nebula in mapped colors about a week ago. Now I'm publishing the same nebula as a visual natural color version. Narrowband emission from hydrogen, oxygen and sulfur (H-a, O-III and S-II) are combined so, that the result is very close to a visual spectrum. Since the ionized hydrogen emits red light and it usually dominates nebulae, images are more or less red. Blueish hues are from ionized oxygen, O-III. Sulfur, S-II, emits red too and it get mixed to a hydrogen emission visually.
Click for a large image
Image is in natural colors from the light emitted by an ionized elements, sulfur, hydrogen and oxygen.
The Sh2-261 (Sharpless 261), also known as the Lower's Nebula, is a faint region of doubly ionized hydrogen. Its apparent dimension is about 50 arcminutes in East-West direction and 30 arcminutes in North-South. So, it has an apparent size about twice the full Moon diameter. Of course the real size of the nebula is much larger! But we have no information about the distance of this hydrogen cloud, so we are not able to determine how large it is. (Source, www.skyfactory.org)
Processing work flow
Image acquisition, MaxiDL v5.07.
Stacked and calibrated in CCDStack2.
Deconvolution with a CCDStack2 Positive Constraint, 21 iterations, added at 25% weight
Color combine in PS CS3
Levels and curves in PS CS3.
Celestron Edge HD 1100 @ f7 with 0,7 focal reducer for Edge HD 1100 telescope
Cameras and filters
Imaging camera Apogee Alta U16 and Apogee seven slot filter wheel
Guider camera, Lodestar x2 and SXV-AOL
Astrodon filter, 5nm H-alpha
Astrodon filter, 3nm O-III
Astrodon filter, 3nm S-II
H-alpha, 9 x 1200s =3h
O-III, 3 x 1200s binned = 1h
S-II, 3 x 1200s binned = 1h
A single uncropped, calibrated and stretched 20 min. H-alpha frame as it comes from the camera