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Tuesday, March 17, 2020

A rare image, Sharpless 205 and NGC 1491 in constellation Perseus

The imaging season is getting shorter up here 65N, in a  few weeks we run out of an astronomical darkness for about six months.

Sharpless lays high at South East at around  nine o'clock  I can shoot it about five to six hours before my view gets blocked by a punch of antennas and the wall. I have about six degree field of view in my current imaging system, the Sh2-205 and NGC 1491 next to it fits very well in my field.

This is a very dim target, undersampled optical configuration, binning and a longish integration time helps to bring out details and faint surrounding nebulosity. I haven't seen many photos about this target around. Total exposure time 18 hours. (Note! 15 hours of it was shot binned down 2x2, that gives equal signal as 60 hours of 1x1 binned exposures!)

Sharpless 205 & NGC 1491
Click for a large image (~1300 x 1300 pixels)

Mapped colors from the emission of ionized elements, R=Sulfur, G=Hydrogen and B=Oxygen.

H-alpha channel alone, labeled

Click for a large image

Image in light emitted by an ionized hydrogen (H-alpha emission line)

A 1:1 closeup

Full resolution detalji, NGC 1491 at middle up

An older long focal length image of  NGC 1491

Click for a large image

Image from Spring 2015, more info here,

NGC 1491 is a very dim target in Perseus. Original image from the Spring season 2015. Image is reprocessed, about twenty hours of new data added from the new wide field image. (Unpublished) Added data is very dim background glow from ionized hydrogen, sulfur and oxygen, it's pretty featureless so difference in resolution does no harm the image. The final photo is now deeper with better colors.


Sharpless 205 (Sh2-205) is a very dim emission nebula in constellation Perseus. The brighter peanut shaped area at the middle is known as Sharpless 205. 

NGC 1491 is a little brighter emission nebula that lays at upper right corner of the image. It has a distance of about 11.000 light years from Earth. A strong stellar wind from a star BD +50 ° 886 is blowing the gas away. The radiation from the star makes the gas glow by ionizing elements in the nebula.

Technical details

Processing workflow

Image acquisition, MaxiDL v5.07.
Stacked and calibrated in CCDStack2.
Deconvolution with a CCDStack2 Positive Constraint, 33 iterations, added at 50% weight
Color combine in PS CS3
Levels and curves in PS CS3.

Imaging optics
Tokina AT-x f2.8 camera lens

10-micron 1000

Cameras and filters
Imaging camera Apogee Alta U16 and Apogee seven slot filter wheel
Guider camera, Lodestar x 2 and an old spotting scope of Meade LX200
Astrodon filters,

5nm H-alpha 3nm S-II and 3nm O-III

Total exposure time 18 hours 
(15 hours was shot binned down 2x2, that gives equal signal as 60 hours of 1x1 binned exposures!)

H-alpha, 15 x 1200 s, binned 1x1 = 5 h
H-alpha, 21 x 1200 s, binned 2x2 = 7 h
O-III, 9 x 1200 s, binned 2x2 = 3 h
S-II, 9 x 1200 s. binned 2x2 = 3 h

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