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Wednesday, March 25, 2020

Sharpless 205, NGC 1491 and Lynds Bright Nebula 696 in visual spectrum

I haven't seen any color photos out of those two large nebulae in this image, SSh2-205 at left and Lynds Bright Nebula 696 at right edge of the photo. The astronomer
Richard Perabo Wilds Helped me to recognize this object, many thanks for him! (NOTE, South is up.) I have publish a mapped color version couple of days ago, it can be seen here,

Sharpless 205, NGC 1491 and  Lynds Bright Nebula 696
You really should click the photo to see the large image!

Visual colors from narrowband channels, H-alpha, O-III and S-II, red emission from ionized  hydrogen is dominating the view, there are some bluish hues from am ionized oxygen too. Star colors are from narrowband channels.

H-alpha channel alone
Click for a large image

This grayscale photo shows only the light emitted by an ionized hydrogen. (H-alpha)
I actually like grayscale photos very much, somehow they are much more delicate to the subject.


This must be one of the dimmest targets I have shot so far. There are very weak emission from the ionized oxygen and sulfur, so I was able to make a three band color composition.
There are lots of 20 min. sub-exposures, total exposure time for H-alpha emission is 25h, for O-III 9h and for S-II 9h. Total 43h from several nights between 28.02 and 21.03.
Total exposure time is 43 hours but the effective exposure time is much more 30 hours of of sub-exposures was taken as binned down to 2x2.  It means that four pixels act like a one pixel, the resolution drops to 1/4 from original but the signal is four times stronger. When binned down 2x2 the signal in 30 hours of exposure has as strong signal as in 120 hours of exposures at binning level 1x1!

My imaging system works better than I thought when I build it. Old Tokina AT-x 300 mm f2.8 camera lens, Astrodon narrowband filter set (H-a 5nm, O-III 3nm & S-II 3nm) and Apogee Alta U16 astro camera with 9 microns pixel size and 4096 x 4096 pixel CCD array. This gives me spatial resolution of about six arc seconds / pixel. Undersampling is a great thing, if you want to capture some very dim nebulae in relatively short time!

I was using my VARES imaging method to this photo. (VAriable RESolution imaging) All the high signal/noise elements, like stars and brighter parts of the nebula are from binning level 1x1. Lower signal/noise elements, like dim background glow and dimmer parts of the nebula clouds, are from binning level 2x2. Lower binning modes, like 4x4 or 8x8, was not used this time. There star field is way too dense at 300mm focal length when shooting at 6 arch seconds / pixel.


This really is a large target, it spans about eleven degrees horizontally.

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

Left half of the mosaic image above as an individual artwork.

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.

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 43 hours 
(30 hours was shot binned down 2x2, that gives equal signal as 120 hours of 1x1 binned exposures!)

H-alpha, 15 x 1200 s, binned 1x1 = 13 h
H-alpha, 21 x 1200 s, binned 2x2 = 14 h
O-III, 9 x 1200 s, binned 2x2 = 8 h
S-II, 9 x 1200 s. binned 2x2 = 8 h

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