SharpCap Forums

This image was captured in the car park of the local village hall at an Astro club meeting. Nebulosity was targeted at the expense of star saturation. Full image here https://www.astrobin.com/393472/ .


Equipment: Altair 66ED refractor, 0.8x reducer/flattener, Altair 183M camera, Celestron CG5 mount.
Software: SharpCap 3.2, FITS Liberator, SiriL 0.9.10, Gimp 2.10.
Capture: 60x60s, 33 darks, 100 bias, 100 flats. *Unguided*.

Mount alignment was achieved with polar scope, 2 alignment stars, 4 calibration stars and an All Star Polar Align. Focus was with a Bahtinov Mask.

SiriL: calibrate, register, stack frames, background extraction, apply histogram transformation and export to TIFF.
GIMP: Curves, levels, shadows-highlights, contrast, slight noise reduction.

The black level setting of 30 in SharpCap was decided by taking a single bias frame and using the minimum black level setting which gave a centralised/balanced histogram in FITS Liberator.


I have been looking into using background extraction in SiriL to process with sky gradient due to light pollution or moon light. The rainbow colour map shows the gradient to good effect. The images below are before and after background extraction has been applied.


If I get a chance, I will repeat this capture with 120x 30s exposure to experiment with the star saturation.

Dave


[ALTAIRH183M]
Output Format=FITS files (*.fits)
Capture Area=5440x3648
Binning=1x1
Pan=0
Tilt=0
Colour Space=MONO12
Fan=On
Temperature=4.7
Black Level=30
USB Speed=1
Auto Exp Target=144
Frame Rate Limit=Maximum
Analogue Gain=200
Exposure=60000
Timestamp Frames=Off
Banding Threshold=35
Banding Suppression=0
Apply Flat=None
Subtract Dark=None
#Black Point
Display Black Point=0
#MidTone Point
Display MidTone Point=0.5
#White Point
Display White Point=1
TimeStamp=2019-02-27T20:47:04.5830221Z
SharpCapVersion=3.2.5926.0

It amazes me that you can capture that much nebulosity so low to the horizon given your latitude and light pollution constraints.

Brian

Lucky Imaging perhaps Brian? I can use this image to help sell the CG5 mount (proves it can do 60s exposures for an hour unguided) in order to fund the next piece of kit. The Clear Outside weather app had me at Bortle 7 at the location this image was captured.

Getting to understand the background extraction tool in SiriL has helped. There is an 'auto' mode but I have had better results from 'manual' mode. By selecting a smaller box size and making sure that the boxes are not placed on any stars or nebulosity seems to give a good improvement to the resultant image. This is the box placement:


Once there is a background model with no signal from the nebulosity, the correction can be applied.


The effect on the rainbow colour map can be seen in my original post. Once the histogram transformation has been applied, there is fairly minimal post-processing to be done in GIMP.

Dave