ASI120MC and DSO's revisited

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ASI120MC and DSO's revisited

Post by turfpit » Tue Jan 02, 2018 2:49 pm

The following are captures from mid December. SharpCap 3.1 beta was used for capture. The application of darks and flats; Debayering (demosaicing) and stacking were carried out in Nebulosity. The post processing of the stacked images was carried out in Photoshop 2018. I have been learning how to use PS, hence the delay in publishing these images.

Some objects worked well, others not so good but I have ideas to try next time I am outside.

All the images were captured using these settings:
  • 100 x 15s
  • gain=20
  • brightness=10
  • 1280 x 960
  • RAW16
  • output to FITS format
100 dark frames with the above settings were also captured, together with 100 flat frames.

Debayer pattern used was BGGR - obtained from the 'Image Headers' tab in FITS Liberator.

The following attached items apply to all the images below:
  • Camera settings file
  • Sharpcap capture screen showing histogram
  • FITS capture file histogram shown in FITS Liberator
Equipment used was:
  • Celestron C8 SCT with CG5 Advanced GT equatorial mount
  • TS 0.5x focal reducer
  • no filters
  • ZWO ASI120MC USB2 camera
  • Toshiba C50 Satellite Pro, i3, 4Gb memory, 500Gb drive, Win 10 64-bit, £140 off eBay
Focusing was achieved by use of a Bahtinov mask.

M42 with M43
M42 with M43.png
M42 with M43.png (127.94 KiB) Viewed 791 times
This image was OK, plenty of nebulosity and the 4 stars of the Trapezium visible. I also converted this image to mono within Photoshop.

M42 mono.png
M42 mono.png (79.06 KiB) Viewed 791 times

M82 Cigar Galaxy
M82 Cigar Galaxy.png
M82 Cigar Galaxy.png (62.27 KiB) Viewed 791 times
I think this is my best M82 to date, plenty going on in the galaxy core. I think I might need to re-focus more often during the longer imaging sessions.

M81 Bode's Galaxy
M81 Bode's Galaxy.png
M81 Bode's Galaxy.png (111.68 KiB) Viewed 791 times
This was the first time I have managed to capture any of the fainter nebulosity for this object. My first process run in Photoshop gave just the bright centre but subsequent attempts using repeated small application of 'Curves' managed to bring out the faintness. I will retry this object with longer exposures/increased gain (as separate changes) as the histogram was not as 'full' and 'stretched' as the M42 histogram.
M81-FITS-histogram.PNG (4.08 KiB) Viewed 791 times

M52 Open Cluster in Cassiopiea
M52 open Cluster in Cassiopeia.png
M52 open Cluster in Cassiopeia.png (65.67 KiB) Viewed 791 times
A reasonable image, next time I will try increased exposure/gain to see if I can capture more stars.

M78 in Orion
M78 in Orion.png
M78 in Orion.png (120 KiB) Viewed 791 times
This image is fainter and so is going to need longer exposures and/or increased gain. More experimentation needed here.

M76 Little Dumbbell Nebula
M76 Little Dumbbell nebula.png
M76 Little Dumbbell nebula.png (83.5 KiB) Viewed 791 times
This image is fainter and so is going to need longer exposures and/or increased gain. More experimentation needed here.

M1 Crab Nebula
M1 Crab Nebula.png
M1 Crab Nebula.png (120.1 KiB) Viewed 787 times
This image is fainter and so is going to need longer exposures and/or increased gain. More experimentation needed here.

For this object, I used the display histogram stretch to check that I had the faint nebula in my display.
display-histogram-stretch-demo.PNG (42.19 KiB) Viewed 787 times

In summary, by analysing the results of previous imaging sessions, I feel that things are moving (slowly) in the right direction for me.

The previous forum post I made using the ASI120MC for DSO's had me using gain=80. By reducing the gain to 20, I have, for the brighter objects, managed to obtain improved images which were less noisy and hence needed less post processing.

Please ask if there is anything I have missed out or not made clear in the write-up.

M42-100x15s-FITS-histogram.PNG (179.69 KiB) Viewed 791 times
M42-capture.PNG (186.08 KiB) Viewed 791 times
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