ASI120MC and Deep Sky Objects

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turfpit
Posts: 81
Joined: Mon Feb 13, 2017 8:13 pm
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ASI120MC and Deep Sky Objects

Post by turfpit » Sun Sep 24, 2017 10:41 pm

Last Thursday/Friday (21/22 Sept 2017) promised a clear night with 1 hour partly cloudy around 23:00. :lol: So the plan was to try to capture some DSOs, using the ZWO ASI120MC, in the following order (so as to minimise slewing the mount) - M57, M27, NGC7000, M33, NGC7635, M52, M82, M42.

The experiences of the imaging session are detailed below, including the problems and failures. There are no APODs in this post - more like a master class in image mangling.
  • Equipment used was a Celestron C8 on a CG5 mount, ZWO ASI120MC camera, TS f6.3 reducer, no filters.
  • Capture laptop was a (new to me) Lenovo ThinkPad X220 with 4gb RAM (upgrade pending), 480Gb SSD, running Windows 10 Pro 64-bit.
  • The rig was powered via a 75Ah leisure/marine battery. The laptop had 2 batteries, so these were swapped during the session.
  • Capture software used was SharpCap 3.1 latest alpha build.
  • Post processing software used was Nebulosity v4.1 for stacking and image processing.
  • For the M42 captures, the 100 and 338 frames were also stacked using Autostakkert v2.9.5 and resultant image processed in Nebulosity. The outputs are compared below.
  • Dark frames were taken (cap on the camera) prior each to capture set and dark frame subtraction was applied during capture. This kept the temperatures for the darks and lights fairly matched.
  • Flat frames were not used (dust motes could be dealt with by using the 'clone tool' in Gimp 2.9.5).
  • Mount polar alignment was via polar scope, followed by a 2 star align to the west of the meridian and 4 calibration stars to the east of the meridian. The mount alignment was carried out with the f6.3 reducer and ASI120MC attached to the scope, with the reticule turned on in SharpCap.
  • All captures were 1280 x 960.
It was intended to stack with Deep Sky Stacker but I kept getting "only one frame to stack". I have used this successfully before but the difference was that in previous processing runs, the dark frames were applied at stack time rather than at image capture time. Hence the Plan B of Nebulosity - had to learn how to use that as well!

The stacking process followed in Nebulosity was:
  • Batch > Normalise Intensity
  • Batch > Align & Combine (translation)
  • Batch > Align & Combine (save stack with Std. Dev. filter 1.5), FITS file produced.
The post stacking image processing steps were:
  • All objects except M42 were binned 2x2:adaptive (after some experimentation)
  • Image > Crop image to remove stacking artifacts
  • Image > Adjust Colour Background (offset) to remove skyglow
  • Image > Digital Development
  • Image > Levels/Power Stretch (small increments repeated)
  • Image > Curves (small increments repeated)
  • Image > Sharpen/blur image > Tighten star edges
M57
50 frames, RAW8, 30s exposure, gain = 80%, brightness = 50%, colour balance auto.
These settings seemed to have produced a satisfactory image.

M57 Ring Nebula.PNG
M57 Ring Nebula.PNG (50.14 KiB) Viewed 99 times

M27
50 frames, RAW8, 30s exposure, gain = 80%, brightness = 50%, colour balance auto.
These settings seemed to have produced a satisfactory image. I managed to capture the faint cones - a first.

M27 Dumbbell Nebula.PNG
M27 Dumbbell Nebula.PNG (110.64 KiB) Viewed 99 times

NGC7000
30 frames, RAW8, 30s exposure, gain = 80%, brightness = 50%, colour balance auto.
Nothing to see here! Either I missed the target completely (the joys of trying to image something unseen) or I need to look at more frames and/or longer exposures. I have a yet as unused Off-Axis Guider which might have to be used but one step at a time.

NGC7000 North American Nebula.jpg
NGC7000 North American Nebula.jpg (4.62 KiB) Viewed 99 times

M33
40 frames, RAW16, 30s exposure, gain = 80%, brightness = 50%, colour red 51% blue 94%.
These settings seemed to have produced a satisfactory image, perhaps experiment with longer exposures such as 60s & 120s.

M33 Triangulum Galaxy.PNG
M33 Triangulum Galaxy.PNG (99.13 KiB) Viewed 99 times

NGC7635
40 frames, RAW16, 30s exposure, gain = 80%, brightness = 50%, colour red 51% blue 94%.
Just about captured it, longer exposures such as 60s & 120s need to be tried with this object I think.

NGC7635 Bubble Nebula.PNG
NGC7635 Bubble Nebula.PNG (75.07 KiB) Viewed 99 times

M52
20 frames, RAW16, 30s exposure, gain = 80%, brightness = 50%, colour red 51% blue 94%.
These settings seemed to have produced a satisfactory image. Next time I will try for more frames/longer exposures to see if there are more stars to be captured.

M52 Open Cluster in Cassiopeia.PNG
M52 Open Cluster in Cassiopeia.PNG (8.61 KiB) Viewed 99 times

M82
20 frames, RAW16, 30s exposure, gain = 80%, brightness = 50%, colour red 51% blue 94%.
These settings seemed to have produced a satisfactory image. Next time I will try for more frames/longer exposures.

M82 Cigar Galaxy (Starburst Galaxy).PNG
M82 Cigar Galaxy (Starburst Galaxy).PNG (92.73 KiB) Viewed 99 times

M42 - 100 frames @ 5s
100 frames, RAW16, 5s exposure, gain = 40%, brightness = 50%, colour red 75% blue 94%.
2x2 binning was not applied during processing of this image.
Plenty of nebulosity, perhaps less red needed. The core was not blown out and the 4 stars of the Trapezium were visible (another first).

M42 Orion Nebula_100x5s.PNG
M42 Orion Nebula_100x5s.PNG (100.79 KiB) Viewed 99 times

For this image, the 100 frames were stacked using Autostakkert. A single Alignment Point was used and the best 75% were stacked. The frames were derotated via Advanced > Experimental features & Parameter Tuning. The resultant stack looked like this:

autostakk_g2_ap1.png
autostakk_g2_ap1.png (24.73 KiB) Viewed 99 times

The resultant image was processed in Nebulosity. An interesting comparison to be had here.

M42 stacked_with_AS_p75.png
M42 stacked_with_AS_p75.png (109.75 KiB) Viewed 99 times

M42 - 338 frames @ 1s
338 frames, RAW16, 1s exposure, gain = 40%, brightness = 50%, colour red 75% blue 94%.
2x2 binning was not applied during processing of this image.
Plenty of nebulosity, perhaps less red needed. The core was not blown out and the 4 stars of the Trapezium were visible. With the short exposure time perhaps an increase in gain is required.

M42 Orion Nebula_338x1s.PNG
M42 Orion Nebula_338x1s.PNG (92.04 KiB) Viewed 99 times

For this image, the 338 frames were stacked using Autostakkert. A single Alignment Point was used and because of the poorer quality images, only the best 50% were stacked. The resultant image was processed in Nebulosity. An interesting comparison to be had here.

M42 stacked_with_AS_p50.png
M42 stacked_with_AS_p50.png (98.6 KiB) Viewed 99 times

In summary, this turned out to be a very useful 9 hour session at the scope. Some useful images acquired, some things to try for the future plus a lot of post processing experience. I also have the benefit of some data covering different types of DSOs (bright, faint, large, small) to experiment with on those cloudy nights. Still plenty to improve and to try out.

Time to evaluate my progress - the following were all acquired about 1 year ago:

M82.png
M82.png (33.91 KiB) Viewed 99 times
M42.png
M42.png (47.61 KiB) Viewed 99 times
M27 mono.PNG
M27 mono.PNG (58.61 KiB) Viewed 99 times
M27 colour.PNG
M27 colour.PNG (103.99 KiB) Viewed 99 times
So I am satisfied that things are moving in the right direction. 8-)

Dave

felipesg
Posts: 15
Joined: Mon Jun 19, 2017 10:29 pm

Re: ASI120MC and Deep Sky Objects

Post by felipesg » Mon Sep 25, 2017 2:13 pm

Hi Turfpit,

What a great night.

Thanks for sharing the pics and for all the details in your post.

Well done.

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