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.
- Output was to FITS files and the images were debayed as GRBG using PIPP, see viewtopic.php?f=35&t=254.
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.
- 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
50 frames, RAW8, 30s exposure, gain = 80%, brightness = 50%, colour balance auto.
These settings seemed to have produced a satisfactory image.
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.
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.
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.
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.
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.
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.
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).
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:
The resultant image was processed in Nebulosity. An interesting comparison to be had here.
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.
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.
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:
So I am satisfied that things are moving in the right direction.
Dave