- NGC2237-Ha_10x600s.jpg (965.62 KiB) Viewed 1706 times
- NGC2237-Ha_10x600s-OIII_10x420s_HOO-v2.jpg (673.04 KiB) Viewed 1366 times
Equipment: Celestron AVX mount, Vixen 81s refractor with 0.67x flattener/reducer, Altair 183M camera, Altair Ha and OIII (Teleskop RGB) 1.25" filters mounted in a ZWO mini filter wheel, QHY mini guider with QHY5LII-M guide cam, powered USB2 hub.
Software: Sharpcap, PHD2, PixInsight.
Data: Bias 50, Flats 10 each Ha and OIII, Darks 20x600s and 20x420s, Lights Ha 10x600s & OIII 10x420s.
Camera settings: gain=562, black_level=100
Focusing: Bahtinov Mask
Calibration, Integration and post-processing were carried out in PixInsight.
The logic for the gain/exposure settings can be found in the spreadsheet depicted at viewtopic.php?t=8322. Hat Tip to Brian (@oopfan) for his input to avoiding photon starvation and achieving colour balance.
Processing the Ha image in PixInsight:
Calibration/Integration via Weighted Batch Preprocessing, WBPP
Screen Stretch and adjust sky background level, Screen Transfer Function (STF)
Gradient Correction
STF + Histogram Transformation
Create Range Mask
CurvesTransformation using Mask/Inverse Mask to stretch object and background
TGV Noise Reduction of background using mask
Slight Histogram stretching
Processing the HOO image in PixInsight:
Calibration/Integration via Weighted Batch Preprocessing, WBPP
Create HOO image using ChannelCombination
Screen Stretch and adjust sky background level, STF
Gradient Correction
STF + Histogram Transformation
Create Range Mask
CurvesTransformation using Mask/Inverse Mask to stretch object and background
CurvesTransformation using Mask/Inverse Mask to increase nebula saturation
TGV Noise Reduction of background using mask
Slight Histogram stretching
Denoise and star reduction via https://www.starfixer.org/
A comparison of single frames (stretched):
- single-frames-compared.JPG (64.45 KiB) Viewed 1706 times
The HOO histogram showing reasonable colour balance after ChannelCombination:
- HOO-histogram.JPG (58.02 KiB) Viewed 1706 times
Evaluation
The OIII data was very noisy and showed little detail, which can be put down to the data being captured as the nebula was sinking into the Manchester light pollution. The Ha data was good, having been captured from 20:00 just after transit. The AVX mount handled the 10m exposures well, rewarding the effort put into polar alignment and star alignment/calibration plus All Star Polar Align (ASPA).
Next time I will try to capture OIII data near the meridian and hopefully add RGB data although the Nebula is now advancing towards the polluted skies.
Planning
The original idea was to create a 2-panel mosaic using information from Telescopius https://telescopius.com/telescope-simulator. This had been planned at the beginning of 2025 but the weather has not been kind.
- mosaic-planning.JPG (60.92 KiB) Viewed 1706 times
I decided to go after a single panel rather than risk another not quite finished project. Maybe next year?
Dave