NGC 4631 and NGC 4656 (Whale and Hockey stick galaxies) - OSC

[Richard_]

NGC 4631 and NGC 4656 – One Session

It's coming towards the end of galaxy season and I'm not sure how many sessions I'll have left before we see the end of astronomical darkness. The weather hasn't been great and having recently caught Covid I'm not sure I'll likely get back out to add to this any time soon. So here's my final result with ~2hrs of total exposure time from my OSC camera. I can only imagine how nice this will look with more time.

Following some advice from a previous thread on my M81 and M82 image, I was able to get much nicer stars by aligning my colour channels before integrating into a master light and by being careful during the stretching phase. I didn't even need to use any form of star reduction at the end so I'm pleased with the outcome! I did originally try binning my images during the debayer phase (SuperPixel method instead of VNG) but my stars did appear more diamond shape (i.e. undersampled) so I stuck with 1x1 binning as captured.

You'll find my processing work flow and a FIT version of my master light should anyone wish to play with my data. Comments and constructive criticism are welcome 🙂

Caldwell32_masterLight_RGB.fit

*** EQUIPMENT ***

Camera: ASI533MC-Pro

Telescope: WO FLT120 (x0.8 reducer)

Mount: EQ6-R

Guide Scope/Camera: WO 50mm Guide scope / ASI290MM

Filter: Baader UV-IR

Peripherals: Beelink Mini-PC, PPBA, Dew Heaters, Sesto Senso 2, ZWO Mini-EFW

 

*** ACQUISITION DETAILS ***

Gain: 100 (unity)

Sensor temp: -10°C

Subs:  68 x 120s (~2.25hrs)

Darks: 100

Flats: 20 (50% of histogram)

Dark Flats: 20

Dates: 24-Apr-2022

Area: Northern Hemisphere, Bortle 5 zone

 

*** PRE-PROCESSING ***

• Calibrate
• Split RGB channels
• Subframe selector, filter out subs by rejecting:
  • FWHM >5
  • Eccentricity >0.6
  • Apply Adam Block weighting
• Align subs to best weighted sub
• Normalised Scale Gradient
• RGB merge, save as XISF

 

*** PROCESSING ***

• Dynamic Crop
• Background extraction
  • DBE, division
  • ABE, division
• Photometric Colour Calibration with Background Neutralisation
  • Select background preview and set upper limit based on preview
• SCNR green
• EZ Denoise
• Masked Stretch
• Starnet++ v2
• On starless version
  • Range selection to mask galaxies
  • HDR and LHE
  • Curves transformation to improve saturation of galaxies
  • Flip mask and reduce background saturation
  • Minor black point clipping on histogram for background
• Pixel Math to insert stars
• Apply star mask
  • Slight increase in colour saturation
• Save as JPEG