NGC2403 - Intermediate Spiral Galaxy in Camelopardalis
Sometimes refered to as the Mini-Triangulum galaxy, NGC2403 is one of my favorite galaxies in the night sky. It is full of star forming regions that speckle it with color throughout. I first attempted this target back in
April of last year.
This image marks my 100th Image posted to Astrobin!! Woooo!!!Equipment:
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Orion 8in F4.9 1000mm Newtonian Reflector
[li]Flocked / Primary mirror replaced due to turned-down-edge[/li]
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Skywatcher F4 Aplanatic Coma Corrector
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Astrodon I Series L, R, G, B broadband filters + 5nm Ha narrowband filter
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ASI183mm Pro cooled to -15C
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Celestron CGEM Mount
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Self tuned / hacks to get guiding stable include:
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Intentional offset polar alignment so dec always pulses in one direction
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Balance "west" heavy (rather than the recommended east) so that the ota "falls" onto the gear teeth rather than get "lifted"
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Factor Reset hand-controller daily (to prevent cgem from being possessed and forgetting where the meridian is on subsequent night)
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Dither in RA only
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Data Acquired using N.I.N.A and Guided with PHD2
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Acquisition Details (excluding rejected frames):
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Red: 53x2min
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Green: 51x2min
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Blue: 49x2min
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Lum: 103x2min
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Ha: 40x10min
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Total: 11.7hrs
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The resulting image is a combination of the following steps:
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Inspected all subs for bad images with Blink, discarding 53 subs from clouds/daybreak/poor-guiding (3.5 hours of discarded data)
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Calibrated all subs with their corresponding master flat and master dark
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Used subframe selector to weight R, G, B and Ha data separately for creating color masters
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Used subframe selector to weight all subs together using the following formula for creating the super luminance:
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(20*(1-(FWHM-FWHMMin)/(FWHMMax-FWHMMin))
+ 10*(1-(Eccentricity-EccentricityMin)/(EccentricityMax-EccentricityMin))
+ 20*(SNRWeight-SNRWeightMin)/(SNRWeightMax-SNRWeightMin)
+ 30*(Stars-StarsMin)/(StarsMax-StarsMin))
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Selected the best sub from subframe and blink to use as a reference frame in stacking
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Created a super luminance by integrating all frames together and drizzled with drop shrink 0.8 scale 1.0 and kernel var k=1.5
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Integrated all Red frames together, Blue frames together and Green frames together to create masters for each color
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Integrated all Ha frames together to create a master Ha image
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Cropped the stacking edges of the integrated masters
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Combined the Red, Green and Blue masters to create a color RGB image
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Superluminance Processing:
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Dynamic Background Extraction
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26 large points (Radius: 75)
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Subtraction/Normalized
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Automatic Background Extractor
[li]Function degree 1 with normalization[/li]
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Independently produce a noise reduced image and a sharpened image
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Noise Reduction was done using TGV Denoise with a low contrast mask and an autostretched local support and MMT with a very protective luminance mask
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Deconvolution was done on a separate copy of the luminance with
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No deringing
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wavelet regularization with 5 layers and strong but reducing amounts/thresholds
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A starmask was created from the Noise Reduction copy to replace the stars with the origional superluminance, eliminating the ringing artifacts from deconvolution as similarly documented by /u/OkeWoke
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The noise reduced copy and the sharpened copy were combined using a luminance-based mask where the high-signal areas were filled in from the deconvolution copy and the low-signal areas were filled in from the noise reduction copy:
Decon*CombineMask+NR*~CombineMask
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RGB Processing:
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Dynamic Background Extraction
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26 large points (Radius: 75)
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Subtraction/Normalized
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Background Neutralization using 5 preview windows and the Preview Aggregator script as the background reference
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Color Calibration using Photometric Color Calibration using the Average Spiral Galaxy as the white reference
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RGB Workingspace set to 1,1,1
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Noise Reduction using TGV Denoise with a low contrast mask and an autostretched local support
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Noise Reduction using MMT with a very protective luminance mask
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Ha Processing:
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Dynamic Background Extraction
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26 large points (Radius: 75)
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Subtraction/Normalized
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Isolated the HII region by subtracting the Red channel from RGB using this guide (Thanks for the tip buras!)
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Extracted Red Channel from Calibrated RGB Image above
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Subtracted the Red Channel with $T-Q*(R-med(R)) and a Q factor of 0.095
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Noise Reduction using TGV Denoise with a low contrast mask and an autostretched local support
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Noise Reduction using MMT with a very protective luminance mask
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This HII data was then added to the RGB image with:
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Curves Saturation to boost the existing color data of the galaxy (adding HII otherwise kept overpowering existing color data)
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Red = $T+B*(Ha - med(Ha))
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Blue = $T
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Green = $T+0.2*B*(Ha - med(Ha))
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B (Boost Factor) = 1.3
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This Ha Data was then added to the luminance image in Pixel Math:
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Red = $T+B*(Ha - med(Ha))
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B (Boost Factor) = 2
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Combining, Stretching and Post-Processing:
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RGB Data Was then stretched using Arcsin followed by Histogram Stretch
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Luminance Data was stretched using Histogram Stretch
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Luminance applied to RGB using LRGB Combination with Chrominance Noise Reduction enabled
[li]Note: Unlike usual I found that through a number of permutations of processing this image the background noise of the RGB image was more appealing so used a mask when applying luminance to the RGB image so luminance's contribution was minimized on the background regions[/li]
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Contrast was enhanced in the Galaxy Core with HDR Multiscale and a Star Mask
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Overall impact of the three brightest stars were reduced with HDR Multiscale and Curves and masks
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Overall impact of the remaining stars were reduced with Morphological Selection
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Curves to enhance contrast
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Final round of noise reduction using ACDNR and Multiscale Median Transformation
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