- Exposure
time: 8 hours, LRGB = 225:85:80:90 minutes
(15 min. L and 5 min. RGB sub-exposures)
- Lens/telescope: INTES 150 mm (6")
MK-69 Maksutov-Cassegrain at f/6
- Image scale: 1.24 arcseconds per
pixel, FOV 68.5' x 51.6' (F = 900 mm at 5.4 micron pixels)
- Camera: SBIG
ST-8300M (T: -25 degrees
Celsius) with Astronomik LRGB filters
- Mount: Astro-Physics Mach1 GTO
(guide rate: 1x, PEM activated)
- Guiding: TS OAG +
SX Lodestar + PHD (small dither, settle
< 0.5)
- SQM: 21.5 magnitude per square
arcsecond
- Location: Etoile St. Cyrice, Hautes-Alpes,
France
- Date: March 9 - 10 and 10
- 11, 2011
Workflow
Image
acquisition in Nebulosity (v2.3.5):
- Capturing
5 flat frames per channel with a Geoptik
Flat Field Generator
- Capturing
15 L light frames of 15 min. and 17 R, 16
G and 18 B light frames of 5 min. per channel
- Capturing
5 dark frames of 15 min. and 5 dark
frames of 5 min.
Pre-processing
in
Nebulosity
(v2.3.5),
Sigma
Beta
10
and
Maxim
DL
(v4.56):
- Pre-processing
the
flat
frames
with
a
master
bias
frame
(from
library)
and
stacking
them (5 per channel) at "Average /
Default" in Nebulosity
- Pre-processing
the
light
frames
with
the
stacked
flat
frames
and
a
master
bias
frame
- Stacking
the dark frames (the 15 min. and 5 min.
series) applying a 0.75 "Standard Deviation Filter" (sigma stacking)
to reject cosmic rays
- Creating
bad pixel maps of the sigma stacked dark
frames
- Subtracting
the
bad
pixels
from
the
pre-processed
light
frames
with
the
bad
pixel
maps
- Applying
"Match histograms" on the pre-processed, bad pixels substracted light
frames
- Aligning
(registering) the matched, pre-processed, bad
pixels subtracted light frames and saving each individual file
- Stacking
the individually saved registered files
(per channel) with "Standard Deviation Masking" algorithm in Sigma
Beta 10
- Combining
the colour channels (RGB ratio 1:1:1.8,
"Bgd Auto Equalize" checked) to create an RGB image in Maxim DL
- Trimming
the dark edges of the L image and RGB
image in Nebulosity
- Applying
the "Digital Development Processing
(DDP)" tool (adjusting Xover) for both the L and the RGB image
- Applying
"Adjust Colour Background
(Offset)" for
the RGB image
- Aligning
the L and the RGB image and saving the
images as 16-bit TIFF files
Post-processing
in
Photoshop
(CS4)
and Maxim DL
(v4.56):
- Placing
the RGB image as a layer on top of the L
image (layer blend mode "Colour") in Photoshop
- Iteratively
adjusting
levels
and
curves
(continiously)
of
both
the
L
and
RGB
layer
in order to get as
much dynamic range as possible without clipping
- Increasing
the colour intensity of the RGB layer
with "Match Colour" and "Vibrance"
- Applying
Lucy-Richardson deconvolution on the galaxies (L layer,
crop of galaxies) in Maxim
DL (PSF radius
1.5, 10 iterations)
- Using
"Select > Colour Range" to select the background for the next filters
- Applying
"GradientXTerminator" and
"Noise Ninja" on both the L and RGB layer in Photoshop
- Applying
"Hasta La Vista, Green!" and
"Colour Blotch Reduction" action on the RGB layer
- Finishing
touches with "Shadows/Highlight"
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