M27 - to dither or not to dither… (Tom Gray)

M27 - to dither or not to dither…

In my line of work, prevention is always better than cure. Having battled walking noise in many of my images (which post-processing only partially removes), I have found a way of dithering my mount to prevent hot pixels from spoiling my Astro images. This involves randomly moving the mount by a few pixels after every exposure, and then using sigma clipping to remove the random hot pixels during the stacking process.

This is my first image after dithering my mount using PHD. I considered doing this manually, but then found that Nebulosity image capture has an auto-dither function which links to PHD. After each exposure the mount moves a random distance and settles before the next exposure starts. I have had to move away from Meade Envisage which has served me well since I started digital imaging, and am missing the auto dark subtraction routine.

A familiar target, and unremarkable image but my first dithered, with no walking noise. It turned out OK despite the lack of data, flats or bias frames; I used darks to remove the amp glow. I used my Optolong L-eNhance filter to collect 40m L and added 15m RGB. Another step forward in my imaging journey, and new software to learn - progress.

Original
B
Final
C

B

Description: This revision combines data from three nights totaling 6 hours - 40m L through L-eNhance filter (Nov), 2 hours OIII and 3.4 hours Ha (Jul). Seeing was not great when I imaged in NB resulting in rather poor stars, therefore I have not stretched this image too much.

Uploaded: ...

C

Description: My final revision focuses on the core of this remarkable planetary nebula. 40m L data through L-eNhance filter (Nov), is layered with the OIII and Ha data from July (revision B), and detail enhanced using the 'flux detail' module. I think this retains the sharpness of the L layer whilst bringing in the colour contrasts from the H and OIII emissions.

Uploaded: ...

UK Astro-Imaging
Optolong L-eNhance filter
Narrowband imaging
Low-Cost Astrophotography
Schmidt-Cassegrain Telescope (SCT) Imagers
Altair Astro 183 M/C Hypercams

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Status	Advanced success
Started	...
Astrometry.net job	5171767
PixInsight job	7KFGSM6M5IP3EQK7QOIWFMNNKDVQ6B1U
PixInsight queue size	n/a
PixInsight stage	TASK_LOG

RA (center)	19h59m36s.30
RA (top/left)	19h58m16s.90
RA (top/right)	20h00m46s.33
RA (bottom/right)	20h00m55s.28
RA (bottom/left)	19h58m25s.42

Dec (center)	+22°43′05″.3
Dec (top/left)	+22°32′01″.4
Dec (top/right)	+22°29′15″.1
Dec (bottom/right)	+22°54′04″.3
Dec (bottom/left)	+22°56′54″.0

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