M106 imaging configuration testing

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Pete
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M106 imaging configuration testing

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Wednesday, 27 Apr 2022

It’s a pretty tough night to be out. Wind 15 mph with gusts to 25 or more. And broken cloud. But the last time out, imaging NGC 4656 the image was completely pixelated with colors, the frames wouldn’t stack and there were mods needed on the lower shutter.

The shutter has undergone extensive modification, I’ve shifted to 2X binning at prime focus, and have targeted a much brighter galaxy for tonight’s test. – M106. I’d last imaged M106 on 31 Mar 2021 at prime focus, 33 X 5 minutes (165 minutes total). It’s wonderful to have a yardstick.

Three sets of images were taken at 3 minutes, 1 minute and 30 seconds. There was no hint of the noise that had plagued me back on the 22nd but the detail at 3 minutes seemed to be over exposed, thus the tries at 1 minute and at 30 seconds.

All of these test images were taken through passing cloud. No frames were excluded from the stack.
M106 6X3min.jpg
M106 6X3min.jpg (354.74 KiB) Viewed 367 times
M106 6 X 3 min, 2X, 120G, -10C, 5 sec guiding
M106 4X1 min.jpg
M106 4X1 min.jpg (327.46 KiB) Viewed 367 times
M106 4 X 1 min, 2X, 120G, -10C, 5 sec guiding
M106 180 x 30 sec.jpg
M106 180 x 30 sec.jpg (93.5 KiB) Viewed 367 times
M106 180 X 30 sec, 2X, 120G, -10C, 5 sec guiding

Analysis:

Mostly good news. Suspect that the huge colored pixel noise from the 22nd was associated with extreme stretching of a dim object. This brighter galaxy stretches nicely with none of the background light problems I’ve had since starting this new sequence of imaging 2 years ago. The new lower dome shutter works like magic.

I’d gone with shorter exposures to minimize blowing out the center of the galaxy and while achieving that objective found that stacking 90 minutes of 180 second exposures doesn’t work anywhere near as well as imaging 3 minute exposures for a shorter time. This was the subject of a study run by Roger M last year and confirms his conclusions.

On the first IP stack check while imaging the flat didn’t kick in and there were severe dust motes on the stacked image. Need to check the filter. (Checked following day and indeed some dust had settled while the scope was stored facing up) Turns out that blowing off a slide-out filter’s many times more convenient than dismounting the camera.

Although the stars were reduced from 10” FWHM to 4.8” FWHM Sharpcap live stack wouldn’t stack, which was a disappointment. There’s never a problem with wide field imaging.

If the sky clears in time, as forecast, I’ll be out tonight applying lessons learned.
Pete P.
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