IC 1318 - Skunked Again

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Pete
Astro Day Coordinator
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Joined: Fri Jun 13, 2003 9:03 pm

IC 1318 - Skunked Again

Unread post by Pete »

There is a brilliant holiday display across the street & there’s a 1st quarter moon high in the SE and it’ll remain high all through this 3-hour imaging session. But the observatory’s in full dark mode, with the bottom shutter installed to completely block terrestrial light from the scope, the upper shutter partially closed to insure that moonlight does not enter the observatory, and all lights (including monitor & keyboard) off or covered.

IC 1318 is in the NE and approximately 50° above the horizon – over the holiday light display be away from the moon.

Reinstalled the Optolong LP-P filter and took new flats & dark flats. Focus is sharp at 4.4 FWHM.

Imaged at 5 min, 1X, -15C, 200 Gain.

Bummer. The first capture, when stretched, exhibits brightness on the left/upper left and darkness on the right side of the image.
Tried again with 1 min exposures. Same same. I feel like the observatory’s haunted.

Tried again without the flat or dark and there’s moderate vignetting through 360°.

Here are the images:

5 minutes partially stretched
5 min partially stretched s.jpg
5 min partially stretched s.jpg (254.4 KiB) Viewed 4158 times

Maybe a shorter exposure will limit possible light pollution? 1 minute partially stretched
1 min partially stretched s.jpg
1 min partially stretched s.jpg (208.79 KiB) Viewed 4158 times
Flat field unprocessed
flat field unprocessed.jpg
flat field unprocessed.jpg (82.25 KiB) Viewed 4158 times
Stretched flat field
flat field stretched.jpg
flat field stretched.jpg (249.2 KiB) Viewed 4158 times

Conclusions & lessons learned:

“light impingement” or whatever this is has been an ongoing problem since I bought this camera 3 years ago. Beginning to suspect that the CMOS chip itself is to blame.

Optics are indeed dirty, but that can be addressed later.

Had this problem years back when using twilight flats but ?

2 more things to try: Capture a twilight flat. And rotate the camera 180°, taking a duplicate image.

20 Dec 2023 Will this work tonight?

OK. Rotated the camera and ran what I think is a good twilight flat:
twilight flat.jpg
twilight flat.jpg (50.66 KiB) Viewed 4158 times
And stretching the hell out of it (couldn’t remove the Bayer pattern:
twilight bayer stretch s.jpg
twilight bayer stretch s.jpg (95.77 KiB) Viewed 4158 times
No different from illuminated panel flat.

Applying the twilight flat, here’s the SharpCap stack:
IC 1318 231220 stack s.jpg
IC 1318 231220 stack s.jpg (214.7 KiB) Viewed 4158 times
The illuminated area rotated with the camera.

Although I can do a crude adjustment in Photoshop working with the lasso tool to bring the corner into conformance:
IC 1318 231220 stack ps laso.jpg
IC 1318 231220 stack ps laso.jpg (212.81 KiB) Viewed 4158 times
It is as I said, crude.

Conclusions and lessons learned:

The telescope was not exposed to light so this isn’t an incident light problem.

The sensitive area rotated with the camera. This is a camera problem. I’ve had this problem since receiving the camera 3 years ago. Didn’t believe that a CMOS chip would do this and still need to research it.

I’m tired of fighting this problem. The sky was clear BUT the moon was up, and moonlit nights seem to be a problem as well. .

Next steps:
1. Try exact same setup on the next moonless night.
2. Research CMOS uniformity
3. Repair or replace or just give it up.
Pete P.
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mark.m
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Joined: Fri Feb 03, 2017 1:13 pm

Re: IC 1318 - Skunked Again

Unread post by mark.m »

Pete:
I'm confused by the rotation thing.

In both the first image and in the rotated image, the corner that has the high background light level is the corner of the image with the bright star. So, in terms of the sky, it's the same part of the sky, not the same part of the camera? When you rotated the camera, the image flipped. The bright corner flipped with the image. I think that means that the origin is in the sky, not in the camera.

- Mark
Mark M, AJ1B
Portsmouth, RI
Celestron 14" and Meade 10" SCTs
QHY268M + SBIG ST-9
GM2000 (10Micron)
American Association of Variable Star Observers (AAVSO) observer code: MMU
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Pete
Astro Day Coordinator
Posts: 4003
Joined: Fri Jun 13, 2003 9:03 pm

Re: IC 1318 - Skunked Again

Unread post by Pete »

Wow! You may be right Mark. I've a follow-up that I've not been able to post as the forum is glacially slow and unforgiving.
Pete P.
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