Sharpless 2-155 The Cave Nebula

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Sharpless 2-155 The Cave Nebula

Unread post by Pete »

Thursday, 1 Sep 2022

Inspired by Roger M’s NGC 7822 I’m looking for some similar less known nebulas to image. And settled on Sharpless 2-155, the Cave Nebula.
The refractor/camera is already set up from Barnard’s E. The night is moonless, transparent and still.

Imaged from 20:28 – 01:28, stretching my stay-awake capability but excited to see what a 4 hour exposure would look like. Regretfully, later found that the last hour (12 frames) were unusable due to an unknown tracking problem causing stars to be elongated along the RA axis.
Cave  37x5m lores.jpg
Cave 37x5m lores.jpg (869.47 KiB) Viewed 36 times
Sh 2-155 The Cave Nebula
20:28 – 01:28 hrs, 1 Sep 2022
102mm f/7 triplet refractor with ASI 2600MC-P camera and Optolong LP-P filter
38 X 3 min, unbinned, gain at 120, -5C cooling, 1 second guide rate

This is a faint nebula and lengthy exposure was needed. It came out better than expected after losing 12 of the 49 frames.
Nebula are best with low f/ numbers and stars are best with large aperture. This one was a struggle with the little refractor. How much better will it be with the f/2 Hyperstar on the 14” Meade? In at 01:41 hrs. It’s 60°F.

Friday, 2 Sep 2022

It took just 11 minutes to mount the HyperStar. The night’s moonless and still but transparency isn’t as good as it was last night, and it eventually deteriorates to the point where high scattered cloud shuts things down prematurely.
Cave HS lo res.jpg
Cave HS lo res.jpg (623.09 KiB) Viewed 36 times
Sh 2-155 The Cave Nebula
20:53 – 23:06 hrs, 2 Sep 2022
14” Meade LX200GPS with f/2 Hyperstar and unfiltered ASI 2600MC-P camera
45 X 3 min, unbinned, 120 gain, 1 sec guiding

Full dark protocol was observed on both nights. Last night’s refractor image was evenly illuminated. But the HyperStar bugaboo just won’t go away. Although there’s absolutely no flaw in the setup there’s a severe light gradient running from L to R, making stretching difficult. The large aperture low f/ number may have worked better but all gains have been wiped out with processing limitations, to the point where the little refractor beats the HyperStar. No explanation as to the source of the light gradient. The flat is good and even. There was no light striking the corrector plate from any angle. And the interior of the dome was dark and black.

At this stage, after working the Hyperstar for 2 years, I suspect that the optics are slightly "out of balance" and that simply less than dark sky was the culprit.

In at 23:17. Temp is 60°F.

Can't bitch 'cuz the refractor image came out surprisingly good. But it's time to remove the Hyperstar.
Pete P.
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Re: Sharpless 2-155 The Cave Nebula

Unread post by menardre »


Nice job with a difficult target. Diffuse nebula are difficult to capture, but your 102mm refractor did a really good job.

Roger M.
Celestron CPC1100 EDGE, Stellarvue 130T refractor dual mounted on iOptron CEM120 on permanent pier mounted in Observatory. Imaging camera ZWO ASI2600 OSC, guide camera Lodestar or ZWO ASI290MM.
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