LDN-1235. Shark.

 Posted: Apr 20th, 2025
Show astrometry on hover
NGC
IC
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Technical Info
Telescope/Lens: Celestron RASA 8
Camera: ZWO ASI071MC Pro
Mount: ZWO AM5
Guide Scope: SkyWatcher 8x50
Guide Camera: QHY5L-II-C
Software: PixInsight
Accessories: Mele PC + NINA, Celestron SCT Focuser
Exposure:
39 x 300" ISO/Gain: 90 - Optolong UV/IR Cut
Yellow zoneLight Pollution:
 Nijniy Novgorod, Russia
 Apr 19th, 2025
3 h 15 m
772
Still struggling with my RASA, got rid of large asymmetric tails from bright stars using a diaphragm, halos caused by re-reflection, most likely on the camera's protective glass, remain. Will try to fix this with a different filter next season.
Resolution: 4830x3146 px
Scale: 8118 KB
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Comments

What is the distance between the sensor and the filter? Maybe try increasing it. And where on earth do you find that gray zone...
20 Apr, 2025 Reply
N0r1s Replied to Oleg Novoselov
And why are you so fixated on the gray zone? It's pretty clear it's an error, but no, you have to make a sarcastic remark. The distance to the sensor is perfect now; the stars are the correct shape across the entire APS-C sensor. I'm seeing this for the first time.
The halos are caused by internal reflections within the glass of the camera's protective window or a filter, which might not have been tested or intended for fast optical systems at all. Here's a good example in this thread.
20 Apr, 2025 Reply
N0r1s Replied to N0r1s
I wrote the first lines in a fit of groundless indignation, and after five minutes it already seemed rude. I apologize. I've fixed the light pollution zone.
20 Apr, 2025 Reply
N0r1s Replied to N0r1s
https://www.cloudynights.com/topic/918216-rasa-8-for-eaa-the-learning-curve/page-2
20 Apr, 2025 Reply
Oleg Novoselov Replied to N0r1s
I'm asking about something else. Is it possible to somehow position the filter at a different distance without changing the working distance, for example, by separating the sensor and the filter as much as possible?
21 Apr, 2025 Reply
N0r1s Replied to Oleg Novoselov
Thanks for the advice! Changing the distance might not be possible—there's a 25mm segment, and 17mm of it is taken up by the camera. I came up with a design, with help from Saturn on the forum, that allows a filter to be installed.
23 Apr, 2025 Reply
The halo is likely caused by filters; with this setup, you can only try a different filter. And where do the diffraction spikes on the RASA come from, like from the secondary mirror supports in a Newtonian?
21 Apr, 2025 Reply
N0r1s Replied to Urmasx
Yes, I read the same thing in the article linked above on Cloudy Nights.
The rays from the spider vanes—I printed a diaphragm-cable organizer like this: https://www.thingiverse.com/thing:5513563/files
Just slightly modified, with the aperture stopped down to 180mm.
23 Apr, 2025 Reply
N0r1s Replied to N0r1s
Regarding the halo - the Astronomik L2 filter will arrive by August, I'll try it out then.
23 Apr, 2025 Reply

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