Why am I getting these star bursts? - Forums

Topic starter

Oct 25, 2023

Hey all, first time poster, long time lurker and I need some help.

I've been working on some data I gathered on the Horsehead and Flame and I can't seem to figure out why I have these starbursts(lines, streaks? I'm not exactly sure what to call them) around a few of the stars.

I feel like it might be my exposure time, which is 5 minutes for RGB and 30 seconds for L, but I wanted to make sure this couldn't be something else like the filters or something with the telescope it's self. If it is exposure time, I'm guessing I'll just need to drop down to something like 120 or 180 seconds instead of 300.

Equipment details are listed. Total exposure time is about 4.5 hours.

https://astrob.in/4y376q/0/

Thoughts and any advice is welcome!

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andrea tasselli

Frequent contributor

Oct 25, 2023

There might be 101 reasons why and without specific tests is hard to give advice (starting from glass strains to protruding clips) . When shooting the Alnitak region is wise to keep exposures short to avoid blowing all those bright stars, both in RGB and L, especially in RGB where you want to preserve the hues. Without recourse to the original raw frames is difficult to give suggestions here.

Johannes Maximilian Möslein

Oct 25, 2023

As Andrea said, it could be a lot of things.
It kinda reminds me of one of my first images with my 80mm triplet refractor:

The weird spikes on bright stars looked so symmetrical, that I thought there's some kind of screws or something in the tube that produces that, but it was actually pinched optics. (Meaning the screws holding the glass are a little bit to tight.)
But make sure that's actually your problem before messing with that.

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Oscar H.

Oct 26, 2023

Well the image looks different and cool to me, the starbursts remind me of human vision when looking at bright lights.

Ckh22

Topic starter

Oct 26, 2023

Thanks for the thoughts Andrea and Johannes. I noticed on an SHH version I took, I'm starting to see just a bit of the burst on 48 Ori. Also, here's a link to a subset of the fits. You can make out the starburst in all of them.

https://drive.google.com/drive/folders/1rxiTqbaI8nKNTP48WlttlfUo7lRF3t-G?usp=sharing

Thanks messierman! I like them too and probably won't worry much about it. When the skys clear I'm going to get some with shorter subs and see what happens.

andrea tasselli

Frequent contributor

Oct 26, 2023

By their very singular aspect and variations of the pattern across filters and locations around the imaging plane I'll hazard there might be striae in the glass. It'll be nice to see what an image of the exit pupil would look like. I'd tend to rule out protrusions in the light bundle as well as pinched optics by retaining clips as they would be pretty fixed and uniform in place and these aren't.

Scott Johnstone

Oct 26, 2023 · Edited: Oct 27, 2023

I have a William Optics Z61 and had the exact same patterns. I sent some sample images to the tech guy where I bought it from and we went back and forth looking at different issues…pinched optic, dew heating set too high etc. It turned out to be because I was extending the dew shield out too far and the friction/compression was pinching the optics a bit. Now I only extend it about 3/4's of the way out and have never had a problem since.

Might be worth a try at least while you're digging for bigger issues.

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