Strange things going on with my stars!

[simmo39]

Hi all, not sure if this is the right place for this but here goes. I went out with my rig the other night to try ang get some data on the Cocoon, all looked good untill I put it inti PI. the nebula looks ok but the stars seem to have halos around them. I can live with some but as I go to the corners they seem to go realy out of shape. I have had this problem for a while but looking back at my other images it seems to be getting worse. My rig is a Askar 400 with FR and im using an Optolong Extreme filter. I know that the filer has a rep for halos but I have had no real problems with it before.

Here is some samples.

Here is the main image

Any ideas or is it just the filter? if so whats a better replacement?

Thanks for looking.

 

[Elp]

https://www.cloudynights.com/topic/741518-weird-halos-around-stars-what-happened/

[simmo39]

8 hours ago, Elp said:

https://www.cloudynights.com/topic/741518-weird-halos-around-stars-what-happened/

Thanks for the pointer, will have a little look at that today.

[simmo39]

Had a look at the image once split into three channels, it shows the same problem on all channels.  Not sure what to try next. I will have a go at getting better focus but I think my focus was not that bad. Just need some good weather to do some experiments.

 

[Elp]

You should be able to check the FWHM size of the stars when you're registering the subs which will give you an idea of focus. With my Z61 I believe my good focus is somewhere near 0.5 and 1 depending on seeing when focusing on a medium bright star.

Regarding halos, the issue is more like when imaging near high mag stars (ie Alnitak within the Horsehead Nebula) you get a halo ring around the star at least two to three times the diameter of the star thick. Yours looks more like when I'm using my Takumar lenses, initially the stars will have red bloat, nearing focus that red bloat decreases, then disappears then green bloat gets larger, it's to do with the lens focusing R,G,B at different points.

Have you tried imaging without a filter to see if the issue is still present. I have read previously some Askars do produce blue star halo bloat and could have something to do with the different wavelengths of light focal points.

Edited November 20, 2023 by Elp

[simmo39]

1 hour ago, Elp said:

You should be able to check the FWHM size of the stars when you're registering the subs which will give you an idea of focus. With my Z61 I believe my good focus is somewhere near 0.5 and 1 depending on seeing when focusing on a medium bright star.

Regarding halos, the issue is more like when imaging near high mag stars (ie Alnitak within the Horsehead Nebula) you get a halo ring around the star at least two to three times the diameter of the star thick. Yours looks more like when I'm using my Takumar lenses, initially the stars will have red bloat, nearing focus that red bloat decreases, then disappears then green bloat gets larger, it's to do with the lens focusing R,G,B at different points.

Have you tried imaging without a filter to see if the issue is still present. I have read previously some Askars do produce blue star halo bloat and could have something to do with the different wavelengths of light focal points.

Hi, yes i have imaged without the filter and I do get a little red bloat but its not as bad as with the filter. The odd thing is looking at older images taken with the filter I get some halo but not half as bad as it seems to have gone on the recent images. It might well be my focus is not as good as I think. Need some good weather to try out some ideas!