Halo / reflexions around bright stars ASI 1600 MMC

schurig

Hello,

Two days ago I integrated IC 443 in H alpha - after stacking the frames a bright halo / reflexion of my f/4 Newton's mirror was visible around a bright star next to IC 443.

So yesterday, I took for every filter (R G B L Ha OIII SII - all ZWO filters) a 4min test exposure of beta And (2,1mag) and the halo appeared more or less with every filter. Moreover, even other symmetrical patterns and rings are visible. In case of SII the main reflexion is visible faintly several times throughout the whole field!

See here:

So what is this and how can it be fixed? It simply ruins all images with bright stars?!

Cheers, Stephan

dansemacabre

Same problem for me and also other people with ZWO filters. I have these terrible reflections even on mag 7,5 stars on f/5,6 scope :(

schurig

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davebl

Halos.jpgI'm having the same problem. I using a 10" Truss Tube RC @f6. It shows up more on the narrow bands and is not there without a filter.

Also the star is off center like I'm out of collimation, but it's position shifts with different filters. Maybe the filters aren't laying flat in

the filter wheel? I looked back at some older shots I took with an 8" steel tube RC @f6 and I don't see the halos.

Dave

dansemacabre

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Sam@ZWO

did you try change the face of the filter?

davebl

did you try change the face of the filter?

I assume you mean turn the filter over. I will try that. I did change the spacing between the filter and the CMOS

and it may have made a slight difference, but still there. I will turn them over today and report back tomorrow.

Dave

davebl

I turned over my narrowband filters and shot some images, but I can't see any difference. It's really evident on bright stars

during long exposures and even shows up on some not so bright stars in those exposures. I can't afford new filters at this time,

so I'm just going to live with it unless someone finds another solution. Otherwise, I really like the camera (ASI 1200mm cool).

I attached a pic of the bubble, if you look at the brighter star below and left of center, you can see the halo.

Good luck to us all.

Dave

Bubble New Final XS.jpg

schurig

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davebl

Hey Stephan,

I actually did take an image without a filter inline and the star looked perfect, no hint of a halo. One thing I did

notice last night was after turning the filters over there was a huge bright halo that appears to be bad vignetting except

the corners are still dark. I didn't really catch it the 1st night as I thought maybe I was having an issue with dew. So I

Turned the filters back over last night and will test tonight. The halo appears on the OIII and SII filters. I'll post some pics

tonight or tomorrow.

I seem to have a problem with tilt in my filters. I'm using the 31mm unmounted and they don't set flush in the wheel and

the washers that hold them in are at an angle to make up for it. Seems like they should fit flush with the wheel. It makes it

difficult to get even tension on the filters. If you tighten one screw a little too much you can actually see the filter tilt.

Anyone else notice this?

Dave

davebl

Halos new.jpgHere's some pics of no filter, OIII and SII filters after flipping over. You can see the huge halo on the filtered shots and nothing on the unfiltered shot.

Dave

davebl

Veil final 2.jpgI'm rethinking my last post about the huge halo being due to the filter. There has been fairly high humidity as of late and I had the same effect last night after turning the filter back over. I now think that it's some form of light pollution reflecting off the moisture in the air. It could also be a dew problem as my secondary dewed over last night around 2am. The smaller halos around the stars are definitely due to the filters. I'm attaching a shot of the Veil that shows this really well.

Dave

schurig

Hi Dave,

I don't think that the big halo is a dew or moisture problem. At least I can say: The test pics of all filters in my first posting were taken right after setting up my equipment in the garden. So there shouldn't be any moisture effect yet. I checked all lenses after the test images, and there was no dew.

So what causes the big halo? That's still the question! As soon as I'll get some starry skies here, I will try the following: Take pic without filters and without Coma Corrector (I use GPU).

Cheers, Stephan

schurig

Hi Dave,

A friend of my mine just told me that there is a "right" and "wrong" side of the filter... see here: https://astronomy-imaging-camera.com/products/accessories/zwo-narrowband-36mm-filter/

This information is new to me. Maybe it was just added recently?

Stephan

davebl

Thanks for the link Stephen. I've never seen that before either. I will check my filters today.

Dave

schurig

Hi,

I was able to make test this evening. I changed my image train a bit, screwed the 15mm T2 extension between Cam and Filter Wheel (before the extension was between Filter Wheel and OAG). So the filters are now 15mm more away from the chip. Took 240s exposures with R and OIII

Result: The halos are still there, but fainter and bigger. I also flipped the R and OIII filters before, because of the instructions of the ZWO site about what side is wrong. Well, at least when it comes to this problem, the side of filter has no effect.

But it has something to do with the filters. The more reflective a filter is, the more evident is the halo. I also suspect the front glas of the Camera!

Stephan

schurig

Here's an example... I cannot believe that there isn't any solution for it :-(

IC 443, 23 à 240sec H-alpha with a 8" F4 Newtonian

davebl

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schurig

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davebl

Thanks for the link Stephen. I noticed he is having multiple reflections and using Baader filters. I'm tempted to remove the cover glass and try that when it clears up here.

Dave

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