183MM PRO - Halos around bright start started to appear

Tondra

I am actively using this camera since May and did not have any major problems. However, recently I recognized the deterioration in the quality of photos - halos around big stars started to appear, which I did not have before. First I thought that this is related to new filters, which I recently installed, but, comparing old and new photos, made with the same filters and a difference of few weeks, I see a major difference.

Now I am excluding different factors, which may have impacted the quality of photos:
1) Filters can't be the issue, since with same filters the quality is different
2) Imaging settings can't be the issue - I am using the same exposure time / gain / etc. as before
3) Issues in the optical train can't be the issue, since nothing changed there

Here are some test photos:
1) M16 - Before the "issue" (OIII)

2) M16 - After the issue. You can see that weird halo appeared around the brightest star (OIII)

Here is the close-up of the same

3) Crescent - before (OIII)

4) Crescent - after (OIII)

I am seriously thinking if camera matrix started suddenly dying, but any other opinion or idea, how to check this is very welcome.

FYI - My rig is located in remote observatory, so I am a bit limited in number of things, I can physically do with the scope, but a week ago technician from observatory checked the whole optical train (re-assembling) and found nothing suspicious.

Thanks!

Astrop

It's unlikely to be the camera. I've been using more than one 183 for years. Adding any filters will likely be the culprit, and distance of the filter from the sensor can make a significant difference, filters need to be as close to the sensor as possible. Poor seeing can cause graininess to photos, thin cloud, as will moon LP or any LP, short exposure, especially when imaging in o3.

Tondra

Astrop , thanks for the response. Here are my thoughts:

filters are ok, since I have some photos with same filters also w/o these artifacts
having filters as close to sensor as possible. Basically, I can't get filters closer to sensor any further, since the camera is already connected with screws directly to the filter wheel. So there is no real middleware in between
Poor seeing... Well, I could imagine if e.g. clouds could make such effect, if during the night part of shots would be with such halos and part w/o it. But all of them have exactly the same structure. Also it's remote observatory, so bortle 2 probably.

I wonder, what kind of other tests I could perform to understand the root cause. I tried with different gain / exposure length / filters now and artifacts are always there.

One other thought I have was about potential dew on the front window of the camera. E.g. I do not have such thing installed https://www.zwoastro.com/product/zwo-anti-dew/. Do you think that this coudl be the root cause or would the effect be different then?

Astrop

Tondra Do you think that this coudl be the root cause or would the effect be different then?

I don't think it's dew because the star shape halos are uniform across the sensor and also there's no loss of contrast I can see in the image, a fogged up part of the image train tends to look like cloud has entered the FOV so you'd see a massive change from image to image. When dew condenses you'll also see dark spots.

Do the grainy halos appear using a different filter? I've just zoomed into your before images, the grain is still there prior. What exposure lengths are you using?

Tondra

Astrop That's also what I am thinking of in terms of dew, that it would not be the same from photo to photo, from one day to another.

With regards to exposure times, I tried with different ones to compare the result. E.g. I normally shoot 10min exposures for narrowband, but I tried now also with 5 min exposures. Of course, 5mins are not so bright, but halos are also there. And these halos appear for all the filters (of course, the more light comes in, the brighter the halo is). E.g. HA has the smalles one, Blue has the biggest one.

With regards to these grains. yes, for big stars there were some artifacts always (and this, I think, is the issue of filters), but that's something I can live with. However, previously there were no such big halos around bright stars and these one really cause a mess.

Astrop

I was going to suggest you try the camera during the day to see if it still has graininess (because signal is strong in daylight so would eliminate/reduce noise being a factor in the image), but you don't have access to it. Have you tried imaging the moon? Again signal will be strong.

Tondra

Astrop hm... good point to try to shoot something else bright. I will try with the moon. And during the day what do you suggest to shoot?

Astrop

Have your hosts changed or installed anything new at their site or anyone around their site? What is their response on the issue?

Tondra

Astrop no, nothing really. They re-assembled the whole rig to check, if there is any dust / dew inside -> nothing...

Astrop

Anything really, just to see if excessive noise is there, try it with a luminence filter if there's one in your efw. Or just wait to do a moon test.

Tondra

Dear all,

Issue is solved. So, in case anyone else runs into the same issue, here is the description of the problem and what I did to solve it / to prevent it from happening again:

somehow humidity got into the shooting chamber of the camera. I came to the remote observatory last week, de-assembled everything and found literally drops of water in the shooting chamber. So I had to open the chamber, clean the glass, which protects the chamber and the glass, glued on the sensor. This helped to resolve the issue

BTW, when I unscrewed everything, the glass, glued to the sensor, looked pretty clean. But it was not - there were very tiny stains, which are not really visible to human eye, but which cause these artifacts.

I also installed the heater from ZWO anti-dew heater strip https://www.zwoastro.com/product/zwo-anti-dew/. Hopefully it helps to avoid such humidity in the future.

P.S. artifacts in flats, which I wrote about in the beginning had exactly the same root cause. After I cleaned everything, flats were good again. So these all were the same issues...