Primary mirror reflections

[barbulo]

Hi all, 

Yesterday I had a small window of opportunity to take the first lights out of my new 294MM. I took a few shots through the ZWO NB filters and the images showed these weird artefacts: 

This example corresponds to the SII filter but they're present in other filter's lights. 

I've searched the web but didn't find a conclusive answer.

Any clue of what's wrong? Anyone experiencing similar issue with this camera and/or filter?

Thanks in advance.

[AKB]

Dust bunnies?  Flats should sort this out.

Tony

[barbulo]

Thank you Tony, but I don't think so since they're not present in the flat frames. They're there even after pre-processing the lights with Darks, Flats and Dark-Flats.

[NiCo10]

At first I thought Dust Bunnies but these seem too aligned?

[AKB]

Reflections of Alnitak, then, …?

Do they move if you change the FOV?

[barbulo]

1 minute ago, NiCo10 said:

At first I thought Dust Bunnies but these seem too aligned?

Yes they are! Forming a pattern! Isn't it weird?

3 minutes ago, AKB said:

Do they move if you change the FOV?

Didn't have a chance. I'll check next clear night. 

[ONIKKINEN]

I would guess them to be reflections between any glass surfaces in the camera side of things rather than something in your mirrors. You have the sensor itself, the sensor window, the filter, and several lenses in your coma corrector. The reflections could be between any of these so im not sure how i would troubleshoot this.

You could try to figure out exactly which surface is responsible for this using the reflection/dust bunny tool: https://astronomy.tools/calculators/dust_reflection_calculator

[rnobleeddy]

I once saw something similar, and it turned out to be caused by a Baader Mark 2 coma corrector paired with the FW + filters spacing I had. In that instance, it was solved by moving to a mark 3, which has better coating.

[barbulo]

Thank you very much @ONIKKINEN 

According to the tool, the distance is around 14mm, so it must be the filters. 
To be honest, when I mounted them in the FW I didn’t realized they have different coating in each side. 😰
 I’ve opened it and turned the Ha and SII around putting the glossy side towards the scope. This difference is not so evident in the broad band filters, so I wonder if they will produce the same artifacts. Will see.

[barbulo]

One month later those reflections reappeared. A bright star in the picture and there they are.

Not so evident in a light frame (left) but boosted after stacking a few of them (right).  

I've tried to remove it in post-processing using this method but there is no way. Hasn't anyone had a similar issue with any filter? 😩

I will try leaving Propus out of the frame or using shorter subs (these were 300s). 

[Clarkey]

I have had exactly the same issue with the same stars. Using my 6" F4 reflector I got these reflections from the filters. All my other scopes are fine so I might have to keep this one for OSC only so I can go without the filters. I did just about manage to remove the halo - but it took quite a bit of work. Not something I am going to go again. (I have no idea what I did to get rid of it though).

[Adam J]

On 06/02/2022 at 15:46, barbulo said:

Hi all, 

Yesterday I had a small window of opportunity to take the first lights out of my new 294MM. I took a few shots through the ZWO NB filters and the images showed these weird artefacts: 

This example corresponds to the SII filter but they're present in other filter's lights. 

I've searched the web but didn't find a conclusive answer.

Any clue of what's wrong? Anyone experiencing similar issue with this camera and/or filter?

Thanks in advance.

Those are reflections between the microlens array and the filter. If its an unmounted filter then you could try flipping the filter over. 

Adam

 

Adam 

[AstroMuni]

On 06/02/2022 at 15:46, barbulo said:

Any clue of what's wrong? Anyone experiencing similar issue with this camera and/or filter?

If its not something thats due to filters or can be corrected by flats, it could be reflections similar to what I am facing. I get similar artefacts when I image in a certain part of the sky and narrowed it down to a street light thats causing reflections in my scope. Plan to put a dew shield on and see if that helps.

Edited March 9, 2022 by AstroMuni

[barbulo]

47 minutes ago, Adam J said:

Those are reflections between the microlens array and the filter. If its an unmounted filter then you could try flipping the filter over. 

Thank you @Adam J. I've already flipped the filter and the reflections are still there. 

31 minutes ago, AstroMuni said:

Plan to put a dew shield on and see if that helps.

Thank you @AstroMuni. Already using dew shield.

It seems that reflections are only produced with very bright stars: Alnitak, Propus... Now trying to avoid them

[AstroMuni]

38 minutes ago, barbulo said:

It seems that reflections are only produced with very bright stars: Alnitak, Propus... Now trying to avoid them

In your images the artefacts are not just around the stars, so suspect there is another culprit out there. Good luck