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I got a new camera a month or so ago, the QHY268M, along with the QHY FW and the Astronomik RGB and CLSCCD and the Antlia 3nm filters (3.5nm OIII as I can't find the 3nm in stock).

I got some images with this setup attached to my SharpStar 61 EDPH MKII with the flattener/reducer and all seemed good.

I've now tried this on my TSOptics Photon 200/1000 newt with the Baader MPCC.

My flats on the newt are awful. There is a huge bright area in the middle, that I assume is a reflection. This causes my flats to over correct the light frames and I end up with a nice clear centre, but horrid edges.

Here is the OIII stack without the flat applied


With the flat


The flat itself


And here is a flat from the SharpStar (it's been cleaned since), but there is no central circle.


And here is a flat from my ASI1600 on the newt


There is something about the combination of the new camera/filters and the newt/mpcc that is causing these ?reflections? when shooting flats, but I have no idea what at this stage, and it means that I have data I can't really use. Any help would be appreciated.



Edit: Just done some tests with the Astronomik broadband filters and I don't see this issue with those, so I'm guessing it's the Antlia filters combined with something. Maybe the MPCC?

Edited by Endolf
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I had some similar issues with my flats last night. The previous day with exactly the same set up they were completely fine (I ended up using the previous days flats as nothing had moved and I ran the same image plan for two nights). I have put it down to condensation on the mirrors or camera. It looked similar to this except the centre of my flat was dark. Could this be something similar?

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My scope has been indoors since about midnight, so I don't think so, the camera cooler is turned off, so there shouldn't be any frost. There wasn't a huge amount of moisture last night when I packed up. I've seen things like it in the past, but normally a couple of hours with the fan on the scope blowing air through and it clears up. The broadband filters seem to be fine too.

I'll try again tomorrow just to check.

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I tried that on the other scope I got bad rings, which I assumed was the reflections from the edge of the filters, but I'll give it another go.

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Yup, I had issues whichever way I had the filters in until I had done that. I "borrowed" some from my ZWO filter wheel, having replaced the narrowband filters in that with the Astronomik 6nm ones. What I haven't tried is turning them round again now the edges are masked. I did have them in the best way round pre masking though.

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