Strange pattern/halo in my pics - Forums

Topic starter

Nov 21, 2022 · Edited: Nov 21, 2022

Hi

I recently bought an Asi294mc camera but so far I haven't been able to get a good shot, as I always get a ring artifact in the center of my images
Some tests that I have been doing is, discard dew on the lens, and using flats ...
I need help to rule out possible causes.

My configuration is:

Asi294mc
Coma Corrector MPCC III Baader
OTA Newton 750/150

the next image has ABE and stretch applied, on the right it has boost stretch to highlight the ring more

PD: sorry for my english

andrea tasselli

Frequent contributor

Nov 21, 2022

Most likely you have a light leak either when you take flats or during imaging or both (but in non-additive way). This happens very often with newts. Remove all possible sources of light leaks, make sure you follow the approved procedure for data calibration (master flat=flats-darkflats) and so on. MOST importantly never ever take flats during daytime.

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Tim Hawkes

Nov 21, 2022 · Edited: Nov 21, 2022

I had a very similar-looking problem - in fact I would say identical - a couple of years back with my AS1294 MC. The solution was quite simple. It turned out that I had used a different image brightness control setting for the darks and the lights. At the time I did not realise that 'brightness' meant the same thing as 'offset' in a ZWO camera and that it is vital that the value (e.g usually set at 10 in my case – with R and B each set at 50) be identical for lights and darks.

i.e. Although it looked very much like a problem with the flats it actually wasn't that in my case but rather the darks not matching the lights. (Note if you are using Sharpcap to make master darks and flats the program is excellent in helping you to organise them into folders but the one thing it doesn't do unfortunately is to prompt you to match and record the brightness setting — which is why I missed the importance of that particular parameter at first)

Tim

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Tim Hawkes

Nov 21, 2022

andrea tasselli:
MOST importantly never ever take flats during daytime

Hi Andrea, I don't understand this point at all. I agree about light leaks but always take flats during the daytime (using a T shirt to diffuse the light) using a setup very similar to the questioner. A Newt, MPCC coma corrector and the same camera and don't have any problems at all of the sort raised in the originall question.

Tim

Russell S

Nov 22, 2022

Hi Javier,

Please check out this 3 part video from Adam Block, which looks like it could solve your issue https://www.youtube.com/watch?v=Kkg441UBNpo
I have similar problems with 6200mm - haven't managed to try the tips in the videos yet.

Good luck,

Russ

Shinpah

Nov 22, 2022 · Edited: Nov 22, 2022

The bright edges/ring center could be ABE doing ABE things, but it could also be incorrect flat calibration (due to bias/gain/offset issues) or it could be a light leak.

The dark donut is very reminiscent of my own light leak, which was from the focuser drawtube having gaps around the edges of the housing.

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John Posavatz

Nov 22, 2022

I've also experienced halo issues, but mine is a very different setup (Sony A7iii, Tamron zoom lens @ 400mm).

I never got to the bottom of it - could be the camera, the lens, or my general lack of experience. I took proper darks, flats and biases, and this is what it looked like in PI following stacking and DynamicBackgroundExtraction.

Well Written

Fco Javier AH

Topic starter

Nov 24, 2022

Hi all!

I think I found the problem, I put a cap on the back of the scope and the rings and weird artifacts are gone, so it was just a simple light leak…

thank you very much to all

Concise