Strange artifact in first light image

[stargazermanc]

I have recently purchased the ASI2600mc pro camera which came bundled with a ZWO filter drawer.

Last night was my first light with the camera and I have noticed a strange circular pattern in the image on the right side.

The image is a widefield M81. 

29 * 300 second exposures

Matching darks and flats

Setup

William Optics ZenithStar73 with flattener

AZ-EQ6 Pro

ASIAIR Pro

ZWO EAF

ZWO filter drawer 

Optolong L-Extreme filter

The back focus is set correctly. Camera, filter drawer, 16.5mm spacer, field flattener.

Camera is set to -10 and 100 gain. Focus is rough focused and then auto focus and refocused every 1 hour or 1 degree change.

I have used the same setup with my 2600mm pro and filter wheel but don't see this same pattern.

Only thing to try is remove the filter drawer but I can't see why that would cause this strange ring pattern?

 

Anyone any ideas what it could be?

Edited January 6, 2022 by stargazermanc

[michael8554]

Might be frost forming on the sensor.

Quite a distinct edge to the cutoff, so might be the filters are not locating centrally.

Post a jpeg of a Flat and a Light.

Your image is showing coma in the corners, FF too close to the sensor ?

Michael

 

[stargazermanc]

I am going to check the back focus measurement and take a new exposure. I am also going to take another exposure without the filter drawer as someone has suggested it might be light leak which has caused like a lensing effect. 

[Realtimedoctor]

I think there is a it of tilt or incorrect spacing with the flatenner, as the stars around the edges are elongated, the right side could just be secondary to a bit of tilt. 

[stargazermanc]

Thank you all for your responses. I have just taken some test exposures after making a change to the back focus and that has cured the issue, the artifact has gone and the stars are nice and round throughout the image.