Can somebody send me a master flat taken with ASI1600MM. I have light circles in my images plaguing the overall result. They are very distinct and could be seen in master flats when auto stretched with Pixinsight. I am attaching two photos. One is a flat taken without a telescope. It shows dark horizontal lines. Once the camera is mounted to a telescope the bright spot in the middle curves the lines into kind of semicircles centered in the right upper corner. It does it with every telescope and with every orientation. This phenomenon reminds me about the Newtonian rings seen with my solar cameras.
I am in despair and already started thinking about sending the camera to ZWO for test and repair because I can't produce any worthy images. If somebody could send me a flat image or a master or at least stretch a flat and let me know. I need to know if this is a problem with my camera only. In addition there is a bright artefact effect always around that same upper right corner. It might be related to the same optical phenomenon causing the circles but I will report on this issue when having supporting material.
