Flats, reflection issues

[DMouse]

Hi, I am having problems getting the flats I have taken to correct my images properly. I apply the flats but still end up with a ring in the middle. I have tried using DBE but it is still there.
Any ideas on whether looking into my equipment being the problem or the flats processing? I am using a 12 inch F4 Newtonian, and a flat panel for calibration. The camera is an ATIK 383L+ mono. I have taken out the 2 adapter rings and painted the inside with matt black paint. It has helped a little but the ring is till there?

Any help in either post processing ideas or equipment tweaks greatly appreciated

Paul

[pfile]

someone on CN had this problem with a newt. seems that his coma corrector was sticking into the tube, creating reflections. check it out:

https://www.cloudynights.com/topic/654342-two-years-and-counting-dealing-with-this-image-artifact-help/


rob

[DMouse]

Ok, I did check my scope for that and the coma corrector does stick out a tiny amount but not even enough to occlude the primary mirror, to be honest it is close to flush with the side of the OTA. The OTA inside is also flocked.

[pfile]

well this wasn't so much about the corrector occluding the mirror as much as it was reflections incident off of the front edge of the corrector... if light can see the edge of the corrector then it can bounce off of it. anyway if you can swing it you might try making sure the front of the corrector is flocked and/or blackened somehow.

rob