[PKay (Peter)]

This morning i refined my technique for taking flats.

I aimed the scope into the pre dawn sky.
Then (using sharpcap) watched the histogram and the live image.
Varying the exposure time I was able to find the optimum exposure to reveal a lens problem.

Tried cleaning the primary lens and fault is still there.

So I have a field flattener. Maybe the problem is there, or maybe on the camera lens?

Quite interesting.