pkoss455 But if it was light I would think that the light image would rotate in the frame when I rotated the camera. The gradient does not rotate when I rotate the camera.
The newer filter wheels actually bolt solidly on to the camera body with four screws, so they rotate with the camera. However, the interface between the filter wheel and the camera body leaks light like a sieve. If you don't have one of those abominations, it is not your problem.
Another place where light can potentially leak is through the back from the ventilation holes of a cooled camera. Try pointing a bright flashlight in there too, and also through the fan blades at the back.
Warm camera components could do it too, since internal warm parts would bypass any IR protection window. If the camera has an anti-dew heater, try keeping it off.
Good luck. At least you won't need dark skies to look for the problem.
Chen
