HELP...Any idea what is causing this?

[William Bristow]

I don’t know the model of the camera you are using but vaguely similar images can be created on shutterless cameras when Auto-dark subtraction is accidentally left enabled in MaxIm (see options menu on the Expose tab of MaxIm’s Camera Control window) and an auto-dark is taken with the telescope uncovered but pointing at a target and then a normal image is taken of the target a little later with a small drift in mount pointing, after automatic subtraction of the auto-dark you are left with black shadows around the side of the star(s) corresponding to the opposite direction of drift, and a zero or negative ADU background pedestal.

If your camera has a shutter and you do use auto-dark subtraction then check that the shutter has not failed in the open position and if the camera doesn’t have a shutter check that auto-dark is not enabled in MaxIm.

Besides the above, any problem with the camera sensor bias voltages or clock timing for the sensor readout due to a camera electronics fault could produce a similar looking image.

William.