HELP...Any idea what is causing this?

[Grady Boyce]

Hello.

We have a FLI Proline backlit CCD. Tonight, these are the images that I am getting, see attached. Any idea what is causing this? Thx. Grady

Bad image.jpg

[Bob Denny]

Someone else with more experience might know, but me? I don't have a clue. It doesn't look good though.

[Dick Berg]

Hi Grady,

Well, I can see that there are numerous "stars" (for lack of a better name :-) scattered over the image. A lot of heavy image processing yields up a passible image. But is it real? Does it look familiar? I can't identify the field because I don't know the plate scale. All-Sky yields nothing. Your .jpg image is about 800x800, probably not the original sensor size of the FLI Proline. In any case, recreating the image doesn't answer your question.

Bad image5.jpg

There seem to be two different problems - the "shadowed" star images and the grey background. Both can be explained as the result of subtracting (or dividing) one image by another, in which the two images are not precisely aligned (horizontally
in this image).

Calibration might be a problem. The usual calibration step is an arithmetic division of the real image by the calibration image, but calibration would not normally generate a grey background. Were new calibration flats taken recently? New calibration masters might have been incorrectly created.

Were all of the images last night were bad, or just one series, or just one? Can you tell me where you were imaging? Otherwise, a problem in the camera readout?

A real conundrum right now. I'm sorry, this is not much help, either.

[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.