What is this

I have the attached image from an lx200 at f3.3 and a Sbig St-6. What is causing this and can I fix it?

Would welcome your insight.

Dan

Attached Image:

Looks like Vignetting to me.
Floyd

Dan,

It looks like vignetting. Here is your image processed in Photoshop to even the background.

Lee

Attached Image:

The best way to correct vignetting is with flat frames. They have the added benefit of correcting any shadows from dust on any of the optical surfaces. All you need is a few images (it is best get an average of a few) taken of an evenly illuminated surface. Don't change the focus or position of the camera. A shot of the twilight sky with t-shirt or towel stretched over the end of the OTA is a quick and dirty way to take a flat frame. Adjust the exposure to get a peak value of 35 to 50% of saturation. Any ccd software can make the correction to your image once you obtain the flats.
Dave

So far it seems that the image can be nicely massaged with Photoshop thanks to Lee. Also vignetting seems to be the evil here, and flats are the answer. I need to read on flats, and have at it. To all of you kind folks who have responded so far much thanks.