I took the first images through my new STXL16200 last Thursday I am getting a lot of noise in the lower left hand corner on all of the images. Can someone tell me what may be causing this ? Is this light pollution, or possibly stray light getting in somehow ? The attached image is a raw image of M45 taken from by back yard (suburban location) with CCDOps with no dark or flat subtraction. The moon was out but not in a position where it would have cast any light into the optical tube.
In a suburban location with the moon out? This is simply a gradient in the sky glow. When you stretch the image to bring out the faint nebulosity, you also amplify any gradient in the background by the same amount. There are software tools, such as the background removal tools in MaxIm DL, that can improve on this... but the best way to get good results is to start with good data. I'd suggest you try it again on a moonless night - it should be a lot better. In a suburban area you likely will still get some gradients, but they will be more manageable to deal with in post processing.
