This image was taken on an SBIG STL-11000 on this GSO 8" RC telescope. It is not meant to show a pretty picture it is for examination of the quality of the star image in the corners. This effect is caused by field curvature and can be corrected. Using this image from a 36x24mm chip you can see what it may look like on your smaller sensor if you wanted. This issue can be corrected easily with a flattener. I could not find any uncorrected images on the web like this, so here you go!