I have noticed for some time that I get an uneven separation or maybe better described as an area near the top of the STL-11002M chip that is darker then the rest. It's more prominent in the flats images which I take using an XLFlatMan panel. The panel is about 8" from the front of my 12.5" f/9 RC mounted on my southern observatory wall. I take the flats when it is completely dark inside the observatory and use ACP's AutoFlat script to adjust the ADU which I have set at 32,000. The same discrepancy can be seen in the raw light images. I've uploaded a master flat and raw image to see in each. what it looks like is a darker area, straight line dividing, about 150 pixels down from center top. I've uploaded a raw 2x2 fits file and a master dark that shows the issue very well. Looking at the CCD chip from the open end of the telescope doesn't show any obstruction that I can see. The imaging train consist of the STL-11002M/FW10/Pyxis 3" rotator, and several AP spacers to bring me to the proper back focus distance. The files can be downloaded here: https://www.dropbox.com/s/gzlnj9i3uwjgjub/NGC1788-S001-R009-C001-Red.fts?dl=0 https://www.dropbox.com/s/t0g21ne7j2hlw6q/Flat Master - AutoFlat-PA310-Red-Bin2-001-West.FIT?dl=0 Thanks for looking, Steve