Jerry, My bad. The most recent 300 sec Gras master dark is now available in the project directory for downloading at: http://fisherka.csolutionshosting.net/astronote/photos/processing/ as file "091206_0141_Darks_300_033.zip" 11mb. For reasons that I do not understand, although these master darks are in the GRAS14 calibration file directory, the flat in the dark file is prefixed "G12". i applied it to the luminance image and it did noticeably improve the result. Enjoy, Merry Christmas - Kurt