An easy way to capture flats (if you have a flat lcd type computer screen) is to set the screen to a white background and shoot them thus:
http://www.smugmug.com/gallery/85204...988_ERAyD-A-LB
I use an Apple 23" screen with the brightness adjusted to lowest level plus three sheets of tracing paper in front of the scope to mute the brightness again. It works perfectly on both my Artemis 110002 mono camera with filters and also with the SXVR-M25C one shot colour camera.