Thank you for the great info, Patrick. I have two questions. Is it possible that the blue filter is insensitive to compensate for the blueness of the atmosphere? Also, could you detail how the flats are made? I had the impression that a new one had to be made for every different setup you use, such as one for a 60-second exposure with a certain focus, another for a 30-second exposure, etc. So I have never done it. Also, what was the illumination source? I had thought that a sheet, etc., stretched over the telescope at dawn would do it, but I really don't know. Thanks, Joe Patrick Wiggins <paw@wirelessbeehive.com> wrote: Chuck, in your earlier message on the subject you wondered about possible blue insensitivity of some cameras. Well, this morning after finishing my routine minor planet work I set to making flat frames for each of my filters. For those who may not know, flats are used to remove the effects of dust in the optical train and are made by pointing the scope/camera at a uniformly illuminated sheet of white cardboard and shooting a whole bunch of pictures through each of the filters. Those pictures are then combined into one master flat for each filter. With no filter I was able to get enough signal to make a good flat in just under 5". For IR it took 10". Red was 15", green (actually a "visual" filter) 90". And then I tried blue. After 360" (6 minutes) I still only had about 1/4 of what I was able to get unfiltered in 5". So I think it's safe to say the SBIG ST-10 is not very sensitive in the blue. BTW, for those that might be interested, for last night's/this morning's galaxy imaging experiment, I settled on M-63. I shot 10 one minute exposures through each of the 5 filters plus another 10 one minute exposures with no filter. Next step it to apply the dark and flat frames to each and then register them all so they all line up nicely. Once that's done I should have 60 frames which, if I understand this stuff correctly, should enable me to add some (all?) together and form a color "pretty picture" of M-63. If anyone is interested I'd be happy to make the data available to others so they can try their hand at it. Cheers, patrick _______________________________________________ Utah-Astronomy mailing list Utah-Astronomy@mailman.xmission.com http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy Visit the Photo Gallery: http://gallery.utahastronomy.com Visit the Wiki: http://www.utahastronomy.com --------------------------------- Be a better friend, newshound, and know-it-all with Yahoo! Mobile. Try it now.