So, Jerry in your dark library you only need the 16 images (4x) per time/temp? When I first looked up Berry’s book on the web I believe it was going for $99.00. I was able to find a copy for $30.00, so I better check out the version of the AIP4WIN CD that came with it. The book is very thorough. It is like a collage level course. I have been reading mine with a pad of paper and a calculator handy to work out the answers for my 350D. I am still trying to figure out the differenced between what applies to a “one-shot” DSLRs and the LRGB try-color guys. One thing I learned is that DSLR guys can’t bin at the imager and don’t bin in processing. I can bin a DSLR later in post processing, but I only get noise reduction at the much greater cost of loss of resolution. It's generally not worth it for DSLR. But, I still read about it. I may get a LRGB outfit someday. For the time being I want to learn all I can using what I have. Jerry, I am glad to know you are so versed in these things. I am sure when I can’t understand a concept you will be able to enlighten me. I am heading back to the book right now. Jim --- On Wed, 3/18/09, Jerry Foote <jfoote@scopecraft.com> wrote: From: Jerry Foote <jfoote@scopecraft.com> Subject: [Utah-astronomy] Bias & Flats To: utah-astronomy@mailman.xmission.com Date: Wednesday, March 18, 2009, 1:58 PM Hi Jim, Actually taking the bias frames would be doubling your effort. Since the darks will already contain the bias information then merely subtracting the darks from either the actual image or from the flat image will remove the bias noise. The only time bias frames need to be taken is if you are going to scale your darks for either exposure time or temperature. Frankly scaling darks is usually a poor substitute for keeping a set of Master darks handy for both exposure time and temperature. Usually darks are very stable over a long period of time (months or even a season). Taking 64 darks might be a little overkill as it produces an 8x reduction in noise. Comparing this with the noise from the actual frame puts it down in the mud. With that said, when it is cloudy and you are tired of the tube why not take them. It will be harder to get sets with varying temperatures which, with their relatively long life, allows you to get them throughout the season and use them next season. Strictly speaking the flats should also be taken at the temperature of the actual image as there is a very slight change in pixel sensitivity with changing temperature. Again this is way down in the mud. I really like Berry's book. It is always ready at hand for that nitty-gritty question. By the way there is a new version of AIP4WIN that has many enhancements particularly for DSLR imaging. Check out the Willman-Bell web site. Jerry Foote ScopeCraft, Inc. 4175 E. Red Cliffs Dr. Kanab, UT 84741 435-899-1255 jfoote@scopecraft.com _______________________________________________ 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