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