A Bias Frame
A Bias Frame: This is an example of a bias frame. A bias frame is essentially a zero time length exposure. It can be used to adjust dark frames when an exact time match with a light frame is unavailable. This is a "sigma" combine of 15 individual bias frames. A "sigma" combine is an average of all non-outlier pixels. If a single pixel in one of the images is very far from the average of the other images, typically because of a cosmic ray strike, that pixel is not included in the average.
Date: October 2009
Camera: SBIG ST-10XE
Processing Notes: Capture with CCDSoft. Combined with Sigma Beta.