Common practice and solid math tell us that more dark and bias calibration frames in your master, the better. More is better, but how many more? To find out I have created as set of 1×1 binned test images. The darks are from 44 and 80 images and the biases are with 48 and 148 frames. Interestingly, I cannot see any difference between the two darks. They seem identical. The biases, on the other hand, are very different, with the bias produced using 148 frames having an obviously lower amount of noise.

It looks like, as expected, more frames are better. But I think I need to get another 100 or so darks to see if I have a similar difference to the bias frames. 44 to 88 dark frames didn’t seem to make a difference. Will having 150 dark frames make a difference?

The frame combination was done in CCDStack using a sigma clip mean combine and a sigma factor of 3.0. I think I need to try a version using PixInsight. Although I do my data reduction in CCDStack because PixInsight does not have bloom removal, and CCDStack’s bloom removal works very well.

The two bias frames, 148 frame version on top

148 frame bias

48 frame bias

The two dark frames, 80 frame version on top

80 frame dark

44 frame dark