Hi Eric,
I also have a K100D, and have recently been attempting some star trails. I've also discovered how noisy the Pentax chip is! When doing a series of repeated 30 sec exposures, it starts off with minimal noise, but after about 10 or 15 consecultive images the noise rapidly builds up (as in your image)
. So try and limit it to 10 shots at a time, and then let the chip recover for a while. Here is an example of 10 stacked 30 second exposues with darks subtracted:
http://www.iceinspace.com.au/forum/s...d.php?p=501625
With respect to the processing, however, I've found that Deep Sky Stacker handles the Pentax RAW format, and the results are much better with RAW files than with extracted JPGs.
Hope this helps.
Cheers,
Stephen