Pentax DSLRs are really good for inexpensive amateur astrophotography thanks to the Astrotracer functionality build into all their latest bodies. Basically they're reusing the sensor shift (IS) with a GPS info about location and gyro for calculating the orientation and track the night sky by moving the sensor - in the result you can expose for over a minute with a wider lens allowing you to keep ISO and noise at much lower levels without using expensive tracking equipment. I did my first ever astro shot last summer and it turned out really nice: http://behindtheviewfinder.com/bandon-and-the-milky-way