Hey
astrophotography on a tripod?
here is what you need to know:
http://http://www.capturingthenight.com/astrophotography-and-the-600-rule/
Darks flats etc: yes.
you do them because of the camera noise which has nothing to do with the lens used.
Speaking of which: a 50mm lens doesn't reach incredibly far so you will get a star field or wide field image. very beautiful!! and especially beautiful with your Sigma lens! (But you won't see the butterfly outline of the Orion nebula in the photos.)
Be sure to post your findings, okay?
waaaaaay down the track, you can do visual observing after having set up your imaging rig.
you'd just need an automatic camera shutter trigger so you don't have to click the remote yourself.
Have fun!!!!!
Annette