Originally Posted by Jon Ruyle
That's a good point Jon, I didn't think of it that way. I guess from experience I have seen less noise from the shorter exposures than one long exposure. I could probably borrow a mechanic's IR thermometer and do some field tests but that might be going over the top.
Also, your absolutely right about wide lenses taking a while to get the trails. That one of mine took around 1.5 hrs and the trails aren't overly long. I guess it's a trade off between the number of stars in the shot and the length of the trails. Might try it out close to 20mm with the same lens next time and see how I go.