Andrews sell 15 * 70mm (and 11 * 70mm and zoom ones) ones that where good, cheap ($149) and very light. At 70mm you get alot more light reach than 50mm - effectively double - which makes a huge difference from my experience.
I'd easily recommend 70mm ones over 50mm - pointing 50mm vs 70mm at Orion or its belt was a chalk vs cheese comparision for me.
http://www.andrewscom.com.au/site-section-11.htm