I am planning on purchasing the 7D this week for use in my wedding videography business. I hope to build an arsenal of lenses over the next year, but my budget is very tight for the time being. That is, I don't mind dropping cash on one really good lens right now, but I can't afford multiple ones. What would you recommend as the best starter lens for video? Low light performance is extremely important as is a zoom lens. I was thinking about the Sigma 50-150mm f/2.8 II EX DC HSM Lens. Would this be a good choice? Any better ideas?