There will come a time, probably early on in your developing passion for photography, where you're going to be staring at lenses like this Sigma Photo 24-70mm f/2.8 with unconcealed longing. That's because, if you had a choice of only one lens to have in unpredictable circumstances, this would probably be it. It's an absolute favorite of wedding pros because it offers a variety of useful focal lengths, plus the light-gathering, background-blurring ways of a big aperture that stays at a constant width through its entire zoom range. So get those impromptu group shots of the old high-school gang — or the festive shot of the bride's face as she climbs into the getaway carriage — and never worry about the time of day, as this lens will deliver the goods in almost any situation.
While this lens is optimized for full-frame cameras, it's highly popular with APS-C shooters as well. On mostcameras with that type of sensor, it will offer a similarly useful effective focal length of 36-105mm. Give it a try snapping impromptu candids at your next party.