looking for opinions on lens

I am about to buy the Canon 5D mark III, but I am also looking at purchasing a new lens to help out with some ot the youth sport pictures I am taking. here is the lens I am looking at Canon EF 100-400mm f/4.5-5.6L IS USM Autofocus Lens. My main concern is the f stop. I know with my 50D and a 2.8 shooting knight baseball games are real grainy.

is there a nother lens you recomend that is in the same price range.

My $.02... Pickup up a used Sigma 70-200 f/2.8. Once you have some time with that lens, you can upgrade to the Canon L version I or wait a little longer for the vII. For sports, I love my 7D. I have a 5D Mark II and rented a Mark III, but the frame rate on the 7D for high speed action is THE ticket for less than $1000 used.

+1

If you're shooting night games, go with the 70-200/2.8 instead of the 100-400... f/5.6 won't cut it in low light.

You're in a tight spot. For night sports you really need at least a 2.8 to lose some of the grain. For baseball a 400mm is a a great range. I guess it will depend how much night baseball you plan on shooting. If I was only going to shoot a few night games (and did not have to shoot the night games), I'd probably sacrifice those games for the longer reach of the 100-400mm. If the majority of the games, or if you had to shoot, the night games then I'd sacrifice the reach. But with that said you really can't go wrong with a 70-200 f/2.8 as you can use that lens for about everything. I'll use the 70-200 for every sporting even I shoot, the only variable will be what lens I use on my other bodies.

I quickly looked at your website, and it appears you do some portrait work outside. The 70-200 is a great lens for that as well, where as the 100-400 not so much. That would be another + for getting the 70-200. I have no ideal what your wallet is like...but I've learned it's cheaper to buy once and cry once. Sure the sigma or early L's will get you what you need, but for the most part you get what you pay for. I've had the original Canon 70-200, the current Sigma 70-200, but now have the new 70-200 L. I could have saved several hundred dollars buy just getting the 70-200 II. It takes a 1.4 ET a lot better then the original giving you close to a 300mm f/4 for you day games. In my opinion you'll use too much IQ putting a 1.4 ET on the original 70-200. It will be up to you if spending the extra $1,000 is worth that (buying new).