bobbyz wrote in post #17015736
Mainly for high school sports with 5dmk3. I used to have 300mm f2.8 IS ver I and it was very nice but then I had two bodies and needed 70-200mm f2.8 on the 2nd camera. With sigma zoom, I can hopefully get with one camera/lens making it lighter for me. Price wise used canon prime goes for almost same as brand new sigma zoom. Sigma zoom AF in AI servo still scares me. Never had issues with canon primes but did with sigma non OS zoom (120-300mm f2.8 non OS) on 1dmk2.
Another option is 120-300mm f2.8 OS non sports model which I think I can pickup easily if I sell my 70-200mm f2.8 IS II and exchange canon 24-70mm f2.8 II zoom with tamron 24-70 VC model. Come to think I haven't used my 24-70mm f2.8 II at all as I like 35L and 35mm f1.4 over it for indoor shots and outdoors for me longer focal lengths work better.
I can only comment on the oldest sigma 120-300 pre-OS, pre-Sport. Compared to the 300 2.8 IS it was more like f/3.0 and 280mm. It had pretty fast focus but, all the same, couldn't keep up with the Canon and the focus just didn't seem to be as precise either, noticeably more misses shooting sports. Sharpness wasn't bad, but the Canon plus 1.4x TC was still a trace better form what I recall though. When people had the choice of which to grab to shoot with, almost everyone grabbed the Canon despite losing the ability to zoom (hand-held zooming with the sigma was awkward anyway, although fine if restricted to a monopod). Canon all the way, all day and night for me.
That said the newer versions use totally new optics and AF logic so my story might have no bearing on the ones you are looking at most, although maybe the non-OS you are looking at is the same? (unless it's a slightly newer one too).
Although speaking of the new Sigmas, I believe they are quite the beasts, and even heavier than the Canon, supposedly enough to feel the difference. If you like to shoot hand-held when you can that might also be a noticeable bonus for the Canon.
It is true, that without a second body you can miss some close shots for football and soccer with the prime, but I'd still rather the Canon prime over the Sigma version I used. I find that far and away more of my best soccer and football shots came from the super-tele vs the 70-200 when I was shooting with two bodies anyway so the zoom wasn't something that would've been as missed as thought (although certainly it is possible, especially in football, to miss something big in the near endzone or immediate sideline with a big prime only and no 70-200 or 24-70). For basketball the Sigma is too long at the short end to sit under the basket, far corner at best plus it's too heavy and unwieldy as a main basketball lens, just something to nab for the far basket now and then perhaps.