Summary: I bought this zoom for its long reach. I couldn't afford the similar canon zooms so I purchase this one. I am using this zoom with the canon 7d for bird photography. Canon 7d is very fast which is perfect for birding. This lens is a good lens overall but for birding I find some issues: 1) The focus is slow 2) The pictures are not sharp like Canon pictures. 3) The zoom is much slower than the camera (Canon 7d). 4) The zoom is heavy.
Summary: pro's 1) You don't need to constantly change lenses. 2) images are tack sharp 3) image stabilization works well con,s 1) autofocus goes hunting at critical times 2) lens is heavy 3) some vignetting at 500. 4) somewhat stiff when going from 50 mm up. 5) exposure metering is also problematic and I often have to go off my eye. I bought this lens because I mainly shoot scenic and wildlife photography with doing minor work in sports, friend's weddings etc.
Excerpt: This is not a lens that can be easily handheld or carried. It is a lens to be taken on excursions devoted to photographing subjects that are appropriate for the long reach of the lens. It is too heavy and bulky to carry in the field on extended hikes just in case you might find a use for it. It needs a sturdy tripod designed to handle the full weight of the lens/camera combination. The lens has a lock to address the lens creep problem. But the lock is poorly designed.
Excerpt: If your thing is wildlife and you want to lug only one lens you may consider the Bigma as it's versatility can not be beat. At 200mm its useful for those quick shots of dragonflies and butterflies. IQ is far from a dedicated macro lens though, but this is to be expected.Three stars for me because the AF is slow,(initial focus acquisition is night and day as compared to my Canon 400 f 5.6) focus limiter might improve it a bit.
Summary: The Sigma 50-500 F/4.5-6.3 APO DG HSM SLD Ultra is a reasonable compromise between shorter and longer lenses. I use it on both a Canon T4i (using the additional lens hood adapter for the APS-C camera) and a Canon 5DIII using the standard Sigma full-frame lens hood. The lens is large, heavy, but physically sound. It comes with a well-padded carrying case that has room for both lens hoods, if you follow the instructions on how to connect these hoods for storage.
Excerpt: This is an affordable long lens which takes decent quality images. It is sharp up to about 400mm, gets soft after that point. The lens, however, is not constructed very well. The auto-focus is clunky, the optical stablization is erratic, and the contact points with the camera body failed for me within 2 weeks of operation (a problem which I understand is common). My lens is presently on its way in for warranty service.
Summary: After reading reviews here and elsewhere, I took the plunge on this lens because I was looking for something a bit longer than Canon's 100mm-400mm lens (which is getting long in the tooth and overdue for a new version). I've been using a Canon consumer grade lens (18-200mm F3.5-5.6 IS) for over a year with outstanding results; I expected to get similar, if not slightly better image quality from the Sigma.
Excerpt: I bought this specifically for a vacation trip to Alaska, and it stopped auto-focusing two days into the trip. I've just sent it off for repair, so I can evaluate their service too! Even with manual focus the wildlife was brought in sharp and clear.