I bought this lens after owning the Tamron 200-500 for several years. I was getting frustrated with the very slow AF on the Tamron. After testing the Sigma for a while I sold the Tamron. The Sigma wins out on AF speed and having IS. There seemed little difference in IQ on the Canon 50D I was then using and, if anything, the Tamron was slightly sharper but not enough to make me want to keep it.
I have now had the Sigma a while. First problem I had was the zoom lock got stuck (it will no longer lock) might have been my fault for forcing the zoom when it was locked, but it now is broken. However, this doesn't make any difference in use and I have just got on with it.
Next problem I had is the lens hood doesn't always attach properly. One day in a bird hide I managed to dislodge it and it fell out the window where I couldn't retrieve it. The cost of a new one from Sigma is ridiculous for a small bit of plastic so I bought a metal screw in one. this works OK but only at the long end. At 150 it gives vignettting and so I might have to bite the bullet and get a replacement Sigma one.
Now, as I said, I was using a crop sensor camera (Canon 50D) and was never totally happy with the results. I decided I would go full frame and bought a Canon 5D Mk3 and was worried that I would be losing out on reach. But actually the new combination gives overall better results even when additional cropping is required.
I find the lens fairly easy to carry around - I just carry it with the tripod mount. It is heavy and I wouldn't want to carry it for miles but the odd few hundred yards is fine. And I have carried it around a few nature reserves for a couple of hours without any problem.
As with the Tamron the results are better in good light, but with the Sigma it is possible to get shots that were impossible with the Tamron.
The lens is better at f8 or above and better if you have enough light to turn the IS (OS) off.
Here are some recent shots with the 5D combo:
http://www.flickr.com/photos/alan-photos/8893027418/
http://www.flickr.com/photos/alan-photos/8893027892/in/photostream/
http://www.flickr.com/photos/alan-photos/8876777474/in/photostream/
The above are all quite big crops and are hand held. This one is taken from a hide resting the lens on a ledge
http://www.flickr.com/photos/alan-photos/8683605622/
This shot was taken at 1/100th sec on a tripod.
http://www.flickr.com/photos/alan-photos/8745624562/
Recently I went out with a friend who has the Canon 100-400 lens. We swapped for a while so he used my Sigma on a 7D and I used the Canon on the 5D. It was difficult to see any difference in quality (we were both hand holding). Now it was a fine sunny day and we were shooting deer not birds, so we didn't have to crop much. But overall it put me off buying the Canon (which I had been considering) as there seems to real advantage for me. Having said that the 7D/Canon 100-400 did give good results in my friends hands so if I was starting from scratch that may be a good combination.
Here are some older shots with the 50D for comparison:
http://www.flickr.com/photos/alan-photos/7067850433/in/set-72157605429740294/
http://www.flickr.com/photos/alan-photos/7047382781/in/set-72157605429740294/
Now none of the above photos are going to make the cover of National Geographic. As a hobby photographer who is more interested in taking reasonable quality record shots of wildlife I see it is overall it is a tricky choice to find a long lens that doesn't cost and arm and a leg to buy. For me the Sigma wins out over the Tamron 200-500 and the Canon 100-400. No doubt others will disagree but the AF speed, the IS and the extra length of the Sigma are the deciding factors. The IQ is, off course, important but under the right conditions (good light/solid support/fast shutter speed and f8 or more) there all three lenses seem to be capable of taking decent shots.
Update: Birds in flight. I recently went on a trip to the Farne Islands and took some shots of birds in flight. I have had limited success in the past with this. The Tamron AF was far too slow and the Sigma on the Canon 50D was better but still not great at holding the AF. On the 5D3 I got a lot better results due to the AF and AF tracking systems.
http://www.flickr.com/photos/alan-photos/9160471114/
I took a lot of shots of course and the hit rate was sill fairly low, but I think that is down to my tracking skills.
Overall the camera body you are using seems to make quite a difference to the performance of the lens - which I guess is fairly obvious but something I didn't really consider too much before.
I have now had the Sigma a while. First problem I had was the zoom lock got stuck (it will no longer lock) might have been my fault for forcing the zoom when it was locked, but it now is broken. However, this doesn't make any difference in use and I have just got on with it.
Next problem I had is the lens hood doesn't always attach properly. One day in a bird hide I managed to dislodge it and it fell out the window where I couldn't retrieve it. The cost of a new one from Sigma is ridiculous for a small bit of plastic so I bought a metal screw in one. this works OK but only at the long end. At 150 it gives vignettting and so I might have to bite the bullet and get a replacement Sigma one.
Now, as I said, I was using a crop sensor camera (Canon 50D) and was never totally happy with the results. I decided I would go full frame and bought a Canon 5D Mk3 and was worried that I would be losing out on reach. But actually the new combination gives overall better results even when additional cropping is required.
I find the lens fairly easy to carry around - I just carry it with the tripod mount. It is heavy and I wouldn't want to carry it for miles but the odd few hundred yards is fine. And I have carried it around a few nature reserves for a couple of hours without any problem.
As with the Tamron the results are better in good light, but with the Sigma it is possible to get shots that were impossible with the Tamron.
The lens is better at f8 or above and better if you have enough light to turn the IS (OS) off.
Here are some recent shots with the 5D combo:
http://www.flickr.com/photos/alan-photos/8893027418/
http://www.flickr.com/photos/alan-photos/8893027892/in/photostream/
http://www.flickr.com/photos/alan-photos/8876777474/in/photostream/
The above are all quite big crops and are hand held. This one is taken from a hide resting the lens on a ledge
http://www.flickr.com/photos/alan-photos/8683605622/
This shot was taken at 1/100th sec on a tripod.
http://www.flickr.com/photos/alan-photos/8745624562/
Recently I went out with a friend who has the Canon 100-400 lens. We swapped for a while so he used my Sigma on a 7D and I used the Canon on the 5D. It was difficult to see any difference in quality (we were both hand holding). Now it was a fine sunny day and we were shooting deer not birds, so we didn't have to crop much. But overall it put me off buying the Canon (which I had been considering) as there seems to real advantage for me. Having said that the 7D/Canon 100-400 did give good results in my friends hands so if I was starting from scratch that may be a good combination.
Here are some older shots with the 50D for comparison:
http://www.flickr.com/photos/alan-photos/7067850433/in/set-72157605429740294/
http://www.flickr.com/photos/alan-photos/7047382781/in/set-72157605429740294/
Now none of the above photos are going to make the cover of National Geographic. As a hobby photographer who is more interested in taking reasonable quality record shots of wildlife I see it is overall it is a tricky choice to find a long lens that doesn't cost and arm and a leg to buy. For me the Sigma wins out over the Tamron 200-500 and the Canon 100-400. No doubt others will disagree but the AF speed, the IS and the extra length of the Sigma are the deciding factors. The IQ is, off course, important but under the right conditions (good light/solid support/fast shutter speed and f8 or more) there all three lenses seem to be capable of taking decent shots.
Update: Birds in flight. I recently went on a trip to the Farne Islands and took some shots of birds in flight. I have had limited success in the past with this. The Tamron AF was far too slow and the Sigma on the Canon 50D was better but still not great at holding the AF. On the 5D3 I got a lot better results due to the AF and AF tracking systems.
http://www.flickr.com/photos/alan-photos/9160471114/
I took a lot of shots of course and the hit rate was sill fairly low, but I think that is down to my tracking skills.
Overall the camera body you are using seems to make quite a difference to the performance of the lens - which I guess is fairly obvious but something I didn't really consider too much before.