I shoot with a Canon EOS 50D usually sporting highlights as a large zoom is extremely important. Of course, the light intensity is not that you get to 50m razor sharp images in a sports hall (F6.3) but for the price I'm satisfied (ask the ISO speed to 3200 noise present, but barely discernible to a layman).
In stadiums with good light excellent. The speed of the autofocus is acceptable - please, you always have to see the price.
The images are crisp and sharp sun, in the hall the Sigma comes in f5,0 - 6.3 in my opinion, the "air" and I have to camera technology and image stabilization, despite working suuuper, tripod and possibly software (subsequently) use.
For quick shots (6 frames / sec) I am sorry to turn off the autofocus because otherwise only the first 3 pictures are really sharp. Since the choice of the host location is very important.
All in all, the Sigma 18-250 / 3.5-6.3 DC OS HSM is a suuuper great lens that I recommend any amateur photographers!
Time will tell (have the Sigma 12 months - about 3000 images), how innovative the durability and robustness. There are too lenses from 2000 - Canon huge differences.
My tip - buy, try and you will be impressed -
Have fun shooting
