I've bought a few days ago, the Sigma 18-125mm (see exact description in the title) and tested it as part of my options extensively. (Also with stabilization) Canon 17-85mm used - for comparison was the - not so bad - kit lens of the Canon EOS 450D (with stabilizer) and the well-known - and controversial. Bathroom tiles, documents, people, buildings and landscapes have had to serve as test subjects. One thing, regardless of the focal length upper limit that is so different, the Sigma the Canon kit lens had scarce and the (comparatively very expensive) Canon beaten clearly 17-85mm. Overall, the differences are not dramatic.
The Sigma produces the wide angle end (naturally - like all other lenses also) distortion, but more moderate than the other candidates, especially compared to the Canon 17-85mm whose distortions are clearly disturbing and its focus in this area, also dimmed, and also ( Surprisingly) opposite the Canon Kit lens wish to unsatisfactory. Randabdunklungen are, so just still visible at Sigma, depending on the subject, here too it is better than the listed competitor.
As for the distortion, they are often confused with perspective distortions. The latter arise when the camera, especially in wide angle, but is not kept straight upward in order to "get it all" building. The then "everything will collapse" is normal and has nothing to do with distortions.
In terms of color reproduction Like the Canon kit lens is best, a subjective impression added, which can be influenced by the choice of the image stems on the camera so not least that this issue be neglected.
The Sigma can also be in the telephoto range provide fast and accurate focus, these three exposure levels, which will bring the stability, I could not reach. A maximum of one step was for me at 125mm it. . That is 125mm compared to 200mm are small format - after the old reverse control so a "normal" shutter speed of 1 / 200s - I still can capture sharp images with 1 / 125s - it was no longer. Although even here a comparison is misleading because the Canon 17-85mm only up 85mm "going", I had the impression that the stability in this Canon lens is a bit more effective.
In the sum of all the properties that can not all be listed here - is not a book to be - I am extremely satisfied with the Sigma. It offers an ideal range of focal lengths, making in all areas (in the corners) sharply, making brilliant colors, the auto focus engine is fast (similar to the USM in Canon) and the handling is beogen on operation, size and weight absolutely fine.
I would recommend it.