on the 550D a very good lens

From the pictures on the 5.6 aperture throughout the zoom range are sharp.

But what is also very important and is often not mentioned, vignetting and chromatic aberration is both the APS-C sensor in a super small extent and ensures a clean image with beautiful colors and great contrast.

Only be slightly out of focus at the edge images with a panel under 5.6 is the reason that I do not give 5 stars.

Many other expensive lenses but to also deliver major problems with a panel under 5.6 a perfect picture.

In the 24 -105 L IS USM is as the Chromatic Aberrations very high which can be quite disfiguring a picture.

The 15-85 IS USM has its problems with vignetting and also fast blurred

The only alternative is the 17-55 2.8 IS USM which is more than 200 but is slightly sharper expensive and the lens hood supplied with has