If you do not like to compromise ...

I photograph professionally wide motifs in confined spaces in low light - a conceivable difficult environment, right? Not for this lens. The Canon EF-L USM 4.0 17-40 is operated with me to a Canon EOS 1D Mark II N and therefore has a focal length multiplier of 1.3 times. The lens has thus still an effective focal length from 22.1 to 52 mm. So you can in the smallest space yet all get out. The image quality is second to none. I have tried the Sigma 12-24 mm, nice wide angle, but blurred. I tried the Sigma 17-35, not so great. I have the Canon 18-50 attempts (then still on the EOS 10D) not to use, good pictures, good sharpness, but on the 1D - a vignetting occurs at about 18 to 24 mm.

The 17-40 L is its length full justice. The lens is compact, high-quality fabrics (made of metal), though not too heavy. The optical performance equivalent to more than the entire zoom range of my idea of ​​a perfect sharpness.

Conclusion: Do not like to try long - buy it now the right lens. This is expensive, but still cheaper than three times the wrong thing.