The lens is one of Canon's L-series (L for luxury), which in turn are one of the best lenses in the world. Of course there is distortion in the super wide angle at 17mm, but can be found in the competition as well, which brings this extreme focal length just by itself.
In addition to the optical quality of L lens, the quality construction is to be commended, and all-metal sealed yet light and dust. A lens hood is supplied. From its dimensions, however, the lens is compared to the kit lens a log, you can see at first glance that this is not a toy. The autofocus is a USM-type, that is, rapidly, silently and with activated AF may at any time be manually rotated the focus ring.
The integrated light intensity is in this objective 4.0. That's not very much, at least if you want to take pictures at minimum light. But this kind of pictures do I do with other lenses. The EF 17-40 I use mainly for landscape photos and Full Body Portraits, if space is tight.
I had in front of the EF 17-40 a Tamron 17-35 for about 300 euros, also an optically very appealing lens. But to the built to last forever Canon it was enough in all respects not reach far.