Canon EF L USM wide-angle zoom lens - 17 - 40mm F/4.0

Overview
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I bought the EF 17-40 f4 L about 3 years ago in order to take urban landcape pictures, as buildings often don't fit into a 28mm "frame". This optic is the widest in the f4 constant aperture series of zoom lenses in the trio that includes the 24-105 super-zoom and the 70-200 telephoto, all of which I now own.

At the time, I owned a 20D body and the 17-40 was my first L Series purchase as the 1.6 crop factor on the sensor meant that you had to go for a super-wide angle lens to get even moderate wide angle shots (17mm becomes 27mm on an APS sensor). Now I own a 5D body and can make full use of the extraordinary wide angle of view this lens can provide. Being a standard EF mount (not EF-S), this lens can be used on all the Canon bodies. My friend had an EF-S 10-22mm but this became redundant when he upgraded his body from a 20D to a 5D.

Build Quality
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This lens is well up there on the build quality, having all the great hall marks of the L Series - great optics, solid construction, low distortion, constant aperture at any focal length and weather-proofing courtesy of o-ring seals on the body join and a non-extending barrel when focussing and zooming. Compared to the other lenses in the series, this is a very compact and light weight unit and the controls are very slick with a great feel to the zoom ring and full-time manual focus ring (so you can use it to adjust focus even when in AF mode).

The front element does not rotate when focussing so you can use filters easily.

One beef I had was that you don't get a lens shade with this lens as standard. The 24-105 and 70-200 by comparision do come with a shade. Even though the lens is one of the cheaper ones, it seems a bit mean to make you buy the shade as an option when spending £500+ on a lens. It's just a bit of clip on plastic, after all.

Performance
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In use, this lens is very easy to handle and produces great sharp images with bags of colour and contrast. With a constant minimum focus distance of just 28cm it also makes a quite good macro lens, capable of taking pictures of quite small objects, a surprise for a super wide lens. If you get too close to your subject and use the 17mm end of the range you can get some pretty extreme perspective distortion (but not fisheye) going out to the edges of the picture. I often use this lens to take pictures of trees, towers, light houses etc. from lying on the ground at their base, framing portrait vertically. I can usually get the whole thing in, from ground to sky! You can also do the advertisers favourite trick of taking a picture of a person from above - huge distorted head and face with seemingly far away tiny body and feet. In short, you can have a lot of fun with this lens!

Shooting at normal distances for landcapes there are minimal barrel distortions and the images are sharp out to the corners. Light fall-off into the corners can be seen when using a full frame body, like the 5D at wide open but not on a APS sensor body (20D, 30D, 40D, etc.) or if you stop down to f5.6 or smaller.

Unlike the other lenses I own, this one does not have image stabilisation. Honestly, it doesn't really matter so much on this lens as being a super wide angle, you don't need such fast shutter speeds to hand hold in low light. If the general rule of thumb is a shutter speed 1.5x the focal length then you can hand hold 17mm shots at about 1/25th second and get acceptable results. With practice, I've been able to get some usable shots at 1/8th second when leaning against lamp posts or fences. It also saves power, as the IS on the other lenses eats into the battery significantly.

AF performance is very fast and accurate with this USM lens. The most common reason for it hunting is when I've pressed the shutter button with the lens cap on! The circular aperture gives smooth blur to backgrounds but given the short focal length and maximum aperture of f4, it never gets really really out of focus.

The 17-40 can almost do duty as a "standard" prime lens (especially on a APS body where it does cover the 50mm range).

Another good thing about this lens is that it's comparatively quite cheap (for a L Series) at around £550 and you can find it discounted heavily on-line or there are always a few going on eBay second hand, as users upgrade to the 16-35.

How About the 16-35 f2.8?
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I also tried a friend's EF 16-35 f2.8 L and optically it compares very well with it's much more expensive brother. The MkI 16-35 that I tried was certainly tempting... usefully wider than the 17mm in practice (suprisingly so, given the 1mm difference on paper) but it was significantly bigger and heavier. It cost twice as much too and I felt that I'd miss the extra 5mm of range at the long end. Conversely, the added background blurring afforded by the maximum aperture of f2.8 was attractive... Tough call.

The new 16-35 MkII is supposed to be better but is even more expensive and MUCH bigger and heavier than the MkI.

Conclusion
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I love the 17-40. It's an outstanding bit of glass and good value for money. If I was buying for a 5D rather than an APS sensor body and I had the extra dosh, I'd probably get a 16-35 MkI but the MkII is just too big and heavy.