Canon EF 17-40mm design and build quality
Mounted on a body like the Canon EOS 400D / XTi or the EOS 30D, the EF 17-40mm becomes a general-purpose lens which competes against a number of popular EF-S models. We've pictured it below alongside the three most common options: from left to right are the Canon EF-S 17-55mm, the EF 17-40mm, EF-S 17-85mm and EF-S 18-55mm lenses, each zoomed-out to their widest focal lengths.
With a diameter of 84mm and shortest length of 111mm, the EF-S 17-55mm is by far the largest of the lenses pictured, and at 645g, the heaviest too. The EF 17-40mm measures 84x97mm, so shares the same diameter as the relatively hefty EF-S 17-55mm, but is 14mm shorter, and at 475g it's also 170g lighter. This makes the EF-17-40mm the same weight as the EF-S 17-85mm, but a little larger. Clearly the first three lenses pictured dwarf the EF-S 18-55mm kit lens, which measures 69x66mm and weighs just 190g.
Pictured below are the same lenses zoomed-in to their longest focal lengths. The EF 17-40mm performs its zoom within the constraints of its outer barrel housing, so doesn’t physically extend. In contrast, the EF-S 17-55 and 17-85mm models both extend by 26mm, although the former does so with a single barrel, while the EF-S 18-55mm extends by 9mm. Clearly the EF-S 17-55mm remains the largest of the group.
As you'd expect for an 'L' model, the EF 17-40mm boasts the best build quality of all four lenses compared here. The construction and materials are of a much higher standard than any of the EF-S lenses so far, which feel quite plasticky in comparison. The EF 17-40mm is also the only one here to claim a high resistance to dust and moisture.
Like all 'L' lenses, the EF 17-40mm's zoom and focusing rings also feel much smoother and more tactile than the EF-S models which makes them much easier to finely adjust; the manual focusing ring is also much bigger than the ones on the EF-S models and feels like it was meant to be used.
Like the EF-S 17-55 and 17-85mm models, the EF 17-40mm also features a USM focusing motor which is both quick and quiet in operation - indeed Canon actually rates the EF 17-40mm as having the fastest AF in its class. Suffice it to say the end section doesn't rotate either, which is good news for users of polarising filters, although they'll need to dig deep for one which will fit on its 77mm thread. At least they won't need to buy a lens hood though - as an 'L' model, Canon supplies one as standard with the EF 17-40mm.
Aperture
In terms of light gathering power, the EF 17-40mm features a constant f4.0 aperture throughout its range; this means the exposure won't change as you zoom from one end to the other. The EF-S 17-55mm is by far the most impressive of the group here though, boasting a bright f2.8 aperture throughout its focal range. This allows it to deliver very small depth-of-fields and comfortably operate under considerably lower light levels. If you're after 'L' build quality and a constant f2.8 aperture in a similar focal range, you'll need to invest a significantly higher sum in the EF 16-35mm f2.8L II.
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