Canon EF 17-40mm f/4L USM Lens
The EF 17-40mm f/4L USM lens is a member of a suite of Canon zoom lenses that retain a constant f4 maximum aperture throughout the zoom range. Designed for use on 35mm SLR cameras, this ultra-wide zoom is ideal for capturing dramatic landscape shots and taking portraits of large groups of people. It will also prove useful for shooting in cramped interiors.[ia] . . [more]
The EF 17-40mm f/4L USM lens is a member of a suite of Canon zoom lenses that retain a constant f4 maximum aperture throughout the zoom range. Designed for use on 35mm SLR cameras, this ultra-wide zoom is ideal for capturing dramatic landscape shots and taking portraits of large groups of people. It will also prove useful for shooting in cramped interiors.
Canon has focused on two key requirements for the serious photographers who will use this lens: optical performance and rugged construction. In both areas most promises have been delivered. The lens contains 12 glass elements, arranged in three groups, with three aspherical elements to counteract the aberrations that beset wide-angle zooms. Different types of aspherical construction are involved and the lens includes two ultra-low-dispersion (UD) elements to minimise chromatic aberration.
The optics are contained within a black body that is built for dust and moisture resistance, and the front filter mount remains fixed in position while the lens is focused, making it ideal for use with angle-sensitive filters, such as polarisers and graduates. Focusing is accomplished by an internal ring-type ultrasonic motor (USM), which is smooth and quiet, and the rotating zoom ring covers an angle of view from just over 49 degrees to 93 degrees. Closest focusing distance is 28cm over the entire zoom range.
Focal length settings are engraved on the lens barrel, a useful feature when you want to set precise magnifications. In addition, the lens includes a depth-of-field gauge, which many photographers appreciate. The lens is supplied with a shallow ‘petal-shaped’ EW-83E lens hood, 77mm lens cap and rear dust cap plus an LP1319 soft case.
We tested the EF 17-40mm f/4L USM lens on two cameras: the EOS 5D, which has a 34 x 36mm sensor, and the EOS 300D where the sensor area is 22.7 x15.1mm. As well as using the lens on both cameras for a series of shots under typical usage conditions, we subjected it to Imatest analysis with both cameras. The results, presented below, are interesting.
As far as handling is concerned, the lens felt comfortable on both cameras, although it was a little more ‘at home’ on the larger, heavier EOS 5D than on the lighter 300D. In use, the lens focused quickly and accurately and showed no discernible tendency to hunt in low light levels. The zoom was smooth and focusing was quiet and, with both cameras, everyday shots were sharp and crisp and showed little or no evidence of flare or ghosting. We found no evidence of rectilinear distortion with either camera.
Imatest revealed some interesting differences in performance between the two cameras, which we will explain in the Insider section on page 60. To understand them, it is important to appreciate that this lens has been designed to image onto a 24x36mm area; performance will be compromised when it is used with a smaller imaging area.
On the EOS 5D, the EF 17-40mm f/4L USM lens turned in an excellent performance across all aperture settings, delivering an average resolution of 2000 line widths per pixel height for uncorrected MTF50 analysis. Chromatic aberration was consistently low, with the highest recorded measurement at 0.040%, which is barely discernible.
A significant drop-off in resolution and increase in chromatic aberration was revealed when the lens was tested on the EOS 300D. Here the uncorrected MTF50 figure dropped to an average of 878.5 line widths per pixel height, while chromatic aberration averaged 0.086%, which is just into the ‘moderate’ range (visible at high print magnifications). These results are not surprising but they confirm the fact that lenses designed for 35mm cameras cannot perform at their best on DSLR cameras with sensors smaller than 24 x 36 mm.
As a ‘partner’ for the EOS 5D – or EOS-1Ds Mark II – Canon’s EF 17-40mm f/4L USM lens does a great job. It will perform equally well on any of Canon’s 35mm SLR film cameras. But you’d be wasting money to purchase it for use with any of Canon’s DSLRs that have a smaller sensor, unless you plan to print shots at A4 size or smaller. 
Focal length range: 14-40mm
Maximum aperture: f4
Lens construction: 12 elements in 9 groups
Minimum focus: 0.28m
Filter size: 77mm diameter
Dimensions (Diameter x L): 83.5mm x 96.8mm
Weight: 475 g
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