One of the major reasons for buying a new lens is for a broader or alternative focal range. In terms of written specifications, the EF-S 17-55, EF-S 17-85 and EF 17-40mm all sport slightly wider coverage than the kit EF-S 18-55mm, while the 17-85mm enjoys a longer reach. The EF 17-40mm is clearly shorter than the kit lens when zoomed-in.

To compare their actual coverage in real-life we shot the same scene with each lens within a few moments of each other from a tripod to ensure a consistent position. Here the lenses were set to their widest focal lengths. Results for all four lenses are pictured below.

With all images opened alongside each other in Photoshop, the EF-S 17-55mm and EF 17-40mm both capture a fractionally wider field than the EF-S 18-55mm as expected, although interestingly the EF-S 17-85mm squeezes slightly more in than any of them; this is apparent even on our shrunken examples below.

Canon EF-S 18-55mm		Canon EF-S 17-85mm		Canon EF-S 17-55mm		Canon EF 17-40mm
18-55mm at 18mm (29mm equiv)		17-85mm at 17mm (27mm equiv)		17-55mm at 17mm (27mm equiv)		17-40mm at 17mm (27mm equiv)

Next up came the telephoto-end of each lens. Again to compare their actual coverage in real-life we shot the same scene with each lens within a few moments of each other from a tripod to ensure a consistent position. Here the lenses were set to their longest focal lengths. Results for all four lenses are pictured below.

Here the longer reach of the EF-S 17-85mm is clear, and gives it greater compositional versatility than the pair which top-out at 55mm, and over twice the reach of the EF 17-40mm.

So in terms of coverage, only the EF-S 17-85mm offers a significant benefit over the kit EF-S 18-55mm lens. The EF-S 17-55mm delivers virtually the same range, while the EF 17-40mm is noticeably shorter.

Canon EF-S 18-55mm		Canon EF-S 17-85mm		Canon EF-S 17-55mm		Canon EF 17-40mm
18-55mm at 55mm (88mm equiv)		17-85mm at 85mm (136mm equiv)		17-55mm at 55mm (88mm equiv)		17-40mm at 40mm (64mm equiv)

Image Stabilisation

The EF-S 17-55 and EF-S 17-85mm lenses both feature Image Stabilisation (IS) facilities which greatly reduce the risk of camera-shake. This allows you to shoot under much lower light conditions without needing a tripod, or increasing the sensitivity and compromising noise levels as a result.

Both lenses claim up to three stops of compensation, which should allow you to use shutter speeds up to eight times slower than before. For example, if the slowest exposure you could confidently handhold at a certain focal length was, say, 1/60 of a second, three stops of compensation should enable you to enjoy the same result at 1/8 (or more accurately, 1/7.5).

As with all anti-shake systems, the effectiveness of IS varies between photographers and the particular shooting conditions, but its benefits are clear. We found they allowed us to handhold much slower exposures than before and eliminated camera-shake on virtually all images. Image Stabilisation is a great reason to upgrade from the EF-S 18-55mm kit lens. For examples of Image Stabilisation in practice, see our Canon 17-55mm and Canon 17-85mm reviews.