To measure and compare the resolving power of each lens using the Canon EOS 400D, we photographed the Enhanced Digital Camera Resolution Chart with each lens set to a focal length of 35mm and an aperture of f8. The 400D was set to Aperture Priority, Large Fine JPEG mode and its Standard Picture Style. All four lenses were tested within moments of each other under identical lighting conditions.

The crops are taken from the original images, saved as High Quality JPEGs in Photoshop CS2 and presented here at 100%. Each number represents 100 lines per picture height (lpph), so a figure of 20 means a resolution of 2000 lpph.

The budget EF-S 18-55mm kit lens unsurprisingly resolves the least detail of the four, with 2000 and 2100 lpph of horizontal and vertical resolution respectively. Interestingly the next step-up in resolving power comes from the priciest of the group: the latest EF-S 17-55 f/2.8 lens, which resolved 2050 and 2100 lpph horizontally and vertically respectively.

The best result in this particular test came from the EF-S 17-85 and EF 17-40 lenses which both resolved 2150 lpph horizontally and vertically. This is an impressive result for the 17-85mm, as the 17-40mm is a premium 'L' model and also designed for full-frame use.

It's also interesting to note the lenses with the highest resolving power also exhibited higher contrast and sharpness in this test; the 17-55mm and especially the 18-55mm exhibited noticeably lower sharpness and contrast here, and we should reconfirm all four lenses were tested during the same session, with identical lighting conditions and camera settings.