Pictured below are the Canon EF 17-40mm on the left and the EF 24-105mm on the right, with both lenses zoomed-out to their widest focal lengths. In this position, each barrel measures 97 and 107mm long respectively.

Both lenses share the same diameter of just over 83mm, and the same filter thread of 77mm; users of polariser or graduated filters will be pleased to learn both employ internal focusing with non-rotating end sections. Like all ‘L’ lenses, hoods and pouches are supplied with each model.

Pictured below are both lenses zoomed-in to their longest focal lengths. Here the EF 24-105mm barrel extends by 33mm, while the EF 17-40mm’s optics adjust within the constraints of its outer barrel, so the lens doesn’t increase in length.

Both lenses share essentially the same build quality, with solid construction, and very smooth zoom and focusing rings. Weighing 500g, the EF 17-40mm does feel quite a lot lighter than the 670g EF 24-105mm though, and when each is fitted to the EOS 5D, the combination is quite a different proposition. Canon claims both lenses are highly resistant to dust and moisture.

In terms of optical construction, the EF 17-40mm employs 12 elements in nine groups. Canon’s Super Spectra Coatings minimise ghosting and flare while the combination of three aspheric elements and Super UD glass reduces distortion and chromatic aberrations.

In terms of focusing, both lenses are quick and quiet thanks to their USM motors; indeed the EF 17-40mm is actually rated as having the fastest AF speed in its class, matching the quick EF 16-35mm f/2.8L model.