- Superb optical performance throughout the zoom range
- Fastest AF speed within its class (same as the EF16-35 f/2.8L USM)
- Highly dust and moisture resistant
- 28cm minimum focusing distance at all focal lengths
With superb optical performance, the fastest AF in its class, dust and moisture seals and a close focusing distance of just 28cm, this lightweight, wideangle lens is especially suitable for use with APS-C and APS-H cameras like the EOS 40D and EOS-1D Mark III. That’s not to say that this lens should only be used on smaller sensor cameras. In fact, for photojournalists, landscape and travel photographers, this is the perfect wideangle lens when matched to full frame cameras, such as the EOS 5D Mark II, because it is lightweight and robust.
Side view of the EF17-40mm f/4L USM lens.
A constant f/4 aperture means the weight can be kept down compared to an f/2.8 lens but the image quality is still higher. It will still perform well in low light where a constant aperture helps with capturing the light effectively at all focal lengths.
It is also favoured in interior photography where the focal range - from a wideangle 17mm to an almost standard 40mm - allows the photographer the versatility to achieve a variety of shots. The focal range and close focusing distance, when used correctly, also allow a large change in perspective.
Two types of aspherical lens elements are used in conjunction with one super ultra-low dispersion (Super UD) element to control and eliminate aberrations and ensure high image quality appropriate to an L-series lens. The USM autofocus ensures sharp pictures, whether the subject is a stationary landscape, or a fast moving car.
An almost perfectly circular diaphragm ensures smooth out-of-focus highlights and pleasing background blur, and the large constant maximum aperture gives plenty of control over depth-of-field. When attached to an EOS-1 series cameras the lens retains the dust and weather sealing characterised by those cameras.
A ring-type USM autofocus motor means you can focus quickly, near-silently and with precision. It also provides full-time manual focus so that you can adjust the focus with the focus ring, without first having to switch the lens to manual focus. This allows you to adjust the focus accurately to ensure it is exactly where you want it to be for the most creative control possible.