EF 17-40mm f/4L USM Prime lens including lens hood EW-83H, lens hat and lens hood The EF 17-40mm f/4L USM is a lightweight wide-angle Canon EF zoom lens. This lens is ideal for digital EOS SLR cameras with a focal length conversion factor of more than 1. Versatile wide-angle lens that is suitable for Canon SLR cameras with a full-frame sensor (EF-mount). You can also use the lens on cameras with an APS-C sensor (EF-S mount). The equivalent focal length is then 27.2-64mm. This is a very versatile zoom range! Given a 5/5 in several reviews such as below. When used in the correct situations, ultra wide angle lenses (20mm or wider on full-frame cameras) can allow photographers to create very dramatic images, thanks to the extreme corner distortion and the stretch in perspective these lenses can create (these can also be considered negatives). Ultra wide angles are best used sparingly, but nevertheless tend to be a very important part of a professional photographer’s kit bag. From what I can gather, quality ultra-wide angle lenses are typically very difficult to design and manufacture for SLR cameras, so tend to be rather pricey. With lenses such as the Canon EF 16-35mm f/2.8L USM II costing well over £1000, the purchase of an ultra-wide angle lens can be difficult to justify. At just over £550, the EF 17-40 f/4L has proved to be a very popular choice for many photographers. Continue reading to see why. Build Quality and Ergonomics As a member of Canon’s illustrious and revered line of ‘L’ series lenses, the Canon EF 17-40mm f/4L USM has superb build quality. The majority of the outer barrel is manufactured from a very high quality polycarbonate and is very durable. The focus ring on this lens is superb. Size and placement are excellent, and turning the ring is smoother than any other lens I have ever used. Similarly, the zoom ring is great, although has slightly less resistance/damping than the focus ring, but this does allow the user to change focal lengths very quickly. When zooming, the inner lens barrel moves internally, which is a very welcome feature, meaning that when coupled with a UV filter, this lens will be weather sealed thanks to the rear ass gasket and seals around the zoom and focus rings. Lens creep is seldom an issue with the 17-40. On camera bodies such as the 5D, 6D, 7D or 1D series, this lens is very well balanced, and feels very comfortable when shooting. Weighing around 500g, having this lens mounted to any of the aforementioned bodies is no problem, even during prolonged periods and even with a battery grip attached. The EF 17-40 features an Ultrasonic focus motor which is both quiet and very fast. At all focal lengths and in most lighting conditions, the 17-40 locks focus almost instantly with no hunting and is very accurate. Performance in AI-Servo mode is also very commendable.