The EF17-40mm f/4L USM was developed as high-end version of the highly acclaimed EF20-35mm f/3.5-4.5 USM lens released in March 1993. Designed for use by professional and amateur users alike, this lens realizes the outstanding image resolution that distinguishes an L-series lens while retaining high cost performance. Featuring a new optical system design, the new lens delivers an expanded zoom range of 17-40mm, with the wide-angle-end 17mm focal length making it ideally suited to digital photography.
The EF17-40mm f/4L USM utilizes a combination of one high-precision molded glass aspherical lens and two replica aspherical lenses to achieve the extended zoom range, while also correcting for a variety of aberrations that arise during zooming. Moreover, a Super UD (ultra-low dispersion) glass element minimizes the chromatic aberration of magnification that tends to occur with wide-angle lenses, eliminating color bleed along the edges of the subject and realizing high image contrast and resolution.
The 17 mm focal length achieved by the EF17-40mm f/4L USM lens also extends wide-angle shooting potential when paired with digital AF SLR cameras, such as the high-end amateur-model EOS 10D , which have smaller imaging areas than 35 mm film. Taking into account the smaller angles of view that result, the new lens realizes a focal range equivalent to 27-64mm in the 35mm format (or 1.6 times) when paired with EOS 10D.
Moreover, the power of the focusing lens group has been increased to allow a minimum focusing distance of just 0.28 meters throughout the entire zoom range. The EF17-40mm f/4L USM also features a circular diaphragm for improved background blur, and utilizes only lead-free glass optics in consideration of the environment. The new lens features a hardy water- and dust-resistant construction,ensuring professional users unfailing performance under even the most grueling of conditions.