Canon EF Autofocus Lenses Canon's reputation for excellence in optics has been well established for years. And with the introduction of EF lenses for the EOS, it's only getting better. EF Lenses have the largest diameter mount of any 35mm camera, which not only strengthens the whole system, but permits optical innovations never before possible. L-Series lenses have better sharpness and contrast because Canon uses aspherical elements to eliminate spherical aberrations. In addition, the L-Series telephotos use UD (Ultra-low Dispersion) glass to reduce chromatic aberration resulting in more accurate colors. A built-in Ultrasonic focusing Motor (indicated by USM) provides pro-quality AF speed with split-second accuracy.The EF 75-300mm f/4.0-5.6 III USM lens offers virtually all of the outstanding features of the earlier model, including compact size, light weight and high performance as well as a wide range of focal lengths-from medium telephoto to telephoto. What has brought down the cost of this new model are the refinements in the materials used for certain mechanical parts, changes to the micro ultrasonic motor drive circuitry, and a revamping of the entire production process. Substantial economies in these areas mean that Canon's superior optics and advanced autofocus technologies will now be available to a much larger audience of EOS SLR users.