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HANDS ON: A bit large for this focal-length range, and heavy, due to solid metal construction of the barrel and image-stabilization apparatus within the lens. Nicely finished in a light taupe crinkle paint. Milled, rubberized focusing ring provides excellent grip, although it's a long reach away, particularly at 400mm. Manual focusing action is very smooth and as well damped as many manual-focus lenses. Big ribbed and rubberized zoom grip provides a very secure grip. Push/pull zooming mechanism is set deliberately loose for smooth, fast zooming action and will creep freely when lens is pointed up or down. Canon, though, provides an unusual (unique?) zoom-damping control: the ring just behind the focusing ring tightens zooming friction when turned clockwise, loosens it when turned counterclockwise. A photographer can set it according to his or her preference, or just leave the zooming loose, then tighten it at a particular setting with a quick spin of the ring. Autofocusing, as per Canon USM practice, is smooth and silent. Windowed distance scale has very legible white meter numbers; the smaller, green footage numbers are harder to see. Lens has infrared focusing correction mark for several focal lengths. As focusing is internal, the lens front does not rotate during focusing, a plus. The supplied reversible, bayonet-mount lenshood has dead black flocking inside and provides excellent shielding from stray light.
The lens comes with a robust tripod mounting collar that can be used as a cradle grip for handholding; it has index marks for vertical and horizontal orientations but no detents. The collar can be removed, but it requires removing the lens from the camera. All switches are very clearly marked with black lettering. The small image-stabilization switch is easy to operate with bare or gloved hands. The nearly flush-mounted switches for stabilization mode, focusing limiter, and AF on/off will be quite difficult to set by gloved hands.
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IN THE LAB: SQF data were well above average at 100mm and 200mm, and average at 300mm. Due to limitations of the testing equipment, SQF could not be read at 400mm, and the accompanying chart shows lines-per-millimeter resolution for this focal length. Here, the lens proved sharp at wide and moderate apertures, but turned in a sub-par performance from f/22 through f/38/40. Virtually no field curvature was seen at 100mm and 200mm, although it was high at 300mm. (Equipment limitations prevented a reading at 400mm.) There was minimal barrel distortion (0.42 percent) at 100mm and 200mm; then noticeable pincushion at 300mm (1.50 percent) and 400mm (1.10 percent). Exposure at the film plane was extremely accurate at every focal length, with the exception of maximum aperture, where there was about 2/5 f-stop underexposure due to light falloff.
At the closest focusing distance of 5 feet, 8 1/2 inches at 100mm (1:15.9), center and corner sharpness was excellent at all apertures, except at f/32, where center sharpness was very good. Optimum performance was at f/4.5. At closest focusing distance of 5 feet, 8 1/4 inches at 400mm (1:4.8), center sharpness was very good from f/5.6 to f/8, good from f/11 to f/16, and acceptable from f/22 to f/40. Corner sharpness was excellent from f/5.6 to f/11, very good at f/16, good from f/22 to f/32, and acceptable at f/40. Optimal performance was at f/8.
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