Canon 17-40mm f/4 EF USM L
Since its debut in 2003, the moderate price, excellent build quality, and convenient zoom range has made this lens into one of Canon's best selling lenses.
This is not a fast lens, but it offers a constant f/4.0 aperture. The optical construction includes one low-dispersion element and three aspherical elements.
It performs well over the entire zoom range. A slight corner softness visible at f/4.0 between 17 and 20mm on FX/135-format. Visible vignetting at f/4.0 and 17 mm on FX/135. No significant sharpness or vignetting issues at 1.6x crop. Low flare. CA is well controlled at wide apertures, and goes away around f/5.6. Best performance at f/8, at smaller apertures diffraction sets in. There is a pronounced, but correctable, barrel distortion at the wide end. This goes away around 24 mm and at the long end there is virtually no distortions.
The mechanical construction is very good, as one expect from an L-lens. The focus motor is of the ring-type and gives fast, silent and precise auto-focus with manual override while in auto-focus mode. The focus and zoom rings turn smoothly and with just the right amount of resistance. The lens move very slightly in and out during focusing, but the movement is behind the filter threads. The filter attaches to the fixed lens barrel and does not rotate nor move. With a filter installed, there is no movement.
This lens is a solid performer at an attractive price point. Good value.
Rating: Ed: 70, User: - (normalized, 0=useless, 50=average, 100=excellent).
Mount: Canon EF.
Aperture range: f/4 to f/22.
Optical zoom: 2.4x.
Close focus distance (CFD): 28 cm / 0.92 ft (from sensor plane).
CFD magnification: 1:4 / 0.25X.
Focus: AF (built-in, ring-type).
Filter diameter: 77 mm.
L x D, W: 97 x 84 mm, 500 g.
IR: May produce a hotspot.
Approximate street price: USD 635 (new, w/o tax).
Canon is a multinational corporation headquartered in Tokyo, Japan specializing in the manufacture of imaging and optical products. Its products including cameras, lenses, flash units, scanners, photocopiers, printers and steppers (used in semiconductor fabrication). The company was founded in 1937 as Precision Optical Instruments Laboratory and renamed Canon Inc. in 1947.