Canon’s EF series lenses are designed for use with EOS digital SLR camera systems, featuring improved optics that include two high-precision Aspherical elements and two new UD-glass elements, resulting in superior image quality; better contrast and sharpness at the outer edges, and a reduction in chromatic aberrations that can sometimes be seen with high-resolution digital SLRs.
From Canon:
The fastest 135mm telephoto lens in its class. Ideal for indoor sports and portraits with background blur. Two UD-glass elements correct secondary spectrum for outstanding sharpness and color. Compatible with Extender EF 1.4x II and 2x II.
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Focal Length & Maximum Aperture: 135mm 1:2.0
Lens Construction: 10 elements in 8 groups
Diagonal Angle of View: 18°
Focus Adjustment: Rear focusing system with USM
Closest Focusing Distance: 0.9m / 3 ft.
Filter Size: 72mm
Max. Diameter x Length: 3.2″ x 4.4″, 1.7 lbs. / 82.5 x 112mm
Weight: 26.5 oz./750g