While most properly called a "crop factor," the 1.6x ratio is more commonly referred to as the "focal length multiplier" since that's how it works in practice. The sub-frame sensor on the Canon Rebel T3i means that it has a smaller angle of view (by a factor of 1/1.6) than a full-frame camera with any given lens. EF-S lenses can't be used on full-frame Canon cameras, nor on their APS-H models with 1.3x crop factors, like the EOS-1D Mark III or Mark IV, but small-sensor cameras like the Canon T3i can use any full-frame lenses in Canon's arsenal. Designed with a smaller image circle (the area covered by the image on the film/sensor plane), EF-S lenses tend to be smaller and lighter than full-frame models with the same focal length and maximum aperture. Like other Canon DSLRs with sub-frame sensors (currently, the Canon Rebel XS, Rebel XSi, Rebel T1i, T2i, T3, EOS 50D, 60D, and EOS 7D), the Canon Rebel T3i will work with pretty much any EF-mount lens ever made, as well as with the special EF-S lenses designed for cameras with APS-C size sensors.
See below for our test results with this lens mounted on the Canon T3i, and see our full review of this lens on. A lens hood and soft case are optional accessories. The lens has a MSRP of US$499.99 if bought separately, and again, costs significantly less when purchased bundled with the camera. Dimensions are 101mm long with a 75.4mm diameter (4.0 x 3.0 inches), and weight is 455g / 16.0 oz. Other specifications include a 6-bladed (rounded) diaphragm, minimum aperture of f/22-f/38 (or f/36 if using 1/3 stop increments), maximum magnification ration of 0.21x (or 1:4.8) at 135mm, and 67mm filter threads. A Stabilizer On/Off switch is also provided. The lens features built-in image stabilization (IS) that is capable of up to four stops of correction. Focusing is internal, and the 18-135mm uses a DC focus motor. The lens is constructed of 16 elements in 12 groups. The second lens option is the Canon EF-S 18-135mm f/3.5-5.6 IS lens, which has a 7.5x zoom ratio, and a 35mm equivalent focal range of 29-216mm. While we've yet to run this newer version through our testing process over at, the preceding lens was quite impressive when compared to those bundled with Rebel cameras preceding the XS, yielding improved sharpness and reduced chromatic aberration.
The lens has a MSRP of US$199.99 if bought separately, but costs significantly less when purchased bundled with the camera. Dimensions are 84.5mm long with a 68.5mm diameter (3.3 x 2.7 inches), and weight is 200g (7.1 ounces). Other specifications include a 6-bladed (rounded) diaphragm, minimum aperture of f/22-f/32, maximum magnification ration of 0.28x (or 1:3.6), and 58mm filter threads. The EF-S 18-55mm II uses a micro DC motor for autofocus, instead of the ultra-sonic motor found on models with the USM designation, and includes both an AF/MF switch and a Stabilizer On/Off switch on the lens barrel. This lens is constructed of 11 elements in 9 groups, and extends during both focus and zoom operation. The lens has a 3.1x zoom ratio, and a 35mm equivalent focal range of 29-88mm due to the T3i's 1.6x "focal length crop" (see below). Compared to the earlier EF-S 18-55mm f/3.5-5.6 IS version, that lens has cosmetic changes and uprated stabilization algorithms said to be good for a four stop improvement, but we believe it to be optically similar to the earlier model. One is an updated variant of a lens first introduced with the Rebel XS, now known as the EF-S 18-55mm f/3.5-5.6 IS II, which also ships with the Rebel T3 and T2i. The Rebel T3i kit is available with two lens choices.