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EF-S - Electronic Focus System.

18-135mm id the focal length. It allows you to zoom in or take wide angle pictures.

F 3.5 - 5.6 is the F-stop rating. It allows for depth of field. That is the range in which the picture will be clear. The smaller the number the shorter the depth of field.

The EF-S 18-135mm f/3.5-5.6 IS covers a range from 29mm-216mm in 35mm format, and is a perfect complement to APS-C cameras.

It features high-quality optics, dedicated image stabilization and is a favorite for EOS users.

It is a high magnification zoom lens, (equivalent to 29-216 in 35mm format); gives high image quality by adopting UD lens, and optical Image Stabilizer - which makes the shutter speed 4 stops faster.