Canon has a long list of abbreviations to describe aspects of various lenses. It's a good idea to learn these conventions, as they're most helpful in quickly discovering some of what each lens has to offer. Here are a few of the most common abbreviations you should know:
♦ EF. Electronic Focus. You'll find EF on all EOS lenses except for a few special ones such as the TS-E tilt-shift lenses, which only focus manually.
♦ FL. Fluorite elements. Fluorite elements are used in conjunction with Low Dispersion glass.
♦ UD. Ultra Low Dispersion glass. UD helps to minimize chromatic aberrations such as the purple fringing one occasionally encounters between dark and bright objects (for example, branches with a bright sky in the background).
♦ USM. Ultrasonic Motor. A more refined version of EF, it is faster and quieter, using ultrasonic vibration to induce motion that turns a rotor. USM lenses also allow you to manually focus while the camera is still in autofocus mode by rotating the focus ring.
♦ IS. Image Stabilization. A built-in image stabilizer allows you to take hand-held shots at slower shutter speeds that would be impossible without this feature. IS is particularly useful for still subjects, as objects in motion will blur at slower shutter speeds. Used in the long lenses, IS is available in other lenses as well. For example, the 24-105mm f/4.0L IS zoom lens includes image stabilization along with the second-generation 70-200mm, the 70-200mm f/2.8L II IS. Altogether, 11 Canon lenses currently utilize IS.
♦ DO. Diffractive Optics. Another Canon world's first, diffractive optics reduce the size and weight of lenses without any quality loss. Currently available in the EF 70-300mm f/4-5.6 DO IS USM lenses, as well as the EF 400mm f/4 DO IS USM lens. Now you know what all those letters mean!
♦ TS-E. Tilt Shift. The name for Canon's three tilt-shift lenses that allow shifts for perspective corrections and tilts for focus corrections.
♦ APO. Apochromatic Optics. Optics that employ SLD (Special Low Dispersion) glass as another method to correct chromatic aberrations, when various color wavelengths don't line up properly with each other. This increases image resolution and decreases color fringing.
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