USM - Ultrasonic Motor. Ultra-silent and ultra-fast autofocus motor for the lens.
Nikon Equivalent - AF-S - Silent Wave motor technology.
IS - Image Stabiliser. A technology that reduces or otherwise eliminates camera shake in a picture during heldheld photography.
Nikon Equivalent - VR - Vibration Reduction.
L lenses - Canon's top-of-the-line series of professional lenses, also known as "Luxury" lenses. Unparalleled optical performance compared to consumer lenses in terms of sharpness, chromatic aberration control, colour balance and saturation.
Nikon Equivalent - ED - Not strictly a "designation" of top-of-the-line. More an indication of the type of material used. ED denotes Exta-low Dispersion glass is incorporated in one or more elements in the lens.
DO - Diffractive Optics. Fresnel-type lens element used in the construction of the lens that allows for very good optical performance yet attaining smaller and lighter lenses.
No Nikon Equivalent as yet.
EF mount - Canon's "electro-focus" mount that is common across the whole EOS series of D/SLRs. Any lens that is made for the EF mount can be used in any EOS camera. Basically the only contacts between the lens and the camera body is electronic--there is no mechanical coupling at all. The lens' AF drive, aperture diaphragm control, etc. is all done in the lens itself, controlled through the EF mount.
Nikon Equivalent - F-Mount - key characteristic is that the F-mount has not changed throughout the evolution of Nikon's cameras both SLR and DSLR. Thus an old manual-focus F-mount can work with all SLRs/DSLRs (there are some caveats with certain specialty lenses). Example: my old AIS Nikkor 50mm f/1.4 manual lens works in ALL modes with the current generation D2h with full matrix metering and flash functions intact.
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EF-S mount is modified version of the EF mount for "short back focus", introduced specifically for the EOS 300D/Digital Rebel camera and the bundled 18-55mm EF-S lens. EF-S mount lenses cannot be used with normal EF mount camera bodies.
No Direct Nikon Equivalent - but Nikon's answer to the digital crop factor are DX lenses which are built with smaller image circles. DX lenses can be used with film SLRs with the caveat that vignetting will occur at the wide angle end of the lens (eg. the 12-24DX will vignette at focal lengths less than 15-16mm; but usable full-frame beyond 15-16mm)
Other Nikon Technologies/Acronyms
i-TTL - Evolution of Nikon's TTL flash technology. Together with CLS, provides fully automated multi-flash setups.
CLS - Creative Lighting System. Nikon's innovation in controlling multiple groups of CLS-capable flashes to provide flexibility and creativity in lighting.
More information on Nikon's lens tech can be found on
Nikon Singapore website. - Click on the Products icon, then Nikkor lenses.