Canon Acronyms and abreviations

Canon use a number of acronyms when describing their lenses. They don't always provide a key to what they mean, so for reference here's a list of most of them.

• AFD - Arc Form Drive focusing motor. Older design, slower and noisier then USM
• AL - Aspheric Lens, used to minimize aberrations.
• CA - normally Chromatic Aberration, but Canon also use this abbreviation for Circular Aperture lenses (lenses with multiple aperture blades shaped to give as circular an iris shape as possible).
• CaF2 - Fluorite element (even more effective than super UD for correcting chromatic aberration). Used in most Super-telephoto lenses.
• E-M - Electronic manual focusing (used on some older USM lenses where manual focusing was done electrically via the USM motor).
• EF - The designation Canon uses for it's standard lens mount. All EF lenses will fit on all EOS bodies.
• EF-S - The designation used for lenses which only cover the area of APS-C digital sensors and which can only be mounted on bodies with an EF-S compatible lens mount - currently (04/07) the Digital Rebel, XT, XTi, EOS 20D and EOS 30D.
• EMD - Electro-Magnetic Diaphragm. All Canon EOS lenses use an electrically controlled aperture.
• EOS - Electro Optic System.
• Float - Floating elements which move to correct aberrations when close focusing. Nikon call this CRC (Close Range Correction).
• FP - Focus Preset. A single focus distance can be preset and instantly returned to. This is available on some super telephoto lenses.
• FR - Filter rotation, front element rotates during focusing.
• FS - Focus Range Selector. Some lenses can restrict focus range for faster operation
• FT-M - Full time manual focus. Manual focus is possible even with lens in AF mode.
• G-E - Groups/Elements. How the individual lens elements are arranged within the lens.
• GMO - Glass-molded (aspheric) Optics, less expensive than ground and polished aspheric.
• I/R - Internal or Rear group focusing (lens length does not normally change during focusing, front element does not normally rotate).
• L - Luxury (?). The designation Canon gives to its professional grade lenses.
• micro USM - A lower cost non-ring version of the USM motor which does not normally support FT-M. Sometimes just called USM in lens names (e.g. the EF75-300/4.0-5.6 III USM uses a micro USM motor).
• MM - Micro Motor focusing motor. Slower and noisier then USM.
• MTF - Modulation Transfer Function. A measure of the lens sharpness (higher is better).
• SF - Soft Focus. The 135/2.8 SF is the only current Canon soft focus lens.
• Super UD - Super ultra low dispersion glass (even more effective than UD for correction of chromatic aberration)
• T/S - Sometimes TS-E. Tilt/Shift. Canon EF lenses that can be shifted and tilted to control the plane of focus and correct perspective distortion.
• UD - Ultra-low dispersion glass used to correct chromatic aberration
• USM - Ultrasonic focusing motor. Fast and silent. Often (but not always) means a USM ring motor with FT-M (see micro USM).