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In this section the most common technical terms will be described. Select the first letter of the abbreviation or term you'd like to search for:A - B - C - D - E - F - G - H - I - J - K - L - M - N - O - P - Q - R - S - T - U - V - W - X - Y - Z
ED
The so called APO elements (like the UD, SUD, CaF2, LD, SLD and ED for example) improve sharpness and contrast by reducing the effects of chromatic aberrations that are typically found in telelenses. These elements work by focussing different wavelengths of light to one point, but the effectiveness depends highly on the quality of the glass that is used. The good elements are highly expensive; the good ones are to be found in the more expensive lenses.
EF
Introduced in 1987 the EF-mount formed the start of the current auto focus lens line-up from Canon. With a diameter of 54mm it provided enough space to accomodate large aperture lenses.
The motor is allways inside the lens, there is no mechanical coupling between the lens and the body. Canon has not issued licenses for third party developers, the have re-engineered the protocols.
EF-S
When the dSLR's were introduced with APS-C sensors it became expensive to produce extreme wide angles. Canon invented the EF-S mount where the last lens element sticks further into the body. The advantage is that there is less glass necessary to produce the lens, which makes it cheaper to produce.
Because this portruding lens element sticks into the body, the normal 35mm SLR's can not work with these lenses: the mirror would bump into it. That's why Canon made it impossible to mount EF-S lenses on these body's. The body's that support EF-S lenses at this moment are: 300D, 350D, 400D, 20D and the 30D.
EX
Sigma uses this term to indicate that a lens belonges in their professional line up. In general the have a better build then they non-EX Sigma lenses, but they are also more expensive