Canon Extender EF

The Extender EF lenses are a group of teleconverter lenses made by Canon

These lenses are used between any compatible EF type lens and any of the Canon EOS line of cameras.

When used with a compatible lens, such as the Canon EF 500mm f/4L IS USM, they will multiply the focal length of the lens by a factor of either 1.4× or 2.0×. This will result in a focal length of 700mm or 1000mm, respectively, with a 500mm lens.

Canon has released six models:

    * 1.4×
    * 1.4× II
    * 1.4× III
    * 2×
    * 2× II
    * 2× III

Technical information

They are constructed with metal bayonets, and engineered plastic ends. There are no moving parts, other than the lens latch lock. Two generations of the extenders exist, the older 1.4× and 2×, plus the newer 1.4× II as well as 2× II. The newer II versions have weather-sealing and anti-reflective surfaces inside the extender body. The optical construction of the 1.4× versions are a of five-element design. Both 2× versions use seven elements, although the optical formula of the II version is different, to improve optical performance

Compatibility information

These Extender EF lenses can only be used with lenses that have a compatible mount. While all EF lenses have mount designs that can be used with EOS bodies, only lenses with accordant mounts can be used with the extender EF lenses. These lenses must have the clearance to accept the protruding lens on the extender, as well as 10 (3 extra) electronic contacts for proper electronic communication with the extender. These extra electronic contacts are used for sending the correct aperture information to the body. When a compatible lens is used with a 1.4× or 2× extender, it will cost the lens a one or two stop decline in aperture size, respectively. Autofocus speed of any used EF lens is also affected. When used with the 1.4× extender, autofocus speed is reduced to a half. When used with the 2× extender, autofocus speed is reduced to a quarter. Image stabilization may not work on lenses that are equipped with an extender, or on certain EOS bodies.

Though not specified by Canon as such, users have reported that the tilt-shift lenses in Canon's line-up can also be used with the extenders[3][4][5]. However, when used with an extender, the lens will not pass on the correct aperture to the camera. The focal length stored in the Exif data will also be incorrect.

List of compatible EF lenses

The following is a list of EF lenses that are compatible with the Extender EF lenses together with their resulting focal lengths, and apertures. Also listed is the autofocus and image stabilization functionality.