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Base curve radius (BCR) or simply base curve (BC) is the measure of an important parameter of a lens in optometry. On a spectacle lens , it is the flatter curvature of the front surface. On a contact lens it is the curvature of the back surface and is sometimes referred to as the back central optic radius ( BCOR ).
Canon in 2011 made the first fisheye zoom lens, both circular and rectangular. That lens was the Canon EF 8-15mm f/4L Fisheye USM. Canon in 2012 made the first wide angle lens with Image Stabilization. That lens was the Canon EF 24mm f/2.8 IS USM. Canon in 2013 created the first telephoto with built-in 1.4× extender.
The Canon TS-E 24 mm f / 3.5L II is a tilt-shift, wide-angle prime lens that provides the equivalent of the corresponding view camera front movements on Canon EOS camera bodies. Though it uses Canon's EF lens mount, it does not provide autofocus.
The Canon EF-S lens mount is a derivative of the EF lens mount created for some Canon digital single-lens reflex cameras with APS-C sized image sensors. It was released in 2003. Cameras with the EF-S mount are backward compatible with the EF lenses and, as such, have a flange focal distance of 44.0 mm. Such cameras, however, have more clearance ...
The Canon EF-M lens mount, introduced in 2012, is a derivative of the Canon EF lens mount designed for use with the Canon EOS M mirrorless interchangeable-lens camera. The EF-M lens mount is one of Canon's two systems for mirrorless cameras, the other being the RF mount .
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As it is designed for Canon APS-C bodies, its field of view is equivalent to a 38mm lens on a full-frame sensor, and operates similar to the Canon EF 40mm f/2.8 STM pancake lens. Compared to the EF 24 f / 2.8 IS USM, the EF-S lens loses IS, but lists for about a fourth of the price.
The base curve (usually determined from the profile of the front surface of an ophthalmic lens) can be changed to result in the best optic and cosmetic characteristics across the entire surface of the lens. Optometrists may choose to specify a particular base curve when prescribing a corrective lens for either of these reasons. A multitude of ...