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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.
Canon New FD lens mounting surface.. The FD lens mount is a breech-lock mount, which is a variation of the common triple-flanged bayonet attachment. The advantage of the breech-lock over the bayonet is that neither the contact surfaces between the body and lens, nor the signalling mechanisms, rotate against each other when the lens is mounted.
In the US market, soft contact lenses are approved by the US Food and Drug Administration. [2] The American Optometric Association published a contact lens comparison chart called Advantages and Disadvantages of Various Types of Contact Lenses on the differences between them. [3] These include: soft contact lenses; rigid gas-permeable (RGP ...
Radius of curvature sign convention for optical design. Radius of curvature (ROC) has specific meaning and sign convention in optical design.A spherical lens or mirror surface has a center of curvature located either along or decentered from the system local optical axis.
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Lens clock. A lens clock is a mechanical dial indicator that is used to measure the dioptric power of a lens.It is a specialized version of a spherometer.A lens clock measures the curvature of a surface, but gives the result as an optical power in diopters, assuming the lens is made of a material with a particular refractive index.
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 ...