Canon FD 55mm f/1.2 AL
|Focal length||55 mm|
|Aperture (max/min)||ƒ/1.2 – ƒ/16|
|Close focus distance||0.6 m (24 in)|
|Construction||8 elements in 6 groups|
|Max. length||55 mm (2.2 in)|
|Diameter||75.8 mm (2.98 in)|
|Weight||605 g (21.3 oz)|
|Filter diameter||58 mm|
The Canon FD 55mm ƒ/1.2 AL is a camera lens made by Canon, first introduced alongside the Canon F-1 single-lens reflex camera in March 1971. It was the first lens for any 35mm SLR system to incorporate an aspherical element. The lens was manufactured until 1980.
The FD 55mm ƒ/1.2 AL uses a variation of the double-Gauss lens design, in which the positive meniscus element of the front Gauss pair is aspherical. In total, the lens has 8 elements in six groups: a front element, two Gauss pairs, and three additional rear elements.
Like a number of other contemporary lenses, the Canon FD 55mm ƒ/1.2 AL incorporated thoriated glass, a kind of optical glass that is doped with thorium dioxide. The inclusion of this compound makes the glass radioactive.
Over time, thorium decay causes F-centers to form in the glass, resulting in an amber discoloration. The discoloration can be repaired by exposure to a source of ultraviolet radiation, such as direct sunlight.
- "FD55mm f/1.2 AL – Canon Camera Museum". Retrieved 2019-01-17.
- "FD55mm f/1.2 S.S.C. Aspherical – Canon Camera Museum". Retrieved 2019-01-17.
- "Radioactive Lens – Canon FD 55mm f/1.2 S.S.C. Aspherical". YouTube. 2011-01-10. Retrieved 2019-01-17.
- "Radiation-induced Discoloration" (PDF). www.sealandair.fr. BIRNS, Inc.