Canon FD 55mm f/1.2 AL

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.[1] The lens was manufactured until 1980.

FD 55mm ƒ/1.2 AL
MakerCanon
Technical data
Focal length55 mm
Aperture (max/min)ƒ/1.2 – ƒ/16
Close focus distance0.6 m (24 in)
Max. magnification0.11
Diaphragm blades8
Construction8 elements in 6 groups
Physical
Max. length55 mm (2.2 in)
Diameter75.8 mm (2.98 in)
Weight605 g (21.3 oz)
Filter diameter58 mm
History
IntroductionMarch 1971
Discontinuation1980

Design
Canon FD 55mm ƒ1.2 AL element diagram

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.

Variants

In March 1975, Canon introduced a multicoated version of the lens, known as the FD 55mm ƒ/1.2 S.S.C. Aspherical.[2]

Radioactivity

Like a number of other contemporary lenses, the Canon FD 55mm ƒ/1.2 AL incorporated thoriated glass,[3] 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.[4]

References
  1. "FD55mm f/1.2 AL – Canon Camera Museum". Retrieved 2019-01-17.
  2. "FD55mm f/1.2 S.S.C. Aspherical – Canon Camera Museum". Retrieved 2019-01-17.
  3. "Radioactive Lens – Canon FD 55mm f/1.2 S.S.C. Aspherical". YouTube. 2011-01-10. Retrieved 2019-01-17.
  4. "Radiation-induced Discoloration" (PDF). www.sealandair.fr. BIRNS, Inc.
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