Canon FD 55mm f/1.2 AL
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| Maker | Canon |
|---|---|
| Technical data | |
| Focal length | 55 mm |
| Aperture (max/min) | ƒ/1.2 – ƒ/16 |
| Close focus distance | 0.6 m (24 in) |
| Max. magnification | 0.11 |
| Diaphragm blades | 8 |
| Construction | 8 elements in 6 groups |
| Physical | |
| Max. length | 55 mm (2.2 in) |
| Diameter | 75.8 mm (2.98 in) |
| Weight | 605 g (21.3 oz) |
| Filter diameter | 58 mm |
| History | |
| Introduction | March 1971 |
| Discontinuation | 1980 |
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.
Design
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
- ^ "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.