EN: Fluorite lens element
Fluorite (FL), a lightweight mono-crystal optical material, has excellent optical properties while reducing overall lens weight to improve balance and handling, especially useful in longer focal length lenses.
Fluorite has extremely low indexes of refraction and dispersion compared to optical glass and features special partial dispersion characteristics (extraordinary partial dispersion), enabling virtually ideal correction of chromatic aberrations when combined with optical glass. This fact has long been known, and in 1880 natural fluorite was already in practical use in the apochromatic objective lenses of microscopes. However, since natural fluorite exists only in small pieces, it cannot be used practically in photographic lenses. In answer to this problem, Canon in 1968 succeeded in establishing production technology for manufacturing large artificial crystals. Thus opening the door for fluorite use in photographic lenses.
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Lenses made with this mineral produce less chromatic aberration (color fringing at edges of objects) than those made of ordinary glass. Canon first artificially created crystal fluorite in the 60s, producing first interchangeable SLR lenses with fluorite elements.
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