50th anniversary of Canon’s first lens with a synthetic fluorite lens

Canon Inc. and Canon Optron, Inc. announce that the world’s first interchangeable lens with a fluorite lens, the FL F300mm f/5.6 today is 50 years old – it was first released for sale in May 1969. Synthetic fluorite is used not only in Canon camera lenses, but also in the company’s other products, including lenses for broadcast cameras and telescopes.

FL F300mm f/5.6 May 1969 Canon’s first interchangeable lens with synthetic fluorite lens elements

Lenses made of fluorite – crystals of calcium fluoride CaF2 – in combination with lenses made of optical glass can almost completely eliminate chromatic aberration. Natural fluorite crystals, however, were too small to be used in photographic lenses. Canon was the first company to make use of fluorite’s special properties in creating a lens which could produce bright images with pinpoint color reproduction more than could be achieved with ordinary optical glass. August 1966 saw the launch of the Canon F Plan program, the goal of which was to develop a high quality lens with synthetic fluorite optical elements. It was then that the company devoted itself to developing high-performance lenses.

A method of synthesizing fluorite crystals was discovered in 1950, making them suitable for use in optical device development. However, special conditions were required to crystallise fluoride crystals: vacuum and temperatures in excess of 1000 degrees Celsius. Therefore, launching mass production of large crystals without impurities was challenging, both in terms of equipment installation and in the manufacturing process itself.

Synthetic fluorite crystal

Despite this, in an effort to develop a high quality lens, Canon specialists successfully synthesized the first fluorite crystals in an electric furnace in March 1967, and in February 1968 mass production technology for synthetic fluorite crystals was introduced. At that time, fluorite could not be polished like regular optical glass. So Canon developed an alternative machine processing technology to polish the brittle material, which, however, took four times longer than the conventional. May 1969 Canon’s first interchangeable lens with a synthetic fluorite lens, the FL F300mm f/5.6. This material has since become an integral part of Canon’s high-performance lenses.

In December 1974 was founded Optron Inc. now Canon Optron , which began mass commercial production of fluorite crystals. In the process of perfecting high-temperature vacuum and temperature control techniques for mass synthesis of fluorite, Canon Optron specialists developed a number of crystalline materials with optical properties. In July 2007, Canon Optron donated 12 lenses to the Smithsonian Astrophysical Observatory, including a synthetic fluorite lens measuring 40 cm in diameter. A telescope with this lens can capture the signals of objects 10 billion light years away.

Canon continually advances imaging technology, focusing on optical elements to ensure that results meet users’ high expectations. Canon will continue to refine the design and manufacture of the high optical performance and reliability products we’re looking for in the world today.

The properties of fluorite

Passing through water or another transparent medium, light refracts. This phenomenon explains the ability of a lens to focus light as it passes through it. However, the degree of refraction depends on the color of the transmitted beam: blue light, for example, composed of shorter wavelengths, refracts more than red light, which is composed of longer wavelengths. As a result, the light from a single source in the lens splits into several rays of different colors with different focal points. This causes a colored fringe in the image called chromatic aberration.

Chromatic aberration occurs when a beam of light passes through the lens system. A combination of a low-dispersion convex lens and a high-dispersion super high-performance lens is used to correct color fidelity&not The lens of the film is a concave sion lens. This reduces aberration by directing the light rays along the same path and aligning the focus points of the beams of different colors. However, even correcting chromatic aberration with lenses cannot completely eliminate the shift of the focus point for green light which is between blue and red light in the spectrum from the total focus point. This weak residual aberration is called secondary chromatic aberration, or secondary spectrum. Fluorite virtually eliminates it completely.

Compared to optical glass, fluorite has a very low index of refraction, unusually low private dispersion, excellent permeability to infrared and ultraviolet light and other outstanding properties. The convex fluorite lens has characteristics not found in conventional optical glass lenses, so it virtually eliminates the secondary spectrum and combines almost all red, green and blue focus points. Thus it is possible to practically completely get rid of chromatic aberration.

Fluorite optical elements significantly improve the performance of super-telephoto lenses, which are highly affected by the secondary spectrum due to their long focal length. This is why Canon uses fluorite lenses in modern lenses such as the EF400mm f/2.8 L IS III USM and EF600 mm f/4L IS III USM both available in December 2018 . Photographers the world over appreciate our super telephoto lenses with fluorite elements for their high contrast and accurate color reproduction.