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Here's a link to a Canon article about their aspherical lens technologies.
Excerpt:
The journey to mass-produce aspherical lens elements involved the incorporation of advanced technologies developed for the space exploration program, culminating in the development of the ALG-Z ultra-high-precision aspherical lens grinder and the ALM ultra-high-precision measuring machine. The use of a laser interferometer ensured fine control over equipment grinding, which made possible surface grinding precision down to units of 100nm for shaping and 50nm for processing. Combined with the uniform grinding and polishing techniques that Canon had developed based on its own theories, these technologies made it possible to mass produce more than 1,000 pieces of ground and polished aspherical lenses per month.
Later, Canon also succeeded in developing plastic-molded (PMo) aspherical lenses, which can be mass produced in larger quantities at a lower cost, and large-diameter glass-molded (GMo) aspherical lenses, which are molded in a machine that incorporates a high-precision aspherical metal mold*.
* 1982: Release of the Canon Snappy 50, the world’s first camera lens to incorporate a PMo aspherical lens element.
1985: Release of the New FD35-105mm f/3.5-4.5, the world’s first interchangeable lens for 35mm full-frame cameras to incorporate a GMo aspherical lens element.
In 1990, Canon developed a fourth aspherical lens production technology that produces replica aspherical lenses by using ultraviolet-light-hardening resin to form an aspherical lens surface layer on a spherical lens element.
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