Aspherical Lenses
The aspherical lens, a development in optical technology that offers genuinely revolutionary optical characteristics, is responsible for the excellent performance and sharp image resolution of Canon's L-series lenses. It nearly seems as though a curtain has been lifted to reveal the visible world behind the lens thanks to aspherical lenses' remarkable sharpness and vivid detail. Because aspherical lenses are so difficult to fabricate, they were for years only the pipe dream of optical engineers. Unlike regular photo lenses, which are spherical, aspherical lenses require a portion of the lens element's spherical surface to be removed at the optical axis. However, because these lenses could not converge parallel light rays at the same focal point, they were theoretically limited. Making an aspherical lens with an ideal curvature — one that converges parallel rays at a single focal point — was the solution.
The degree of asphericity is very small in some aspherical lens designs. It looks just like a spherical lens to the unaided eye. The curvature degree is so small that one needs to calculate precision processing tolerances to within one-tenth of a millimetre, or 0.1 micron. Canon unveiled the FD55mm f/1.2AL in 1971, even though there were still some issues with mass production at the time. It was the first SLR lens ever made with a ground aspherical lens element (without a mirror-lock mechanism). Canon decided to boost aspherical lens research and increase production volume in response to the positive reception this lens received. The company was able to launch the first mass-production nanometer-class machinery in the world, featuring tolerances of less than one-millionth of a millimetre, in just two years.
The precision with which the lenses are polished is as low as 0.02 micrometres, or 1/32 of the height of a visible light wavelength. The L-Series lenses are the only ones that offer the high optical performance that is guaranteed by this meticulous precision.
The technology used to manufacture spherical lenses kept developing. Large-diameter glass-molded (GMo) aspherical lens research and development started in the 1980s, and these components were successfully applied to practical use in 1985. Superior surface tolerances are achieved with glass moulding technology by using aspherical, high-precision metal moulds and high-temperature melted glass. In 2007, the first concave aspherical lens was created using this technology. Many of the RF L-series lenses available today are built using the same technology.
High-temperature melted glass and aspherical lenses.
The replica aspherical lens from Canon, which was created for the EF lens series in 1990 and is distinguished by a high degree of design freedom in terms of size and material choice for the spherical base lens element, is one aspherical lens that meets a range of needs. As part of the RF lens series, a replica aspherical lens is also used in the RF24-105mm f/2.8L IS USM Z. Advancements in manufacturing techniques have resulted in replica aspherical lenses possessing a surface precision that surpasses that of EF lenses. The new lens offers consistent performance at a bright aperture of f/2.8, a focal length range of 24mm-105mm, and a smaller size due to its increased freedom in optical design.