In the previous article, we discussed “What are the Hydrogel materials used to make contact lenses?”. In this article, let’s talk about “What is an aspheric lens?”.
What is an aspheric lens?
Strictly speaking, any lens with a refractive surface that is not a sphere is an aspheric lens, including ordinary astigmatism lens, progressive multi-focal lens, Aspheric apical lens, etc. But customarily, our daily aspheric lens refers to the Aspheric apical lens. From the center of the lens to the periphery, the radius of curvature increases (the surface of the lens flattens out).
The origin of aspheric lens
The Visby glasses, unearthed in Gotland, Sweden, are the earliest aspheric lens found. The Vikings in the 11th century used it as a magnifying glass, and some of the best ones were made of silver, making them look like handicrafts. In 1667, Francis Smethwick grinds the first high-quality aspheric lenses and presents them to the Royal Society. That's a telescope with three aspheric elements. In 1956, Elgeet, which originally designed and manufactured optical instruments for the U.S. Navy, produced the world's first mass-produced aspheric lens for photography (Golden Navitar 12mm F1.2) for a 16mm film machine. Today, aspheric lenses are found in everything from tall telescopes to missile guidance systems to camera lenses. In the glasses we wear, the aspheric lens is familiar to consumers.
Types of aspheric lenses
There are two types of aspheric lenses: single aspheric surface (single aspheric surface for short, different from the outer aspheric surface and inner aspheric surface) and double aspheric surface (double aspheric surface for short). For the outer aspheric surface, convex is an aspheric surface and concave is a spherical surface. For the inner aspheric surface, a convex surface is a sphere, and a concave surface is an aspheric surface. In addition to correcting aberrations, the double aspheric lens also improves the effective field of vision compared to the single aspheric surface. When people's eyes look through the edge of the lens to see things, like driving when looking at the reflective mirror, it often affects vision because of the large aberration at the edge of the lens. Previous designs of aspheric plates have analyzed a single ray of light passing through the center of the pupil. Wavefront technology controls the entire beam of light passing through the pupil, eliminating high-order aberrations.
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