What is an aspherical lens? What are the characteristics and advantages of aspheric lenses?

Aspheric lens is a combination of optical lens or compound lens, and at least a little different parts of the surface do not have the same spherical center. A compound lens containing at least one such lens is called an aspherical lens. Most lenses are spherical, so the distance from each point on a specific surface to the center of the sphere (radius or center point) is equal, and the front surface and back surface of the lens are almost all spherical surfaces with different radii. The biggest defect of this design principle is the inevitable spherical aberration, which can only be corrected by aspheric lens. Spherical aberration is caused by the spherical surface of the lens. The light emitted from the same object point on the optical axis passes through the lens and converges on different points in the image field space, so that the position of the image end is shifted. Different from ordinary concave-convex lens, aspheric lens has a simple spherical surface, the thickness of aspheric lens is large at the edge of the lens, and the mirror surface is aspheric. The function of aspheric lens is to change the curvature of lens surface, so that the focal positions formed by paraxial light and far-axis light coincide. When the near-axis light and the far-axis light both fall on the same focal plane, the light spot will disappear and the imaging clarity will be improved.