In 1971 they came up with their aspherical interchangeable lens for the SLR this is to correct various types of lens aberrations and improve image quality. The lens was manufactured to satisfy whether in entry-level models or high-performance models designed for professional users. In manufacturing this the need to have control over the curvature of the submicron level with a precision of 1/10,0000th of a millimeter, seemed very unachievable.
Eventually in 1971 Canon finally released an interchangeable lens for SLR cameras that included aspherical lens elements. Since then, they have been able to continue to refine processing methods and precision technology, spearheading the constant improvement of image quality via aspherical lenses.
Image shot with the aspherical lens.
The aspherical lens is a conventional lens that has a curved surface shape. Compared to light rays passing through the center of a spherical element, rays entering from its peripheries must travel a longer distance in order to reach the image plane, resulting in the light rays converging at different positions. The ray of light that is supposed to be rendered as a point light is blur causing an effect called spherical aberration.
When it comes to aspherical lenses, the curvature changes towards the lens peripheries, ensuring that all light rays converge at the same position, which reduces spherical aberration.
You can find more details about canon’s achievement in the last fifty years in the link below.
