what is aspheric
Aspheric Lens: An aspheric lens is designed for aberration correction. With the help of aspheric lens, the image formed is distortion free. An aspheric lens is a lens whose surfaces profile neither a portion of a sphere nor of a circular cylinder. Since it is not spherical, the conventional processes no longer apply to making aspheric surfaces. This is why aspheric cost many times what spherical surfaces do.