It is reasonable to assume that anyone planning to study lens design is already familiar with the basic facts of geometrical and physical optics. However, there are a few points that should be stressed to avoid confusion or misunderstanding on the part of the reader.
2.1.1 Object and Image
All lens design procedures are based on the principles of geometrical optics, which assumes that light travels along rays that are straight in a homogeneous medium. Light rays are refracted or reflected at a lens or mirror, where they proceed to form an image. Due to the inherent properties of refracting and reflecting surfaces and the dispersion of refracting media, the image of a point is seldom a perfect point ...