ABSTRACT
An optical system is basically formed by lenses and mirrors, but it has an extremely large number of possible configurations and requirements, as pointed out by Hilbert and Rodgers. The speed of a microscope objective is very high and that of the single magnifier is very low. The required resolution of a microscope objective is quite high, but for a single lens, it is low. An interesting and important characteristic of imaging optical systems is the total number of picture elements it produces (pixels), which depends on the f-number and on the aperture diameter. The number of possible lens and mirror combinations is almost infinite. A single lens is the simplest optical instrument and has many applications. One important use is as a simple microscope or magnifier. Another application is as a simple photographic lens.
