ABSTRACT
The parallel-sided block of glass hardly deserves the title ‘optical component’; it is such a basic, simple, optical element. The plane that passes through the focal point and is also perpendicular to the optical axis is then known as the focal plane. As with lenses, incident parallel rays close to the optical axis will be focused further away from the mirror than will rays more distant from the optical axis. Rays near the optical axis are brought to a focus further away from the lens than are rays more distant from the axis. Many optical systems are, of course, designed to be used in conjunction with the human eye — that is, with the eye as an integral part of the system, looking through the microscope or telescope, and not just observing an image thrown onto a screen.
