ABSTRACT
The basic optics for an image-intensified viewing system consists of an objective lens and a camera lens. There are three primary characteristics for which any lens is designed, aside from the overall quality and performance level necessary for the particular application. These three characteristics are focal length, relative aperture, and field of view. In a simple lens, focal length is usually of most importance. Focal length is simply the distance measured from the lens to a focal point. The importance of focal length lies in the fact that this is the determining factor in the magnification at which a scene is an image on the television camera tube. Although relative aperture is the correct technical term, the much more common term used to describe this characteristic of a lens is called speed. The field of view of the lens does not necessarily dictate the lens diameter.
