Image formation has many meanings to various groups or individuals; however, in geometrical optics its definition is very clear in that it refers to the formation of a light pattern to replicate a scene. The light (radiant power) pattern formed by the optical phenomenon resembles the scene or object, and is called an image. In geometrical optics, an image-forming optical system creates a radiant pattern in two dimensions that resembles the scene that a human eye would perceive as the object. There are two general classes of images in geometrical optics: those formed by lenses and those formed by projections. In present day cameras, lenses are by far the most common means of obtaining an image.

Pinhole camera

One example of a projection system is the pinhole camera, also referred to as camera obscura (Latin for “dark chamber”), which uses a tiny pinhole to collect light without the use of a lens. Figure 3.1 illustrates this simple concept. You may recall, as a child, sitting inside a box while viewing an image projected through a pinhole onto the inside wall. The light from an object passes through a small aperture along a ray, to form an image on a surface. This image may either be projected onto a translucent screen for viewing through the camera, or onto an opaque surface for viewing in reflection.