Positive & Negative Components

Technical note discusses two types of optical components that can be defined in terms of their effect on an incident-light beam.

Two general types of optical components can be defined in terms of their effect on an incident-light beam. Let a parallel beam of light be incident on an optical element: since the optical interface is curved, parallel rays striking the lens at different heights have different angles of incidence and therefore experience varying amounts of refraction. As a result, the exiting light beam converges or diverges in a specific manner.

Positive and Negative Components diagrams

A positive lens or concave mirror causes the light to converge at a defined focus. If the incident light were diverging, the positive element would cause it to diverge less rapidly or converge; if the light were converging, the element would cause it to converge more rapidly. Positive lenses can be classified in general types by their radii of curvature, as illustrated in Figure 2A, and are always thicker at their centers than at their edges.

Negative elements include negative lenses and convex mirrors. They cause parallel light to appear to diverge from a defined focus, make divergent light diverge more quickly, and cause convergent light to converge less rapidly or to diverge. Various negative elements are shown in Figure 2B; note that all of these lenses are thicker at their edges than in their centers.

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