Fresnel lens

Definition: Flat optical component that has the effect of a lens element. * Effectively consists of successive narrow rings of the lens which are flattened: in plan view, the lens consists of concentric rings; in section it is jagged like a row of teeth. * Can be of postive or negative power. * Used to replace normal lens to reduce weight and thickness where image quality is not critical e.g. light-house or search-light collecting lens or as a field lens to improve light distribution in camera viewfinders.

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