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In film and photography, a prime lens is either a photographic lens whose focal length is fixed, as opposed to a zoom lens, or it is the primary lens in a combination lens system. Confusion can sometimes result due to the two meanings of the term if the context does not make the interpretation clear. Alternative terms primary focal length, fixed focal length, and FFL are sometimes used to avoid ambiguity. == As alternative to zoom lens == The term ''prime'' has come to be used as the opposite of ''zoom;'' that is, a prime lens is a fixed-focal-length, or unifocal lens, while a zoom lens has a variable focal length. While a prime lens of a given focal length is less versatile than a zoom, it is often of superior optical quality, wider maximum aperture, lighter weight, smaller size. These advantages stem from having fewer moving parts, optical elements optimized for one particular focal length, and a less complicated lens formula which means that they suffer from fewer problems of optical aberration. The larger maximum aperture (smaller f-number) allows photography in lower light, and a shallower depth of field. A normal lens or "normal prime" is a lens with a focal length about equal to the diagonal size of the film or sensor format, or that reproduces perspective that generally looks "natural" to a human observer under normal viewing conditions. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Prime lens」の詳細全文を読む スポンサード リンク
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