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In photography, a secondary lens is a lens designed to be used in conjunction with another lens, called the primary lens. A secondary lens may be designed to be used either in front of the primary lens, between it and the subject, or behind the primary lens, between it and the film. Secondary lenses are typically simpler in mechanical design than other photographic lenses. Normally but not always there is no provision for control of focus or aperture, as these are achieved by the controls on the primary lens. ==Lenses used in front of the primary lens== Examples of secondary lenses designed to be used in front of the primary lens are: * Fisheye adaptors * Corrected wide angle adaptors * Telephoto adaptors such as teleside converters * Close-up lenses All of these typically mount on the filter ring of the primary lens. Front-mounting secondary lenses are commonly used to provide wide-angle and telephoto lenses for cameras which lack the facility to change the primary lens, such as consumer and "prosumer" video cameras and camcorders, bridge cameras, point-and-shoot cameras and some older consumer medium format cameras. 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「Secondary lens」の詳細全文を読む スポンサード リンク
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