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In photography and videography, a lens adapter is a device that enables the use of camera and lens combinations from otherwise incompatible systems. The most simple lens adapter designs, passive lens adapters provide a secure physical connection between the camera and the lens. Some passive adapters may include a mechanism for manual iris control. So called, active lens adapters will include electronic connections, enabling communication between the lens and the camera.〔Plant, Ian. ("Lens Adapters: An Introductory Guide" ), 11 February 2013.〕 Some lens adapters include a special optical element called a telecompressor, focal reducer, or more recently a "speed booster," a genericised trademark that refers to the popular Metabones® Speed Booster® line of lens adapters.〔(Metabones Speedbooster Tele-Compressor Speeds Up Mirrorless Cameras )〕 This type of adapter is designed to reduce focal length, increase lens speed, and in some instances improve MTF performance. The depth-of-field adapter (also called a DOF adapter or 35mm adapter) is a largely obsolete device that uses a ground glass focusing screen to enable the use of interchangeable lenses on a fixed lens camcorder.〔Bloom, Philip. ("35mm Adapters" )〕 There are also lens adapters made for other optical systems, including microscopes and telescopes. == Basic design == Most lens adapters feature a male fitting and a female fitting. The male fitting attaches to the camera, and the female fitting attaches to the lens. There is also an opening in the center to allow the light to pass through. Lens adapters can be shorter or longer, based on the respective flange focal distance of the lens and camera being adapted. Flange focal distance is the key specification in determining whether or not a particular type of lens can be adapted to any given camera. Generally speaking, cameras with a shorter flange focal distance can be adapted to a greater diversity of lenses. This is because there must be enough room to fit an adapter between the lens and the camera. It is possible to physically mount a lens with a short flange focal distance on a camera with a long flange focal distance, but this will make it impossible to achieve infinity focus. The effect will be similar to that of an extension tube, because the lens will be mounted further from the image plane than intended. Some lens adapters utilize an optical element to compensate for this, but these types of adapters have a reputation for degrading image quality. 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「Lens adapter」の詳細全文を読む スポンサード リンク
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