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A pinhole camera, a variation of Camera obscura, is a simple camera without a lens and with a single small aperture, a ''pinhole'' – effectively a light-proof box with a small hole in one side. Light from a scene passes through this single point and projects an inverted image on the opposite side of the box. Exposures can typically range from five seconds up to as much as several hours. The effect was noted in the 5th century BC in China and has been refined over the centuries. ==Description== A pinhole camera, also known as camera obscura, or "dark chamber", is a simple optical imaging device in the shape of a closed box or chamber. In one of its sides is a small hole which, via the rectilinear propagation of light, creates an image of the outside space on the opposite side of the box. A pinhole camera is completely dark on all the other sides of the box including the side where the point is created. This part is usually painted black, but black boxes are also used for this purpose. There is also a thin screen which looks like a projector sheet, and is put in between the dark side adjacent to the pinhole. Up to a certain point, the smaller the hole, the sharper the image, but the dimmer the projected image. Optimally, the size of the aperture should be 1/100 or less of the distance between it and the projected image. Because a pinhole camera requires a lengthy exposure, its shutter may be manually operated, as with a flap made of light-proof material to cover and uncover the pinhole. Typical exposures range from five seconds to several hours. A common use of the pinhole camera is to capture the movement of the sun over a long period of time. This type of photography is called solargraphy. The image may be projected onto a translucent screen for real-time viewing (popular for observing solar eclipses; see also camera obscura), or can expose photographic film or a charge coupled device (CCD). Pinhole cameras with CCDs are often used for surveillance because they are difficult to detect. Pinhole devices provide safety for the eyes when viewing solar eclipses because the event is observed indirectly, the diminished intensity of the pinhole image being harmless compared with the full glare of the Sun itself. World Pinhole Day is held on the last Sunday of April.〔http://www.bbc.co.uk/news/in-pictures-22150973〕 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「Pinhole camera」の詳細全文を読む スポンサード リンク
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