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Projector

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Projector

Acer projector, 2012

A projector or image projector is an optical device that projects an image (or moving images) onto a surface, commonly a projection screen.

Most projectors create an image by shining a light through a small transparent lens, but some newer types of projectors can project the image directly, by using lasers. A virtual retinal display, or retinal projector, is a projector that projects an image directly on the retina instead of using an external projection screen.

The most common type of projector used today is called a video projector. Video projectors are digital replacements for earlier types of projectors such as slide projectors and overhead projectors. These earlier types of projectors were mostly replaced with digital video projectors throughout the 1990s and early 2000s (decade), but old analog projectors are still used at some places. The newest types of projectors are handheld projectors that use lasers or LEDs to project images. Their projections are hard to see if there is too much ambient light.

Movie theaters use a type of projector called a movie projector. Another type of projector is the enlarger, a device used to produce photographic prints from negatives.

Contents

  • History 1
    • Early history of projectors and cameras 1.1
    • The first image projectors 1.2
    • The 20th century to present day 1.3
  • See also 2
  • Notes and references 3
  • External links 4

History

Early history of projectors and cameras

Projectors share a common history with cameras. As far back as the 4th century BC, Greeks such as Aristotle and Euclid wrote on naturally-occurring rudimentary pinhole cameras. For example, light may travel through the slits of wicker baskets or the crossing of tree leaves.[1] (The circular dapples on a forest floor, actually pinhole images of the sun, can be seen to have a bite taken out of them during partial solar eclipses opposite to the position of the moon's actual occultation of the sun because of the inverting effect of pinhole lenses.)

It was the 10th-century Ibn al-Haytham (Alhazen), who published this idea in the Book of Optics in 1021. When Ibn al-Haytham began experimenting with the camera obscura, he himself stated, Et nos non inventimus ita, "we did not invent this".[2] He improved on the camera after realizing that the smaller the pinhole, the sharper the image (though the less light). He provides the first clear description for construction of a camera obscura (Lat. dark chamber). As a side benefit of his invention, he was credited with being first man to shift physics from a philosophical to an experimental basis.[3]

In the 5th century BC, the Mohist philosopher Mo Jing (墨經) in ancient China mentioned the effect of an inverted image forming through a pinhole.[4] The image of an inverted Chinese pagoda is mentioned in Duan Chengshi's (died 863) book Miscellaneous Morsels from Youyang written during the Tang Dynasty (618–907).[5] Along with experimenting with the pinhole camera and the burning mirror of the ancient Mohists, the Song Dynasty (960–1279) Chinese scientist Shen Kuo (1031–1095) experimented with camera obscura and was the first to establish geometrical and quantitative attributes for it.[5]

Ancient pinhole camera effect caused by balistrarias in the Castelgrande in Bellinzona

In the 13th century, Robert Grosseteste and Roger Bacon commented on the pinhole camera.[6] Between 1000 and 1600, men such as Ibn al-Haytham, Gemma Frisius, and Giambattista della Porta wrote on the pinhole camera, explaining why the images are upside down. 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.

The first image projectors

The first known record of what might portray the idea of projecting an image on a surface is a drawing by Johannes de Fontana from 1420. The drawing was of a nun holding something that might be a lantern. The lantern had a small translucent window that contained an image of a devil holding a lance [1]. Leonardo da Vinci also made a similar sketch in 1515. These drawings are likely to have inspired the creation of the earliest image projector, a device called a magic lantern.

In the 17th century, the first

External links

  1. ^ "Light Through the Ages".
  2. ^ Adventures in CyberSound: The Camera Obscura
  3. ^ "How Islamic inventors changed the world", The Independent. Accessed April 6, 2007
  4. ^ Needham, Joseph (1986). Science and Civilization in China: Volume 4, Physics and Physical Technology, Part 1, Physics. Taipei: Caves Books Ltd. Page 82.
  5. ^ a b Needham, Joseph (1986). Science and Civilization in China: Volume 4, Physics and Physical Technology, Part 1, Physics. Taipei: Caves Books Ltd. Page 98.
  6. ^ A reconsideration of Roger Bacon's theory of pinhole images
  7. ^ Pfragner, Julius. “Index.” The Motion Picture: From Magic Lantern to Sound. Great Britain: Bailey Brothers and Swinfen Ltd. 226. Print.
  8. ^ Waddington, Damer. “Introduction.” Panoramas, Magic Lanterns and Cinemas. Channel Islands, NJ: Tocan Books. xiii-xv. Print.
  9. ^ Ars Magna Lucis et Umbrae. Athanasius Kircher. 1671. Retrieved 19 August 2010. 
  10. ^ Pfragner, Julius. “An Optician Looks for Work.” The Motion Picture: From Magic Lantern to Sound. Great Britain: Bailey Brothers and Swinfen Ltd. 9-21. Print.
  11. ^ Barber, Theodore X. “Phantasmagorical Wonders: The Magic Lantern Ghost Show in Nineteenth-Century America.” Film History 3,2 (1989): 73-86. Print.
  12. ^ Eds. Crangle, Richard, Heard, Mervyn, and van Dooren, Ine. “Devices and Desires.” Realms of Light. London, England: The Magic Lantern Society, 2005. 11-45. Print.
  13. ^ Eds. Crangle, Richard, Heard, Mervyn, and van Dooren, Ine. "Devices and Desires." Realms of Light. London, England: The Magic Lantern Society, 2005. 11-45. Print.

Notes and references

See also

Late in the 20th century, slides were replaced with digital images.

Another type of projector called slide projectors were common in the 1950s to the 1970s as a form of entertainment; family members and friends would gather to view slideshows.

In the late 1950s and early 1960s, overhead projectors began to be widely used in schools and businesses. The first overhead projector was used for police identification work. It used a cellophane roll over a 9-inch stage allowing facial characteristics to be rolled across the stage. The U.S. Army in 1945 was the first to use it in quantity for training as World War II wound down.

In the early and middle parts of the 20th century, a new type of low-cost projectors called opaque projectors were produced and marketed as toys for children. The opaque projector is a predecessor to the overhead projector. The light source in early opaque projectors was often limelight, with Incandescent light bulbs and halogen lamps taking over later.

The 20th century to present day

[13]

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