新目标英语第九单元SELF CHECK -2的作文怎么写啊 20
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The forerunner to the camera was the camera obscura. The camera obscura is an instrument consisting of a darkened chamber or box, into which light is admitted through a convex lens, forming an image of external objects on a surface of paper or glass, etc., placed at the focus of the lens. The camera obscura was described by the Arabic scientist Ibn al-Haytham (Alhazen) in his Book of Optics (1015–1021). Alhazen's work appeared in Latin translation as De Aspectibus ("Concerning vision") in about 1200, and the book influenced Roger Bacon's reflections on producing images using pinholes. Bacon's notes and drawings, published as Perspectiva in 1267, are partly clouded with theological material describing how the Devil can insinuate himself through the smallest of spaces by magic, and it is not clear whether or not he produced such a device. On 24 January 1544 mathematician and instrument maker Reiners Gemma Frisius of Leuven University used one to watch a solar eclipse, publishing a diagram of his method in De Radio Astronimica et Geometrico in the following year. In 1558 Giovanni Batista della Porta was the first to recommend the method as an aid to drawing. The actual name of camera obscura was first applied to the technique by mathematician and astronomer Johannes Kepler in his Ad Vitellionem paralipomena of 1604; he would later improve the apparatus by adding a lens and making it transportable, in the form of a tent. Irish scientist Robert Boyle and his assistant Robert Hooke later developed a portable camera obscura in the 1660s.
The first camera that was small and portable enough to be practical for photography was built by Johann Zahn in 1685, though it would be almost 150 years before technology caught up to the point where this was practical. Early photographic cameras were essentially similar to Zahn's model, though usually with the addition of sliding boxes for focusing. Before each exposure, a sensitized plate would be inserted in front of the viewing screen to record the image. Jacques Daguerre's popular daguerreotype process utilized copper plates, while the calotype process invented by William Fox Talbot recorded images on paper.
The first camera that was small and portable enough to be practical for photography was built by Johann Zahn in 1685, though it would be almost 150 years before technology caught up to the point where this was practical. Early photographic cameras were essentially similar to Zahn's model, though usually with the addition of sliding boxes for focusing. Before each exposure, a sensitized plate would be inserted in front of the viewing screen to record the image. Jacques Daguerre's popular daguerreotype process utilized copper plates, while the calotype process invented by William Fox Talbot recorded images on paper.
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