北京有哪些留学托福培训机构比较优质

“北京有哪些留学托福培训机构比较优质”托福考试更利于申请奖学金，尤其是助教奖学金。托福可以帮助留学生尽早体验留学生活。

北外雅思培训学校根据学生的学习情况，在课下及自习课上为学生一遍又一遍的耐心辅导。 我们有充满爱心又认真负责的生活管理教师，我们把学生当成自己的孩子，在生活给他们无微不至的照顾，同时也在时时告诫他们不能放下学业，一切以学习为重。 所有教职员工本着以学生为本的办学理念，用爱心去关爱每一位学生，用耐心去教导每一位学生，尽我们最大的努力让每一位学生都在这里圆自己的留学梦想。

托福阅读备考中，对于一些常考的内容，我们也要了解一下具体的背景知识。这样能够辅助我们更好地来完成文章的阅读。下面小编为大家整理了“摄影术的发展”，供大家参考。

The camera obscura is an optical device that projects an image of its surroundings on a screen. It is used in drawing and for entertainment and was one of the inventions that led to photography and the camera. The device consists of a box or room with a hole in one side. Light from an external scene passes through the hole and strikes a surface inside where it is reproduced rotated 180 degrees (thus upside-down) but with color and perspective preserved. The image can be projected onto paper and can then be traced to produce a highly accurate representation.The largest camera obscura in the world is on Constitution Hill in Aberystwyth Wales.

Using mirrors as in the 18th-century overhead version it is possible to project a right-side-up image. Another more portable type is a box with an angled mirror projecting onto tracing paper placed on the glass top the image being upright as viewed from the back.

As the pinhole is made smaller the image gets sharper but the projected image becomes dimmer. With too small a pinhole however the sharpness worsens due to diffraction. Some practical camera obscuras use a lens rather than a pinhole because it allows a largeraperture giving a usable brightness while maintaining focus. History

The camera obscura has been known to scholars since the time of Mozi and Aristotle.The first surviving mention of the principles behind the pinhole camera or camera obscura belongs to Mozi a Chinese philosopher and the founder of Mohism. Mozi correctly asserted that the image in a camera obscura is flipped upside down because light travels in straight lines from its source. His disciples developed this into a minor theory of optics.

The Greek philosopher Aristotle understood the optical principle of the pinhole camera.He viewed the crescent shape of a partially eclipsed sun projected on the ground through the holes in a sieve and through the gaps between the leaves of a plane tree. In the 4th century BCE Aristotle noted that "sunlight travelling through small openings between the leaves of a tree the holes of a sieve the openings wickerwork and even interlaced fingers will create circular patches of light on the ground." Euclid’s Optics presupposed the camera obscura as a demonstration that light travels in straight lines.In the 4th century Greekscholar Theon of Alexandria observed that "candlelight passing through a pinhole will create an illuminated spot on a screen that is directly in line with the aperture and the center of the candle."

In the 6th century the Byzantine-Greek mathematician and architect Anthemius of Tralles (most famous for designing the Hagia Sophia) used a type of camera obscura in his experiments.

In the 9th century Al-Kindi (Alkindus) demonstrated that "light from the right side of the flame will pass through the aperture and end up on the left side of the screen while light from the left side of the flame will pass through the aperture and end up on the right side of the screen."

Alhazen also gave the first clear description and early analysis and invented the camera obscura and pinhole camera. While Aristotle Theon of Alexandria Al-Kindi and Chinese philosopher Mozi had earlier described the effects of a single light passing through a pinhole none of them suggested that what is being projected onto the screen is an image of everything on the other side of the aperture. Alhazen was the first to demonstrate this with his lamp experiment where several different light sources are arranged across a large area. He was thus the first to successfully project an entire image from outdoors onto a screen indoors with the camera obscura.

The Song Dynasty Chinese scientist Shen Kuo experimented with a camera obscura and was the first to apply geometrical andquantitative attributes to it in his book of 1088 AD the Dream Pool Essays. However Shen Kuo alluded to the fact that the Miscellaneous Morsels from Youyang written in about 840 AD by Duan Chengshi during the Tang Dynastymentioned inverting the image of a Chinese pagoda tower beside a seashore.In fact Shen makes no assertion that he was the first to experiment with such a device. Shen wrote of Cheng’s book: "[Miscellaneous Morsels from Youyang] said that the image of the pagoda is inverted because it is beside the sea and that the sea has that effect. This is nonsense. It is a normal principle that the image is inverted after passing through the small hole."

In 13th-century England Roger Bacon described the use of a camera obscura for the safe observation of solar eclipses.At the end of the 13th century Arnaldus de Villa Nova is credited with using a camera obscura to project live performances for entertainment.Its potential as a drawing aid may have been familiar to artists by as early as the 15th century; Leonardo da Vinci described the camera obscura in Codex Atlanticus. Johann Zahn’s "Oculus Artificialis Teledioptricus Sive Telescopium which was published in 1685 contains many descriptions and diagrams illustrations and sketches of both the camera obscura and of the magic lantern.

Giambattista della Porta is said to have perfected camera obscura. He described it as having a convex lens in later editions of his Magia Naturalis the popularity of which helped spread knowledge of it. He compared the shape of the human eye to the lens in his camera obscura and provided an easily

understandable example of how light could bring images into the eye. One chapter in the Conte Algarotti’s Saggio sopra Pittura is dedicated to the use of a camera ottican painting.

Camera obscura from a manuscript of military designs. 17th century possibly Italian.

The 17th century Dutch Masters such as Johannes Vermeer were known for their magnificent attention to detail. It has been widely speculated that they made use of such a camera but the extent of their use by artists at this period remains a matter of considerable controversy recently revived by the Hockney–Falco thesis.

The term "camera obscura" itself was first used by the German astronomer Johannes Kepler in 1604.The English physician and author Sir Thomas Browne speculated upon the interrelated workings of optics and the camera obscura in his 1658 discourse The Garden of Cyrus thus:

For at the eye the Pyramidal rayes from the object receive a decussation and so strike a second base upon the Retina or hinder coat the proper organ of Vision; wherein the pictures from objects are represented answerable to the paper or wall in the dark chamber; after the decussation of the rayes at the hole of the hornycoat and their refraction upon the Christalline humour answering the foramen of the window and the convex or burning-glasses which refract the rayes that enter it.

Four drawings by Canaletto representing Campo San Giovanni e Paolo in Venice obtained with a camera obscura (Venice Gallerie dell’Accademia)

Early models were large; comprising either a whole darkened room or a tent (as employed by Johannes Kepler). By the 18th century following developments by Robert Boyle and Robert Hooke more easily portable models became available. These were extensively used by amateur artists while on their travels but they were also employed by professionals including Paul Sandby Canaletto and Joshua Reynolds whose camera (disguised as a book) is now in the Science Museum (London). Such cameras were later adapted by Joseph Nicephore Niepce Louis Daguerre and William Fox Talbot for creating the first photographs.

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