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Designing a lens can be compared to playing chess. In chess a player tries to trap his opponent's king in a series of moves. In creating a lens a lens designer attempts to “trap” light by forcing all the rays arising from a single point in the subject to focus on a single point in the image, as a consequence of their passing through a series of transparent( 透明的) elements with precisely curved surfaces. Since in both cases the ultimate goal and the means by which it can be attained are known, one is tempted to think there will be a single best decision at any point along the way. The number of possible consequences flowing from any one decision is so large, however, as to bevirtually, if not actually, infinite. Therefore in lens design, as inchess, perfect solutions to a problem are beyond reach. Although this article will be concerned only with the design of photographic lenses, the same principles apply to all lenses. The lens designer has one enormous advantage over the chess player: the designer is free to call on any available source of help to guide him through the staggering number of possibilities. Most of that help once came from mathematics and physics, but recently computer technology, information theory,chemistry, industrial engineering and psychophysics have all contributed to making the lens designer's job immeasurably more productive. Some of the lenses on the market today were inconceivable a decade ago. Others whose design is as much as a century old can now be mass produced at low cost. With the development of automatic production methods, lenses are made by the millions, both out of glass and out of plastics. Today's lenses are better than the best lenses used by the great photographers of the past.Moreover, their price may lower, in spite of the fact that 19th century craftsmen worked for only a few dollars a week and today's lenses are more complex. The lens designer cannot fail to be grateful for the science and technology that have made his work easier and his creations more widely available, but he is also humbled: it is no longer practical for a fine photographic lens to be designed from beginning to end by a single human mind. 1.Lens design and chess playing are similar in that ____. A) the final goal and the means by which it can be reached are known B) perfect solutions to a problem can be found C) any one decision at any point along the way to the goal can bring numerous possible results D) both A and C 2.The final goal of designing a lens is ____. A) to trap the opponent's lenses B) to focus light with lenses C) to hand make lenses at low cost D) to reflect light by means of curved surfaces 3.After the passage the author will talk about ____. A) the principles of designing lenses B) techniques of making contact lenses C) the design of photographic lenses D) styles of lenses 4.Which of the following words cannot be used to describe today's lenses? A) More delicate. B) Cheaper. C) Numerous. D) Unpopular. 5.Lens designers today ____. A) have a large source of help to fall back on B) receive a low salary C) are less respectable than those of the past D) are not decisive in the lens design Over vast areas of every continent,the rainfall and vegetation necessary for life are disappearing.Already more than 40 percent of the earth's land is desert or desert like.About 628 million people—one out of seven—live in these dry regions.In the past,they have managed to survive,but with difficulty.[ZZ(Z]Now largely through problems caused by modern life,their existence is threatened by the slow,steady spread of the earth's deserts. Scientists still do not understand all the complex problems of the desert,but there have been many ideas for saving the land.Sandi Arabia has planted 10 million trees to help keep the sand from taking over fertile areas.The Israelis are aga in using some of the water collection systems left by the ancient people in the Negev desert.They plan to water their orchards with the extra water.Some Sahel farmers still raise cattle on their poor farm land,but before the cattle are sold, they are taken to greener lands in the south to get fat. 6. What is the article mainly concerned? A.The problem of spreading desert. B.The rainfall and vegetation in desert areas. C.The water collection systems. D.The difference between modern life and ancient life. 7. “one out of seven” refers to____. A.more than a third of the lands' earth B.the percentage of the earth's land that is desert-like C.the number of people who live in dry regions D.a day of a week 8. In paragraph 2,“they are taken to the greener lands in the south.”They refers to____. A.the Sahel farm land B.the farmers C.the cattles D.the trees 9. How many ideas for saving the land are described? A.Five. B.Two. C.Four. D.Three. 10. Which of the following statements is true, according to the passage? A.The earth's desert are slowly spreading. B.One out of 10 people lives in dry regions. C.Their life in the desert is threatened now by traditional problems. D.New water wells can solve the problem in Africa's desert. |
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