Designing Lens

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 converge on a single point in the image，as a consequence of their passing through a series of transparent 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，how-ever，as to be virtually， if not actually， infinite．There fore in lens design，as in chess，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．

设计镜头

设计一个透镜就好比是下棋。下棋时，棋手试图在连续的几着中困住对手的王。而制造透镜时，一个透镜设计师就要试图“困住”光，其方法就是当光线穿过一系列具有精确曲面的透明元件之后，迫使源自于物体某一点的所有光线聚合为图像的某一点。既然在这两种情况中，最终目标以及达到该目标的手段都是明确的，人们自然会想到将有一个从任何角度来看都是最好的决断。而从任何一个决断推演出来的可能结果，其数目之巨，几乎是无穷，尽管实际上还不是这样。因此，在透镜设计中，就像在下棋中一样，问题的最佳答案是难以企及的。本文所及虽然只是摄相机镜头的设计，但这些原理同样适用于所有的透镜。

透镜设计师比起棋手来，有着巨大的便利：他可以自由调用各种有用的资料来引导自己从数目大得惊人的各种可能性中进行选择。这种帮助曾经来自于数学与物理学，但现在，计算机技术、信息理论、化学、工业技术以及心理物理学都使透镜设计师的工作无可估量地多产。今天市场上的一些透镜在10年以前还是难以想象的，其他一些制造了上百年的透镜，现在能够低成本地成批生产。随着自动化生产手段的发展，玻璃透镜和塑料透镜二者成百万地生产。今天的镜头比过去大摄影家们所使用的最好的镜头还要好，尽管19世纪的工匠一个星期的工作只有几美元，今天的透镜又更为复杂，但今天透镜的价格比过去还低。透镜设计师不能不感谢科学技术，因为它们使他的工作更为简易，使他的创造运用更为广泛。不过，他也因此变得谦卑：一个好镜头自始至终由一个人的智慧设计出来已不再实际可行。