| 摘要 |
PURPOSE:To obtain an lightweight, inexpensive lens system while eliminating variation with temperature in focal length by using optical glass for either of the 1st and the 5th lens of five-group five-element constitution and plastic for other four lenses, and satisfying a specific inequality. CONSTITUTION:The lens system consists of five elements in five groups, i.e. the 1st biconvex lens, the 2nd meniscus lens having a convex surface on an object side, the 3rd biconcave lens, the 4th meniscus lens having a convex surface on the image side, the 5th biconvex lens. In this case, the 1st or 5th lens is made of optical glass and other four lenses are made of plastic; and this system satisfies the inequality. Consequently, the variation with temperature in focal length is reduced to a submultiple as compared with a lens system consisting of lenses all made of plastic, and the low-cost lens system is realized by using lightweight plastic lenses which need not be polished. |
