利用准直管法测凹透镜的焦距

介绍了利用准直管精确测量凹透镜焦距的方法，该方法借助一个焦距较长的凸透镜与被测凹透镜组成无焦系统，可以使准直管出射光束的张角发生改变；用一辅助凸透镜与一测微目镜进行平行光束的会聚，测出准直管玻罗板线对在辅助凸透镜焦平面上所成像的大小；经过相应计算可得到被测凹透镜的焦距。

Measuring the focal length of concave lens using collimator

A method of accurately measuring the focal length of a concave lens using a collimator is introduced. Firstly, a telescope system is made up with a concave lens and a long-focus convex lens, by which the angle of the parallel beam from the collimator can be change. Then using another convex lens and a micrometer eyepiece the altered parallel rays is focused, and the imaging size of line pair of collimator imaged on the another convex lens is measured. Finally, the focal length of the concave lens can be calculated.