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本文主要论述了用焦度仪测量接触镜片后顶焦度(即测量后顶焦距)的有关问题。提出了测量接触镜片后顶焦距的主要问题是确定后顶点的轴向定位基准以及实际焦点的位置,其中实际焦点最为关键。由于接触镜片本身带有较大的像差,实际焦点位置与入瞳大小紧密相关,因而入瞳大小的规定非常重要。文中在分析有关接触镜片光学特性后认为:只要规定了能表征人眼实际情况的入瞳数值,就能计算出对应的实际焦点位置,该焦点位置即是像方光轴截面弥散斑最小处,也是焦度仪实际测量位置,它与近轴光焦点位置偏差很大。文中同时给出计算实际焦点位置的计算公式。
This article mainly discusses the use of power meter to measure contact lenses after vertex (ie, after measuring the top focal length) of the issues. The main problem of measuring the top focal length of the contact lens is to determine the axial positioning reference of the posterior vertex and the position of the actual focal point. The actual focal point is the most important issue. Due to the contact lens itself with a larger aberration, the actual focus position and closely related to the size of the entrance pupil, and thus the size of the entrance pupil is very important. After analyzing the optical characteristics of contact lenses, we think that as long as the value of entrance pupil that can characterize the actual situation of the human eye is specified, the corresponding actual focus position can be calculated, which is the minimum at the cross section of specular optical axis, It is also the actual measuring position of the focal instrument, which deviates greatly from the focus position of the paraxial light. In the meantime, the calculation formula for calculating the actual focus position is given.