等光程 meaning in English

aplanatic
aplanatism

In chapter three , the importance of maintaining the equal optical path between measuring beam and reference beam in measuring horizontal and vertical vibration table are analyzed , and the factors having effect on contrast degree of interference fringe are introduced . for improving the accuracy of laser - vibration - measuring - system , the phase - modulation - multi - period - average method and the vibration isolated of system are analyzed
第三章分析了光路设计中的等光程问题的重要性，以及影响干涉条纹对比度的相关因素；并从提高测量精度的角度分析了调相多周期平均法和系统的隔振。