A proper starting point is dertermined at first by attempting ray, then position of principal ray and marginal ray is calculated with iteration method.
本文介绍先借用尝试光线确定一个适当的起始点，然后用迭代法计算出主光线和边缘光线的位置，最后给出计算实例。
In the spot diagram formed by a specified beam,the center of the spot for calculating chromatic aberration should not be the cross point of principal ray with image plan,but the weighted mean of coordinates of all traced rays,namely,centroid of rays,which is determined by the distribution of traced rays.
在一束特定成像光束所形成的弥散斑上,作色差计算的光斑中心不是主光线与像面的交点,而应该是弥散斑中所有光线交点的"重心"所在,也就是所谓的质心,它是由被追迹的光线的分布和数量决定的。