SYNOPSYS软件Object Input Description的请教

初步接触SYNOPSYS软件，以前一直用的是ZEMAX。在看手册中关于物高定义时候“3.1.1 Object Input Description”，对这段话一脸懵，大家可以交流一下该如何理解，用在哪里


OBF is identical to OBA except that it is intended for systems where the object beam is very fast（什么叫非常快）. In this case it is not appropriate to base a ray position in the entrance pupil on a linear fraction of the pupil height（此为何意）, as all of the other options do. Instead, this quantity is converted into a fractional sine of an angle, and the ray height then follows what one would expect if the object beam satisfies the Abbe sine condition. The effect is to produce a uniform ray distribution in the output beam of the lens. Without this feature,the latter would be weighted unevenly, with more rays at the periphery of the pupil than at the center. Both real and paraxial rays are affected.

"very fast"是指相对孔径大, Fno小, 比如说接近1. 当相对孔径很大的时候, 就要按孔径角的正弦值来均分入射光线, 而不是按在入瞳上的入射高度来均分入射光线.