求助 code v 的二句英文 不太懂其中的涵意 請各位前輩指點

2.Use the RSI ray for the upper marginal ray for field 2 to determine the obscurations
on surfaces 2 and 3 (Hint: look at the ray height on S5). These obscurations make a
hole in the corrector to prevent the light from passing through the corrector lens
twice.
3. Use a targeted ray for the negative full field to hit the edge of the obscuration on
surface 2 to determine the size of the obscuration on surface 1. This obscuration
prevents ghost images (prevents rays from going through the hole in the corrector
lens).
請各位前輩指點一下 看不太懂它要表達的意思 此為code v使用手冊的一個範例  謝謝