Tip #1: Finding Critical Objects During Stray Light Analysis

When doing stray light analysis, it is vital to identify all objects that are seen from the detector. Dr. Bob Breault calls these "critical objects". These objects are important, because 100% of the stray light comes from them. If you can't see an object (either directly, or reflected in a mirror) then you cannot get stray light from it. The mirrors in optical systems make finding critical objects a difficult task; it's hard to do by intuition (unless your Bob Breault, who is really good at it). I solve this problem by placing a source on the detector and tracing backwards through the system. Any object in ASAP that is intersected by the rays from this source is a critical object. The ASAP STATS command, or the TRACE STATS command, prints a table of all of the objects that rays intersect, and this is the list of critical objects. The only burden on the user (after building the model) is to trace enough rays to get a good sampling of the system.

The advantage of this approach is:
   
1. It's easy. It is not necessary to have a degree in optics to find a complete list of critical objects. ASAP is doing the work.
   
2. It's unbiased. ASAP has no preconceived ideas about what is and is not seen from the detector. This allows users to identify critical objects that they may not think of on their own.
   
3. It's three-dimensional. People can often visualize things well in two dimensions, but it's hard to find "skew" paths that move through a complex three-dimensional geometry. Of course, ASAP (with its fast and fully non-sequential ray tracing) has no difficulties with this.

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杂散光分析技术的基本思想，好文章！自己给自己顶一个！