在FRED中通过倒追和正追的方式确定光机系统的关键面、照明面和重要面。照明面是指光学系统中被外界杂散光源照亮的面;关键面是可以从探测中看到的面;关键面和照明面的重叠面即为重要面。重要面是光机系统中一次杂散辐射的主要来源，杂散光的抑制也就是努力减少重要面的数量。 aH^{Vv$]M@
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Node Name Universe Detector <i7agEdZD
6 Geometry.fastcass.Primary mirror.Reflecting Surface 8.73949821062508 .339134565809722 \ CwtX(6.
7 Geometry.fastcass.Primary mirror.Back Surface 0 0 N xB+?
8 Geometry.fastcass.Primary mirror.Edge 0 0 x /_dW
9 Geometry.fastcass.Primary mirror.Hole 0 1.00188578326391E-04 25&nwz
11 Geometry.fastcass.Secondary mirror.Reflecting Surface 8.71700830771184 .420485262312074 $owb3g(%4
12 Geometry.fastcass.Secondary mirror.Back Surface 0 0 xH@ 'H?
13 Geometry.fastcass.Secondary mirror.Edge 0 4.83222296869994E-09 pj@Yqg/
16 Geometry.fastcass.dewar.FPA.detector array 6.28915267493816 1.09779504189775E-02 H9:%6sds
18 Geometry.fastcass.dewar.dewar window.Surface 1 8.70787200780954 1.01116317462709 X \'E4
19 Geometry.fastcass.dewar.dewar window.Surface 2 8.70787200780954 1.0111548796955 Vku#;:yUb^
20 Geometry.fastcass.dewar.dewar window.Edge 0 8.29493159668308E-06 "B?R|
Xg
22 Geometry.fastcass.dewar.outer wall.Surf 1 0 4.61988409432715E-05 8E
9{
Gf
24 Geometry.fastcass.dewar.retaining ring.Surf 2 0 5.38379092582642E-05 #~*XDWvIS~
27 Geometry.main barrel.Surf 3 1.45194696071729E-02 4.48783425373457E-03 1W0.Ufl)
29 Geometry.Primary baffle.Surf 3 1.44803828118383E-06 .597464630934777 } bCK
31 Geometry.Secondary baffle.Surf 3 .969627358028687 .137673353852238 h,.fM}=H
32 Geometry.Secondary baffle.Surf 4 1.1502279482165E-12 1.42111455012594E-03 Z !Z,M' "
33 Geometry.Secondary baffle.Surf 5 .727220518519163 6.21692034227466E-05 zM\IKo_"
36 Geometry.Secondary struts.strut a.Surf 6 .97011784785664 1.11300844081723E-02 <L2GUX36#
38 Geometry.Secondary struts.strut b.Surf 6 5.49202068783075E-14 1.09981876986085E-02 5Abz 5-^KH
40 Geometry.Secondary struts.strut c.Surf 6 .242406839506173 1.09806859127091E-02 D2V v\f
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Node 为几何结构节点数，Universe为空间光源正向追迹的效果，Detector是反向追迹的效果。 ]p\u$VY9
软件打开后，运行critical and illuminated objects脚本，可生成上述结果。
