1问题的提出2013年江苏高考一道光学试题涉及到单反相机的取景器问题,原题如下.题目.如图1为单反相机取景器的示意图,ABCDE为五棱镜的一个截面,AB⊥BC.光线垂直AB射入,分别在CD和EA上发生反射,且两次反射的入射角相等,最后光线垂直BC射出.若两次反射都是全反射,则该五棱镜折射率的最小值是多少?(计算结果可用三角函数表示)根据题意可得,入射角为22.5°,且截面CD与水平面之间、EA与竖直面之间的夹角也均为22.5°,如图2.不过 1 questions put forward Jiangsu University entrance exam in 2013 an optical test questions related to the SLR camera, the original title is as follows. As shown in Figure 1 for the SLR viewfinder schematic, ABCDE a pentaprism cross section, AB ⊥ BC. Light Vertical AB injection, respectively, in the CD and EA on the reflection, and the two reflection angle of incidence is equal to the final light vertical BC out. If the two reflections are total reflection, the pentagonal refractive index is the minimum? (Calculated results can be used trigonometric function) According to the topic, the incident angle of 22.5 °, and the cross-section between the CD and the horizontal plane, EA and the vertical angle between the surfaces are also 22.5 °, but not