Included in this discussion are mirrors with spherical and aspheric surfaces, which are single-surface reflectors, and the Mangin mirror, which is a catadioptric element. The advantage of a pure reflector is that it is free from chromatic aberration and therefore suitable for applications over the entire optical spectrum. This property allows alignments of IR systems in the visible spectrum because there is no focus shift.
12.2 Spherical Mirror
We apply again the third-order aberration equations. With the object at infinity and the aperture stop at the mirror, the aberrations are spherical aberration, TSC=ây 3 8 =âf 64 , sagittal coma,CC=y 2 u p =u p f , astigmatism, TAC=ây u 2 p =âu 2 p f , Petzval curvature, TPC=y u 2 p =u 2 p f , and distortion is zero.
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