Where is the angle of incidence in a periscope?
1st answer is correct for mirrors but not for prisms, which are used in high-quality periscopes. For each prism the angles of incidence and exit are 90 deg on the nondiagonal sides and the reflection takes place on the diagonal side at 45 deg incidence resulting in a 90 deg path change per prism. The result is just like that obtained with mirrors but without the blurring due to internal reflection in the mirror glass. (Front-surface mirrors are impractical in periscopes because of the likelihood of surface contamination in typical use.
