Abstract: Optical apparatus for transferring a portion of radiation emitted from a radiation source having a first line of sight to a radiation sensor having a second line of sight comprising a corner cube having first and second reflective ends arranged to intersect at predetermined orientations with a predetermined one of the first and second lines of sight and each having a predetermined orientation relative thereto; prismatic apparatus mounted onto one or both of the first and second reflective ends so as to define a common interface therewith; and an optical coating provided at the interface defined by the one or both first and second reflective ends and the prismatic apparatus for permitting passage of a first portion of radiation while deflecting a second portion of radiation.