Device for observation through a wall in two opposite directions

摘要

An episcope is provided which allows viewing in either the forward or rearward directions through the same episcope. A parallelogram shaped main optical unit has a forward facing first objective lens and a first eyepiece lens. Light entering through the first objective lens strike one pair of faces of the main optical unit at an angle greater than or equal to the critical angle so that it is reflected by the parallel faces through the first eyepiece. An upper optical unit is disposed above the main optical unit and has a rearward facing objective lens. Light is reflected in the upper optical unit to pass into the main optical unit through the same face which reflected light coming from the first objective lens, the light from the second objective lens striking this face at an angle less than the critical angle. This light coming from the rearward direction is either reflected by a lower surface of the main unit to pass through the first or a second objective lens, or is transmitted entirely through the main optical unit into a lower optical unit, where it is reflected through a second eyepiece lens. The light beam coming through the first objective lens is reflected a total of an even number of times. The light beam entering through the second objective lens is reflected a total of an odd number of times. The upper, main and lower optical units may be separated from one another by layers of air.