Apparatus for emitting or detecting two beams of light along a common axis

An apparatus for emitting or detecting light travelling along a first axis, including:

• a lens body, and
• first and second light handling units;
• the lens body including a ball and a reflector contained within the ball,
• the ball being transparent and having a surface, the surface defining a total surface area of the ball and having substantially spherical curvature over substantially all of the total surface area;
• wherein, when the reflector is considered as projected along the first axis onto a reflector plane, the reflector plane being a nominal plane passing centrally through the ball and normal to the first axis, the reflector occupies less than all of an area of the reflector plane bounded by the surface;
• the apparatus being arranged to define first and second conjugate focal planes relative to a subject plane,
• and to transmit light entering or leaving the lens body along the first axis and travelling between the lens body and the subject plane, such that:
• a first portion of the light travels through the ball and past the reflector between the subject plane and the first light handling unit located at the first conjugate focal plane, and
• a second portion of the light travels through the ball and is reflected from the reflector between the subject plane and the second light handling unit located at the second conjugate focal plane;
• wherein either
• (a) the first light handling unit includes a first light emitter, and the second light handling unit includes a second light emitter;
• or
• (b) the first light handling unit includes a first light detector, and the second light handling unit includes a second light detector.