Gun Sight, Reflector, Mk IIIA 7A/1313 RAF

Here is a WWII-era Reflector Gun Sight Mk IIIA, 7A/1313.  The Mk IIIA was adopted by the RAF as the standard turret and free gun sight for their aircraft.

The Mk IIIA consisted of a detachable lamp unit and an upright sight head. The lamp unit is removed by depressing a small button on the bottom of the housing, revealing the bulb and circuitry (this example is quite tight). The brightness of the bulb was adjusted by the gunner by rotating the rheostat knob. The bulb illuminated the reticle which was projected through the lens onto the glass reflector from below. The glass reflector is contained within the housing above the lens. The reflector housing has a flip-up sun screen, which is engaged by turning a small knob on the side. 

It is in reasonable condition given its age. The glass is intact as is the housing.  Measures ~ 4 inches tall, and 3 inches by 3.5 inches wide.