Answer: specula

AnswerCrossword Clue
SPECULAReflectors used in optical instruments.
speculaany of several bronze alloys with a high tin content, often containing other materials, as silver, brass, lead, zinc, or arsenic, used for making mirrors and reflectors
speculamirror or reflector, esp. one of polished metal, as on a reflecting telescope
speculainstrument for rendering a part accessible to observation, as by enlarging an orifice