Lens unit and vehicle-mounted infrared lens unit

Abstract

Provided are a lens unit and a vehicle-mounted infrared lens unit capable of correcting a focal shift due to a temperature change without increasing the apparatus size, complicating a production process, and increasing the costs. In a vehicle-mounted infrared lens unitconfigured such that a plurality of infrared lenses are held by a barreland a spaceris interposed between two infrared lenses, a first infrared lensis held sandwiched between the spacerand a lens holding portionof the barrel. The spacerand the barrelare formed of materials having different thermal expansion coefficients. An O-ringis interposed between a lock portionof the lens holding portionand the first infrared lens. Thermal expansion of the spacerallows the first infrared lensto move in the axial direction against the elastic force of the O-ring. When the spaceris shrunken, the elastic force of the O-ringallows the first infrared lensto move in the opposite direction.