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 unit 4 configured such that a plurality of infrared lenses are held by a barrel 30 and a spacer 40 is interposed between two infrared lenses, a first infrared lens 10 is held sandwiched between the spacer 40 and a lens holding portion 31 of the barrel 30. The spacer 40 and the barrel 30 are formed of materials having different thermal expansion coefficients. An O-ring 60 is interposed between a lock portion 32 of the lens holding portion 31 and the first infrared lens 10. Thermal expansion of the spacer 40 allows the first infrared lens 10 to move in the axial direction against the elastic force of the O-ring 60. When the spacer 40 is shrunken, the elastic force of the O-ring 60 allows the first infrared lens 10 to move in the opposite direction.

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 unit 4 configured such that a plurality of infrared lenses are held by a barrel 30 and a spacer 40 is interposed between two infrared lenses, a first infrared lens 10 is held sandwiched between the spacer 40 and a lens holding portion 31 of the barrel 30. The spacer 40 and the barrel 30 are formed of materials having different thermal expansion coefficients. An O-ring 60 is interposed between a lock portion 32 of the lens holding portion 31 and the first infrared lens 10. Thermal expansion of the spacer 40 allows the first infrared lens 10 to move in the axial direction against the elastic force of the O-ring 60. When the spacer 40 is shrunken, the elastic force of the O-ring 60 allows the first infrared lens 10 to move in the opposite direction.

Abstract: When a groove is provided for letting gas out of a die for molding a material constituting an optical element, a warped shape is sometimes transferred to the lens or other optical element molded from the material. When a through-hole is provided in a hollow body disposed on the outside of the external peripheral surface of the die, the strength of the body is severely reduced. In the present invention, a groove for letting out gas is provided in at least part of the internal peripheral surface of the body facing the die.

Abstract: A die assembly includes a barrel die (4) having a tubular inner face, a sleeve (5) covering an outer peripheral surface of the barrel die, and a pair of core dies (1, 2) for pressing a preform inside the tubular inner surface of the barrel die. At least one of the paired core dies (1, 2) is slidable and guided along the tubular inner surface of the barrel die (4). The sleeve (5) does not transmit light having a wavelength of 5 ?m or shorter and has a thermal conductivity of 70 W/m·K or greater.