Abstract: The invention relates to an infrared optical system which is capable of providing an effective focal length of about 240 mm, but fitting into a spherical package whose diameter is approximately 150 mm. To achieve such a degree of compactness, the invention employs an optical path including three reflections, which in combination define a question-mark-shaped optical path. Between the first and second reflections, the transmitted beam is passed through a focal plane and then is recollimated, and the collimated beam is then passed through the succeeding two reflections, after which it is directed telecentrically onto a detector. The invention further relates to a specific combination of lenses.

Abstract: The invention relates to an infrared optical system which is capable of providing an effective focal length of about 240 mm, but fitting into a spherical package whose diameter is approximately 150 mm. To achieve such a degree of compactness, the invention employs an optical path including three reflections, which in combination define a question-mark-shaped optical path. Between the first and second reflections, the transmitted beam is passed through a focal plane and then is recollimated, and the collimated beam is then passed through the succeeding two reflections, after which it is directed telecentrically onto a detector. The invention further relates to a specific combination of lenses.

Abstract: A system for adjustably locating a lens (16, 18) as a function of the temperature of the lens, comprising a housing (12) and a lens mount (14) which is movable in an aperture in said housing in an axial direction, the lens being mounted in the lens mount. An axially extending chamber is defined between a radial surface of a radially extending portion (34) of the housing and a radial surface (32) of a radially extending portion (22) of the lens mount. A fluid is accommodated in the chamber, the fluid having variable volume as a function of temperature, such that the distance between the two radial surfaces, and thereby the location of the lens, is variable as a function of the temperature of the fluid.

Abstract: A device for use with infrared lenses to determine the optimum focal plane. The device comprises an infrared energy source, a collimating lens and an energy sensor to determine the energy level from the energy source to provide a normalizing signal. An infrared energy detector may be moved toward and away from the lens which is to be calibrated in order to test various planes within the depth of focus of the lens. A knife edge shutter is stepped across the path of energy at each of the positions to determine specific read outs of energy at each position of the knife edge shutter. The energy which passe the knife edge shutter is then delivered to a computer where the signal has been normalized by the sensor previously described. The computer reads out the signals corresponding to energy level at successive steps of the knife edge shutter. The computer is programmed to step the detector to successive positions and then the shutter to successive positions across the focal plane.