Short-focal-length optical passive athermalization uncooled long-wave infrared optical system

The invention discloses a short-focal-length optical passive athermalization uncooled long-wave infrared optical system, which sequentially comprises a first lens, a second lens, a third lens and an uncooled long-wave infrared detector protection window from an object space to an image space along the same optical axis direction, the first lens has positive focal power, the front surface of the first lens is a spherical surface, and the rear surface of the first lens is a binary diffraction surface of which the substrate is an even-order aspheric surface; the second lens has negative focal power, the front surface of the second lens is a spherical surface, and the rear surface of the second lens is an even-order aspheric surface; the third lens has positive focal power, the front surface of the third lens is an even-order aspheric surface, and the rear surface of the third lens is a spherical surface. The effective focal length of the optical system is 37mm, the total optical length is 37mm, the F number is 1