System and method for testing defocusing sensitivity coefficient of lens in low-temperature lens

The invention discloses a system and a method for testing a defocusing sensitivity coefficient of a lens in a low-temperature lens. The system comprises a black body, a four-rod target, an infrared window, a vacuum collimator, a low-temperature environment simulator, a platform car, an infrared detector, a five-dimensional adjusting table, a temperature controller system and a supporting tool. According to the method, a four-rod target at the focal plane of a collimator is imaged on an infrared detector through an imaging method, the infrared detector is adjusted through a five-dimensional adjusting table, and the optimal focal plane position is determined through a transfer function walking over-focus test. A thermistor and a heating piece are attached to a lens of the low-temperature lens and connected to a temperature controller system through wires, and the temperature of the lens can be read and controlled in real time. The defocusing sensitivity coefficient of the lens is calculated by testing the optim