Detection device and detection method for optical back focal length of thermal imaging lens

The invention discloses a detection device and detection method for the optical back focal length of a thermal imaging lens, and belongs to the technical field of optical lenses. The detection device comprises an infrared light source, a target, a collimating and beam expanding lens, a spectroscope, a total-reflection lens, a standard lens, an infrared detector and a control device which are sequentially arranged, and the detection device has an adjustable working state. The detection method comprises the steps that the positions of all the parts in the detection devices are regulated to the state that the centers are at the same height and are coaxial; the spectroscope is regulated to the position where a 45-degree included angle is formed between the spectroscope and the system optical axis; the standard lens and the infrared detector are regulated to the position where the infrared detector is located at the back focal plane of the standard lens; the standard lens and the infrared detector are regulated to