Bifocal infrared night vision lens

The invention relates to an optical system design of an infrared night vision lens, in particular to a bifocal infrared night vision lens, which is characterized in that four front lenses form an afocal system, and three rear lenses are combined with the front lenses to form a night vision imaging system with a fixed focal length, so that the bifocal infrared night vision lens is more suitable for infrared night vision thermal imaging application; comprising an afocal telescope system composed of four front lenses. The afocal telescope system sequentially comprises a large-aperture long-focal-length first positive lens (2), a long-focal-length second positive lens (3), a first negative lens (4) and a second negative lens (5), and further comprises a positive lens group consisting of three rear lenses, and the positive lens group sequentially comprises a third positive lens (7), a fourth positive lens (8) and a fifth positive lens (9), wherein the fourth positive lens (8) and the fifth positive lens (9) are sp