Design of cooled MWIR continuous zooming optical system with high zoom ratio

By using the mechanical compensation method, a two-component continuous zooming optical system model was established. Under the guidance of this model, a high zoom ratio continuous zooming optical system with tridimensional distribution was designed for the cooled focal plane array detector with mid-wave infared (MWIR) of 640×512 and pixel size of 15 μm. The working wave band of the system was 3.5 μm~4.8 μm, the focal range covered 30 mm to 500 mm, and the working temperature range covered -40℃~+60℃. In the zooming process, the F number was fixed at 4, and with 100% cold diaphragm effect. In the design process, the cold reflection of the system was analyzed in detail, and the cam curve wasdesigned optimally. The design results show that in the 0.8 field of view(FOV), the optical modulation transfer function(MTF) in whole temperature range is greater than 0.25 at 33 lp/mm and greater than 0.4 at 25 lp/mm. And in the full FOV tolerance, the MTF is greater than 0.13 at 33 lp/mm. This system has the advantages of smooth zooming track, excellent cold reflection suppression characteristics, good imaging quality and good environmental adaptability.