An infrared zoom optical system in the long wave 8 -12 μm region was designed. The detector was a 320×256 focal plane array (FPA) with a pixel pitch of 25 μm. The optics was a 3:1 f/1 zoom lens, the effective focal length ranges from 50 mm to 150 mm and the total length of the system was 209. 5 mm.The relative aperture was invariant during the zoom process. The system had only five elements whose material was all but germanium. By using mechanical compensation, the binary surface and aspheric surface were used to simplify the configuration; as a result, the volume was decreased and the image quality improved. The image quality evaluation result shows that the MTF is higher than 0. 5 in all field of view at the spatial frequency 20 lp/mm.%对于320×256非制冷焦平面阵列探测器(像元尺寸25 μm×25 μm),设计了工作在8～12μm波段折射式红外连续变焦光学系统.该系统在变焦过程中相对孔径不变,F/#为1,系统变倍比为3∶1,焦距50～150mm,光学筒长209.5mm.该系统由5片透镜构成,并且仅使用锗一种材料.该系统采用机械补偿的方法,通过引入非球面和衍射面,使系统结构简化,并且提高了成像质量.系统在空间频率为20 lp/mm处,各个视场的MTF均在0.5以上.
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