大相对孔径中波红外变焦系统的小型化设计

Miniature design of large relative aperture MWIR zoom lens

大相对孔径变焦系统在像差补偿自由度较少的光学补偿式变焦系统中,通常需采用较多的镜片才能完成像差校正,导致系统体积和质量不甚理想。通过合理分配变焦参数,优化变焦系统结构,并进行非球面与衍射面复合叠加设计,完成了一个仅含8片透镜的光学补偿式变焦系统。相对孔径1∶1.8,采用320像素×240像素制冷焦平面探测器,工作波段3μm^5μm,变倍比为5×,实现了30mm/60mm/90mm/150mm四档变焦,冷光阑效率100%。折叠光路后,体积约为210mm×100mm×85mm,结构紧凑,以较少的镜片数辅以机械结构的光学补偿变焦方式有效减轻了整机质量。

Optical system with a large relative aperture has a larger entrance pupil than its counterparts when their focal lengths are equal,so more energy collected and further distance detected.But due to its large aperture,the aberrations increase,which requires more lenses to correct and consequently cause application restrictions by volume and weight.To tackle this issue,zoom parameters were calculated and optimized reasonably,moreover by adopting compounded aspheric and diffractive surfaces,a reimaging zoom mid-wave infrade(MWIR)system with only 8lenses was designed.The Fnumber is 1.8and the spectrum is 3μm^5μm.For a320×240pixels detector with cooled focal plane array(FPA),the magnification is 5×,and the four fields of view(FOVs)are 30mm/60mm/90mm/150 m.The optical aperture stop matches the detector's and the cold stop efficiency is equal to 100%.Two reflective mirrors are applied to fold the optical path,giving a compact volume of around 210mm×100mm×85mm.Less lenses and simple zoom machinery effectively reduce the weight.