For cool 320×240 detector with staring focal plane array

a middle infrared continuous zoom a optical system was presented. The optical system using optical configuration of reflect mirror fold is composed of a zoom object lens system and a secondary imaging system

including seven lenses and two reflectors. Based on the practical requirement and feature parameters of detector

the optical design parameters were given. Using zoom system principle and optical design software

the schematic diagram

modulation transfer function (MTF) curve

spot diagram

and Root Mean Square (RMS) value of the spot diameter were investigated. Finally

the cold reflection ray-tracing of short EFL end was studied and the correlative schematic diagram was also given. The results indicate that the optical system with 3.7~4.8 μm spectral region can realize 50~500 mm continuous zoom and satisfy 100% cold shield efficiency. It has the advantages of simple structure

high image quality

short zoom path and smooth zoom locus. And moreover

only one aspheric surface is adopted in the system

so the system is in a low price and easy to machine and adjust.