For cool 320×240 detector with staring focal plane array

a middle infrared continuous zoom optical system is presented. The optical system

which is composed of 8 lens

adopts the optical structure form of secondary imaging and front group lens moving along the optical axis. Based on practical application requirement and feature parameters of the detector

the optical design parameters are given. Then used zoom system principle and optical design software the schematic diagram

modulation transfer function (MTF) curver

spot diagram

and root mean square value (RMS) of the spot diameter are investigated. The parameters of the system is 1.96 f/number

100% cold shield efficiency

180mm/60mm effective focal length (EFL)

3-5 μm spectrum region

and 75% transmission. The optical system is analyzed from two mode of narrow field of view (NFOV) and wide field of view (WFOV). It has the advantages of simple structure

high image quality. And moreover

only one aspheric surface is adopted in the system

so the system has the benefits of low price and easy to machining and adjust.