Design Of Infrared Zoom Optical System

Zoom lens of high-performance plays an important role in civil application and military application. For instance, zoom lens is widely used in digital camera to meet the different photographing requirements of scenery, which is also used for target detection and identification in military application. Infrared optical systems receive the infrared radiation of the target to detect and identify the target. Therefore, infrared zoom system is critical for the imaging quality.This paper designs an infrared zoom optical system which adopts the construction of front fixation group, multiplying group, compensation group and rear fixation group according to the technical index requirements of long wave infrared zoom optical system based on optical design software ZEMAX. It is applicable for system generated imaging of long wave of 8μm～12μm with 15 times zoom ratio. Use negative group compensation for zoom movement, the result of design is:when cut-off frequency is llmm/lp, MTF curve is above 0.7, full field is 0.6, and wave aberrations of four fields are all below 0.25λ, the design index requirement is then satisfied.The construction of the system is further improved taken into account such factors as processing, installation, testing and production cost. Aspheric surface is introduced for the surface with bigger aberrations; the quality of imaging is thus improved by the adoption of aspheric surface. There is only one material in the infrared system that will cause color difference; and another new infrared material is adopted to avoid color difference, moreover, aspheric surface is substituted with spherical mirror to reduce the difficulty of processing, installation and testing, to reduce the cost, decrease the weight of system and make the construction of the whole system more compact. The result of the improved system design is:when cut-off frequency is llmm/lp, curves of four fields almost equal to 0.7 approaching diffraction limit. The RMS radii of each field are 7.479μm,18.638μm,21.348μm, 27.624μm separately. Wave aberrations are below 0.038λ, both imaging quality and design index requirements can be satisfied.