Design of a Day Night Confocal Passive Heatless High Zoom Ratio Zoom Optical System

日夜共焦变焦光学系统常用于安防等领域，但是由于光学材料在不同环境温度的变化导致各焦距位置改变，影响成像质量，给无热化变焦系统的设计带来较大困难，同时大视场角带来大的畸变以及轴外视场变化，增加了设计难度。同时优化日夜共焦，不同焦距不同温度下可见光近红外离焦范围很难满足实际使用。针对上述问题，本文从变焦系统设计条件出发，结合消色差和消热差方程，设计了一款可见光近红外20倍变倍比被动无热化连续变焦光学系统，系统F数恒定为4.8，焦距范围为6~120 mm，最大视场为64.69˚~3.62˚，波长范围0.48~0.85 um，适合1080P像元3.45 um的探测器。该系统总透镜数为18片国产球面镜，采用四组元正组补偿，总长225 mm。本设计采用全球面透镜成本低，变焦中实现日夜共焦且无需滤光片进行切换，轴向色差小，色焦移满足焦深范围。并对本系统进行被动无热化设计，变焦全程及其在−40℃到60℃的成像质量均达到要求。该光学系统在变焦过程中保持良好的成像性能，其公差设计符合当前加工工艺要求。系统架构经过优化设计，具有装配简便、调试容易等特点，适用于安防监控等多种应用场景。The day and night confocal zoom optical system is often used in security and other fields, but due to the change of optical materials in different ambient temperatures, the position of each focal length changes, which affects the imaging quality, and brings great difficulties to the design of the athermalized zoom system. At the same time, the day and night confocal is optimized, and it is difficult to meet the practical use of visible and near-infrared defocus ranges at different focal lengths and temperatures. In order to solve the above problems, starting from the design conditions of the zoom system, combined with the achromatic and athermic equations, a visible near-infrared 20x zoom ratio passive athermalized continuous zoom optical system was designed, with a constant F-number of the system, a focal length range of 6~120 mm, a maximum field of view of 64.69˚~3.62˚, and a wavelength range of 0.48~0.85 um, which is suitable for detectors with 1080P pixels of 3.45 um. The total number of lenses in the system is 18 domestic spherical mirrors, which are compensated by four elements and have a total length of 225 mm. This design adopts a global lens with low cost, day and night confocal in zoom and no filter switching, small axial chromatic aberration, and color focus shift to meet the depth of focus range. The system is designed to be passive and heatless, and the zoom process and its imaging quality from −40˚C to 60˚C meet the requirements. The optical system maintains good imaging performance in the zoom process, and its tolerance design is in line with the current processing technology requirements. The system architecture is optimized and has the characteristics of simple assembly and easy debugging, which is suitable for various application scenarios such as security monitoring.