Active Athermalization Design of Infrared Zoom Lens for Fire Monitoring Based on Opto-mechanical Integration Analysis

The F-number and focal depth of infrared monitoring zoom lens are relatively small; therefore, the temperature change can easily cause defocusing, resulting in the deterioration of imaging quality. This article is aimed at the technical requirements for the clear imaging of the fire monitoring infrared zoom lens in the range of -40℃ to 50℃. The finite element method is used to analyze the rigid body displacement and rotation of the front and rear mirrors of each lens under temperature changes and import the rigid body displacement into the Sigit optical-mechanical integrated analysis software to simulate the defocus of the lens under temperature change conditions. The analysis result shows that the focal length variable is between -0.16 to 0.4 mm and the focusing amount is 0.108 to 0.188. In response to the above situation, two cams and two sets of actuators are used to control the movement of the zoom group and the compensation group respectively, for realizing the active athermalization design of the lens to ensure that the imaging is still clear under the condition of temperature change. Finally, the temperature adaptability of the lens optical resolution is evaluated through a temperature reliability experiment. The experimental results show that the spatial resolution is greater than 30 lp/mm during temperature change. The image quality is basically clear during zooming process.