A high-speed and small-volume IR zoom lens using root-exchange theory and DOE element

TLDR: In this article, a high-speed and small-volume mid-wave IR zoom lens capable of 16× magnification using a 320×256 IR FPA detector has been described, which can be continuously adjusted by simply moving two lens groups, which uses the root exchange theory.

Abstract: The high-speed and small-volume mid-wave IR zoom lens capable of 16× magnification using a 320×256 IR FPA detector has been described. The system magnification can be continuously adjusted by simply moving two lens groups, which uses the root-exchange theory. The object-image exchange theory and root-exchange theory are presented. The structure using root-exchange theory can get large zoom ratio with simple volume and the smooth zoom curve. Mechanically compensated IR zoom lens design has these questions: firstly, big volume caused by complex optical structure; secondly, limited IR material and obvious focus shift with temperature change. The zoom lens using mechanically compensated method has solved all the questions that existed in traditional system. The system also contains much less optical material and has a very simple structure by using DOE elements. The element of first moving group and the second element of the second moving group are both DOE. As the DOE has minus Abb number, which is opposite of refractive materials, it can minimize the higher order chromatic aberration. Based on the characteristics, the chromatic aberration was balanced. Research on the thermal analysis and compensation is considered. The passive athermalization is made by DOE elements. DOE elements make the zoom lens maintain its performance when it is operating between -20°C and 60°C.The results show the high magnification zoom lens design performance, with small volume and light weight. The aberration of the system were well corrected and diffraction limited performance was achieved in required temperature range.