Automated Design Of Three-element Zoom Lens With Fixed Focal Points

The traditional zoom system is designed on the basis of the conjugate planes in the optical system which is stable during the whole zoom process.However,in some application scenarios,the focal planes of the optical system is required to maintain stability during the zoom process,and the mature theories for zoom optical system is no longer applicable.The mentioned special zoom optical system has important applications in the field of optical information processing,precision measurement and machine vision.In the frame of geometrical optics,the paraxial properties of the mentioned special zoom system is analyzed.The axial displacement equation for three-component zoom system is derived,and it can be generalized to the zoom systems with more than three components by using the recursion formula.Then,a mathematical model is established for the design work based on the particle swarm optimization(PSO),and the merit function in the optical system is used as the fitness function to evaluate the system.The design of zoom system is transformed into the problem of finding the optimal solution in the search space.According to the characteristics of zoom system,we modify the PSO algorithm.We verify the convergence property of the modified PSO method,and compare it with Monte Carlo method.The results show that the proposed method has stability and high efficiency.Then we design a series of first-order design results for different application scenarios and design requirements based on the proposed method.Compared with existing design result,our designs are more compact and easier to obtain high zoom ratio.In order to further prove the effectiveness of this method,we further optimize the first-order design results,and give the actual lens design results and performance analysis.The experimental results show that PSO method is a promising tool,although it is simple in concept.It can automatically retrieve the best starting point for a complex optical system,which is an important step to realize automatic optical design in the future.