The Debugging Method For A Large Field Off-axis Reflection-type Optical System

Although the off-axis reflection optical system increases the field of view without the central obscuration,it is difficult to adjust the system,and its adjustment accuracy is the key factor affecting the final image quality.This thesis studies on the adjustment of the off-axis reflection optical system.Firstly,it introduces the mathematical model of the sensitivity matrix of optical system,which can combine the characteristics of optical system,the pupil wavefront aberration of optical system and the amount of misalignment.Sensitivity matrix is the attribute of each optical systems.The determined optical system consists of a uniquely determined sensitivity matrix,which can reflect the influence of the eccentricity of the element or the amount of tilt imbalance on the aberration of the optical system.Autocollimation interferometry can directly measure Zernike coefficient at the pupil plane of the misaligned optical system.The optical system in this thesis includes three-mirror optical structure and the rear transmission lens group.In the three-mirror optical structure,the secondary mirror is spherical,the main mirror is hyperboloid,and the third mirror is flat sphere.The accuracy of the mirror surface will have a great effect on the image quality of the system.This thesis discusses the processing technology of quadric surface mirror and analyzes the measure method.Combined with actual situation,using Offner compensator to measure hyperboloid surface of the main mirror.A compensation lens is placed near the center of curvature of the third mirror to test the three mirror surface.The compensator and compensation optical path are designed through aberration theory.Analyzing the ghost image and tolerances of compensators to make sure the possibility of the application of the compensator and the compensation lens engineering.After testing,RMS of the main mirror is 0.0199,and RMS of the third mirror is 0.0198,which is in line with the accuracy requirement.(?=632.8nm).Using Inverse Sensitivity of Zemax to make tolerance analysis for optical systems with reference to MTF,then the influence of the tolerance of the components of the system on the image quality of the optical system is obtained.Reasonably distributing the tolerance of the optical system and through Zemax simulating the influence of misalignment of the elements in the system on the Zernike coefficient,in order to make a reverse guidance to the adjustment of the misaligned element.The self-collimating test method is used to adjust the system.The second mirror is the benchmark,the position of the main mirror and the third mirror are adjusted.The precision testing instrument is used to measure the size of the mechanical component according to the tolerance distribution.Installing adjusting tool and using centrescope to adjust the subsequent transmission optical elements.After adjusting,RMS of the center field can reach 0.0357?(?= 632.8 nm),and at 75 lp/mm MTF = 0.605.RMS of the middle right field and RMS of the edge left field are 0.0558?,0.0653? reapectively,correspondingly the MTF at 75 lp/mm are 0.0574,0.0570,closing to the diffraction limit.