Research On Large Aperture Lens Imaging System

Video monitoring security system is the most important means of prevention,its importance is self-evident.With the demand of security monitoring,all-weather monitoring has emerged.The camera with ordinary aperture lens is unable to image clearly in the dark environment.Although it can obtain clear images under low illumination under the irradiation of infrared supplementary light,it can only form black-and-white images and lose important color information.The amount of light entering the lens is proportional to the square of the relative aperture.Increasing the aperture of the lens will allow more light to enter the system.In the same low-light environment,the image details of the large-aperture system will be clearer and the advantages will be obvious.However,large aperture lens requires high assembly accuracy of the whole imaging system.In the lens with the same focal length,because the focal depth of the lens with large aperture is shorter,the traditional assembly method will lead to a low pass rate,which greatly affects the production efficiency.The depth of focus is short,and the CMOS(Complementary Metal Oxide Semiconductor)photosensitive surface must be perpendicular to the optical axis of the lens during assembly to ensure that all of it falls within the depth of focus of the lens.The factors that currently affect the above assembly accuracy are: the verticality error of the lens and the lens holder,the mounting error of the lens mount on the PCB(Printed Circuit Board),CMOS package and soldering error.The first two factors can be reduced by special tooling.CMOS package and soldering errors are objective and difficult to eliminate completely by improving package and soldering accuracy.In this paper,the flatness adjustment device is designed by separating the lens holder positioning surface and the CMOS plate,and the verticality of the lens holder positioning surface and the CMOS photosensitive surface is measured by the laser collimator,and the CMOS photosensitive surface and the lens holder positioning surface are adjusted by using a six-degree-of-freedom platform.Parallelism to furthereliminate the effects of CMOS package and soldering errors.The main work of this paper is as follows:(1)The influence of the tilt angle of the image plane on the size of the speckle of different aperture lenses is analyzed by Matlab theory modeling.Under the same tilt angle,the diffuse pattern formed by the large aperture lens is larger than the diffuse pattern formed by the small aperture lens.(2)Theoretical modeling The influence of the tilt of the large aperture lens and the ordinary aperture lens on the MTF(Modulation Transfer Function).The two models of F1.2 and F2.8 were optimized by Zemax optical simulation software.The effects of different angles of image tilt on the optical system MTF were studied.(3)Analysis of errors in the imaging system,including lens back focus,lens mount,PCB shape variable test,and the impact of CMOS slice analysis on the imaging system.(4)In order to ensure the imaging quality of the F1.2 system,the device designed the adjustment flatness to adjust the flatness of the lens holder positioning surface and the CMOS photosensitive surface to ensure that the angle between the positioning surface and the photosensitive surface is 0.08°.Within the scope.Finally,through large-scale verification,the excellent rate reached more than 97%.