Analysis And Calculation Of The Veiling Glare Index In Optical Systems

In the imaging process of optical system,there are a few non-imaging beams on the detector besides the normal light path.The phenomenon of these non-imaging beams spreading on the detector is called stray light.The existence of stray light will lead to the decline of imaging quality of optical system.Therefore,stray light analysis and stray light suppression are indispensable during optical system design.In this paper,the basic theory of stray light analysis in optical system is introduced in detail.The veiling glare index(VGI)and point source transmittance(PST)of the evaluation index of stray light in optical system are expounded.For a long time,people have devoted themselves to the accurate detection of veiling glare index,and have carried out a lot of theoretical and experimental research work.Generally,the veiling glare index is obtained only after the optical system is processed,and if the measured results are not satisfactory,the stray light suppression method of the optical system needs to be adjusted to enhance its suppression effect.In this paper,a method for calculating the veiling glare index in optical design stage is presented.In this method,the optical simulation software TracePro is used to modeling,analyze and do ray tracing for optical system.The simulation results are fitted by the mathematical analysis software MATLAB,and the veiling glare index is finally obtained.Because catadioptric optical systems(such as Cassegrain system,R-C system,etc.)have large aperture and a circular aperture in the center of the primary mirror,stray light has a serious impact on such systems.In this paper,the extinction measures of refractive and reflective optical system,such as bafflr and shielding ring,are described in detail.When designing the baffle,we found that the length of the outer baffle designed by traditional methods is too long,which makes the weight and volume of the optical machine system increase seriously;or the aperture of the secondary mirror baffle is larger,which makes the central obscuration increase and reduces the illumination of the imaging beam on the image plane.To solve this problem,this paper presents a design method of built-in baffle.A typical R-C optical system is designed with a built-in baffle.The results show that the length of the outer baffle is significantly shortened,the central obscuration is reduced,and the ability of stray light suppression is closed to that of the traditional method.