The stray lights will exist in every optical-mechanical system, which is impossible to completely eliminate, but can be reduced through certain methods. The methods of suppressing stray lights are mainly three aspects: optical design, mechanical structure and surface finishing. 

·  In terms of optical design, stray lights can be suppressed by the design of optical lenses, characteristics of mirror plane, the degree of lens finish, optical filter and the design of      diaphragm. 

·  In terms of mechanical structure, there are two ways: one is designing a shading structure mainly including lens hoods, blocking rings, shading baffles and so on; the other is designing an extinction screw thread in the inner wall of modules such as lens barrels. 

·  In terms of surface finishing, it can reduce the Bidirectional Scattering Distribution Function(BSDF) on the surface to suppress the stray lights by changing the roughness, blackening, painting the matting agent, coating the lens surface with anti-reflection film and so on.