Dual Reflector System Stray Light Suppression

Two-mirror system with small size, long focal length and no chromatic aberration is used widely in large-scale optical instrument; however, it is very difficult to suppress stray light in the system because of its obscuration and strict structure, especially stray light incident on image plane without across primary and secondary mirror or corrective and field lens. In this paper, suppressing stray light in two-mirror main objective is studied in accordance with the demand of optical instrument used in shooting range, including the following points:1) First of all, several related conceptions such as Bi-directional Reflectance Distribution Function (BRDF), crucial surface and illuminated surface are introduced and so is the research methods of stray light transfer path .And then, basic methods of suppressing stray light are analyzed and summarized from energy transfer equation of stray light; in the end, a definition of veiling glare index is given and its measuring methods are introduced. From the use of equipment requirements, the stray light suppression system capacity is analysed.2) According to requirement of suppressing stray light in two-mirror system, vertex coordinate formulas of inner baffle are deduced based on geometrograph in the case of certain obscuration, viewing field and vignetting. In order to reduce the obscuration, conical baffle of secondary mirror is ameliorated into a shutter one. Outer baffle is designed when angle of stray light suppressing is foregone and the vanes are designed in C-language program. Finally, the same-height vanes in drawtube between primary and secondary mirrors are designed for further suppressing the stray light in two-mirror system.3) Three-dimensional model of the two-mirror system is built and transmission path of stray light is gained by analysing and looking for critical surface and illuminated surface. Veiling glare index mensurated in Tracepro is 6.4%, some methods should be taken to reduce stray light. So the common one-stage conical baffle is improved into two-stage baffle. The correctness of baffle design has been proved by an example and its simulated analysis, veiling glare index of modified two-mirror system is 4.1%, meanwhile an effective way of suppressing stray light is provided.