During adjusting beam paths, the co-beam, a combination of the measuring beam and the reference beam, is not restricted to being perpendicu lar to the light sensitive surface of the object, but keeping the measuring beam and the reference beam co-axial proved to be crucial 在光路调整中,它对测量光与参考光的合光光束是否垂直于探测器光敏面要求不高,但对两光束合光同轴度则有严格要求。