This invention relates to a system for evaluating the concentricity of a hollow cylindrical member which is relatively microscopic and whose inner and outer diameters differ very much.
Generally an optical-fiber connector for use in an optical communication system is a hollow cylinder having an outer diameter of about 2.4 mm and an inner diameter of about 125 .mu.m. The optical-fiber connector being so small, its concentricity is measured through a microscope in the prior art. More specifically, its end face is observed through a microscope. The enlarged image of the end face is put on cross hairs (i.e. X and Y reference lines) provided in the eye field of the microscope, thereby evaluating the concentricity of the connector.
The end of the optical-fiber is chamfered. Thus, the distance between the flat end face of the connector and the objective lens of the microscope is shorter than the distance between the objective lens and the point where the chamfering meets the outer periphery of the connector. It is therefore necessary to bring the microscope into focus twice, first for obtaining a clear image of the flat end face and then for obtaining a clear image of the circumference of the connector. This work is tiresome to the microscope operator, who evaluates the concentricity of the connector. The longer the operator works, the more tired he or she will be and the more errors he or she will make. This method therefore fails to evaluate the concentricity of the optical-fiber connector with a sufficient accuracy.