Quantitative Measurement of Aberration by Ronchi Test (Part III)

Examples of Testing the Quality of Optical Glass

Abstract

In Part I¹⁾, one of the authors showed that the homogeneity of optical glass could be tested by measuring the astigmatism by Ronchi test. In this report, examples of testing are given for which the following types of glass are selected and tested.
Normal astigmatism is assumed and inclination of central line caused by defocussing is measured :and the results are used to calibrate the astigmatism. Anomaly of refractive index is detected by the local change of fringe width. With a large mass of glass, numbers of local defects prevent the detection of normal astigmatism, yet in one instance, glass of almost normal astigmatism was found among the samples for the use of Schmidt plate. Decrease of 4.3•10^-8 in astigmatism was observed by careful annealing. A test on a large plate of flint glass manufactured by casting-clearly revealed the traces left by streaming of glass.