MEASUREMENT OF THE ANGLE OF DEVIATION OF A PENTA PRISM

The angle of deviation of a penta prism is the angle between the direc tion of incident and emergent rays and for a perfect prism it is exact ly 90 degrees. It is a difficult task to make a perfect penta prism, c onsequently one has to tolerate a prism with an angle of deviation a l ittle less or more than 90 degree. Any departure from 90 degree is reg arded as an error in the penta prism. In the present article, a simple method has been described to measure the angle of deviation of a pent a prism by using a spectrometer and two auto-collimators. The accuracy of the method depends upon that of spectrometer/auto-collimator scale s.