Beerden, L., Flerackers, E. L. M. and Janssen, H. J.
Phase contrast microscopy.  European Journal of Physics 6: 139-142 (1985).

The use of the microscope is a subject of general interest in courses on medicine and life sciences. White light illumination, phase-contrast and even interference microscopy are techniques currently used in such courses. An experimental demonstration of the working principles of a phase-contrast microscope for individual students and also for small groups is described, with particular emphasis on the importance of the phase-contrast method in making visible almost totally transparent objects.