A Unit-Magnification Optical System for the Attainment of Long Working Distances in Microscopy

To fill an application for a microscope with a long working distance, several optical systems are reviewed. Of these, a system giving unit magnification to be used in conjunction with a conventional microscope is selected as suitable. This consists of a spherical mirror used with the object near its centre of curvature. The aberrations of such a system are discussed and means of correcting them described. Modifications necessary to enable vertical illumination to be used are also described, and photographs taken by means of an experimental system are shown. Other applications of the same system are suggested and designs given for a miniature system capable of being used on an ordinary microscope for an immersion objective for nuclear plate work and for a water immersion system for biological applications.