Reflecting microscope, after Robert Smith (1738)

For a long period it was very difficult to design telescopes and microscopes which supplied a sharp and clear image. One of the problems, caused by the use of lenses, was chromatic dispersion. Because the different colours of light were refracted by the glass differently, an unclear, discoloured image was formed, especially at the edges. Around the middle of the seventeenth century, people tried to solve this problem by using mirrors instead of lenses. For mirrors, the path of the light beam is independent of the colour of the light. Thus the French Laurent Cassegrain devised a mirror system for the telescope in 1671. Based on this design, the English physicist Robert Smith came with the idea to implement this system in a microscope too. Therefore, the optical system of this microscope is the same as the reflecting telescope devised earlier by Cassegrain. The magnification factor of this microscope is about 40.