Condenser (optics)

Light from the illumination source of the microscope passes through the diaphragm and is focused by the lens(es) onto the specimen.

The display unit allows for digitally synthesised filters for dark-field, Rheinberg, oblique and dynamic (constantly changing) illumination under direct computer control.

Without this oil layer, not only is maximum numerical aperture not realized, but the condenser may not be able to precisely focus light on the object.

Robert Hooke used a combination of a salt water filled globe and a plano-convex lens, and shows in the 'Micrographia' that he understands the reasons for its efficiency.

With the development of the modern achromatic objective in 1829, by Joseph Jackson Lister, the need for better condensers became increasingly apparent.

English makers early took up this improvement, due to the obsession with resolving test objects such as diatoms and Nobert ruled gratings.

By the late 1840s, English makers such as Ross, Powell and Smith; all could supply highly corrected condensers on their best stands, with proper centring and focus.

[citation needed] On the Continent, in Germany, the corrected condenser was not considered either useful or essential, mainly due to a misunderstanding of the basic optical principles involved.

Thus the leading German company, Carl Zeiss in Jena, offered nothing more than a very poor chromatic condenser into the late 1870s.

When the leading German bacteriologist, Robert Koch, complained to Ernst Abbe that he was forced to buy a Seibert achromatic condenser for his Zeiss microscope in order to make satisfactory photographs of bacteria, Abbe produced a very good achromatic design in 1878.