Lieberkühn reflector

[2][5] The principle is explained for a modern upright compound microscope, where the light source illuminates the specimen from below.

When using the Lieberkühn reflector, the opening in the microscope stage is covered with a flat glass plate upon which the specimen is placed.

[7] When matte white surfaces replace a reflective Lieberkühn mirror, the specimen is illuminated with scattered light.

[7] A Lieberkühn mirror is usable only if the specimen is small enough to allow sufficient light to pass laterally.

René Descartes published his book Dioptrics in 1637, in which Chapter 9 dealt with glasses, telescopes, and microscopes.

In England, Lieberkühn was credited with the invention of this reflected light illumination, and corresponding devices were named after him.

[13] The earliest documented use of the term was by Benjamin Martin (1704–1782) in a microscope description from 1776 as "concave speculum or lieberkuhn".

[15] But by far the most useful of Lieberkuhn's microscopes was the one for viewing opaque objects, by means of which he made so many important discoveries in the minute structure of the mucous membrane of the alimentary canal, as to immortalize his name.

The Lieberkuhn, is that part of the instrument which is the most important, and is in general use even in the present day.In German-language microscopy books from 1950[17] and 1957, the invention is also attributed to Lieberkühn.

Lieberkühn introduced the concave mirror named after him for reflected light illumination in 1738, as it was used in similar form by Descartes 100 years earlier.

New metallic mirror surfaces reflected UV light for excitation very well, resulting in bright fluorescences.

Two images, one showing the device from the mirrored side and another from the other side.
A Lieberkühn mirror from Emil Busch AG (now Rathenower Optische Werke) circa 1930, digital collection of the Deutsches Museum . [ 1 ]
Diagram of illumination with Lieberkühn reflector. Light comes from below (vertical lines) and is reflected (dashed lines) on the concave surface of the mirror (black circular bars) to fall on the object (circle). The objective (not depicted) is located within the gap of the concave reflector. From [ 6 ] .
Drawing of a simple microscope by Descartes, 1637. The specimen (E) is held by a metal pin (G). The incoming light is redirected onto the specimen by the mirror. The specimen is magnified by the plano-concave glass lens at the bottom of the housing and viewed by the observer's eye.