Description
The compound microscope was developed during the 17th Century and was closely related to the refracting telescope. Its popularity increased after the publication in 1665 of Robert Hooke’s (1635-1703) Micrographia. Micrographia contained detailed pictures, never before seen, of insects magnified using a compound microscope.

A compound microscope uses two or more lenses. The lenses are held at certain distances from each other and are mounted inside a rigid tube. The tube was usually made from pasteboard, ivory, or most commonly, brass. The basic compound microscope magnifies an image in two stages -

Stage one: Light from a mirror is reflected up through the specimen into a powerful objective lens.

Stage two: The image produced by the objective lens is magnified again by the eye lens, which works like a simple magnifying lens.

The first compound microscope consisted of a simple barrel which would have been held up to the light. Later developments ensured that the compound microscope had a stable base, usually a brass stand and a side pillar.

In the 17th Century, the compound microscope had some serious drawbacks which made it easier to use a simple microscope (which have only one lens) instead. The image produced by a compound microscope was often affected by two types of aberration, known as chromatic and spherical. These aberrations caused blurring to the image (spherical) and the edge of the specimen to colour (chromatic). Chromatic aberration was removed at the end of the 18th Century by Harmanus van Deijlan, an instrument maker in Amsterdam. In 1830, spherical aberration was overcome by Joseph Lister who developed the achromatic lens. Achromatic lenses became widely used in microscopes in the 1850s and are still used today.