"Drum" compound pocket microscope

Its circular tube has a consistent diameter. At the top is the eyepiece and at the bottom is the lens. The tube is inside a drum and both pieces move vertically with the help of a rack mechanism, which is controlled by a side screw for macroscopic focusing. The stage is round with a central hole to let the light pass through, and underneath it is a ring to hold the slide in place. Below the stage is a concave mirror, which moves in one direction only. The base is round and made up of a ring, which holds 2 lateral plates to form the pillar of the microscope.

Benjamin Martin (1704–82) was a prolific microscope maker and author of a wealth of books and treatises on optics, and mathematical and scientific instruments. In 1780 he formed the company "B. Martin & Son" with his son. He was the man who invented this type of "drum microscope," which was incredibly popular during the 18th and 19th centuries. A large number of them were produced and significant improvements were added to Martin's initial design. This kind of instrument was easy to handle and transport, and had major benefits, especially for fieldwork.