Zacharias Janssen (ca.1588-ca.1631) was a Dutch spectacle-maker of Middelburg, son of Hans Janssen. He is sometimes given the credit for inventing the first compound microscope, probably with the help of his father in the year 1595, although the origin of the microscope is a matter of debate.

Zacharias Janssen is said to have made his fortune by counterfeiting Spanish copper coins in order to harass the enemy. However, he later continued counterfeiting gold and silver coins. For this he was convicted and sentenced to be boiled in oil (Boorstin, Discoverers, 315).

Zacharias' son would later testify under oath that Hans Lippershey, also from Middelburg, had stolen his father's idea for a telescope. However, this is supposed to have occurred at a time when Jansen would have been only 2 years old. Since Zacharias was very young at that time, it is possible that his father Hans made the first one, and young Zacharias took over the production.

The first compound microscopes produced by the Janssens was simply a tube with lenses at each end. The magnification of these early scopes ranged from 3X to 9X, depending on the size of the diaphragm openings.

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