Concave lens use – Galileo's telescope
In 1609, Galileo became the first person to study the heavens using a telescope. His first telescope was only 8x magnification. But that year he also developed a 20x magnification one which he used to study the moon and planets.
Galileo used a telescope that was made up of just a convex lens and a concave lens. Far more powerful telescopes were developed using two convex lenses in a line (please see Mammoth Memory convex lenses and their uses).
Below is a section through and ray diagram of Galileo's telescopes:
The convex lens collected and converged the light. The concave lens made the light parallel again.