Galileo’s refracting telescope (1609)

Galileo’s refractor used two lenses to concentrate the light from celestial objects, delivering more light to the human eye than it can gather on its own. The light was refracted through a spherical lens, forming an image.

The spherical shape of Galileo’s primary lens made the images blurry. The lens also split light into colors, creating a fringe of color around bright objects.