With refractors growing to over a hundred feet long and increasingly difficult to handle, telescopes were ready for a new design.
They got it thanks to Sir Isaac Newton, a brilliant scientist at a time when “scientist” wasn’t even a word. Newton was known as a “natural philosopher” — he studied the natural world. He used observation, evidence, and calculations as a basis for his conclusions.
During the 1680’s in England, Newton built a small but powerful telescope. The images produced by this telescope were free from chromatic aberration, the rings of color that surrounded bright objects.
He did this by changing the telescope’s most basic element: its primary lens. Newton replaced the convex glass lens with a spherical mirror that reflected and focused the light. By changing the primary lens to a mirror, he launched a new class of telescopes: reflectors.
Newton understood that chromatic aberration was caused by refraction. Other scientists thought chromatic aberration was caused by light bouncing off flaws in the glass, but Newton realized that the glass itself was causing the light to separate into colors. When the light passed through the lens, the different colors of light bent by varying degrees. Violet light bent the most and red light bent the least.