Telescopes from the Ground Up

Refracting telescopes get better — and longer

Though the Catholic Church had tried to silence Galileo, his ideas caught fire. The telescope spread across Europe along with a new philosophy of basing scientific judgments only on measurable evidence.

The next leap in the technology of refracting telescopes occurred because of a man who would never actually build one. Johannes Kepler, a German-born astronomer who studied optics, was the first to understand how a glass lens focuses light.

Kepler suggested changes in the shape and placement of the telescope lenses to widen the field of view and improve the quality of the image. First he replaced the concave eyepiece lens with a convex lens. This change let the telescope see a much larger area. Eventually, people stopped using the design made popular by Galileo and adopted Kepler’s two-convex lens design.

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