refracting telescope

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$The historical 91-cm (36-inch) refractor at the Lick Observatory on Mount Hamilton, near San Jose, Calif.$ $The Great Lick Refractor telescope, a large silver tube mounted inside the domed ceiling of Lick Observatory on Mount Hamilton, California.$ $refracting telescope$

refracting telescope

Also known as: refractor

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July 13, 2026

Quick Summary

The historical 91-cm (36-inch) refractor at the Lick Observatory on Mount Hamilton, near San Jose, Calif.

A refracting telescope, or refractor, uses a lens to bend light and magnify distant objects. This bending of light is called refraction. The primary lens, known as the objective lens, gathers light from a celestial object and focuses it. A second lens, the eyepiece, then magnifies this focused image for the observer.1

Refracting telescopes are commonly used to view objects like the Moon, planets such as Jupiter and Mars, and binary stars. The size of the objective lens, called the aperture, determines the telescope's light-gathering power. While effective, refractors can suffer from distortions like chromatic aberration, where different colors of light do not focus at the same point. The largest refractor ever built had a 1-meter aperture.12

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telescope
Refracting telescopes
Commonly known as refractors, telescopes of this kind are typically used to examine the Moon, other objects of the solar system such as Jupiter and Mars, and binary stars. The name refractor is derived from the term refraction
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Commonly known as refractors, telescopes of this kind are typically used to examine the Moon, other objects of the solar system such as Jupiter and Mars, and binary stars. The name refractor is derived from the term refraction
Read More

John Dollond
…who developed an achromatic (non-colour-distorting) refracting telescope and a practical heliometer, a telescope that used a divided lens to measure the Sun’s diameter and the angles between celestial bodies.
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…who developed an achromatic (non-colour-distorting) refracting telescope and a practical heliometer, a telescope that used a divided lens to measure the Sun’s diameter and the angles between celestial bodies.
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astronomy
Telescopic observations
Optical telescopes are either refractors or reflectors that use lenses or mirrors, respectively, for their main light-collecting elements (objectives). Refractors are effectively limited to apertures of about 100 cm (approximately 40 inches) or less because of problems inherent in the use of large glass lenses. These distort under their…
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Optical telescopes are either refractors or reflectors that use lenses or mirrors, respectively, for their main light-collecting elements (objectives). Refractors are effectively limited to apertures of about 100 cm (approximately 40 inches) or less because of problems inherent in the use of large glass lenses. These distort under their…
Read More

telescope
Evolution of the optical telescope
Refractor telescopes, too, underwent development during the 18th and 19th centuries. The last significant one to be built was the 1-metre (40-inch) refractor at Yerkes Observatory. Installed in 1897, it was the largest refracting system in the world. Its objective was designed and constructed by…
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Refractor telescopes, too, underwent development during the 18th and 19th centuries. The last significant one to be built was the 1-metre (40-inch) refractor at Yerkes Observatory. Installed in 1897, it was the largest refracting system in the world. Its objective was designed and constructed by…
Read More

Keplerian telescope
…the basis for the modern refractive telescope, named after the great German astronomer Johannes Kepler. Its eyepiece, or ocular, is a convex (positive, or convergent) lens placed in back of the focus, the point at which the parallel light rays converge; and the instrument produces an inverted (“real”) image that…
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…the basis for the modern refractive telescope, named after the great German astronomer Johannes Kepler. Its eyepiece, or ocular, is a convex (positive, or convergent) lens placed in back of the focus, the point at which the parallel light rays converge; and the instrument produces an inverted (“real”) image that…
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Charles Tyson Yerkes
The observatory’s 40-inch (102-centimetre) refracting telescope is still the largest refractor in the world.
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The observatory’s 40-inch (102-centimetre) refracting telescope is still the largest refractor in the world.
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