A Brief History of Optical Telescopes

The first example of a working telescope was invented in 1608 by Hans Lippershey of Middleburg, The Netherlands. Through others, his arrangement of mirrors and lenses would go through countless evolutions over time, and come to be one of the most useful scientific inventions in history.

Optical Forerunners

The optical properties of convex and concave transparent objects have been known for thousands of years. The first glass lenses were not created until the late 1200s, when techniques for making glass had advanced enough to produce relatively inexpensive, relatively clear glass. Advancements in grinding and polishing glass also contributed significantly.

Before long, small, wearable sets of lenses were used to correct visions—the first eyeglasses. Methods of correcting both farsightedness and nearsightedness were created. These lenses, along with greatly refined glass mirrors, further set the stage for the telescope.

The First Telescopes

Though two others made their own claims to the device’s invention at the same time, Lippershey, spectacle maker, was the first disseminate designs for the telescope, and the first to apply for a patent.

Lippershey’s original telescope was composed of a single convex lens and a single concave lens in a wooden tube, providing 3X magnification. Soon, the “Dutch perspective glass” was being built by lens and spectacle makers throughout the Netherlands, spreading quickly across Europe and evolving rapidly with new technological advancements.

Sir Isaac Newton is credited with creating the first practical reflector in 1668, using a design that included a small, flat, diagonal mirror that reflected light into an eyepiece mounted on the side of the telescope.

telescope

The achromatic telescope was invented by Chester Moore Hall in 1733. Using improved lenses, these telescopes reduced color aberrations and could be far shorter and  more functional than previous designs. Hall did not widely publicize his discovery, and the achromatic telescope did not see wide use until John Dollond began producing them in large quantities in the late 1750s.

The Telescope Gets Larger & More Powerful

In 1789, Sir William Herschel built a giant telescope, forty feet long and with a mirror four feet in diameter. This reflector design, with its huge mirror, was capable of gathering hundreds or thousands of times more light than a refractor telescope.

In 1856, a new process of depositing layers of silver on glass telescope mirrors was discovered by Leon Foucault and Karl August von Steinhall. The silver layer provided much greater reflectivity and longevity that the finish on the speculum mirrors used until that time. It also possible to remove and renew the coating without unwanted modification of the glass substrate.

Using improvements to this technique and other technological advancements, the first large, modern research reflectors were built in the early 20th century. These telescopes were designed specifically for high quality photographic imaging and installed in remote high altitude locations. Examples include the Hale telescope at the Mount Wilson Observatory (built in 1908) and the Mount Wilson Hooker telescope (1917), which measured 100 inches in length.

In 1932, a replacement for the telescopes’ silver lens coating was developed. Using thermal vacuum evaporation, a much longer lasting aluminum coating could be applied. An aluminized lens was used in what was then the world’s largest telescope, the 200 inch Hale reflector at Mount Palomar, in 1948.

Photo credit: El Bibliomata / Foter / Creative Commons Attribution 2.0 Generic (CC BY 2.0)

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