Refracting telescope

Zeiss2

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Kepschem

Galileantelescope

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Houghton Typ 620.73.451 - Johannes Hevelius, Machinae coelestis, 1673

Yerkes Observatory Astro4p6

Irving Porter Church Telescope

Refracting telescope

The refracting telescope, also known as a refractor, is a type of optical telescope that uses a lens as its objective to form an image. The refracting telescope design was originally used in spy glasses and astronomical telescopes but is also used for long-focus camera lenses.

History

The first practical refracting telescopes appeared in the Netherlands in about 1608, and were credited to three individuals, Hans Lippershey and Zacharias Janssen, spectacle-makers from Middelburg, and Jacob Metius of Alkmaar. The invention of the telescope was a significant milestone in astronomy. Galileo Galilei, in 1609, was the first to use a telescope for astronomical purposes after hearing about the Dutch invention. He made his own version of the telescope which allowed him to observe celestial bodies more clearly than ever before.

Design and Construction

A refracting telescope works by bending light as it passes through the lens at the front of the telescope. The lens is called the objective lens. This bending of light, or refraction, causes the light rays to converge to a focus. A second lens, the eyepiece, is used to magnify the image formed by the objective lens.

The most common type of refractor is the achromatic refractor, which uses two or more lenses to correct for chromatic aberration. A more advanced type, the apochromatic refractor, uses special materials and more lenses to provide even greater correction of chromatic aberration.

Advantages and Disadvantages

Refracting telescopes have several advantages. They are sealed tube systems, which protects the optics from atmospheric elements, resulting in less maintenance. The fixed optical alignment is more stable and does not require adjustment. However, refractors are generally more expensive than reflecting telescopes of the same aperture size due to the cost of lens-making materials and the complexity of the lens design to correct for optical aberrations.

Uses

Refracting telescopes are used in a variety of applications, from backyard astronomy to research-grade observatories. They are particularly valued for their ability to provide high-contrast views of planets and double stars. Due to their design, they are also used in terrestrial viewing and as telephoto lenses for photography.

See Also

• Telescope
• Optics
• Astronomical telescope
• Galileo Galilei
• Chromatic aberration

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