Refractor telescopes are of the design most would envision when thinking of a telescope today. The long thin tube, a lens at one end, an eyepiece at the other, and an image focused and observed. After almost 400 years, this classic design remains relatively unchanged, and its primary purpose of star-gazing, exploration and discovery – also the same.
Invented by Hans Lippershey in 1608, the refractor telescope was actually developed for military use. Galileo Galilei however thought otherwise and took his knowledge of the invention and refraction and created an instrument of his own: for astronomical purposes. As a result, exploring and better understanding the universe was to take a giant leap forward.
Defined by its long thin tube design, the refracting telescope uses a lens (the objective lens) at the front end, to collect light. At the back of the telescope, there's another lens – the eyepiece or ocular – that the observer looks through. The collected light is "refracted" or bent using lenses. It is then focused and magnified at the ocular end and through the eyepiece, the image is brought into view. Its best images are typically those from long distances and not surprisingly, the refracting telescope is best suited for observation of the moon, planets, the sky.
Indeed, refractor telescopes are highly regarded for their sharp images of long-distance objects. However, for shorter-length images, there is a tendency for chromatic aberration and/or spherical aberration, which can lead to a halo effect surrounding bright objects. This results in a less-than-clear view, which is a consideration when looking for the right telescope for to purchase.
Historically, there have been variants of the refracting telescope, which are still in use today. These include the Keplerian Telescope, which uses a convex lens rather than a concave one like Galileo's. The difference is a wider field of view due to the refracting light rays converging. There is consequently, a higher degree of possible aberration. To counter this, a high f-ratio (the diameter of the "entrance pupil," where the light enters the optical device) is needed.
In addition to the Galilean and Keplerian designs, there's also the achromatic refractor, which uses two pieces of glass to create the objective lens, and the apochromatic refractor, which focuses three wavelengths in the same plane to help minimize chromatic aberration.
Observatories all over the world use refractors to get closer to the stars. Notable refractors include the Paris Observatory, Nice Observatory, and the Chabot Space and Science Center in Oakland, California, which features two refractor telescopes "Leah" (1883) and "Rachel." Commissioned in 1914, "Rachel" is regularly open to the public and is the largest such telescope in the western United States.
lee said:
i have a hq micro reflector telescope . any good or bin it
Tuesday May 20, 2008, 10:11 PM
lee said:
Im not surre. =P
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