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					Keyword: refracting telescope
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Galileo Gets Credit For Refracting Telescope

Galileo is given credit for developing the first refracting telescope in
1609, but it was the work of three eye doctors in 1608 that led him to
merge their lenses with his understanding of refraction’s effects that
led to the invention of the refracting telescope. There are two basic
parts to a refracting telescope, a convex objective lens and a concave
lens in the eyepiece.

The convex, or refractive lens at the and of a refracting telescope
refracts, of bends, light as it enters the glass and focuses is on a
single plane. This causes the image to appear upside down, but the
concave lens on which the image is focused makes it appear upside right.
By using a refracting telescope, the image can appear not only closer,
but also brighter and clearer.

While Galileo refracting telescopes are still widely used today, they
offer a limited field of view. For example, the Chabot Space and Science
Center in Oakland, California houses an eight-inch and a 20-inch
refracting telescope. Their simplicity may also shows signs of spherical
aberrations. Achromatic lenses, developed in 1773, uses a convex lens and
a flat lens placed together to help reduce spherical and chromatic
problems.

Working To Keep Colors Together

The biggest problem with a refracting telescope is that during the
refracting of the light, the color spectrum tends to separate during the
light bending process. This is referred to as chromatic aberration and,
although using concave and flat lenses together, creating an achromatic
lens has reduced this problem, it is still a concern in larger lenses. A
26-inch telescope in Washington, D.C. is one of the largest in the
country.

Although glass for lenses as large as 40-inches has been cast, they have
not been used due to the imperfections in the glass distorting the color
rays as it passes through. The importance of have the entire spectrum hit
the focal place at the same time and in the same position is what has
stopped refracting telescope construction for professional use.

Some observatories still use a refracting telescope and many private
users find them useful for astrology observations as the lens’ position
within the enclosed tube can provide a steadier image as opposed to a
reflective telescope that counts on mirror reflecting the image from the
objective lens to the eyepiece. As light from an image enters it will be
reflected by the primary mirror to a secondary mirror and then to the
eyepiece.

				
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