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.
