Since the magnification depends on the focal lengths, usually, astronomers have a variety of eyepieces on hand. If M is the magnification of the refracting telescope, f o is the focal length of the objective, and f e is t he focal length of the eyepiece, then the magnification is given as: A refracting telescope’s magnification depends on the focal lengths of the lenses used in it that is the objective and the eyepiece.Ī refracting telescope's magnification is determined by dividing the objective's focal length by the eyepiece's focal length. Magnification Formula for Refracting TelescopeĪny optical instrument's magnification is determined by how much larger the picture is as compared to the object. f o and f e are the focal lengths of the objective and the eyepiece lens, respectively. The image formed at this focal point is then adjusted to be at the focal point of the eyepiece which gives a magnified and better image. In the ray diagram, the parallel light rays coming through the objective lens are focused at the focal point of the lens. If the image formed is adjusted to be at the focal point of the eyepiece, the final image will be formed at infinity and the image is therefore highly magnified and erect.īelow is a schematic and a ray diagram of a refracting telescope which will help understand the principle of the refracting telescope in a better way. Now, this image cannot be used to observe distant objects and this is where the eyepiece lens comes into play. The image created at this focal point is real, inverted, and diminished. The rays that are not parallel converge upon the focal plane. The objective lens refracts the light and it causes parallel light rays from distant objects to converge at a focal point. It then focuses the light and is presented to us with a brighter, clearer, and magnified virtual image. The objective lens and the eyepiece lens are used together to gather more light at a point than the human eye can collect. Working Principle of Refracting TelescopeĪll the refracting telescopes are based on the same principle that we are about to discuss in this section. The image is formed by reflecting the incoming light.Įxamples: The Keck II telescope in Mauna Kea, Hawaii, Gran Telescopio Canarias in La Palma, Spain Its main lens have 1.02 metres in diameter), James Lick telescope (91 cm in diameter).Ī reflecting telescope is an optical telescope that uses a mirror as its objective to form the image. Then, this news spread like a wildfire which reached Galileo Galilei in May 1609 and he then constructed his own version and used it to make astronomical observations.Įxamples: Yerkes Observatory (the largest refracting telescope ever built. A spectacle maker named Hans Lippershey from Middleburg tried to patent it but was unsuccessful. The first record of a refracting telescope is in the Netherlands around 1608. Refracting telescopes were the earliest telescopes to be devised. These primary and eyepiece lenses are fixed at the ends of two coaxial tubes and parallel rays from a distant object enter the telescope. The two lenses used in a refracting telescope are the objective or primary lens, which is used to refract or bend the light to a focus point, and some type of eyepiece. The refracting telescope gets its name from the fact that it uses refracting elements, i.e., lenses. Refractive TelescopeĪ refracting telescope is an optical telescope that forms an image with a lens as its objective. Magnification: making objects look bigger (closer to us). Resolution: Telescopes resolve incoming light so that finer details can be seen. The telescopes focus incoming light rays on a small area. Since the invention of telescopes, astronomers have been able to see new phenomena and objects by looking into the vast space. There are two main types: refractive and reflective telescopes. A telescope is an optical device in which light from distant objects is gathered and focused by lenses, curved mirrors, or a combination of both. In this article, we will learn about refracting telescopes.
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