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What are the main components of an optical telescope?
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Telescope
Aerial view of the Keck Observatory's twin domes, which are opened to reveal the telescopes. Keck II is on the left and Keck I on the right.
The main components of an optical telescope are the objective lens or mirror and the eyepiece. The objective lens, in a refracting telescope, is the first lens that light passes through from a celestial object. It gathers light and forms an initial, inverted image at its focal plane. In a reflecting telescope, a concave mirror serves as the objective, reflecting light to a focal point. The eyepiece is a second lens placed behind the focal plane, which magnifies the image formed by the objective, allowing the observer to view it. The diameter of the objective is known as the aperture, and it determines the telescope's light-gathering power.123