an astronomical telescope a telescope is an optical tool that increases the apparent size of distant objects as well as their apparent brightness they work by using one or more curved optical lenses or mirrors to gather light or electromagnetic radiation and to bring to focus the image that can be observed or studying an astronomical telescope is used to observe heavenly bodies like new and stars requirements two convex lenses one with 2.5 centimeters aperture and 10 centimeters focal length and the other with 3 point 8 centimeter aperture and 50 centimeters focal length 2 plastic tubes fitting into each other.you method the body of telescope is made with the two plastic tubes one slid smoothly into the other the diameter of one tube should be slightly less than the diameter of the eyepiece and that of the other slightly less than the diameter of the objective lens the length of the tubes should be 2/3 of the distance required between the lenses to get a sharp image take the lenses and stick them to the ends of the tubes point the telescope at a distant object in the sky and slit the tubes in and out until a sharp image is seen the length will be equal to the sum of the focal lengths of the two lenses an inverted image of the object is obtained