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L7-24: TERRESTRIAL TELESCOPE - TV 9 years 11 months ago #938

  • zzfixk21
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ID Code: L7-24
Purpose: To illustrate how a terrestrial telescope works.
Description: The TV camera functions as the eye, so what the eye sees can be viewed on a monitor or the rear projection screen. A 10 cm or 5 cm convex lens acts as the eyepiece, a large 20 cm convex lens is the objective lens, and a 10 cm convex inverting lens between the objective and the eyepiece, with the TV camera focused at infinity (relaxed eye). The rule is positioned across the lecture hall (at infinity) from the telescope. The image is seen to be erect and to have a magnification M=f(ob)/f(eye). The magnification can be checked by viewing a two-meter stick with the TV camera directly and then with the telescope.

The photographs below show the image with no telescope (left), using a 20cm focal length eypiece (M=2), and using a 10cm focal length eyepiece (M=4). Vignetting is seen in both telescopic images, and is very obvious in the center image.

To set up in practice, set the camera focus and lens positions and move the objective lens until the image is seen by the camera. The inverting lens is used with equal object and image distances (twice the focal length), and provides no magnification.

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