Astronomy - Refracting Telescopes
This is made with 2 lenses, the objective lens and the eye piece lens.
The eye piece lens must have a small focal length because it only has to send the light from the objective lenst down the telescope to the eye piece lens.
The objective lens must have a large focal length to receive the furthest away objects.
The total length of the telescope is the sum of the focal length of the objective lens plus the focal length of the eye piece lens.
The diameter of the objective lens should be as big as possible. The larger it is the more light it can take in to the telescope.
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