<unk>  is the study of the refraction of light, especially by lenses. Telescopes that create their image with an objective that is a convex lens (refractors) are said to be "dioptric" telescopes.
An early study of<unk>  was conducted by Ptolemy in relationship to the human eye as well as refraction in media such as water.  Understanding of the principles of<unk>  was further expanded by Alhazen, considered as the father of modern optics.
Dioptrics
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