Huygens' eyepiece

noun
  1. physics a telescope eyepiece consisting of two planoconvex lenses separated by a distance equal to half the sum of their focal lengths, which are in the ratio of three to one, and oriented so that their curved surfaces face the incident light

Word Origin for Huygens' eyepiece

C19: named after Christiaan Huygens (1629–95), Dutch physicist
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