| 摘要 |
PROBLEM TO BE SOLVED: To provide a telecentric optical system in which focusing is possible while double-telecentric property is always maintained even when the conjugate distance changes. SOLUTION: The optical system has telecentric arrangement in both of the object side and image side, both of a fixed lens group (GrF) and a moving lens group (GrR) consist of an afocal optical system. The fixed lens group (GrF) consists of a positive first group (Gr1) and a positive second group (Gr2), and has an aperture (SP) at the back focal point of the first group (Gr1). The moving lens group (GrR) is a focus lens group which consists of a negative third group (Gr3) and a positive fourth group (Gr4), which satisfies the relation of f3≠-f4 (wherein f3 and f4 are the focal distances of the third group (Gr3) and fourth group (Gr4), respectively), and which can move to focus the object with different distance from the object while the telecentric state is maintained.
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