| 摘要 |
A variable power finder is proposed, which comprises: an objective system; an inverting system; and an ocular system, in order from object side. The third lens group of the objective system is constituted by one lens prism having at least one reflection surface, and following expressions are satisfied: <?in-line-formulae description="In-line Formulae" end="lead"?>f 3 /fw>=2.5 (1)<?in-line-formulae description="In-line Formulae" end="tail"?> <?in-line-formulae description="In-line Formulae" end="lead"?>-1.0<(R 32 +R 31 )/(R 32 -R 31 )<1.0 (2)<?in-line-formulae description="In-line Formulae" end="tail"?> <?in-line-formulae description="In-line Formulae" end="lead"?>L 1 /fw<SUP>2</SUP><=0.45 1/mm (3)<?in-line-formulae description="In-line Formulae" end="tail"?> <?in-line-formulae description="In-line Formulae" end="lead"?>L 2 /fw<SUP>2</SUP>>=0.03 1/mm (4)<?in-line-formulae description="In-line Formulae" end="tail"?> where f 3 is a focal distance in millimeters (mm) of third lens group, fw is a focal in mm distance at wide angle end of objective system, R 31 is a curvature radius of object side lens surface of lens prism, R 32 is a curvature radius of image side lens surface of lens prism, L 1 is an air equivalent distance in mm from middle imaging surface to object side lens surface of lens prism, and L 2 is a distance in mm from middle imaging surface to image side lens surface of lens prism.
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