| 摘要 |
An eyepiece lens includes first lens group G 1 having a negative refracting power including a negative meniscus lens with a concave surface facing eyepoint E.P side, second lens group G 2 having a positive refracting power including a lens with both convex surfaces on both ends, and third lens group G 3 having a negative refracting power including a negative lens. The first-third lens groups are arranged in an order from eyepoint E.P side, and the eyepiece lens is capable of varying a diopter by moving the second lens group along an optical axis. The eyepiece lens is configured by aspherical surfaces to make the positive refracting power weak while at least one surface of the convex surfaces of the lens deviates from the optical axis. Further, conditions of a following formula are satisfied: <?in-line-formulae description="In-line Formulae" end="lead"?>1.6<f1/f3<2.5<?in-line-formulae description="In-line Formulae" end="tail"?> <?in-line-formulae description="In-line Formulae" end="lead"?>-0.55<S3<=0<?in-line-formulae description="In-line Formulae" end="tail"?> where a focal length of first lens group G 1 indicated f1, a focal length of third lens group G 3 indicates f3, and a shape factor of third lens group G 3 indicates S3, (provided shape factor S3 is defined by a conditional formula <?in-line-formulae description="In-line Formulae" end="lead"?>S3=(re<SUB>3</SUB>+rs<SUB>3</SUB>)/(re<SUB>3</SUB>-rs<SUB>3</SUB>)<?in-line-formulae description="In-line Formulae" end="tail"?> where re<SUB>3 </SUB>indicates a radius of curvature of third lens group G 3 on the eyepoint side and rs<SUB>3 </SUB>indicates a radius of curvature thereof on the object side, and the formula is computed with a paraxial radius of curvature when the surface is the aspherical surface.).
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