Zoom finder optical system
AssigneeMinolta Co., Ltd.
InventorsKatsuto Tanaka, Kyoko Yamaguchi
Life of this patent
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Abstract
A zoom finder optical system of real image type of the present invention is provided with an objective lens system of a positive refractive power, a condenser lens of a positive refractive power and an eyepiece system of a positive refractive power from an object side. The objective lens system includes from the object side a first lens unit of negative refractive power, a second lens unit of a negative refractive power, a third lens unit of a positive refractive power and a fourth lens unit of a positive refractive power.
Claims31
A zoom finder optical system of a real image type comprising, from an object side:
- objective lens system of a positive refractive power;
- a condenser lens of a positive refractive power provided near an image formed by said objective lens system;
- and
- an eyepiece system of a positive refractive power,
- wherein said objective lens system includes from the object side a first lens unit of a negative refractive power, a second lens unit of a negative optical power, a third lens unit of a positive refractive power and a fourth lens unit of a positive refractive power,
- wherein zooming is performed by varying each distance between said first, second, third and fourth lens units.
A zoom finder optical system of a real image type comprising, from an object side:
- an objective lens system having a first lens unit of a negative refractive power;
- a second lens unit of a negative refractive power;
- a third lens unit of a positive refractive power;
- a fourth lens unit of a positive refractive power;
- an erecting optical system including prisms having a plurality of reflecting surfaces;
- and
- an eyepiece optical system of a positive refractive power,
- wherein zooming is performed by varying each distance between said first, second, third, and fourth lens units,
- wherein the fourth lens unit consists of one convex surface having a positive power;
- and
- wherein said surface functions as an entrance surface of the prisms provided on the most object side of said erecting optical system.
A zoom finder optical system of a real image type comprising from an object side a first lens unit of a negative refractive power, a second lens unit of a negative refractive power, a third lens unit of a positive refractive power, a bi-convex Porro prism, a bi-plano Porro prism and an eyepiece system of a positive refractive power,
- wherein the following conditions are fulfilled:
- ##EQU8## where f.sub.1 is a focal length of the first lens unit, f.sub.2 is a focal length of the second lens unit, f.sub.3 is a focal length of the third lens unit, and f.sub.4 is a focal length of an object side surface of the bi-convex Porro prism.
A zoom finder optical system of a real image type comprising, from an object side:
- an objective lens system having a first lens unit of a negative refractive power;
- a second lens unit of a negative refractive power;
- a third lens unit of a positive refractive power;
- a fourth lens unit of a positive refractive power;
- an erecting optical system including prisms having a plurality of reflecting surfaces;
- and
- an eyepiece optical system of a positive refractive power,
- wherein zooming is performed by varying each of the distances among said first, second, third, and fourth lens units, and
- wherein the fourth lens unit consists of one convex surface having a positive refractive power, and
- wherein said surface functions as an entrance surface of the prism provided on the most object side of said erecting optical system.
A zoom finder optical system of a real image type comprising, from an object side:
- an objective zoom lens system of a positive refractive power;
- an erecting optical unit for erecting an image formed by the objective lens system;
- a condenser lens of a positive refractive power;
- and
- an eyepiece system of a positive refractive power,
- wherein said objective lens system includes, from the object side, a first lens unit of a negative refractive power, a second lens unit of a negative refractive power, a third lens unit of a positive refractive power, and a fourth lens unit of a positive refractive power, and said second and third lens units are moved along an optical axis during zooming.
A finder optical system of a real image type comprising, from an object side:
- an objective zoom lens system of a positive refractive power;
- a condenser lens of a positive refractive power, and
- an eyepiece system of a positive refractive power,
- wherein said objective lens system includes, from the object side, a first lens unit of a negative refractive power, a second lens unit of a negative refractive power, a third lens unit of a positive refractive power, and a fourth lens unit of a positive refractive power,
- wherein the second and third lens units are moved along an optical axis to provide a zooming function while the fourth lens unit is fixed during the zooming function, wherein the following conditions are fulfilled:
- ##EQU10## where .function..sub.1 is a focal length of the first lens unit, .function..sub.2 is a focal length of the second lens unit, .function..sub.3 is a focal length of the third lens unit, and .function..sub.4 is a focal length of the fourth lens unit.
Dependencies are inferred from the claim text.