Real image mode variable magnification finder

• US 6,333,815 B1
• Filed: 11/03/2000
• Issued: 12/25/2001
• Est. Priority Date: 12/26/1997
• Status: Expired due to Term

• Current Assignee: Olympus Optical Company Ltd. (Olympus Corporation)
• Original Assignee: Olympus Optical Company Ltd. (Olympus Corporation)
• Inventors: Takahashi, Toshio
• Primary Examiner(s): NGUYEN, THONG Q
• Application Number:
  US09/704,700
• Time in Patent Office: 417 Days
• Field of Search: 359/362, 359/432-433, 359/676-690, 396/373-386
• US Class Current: 359/432
• CPC Class Codes: G02B 23/14 Viewfinders for photographic apparatus G03B13/02

Abstract

A real image mode variable magnification finder includes, in order from an object side, an objective optical system with positive power, having at least three lens units; an image erecting device; and an ocular optical system with positive power. This finder also satisfies the following condition:

0.1≧β_W Z/D_W≧0.080

where β_W is a magnification at a wide-angle position of the finder, Z is the variable magnification ratio of the finder, and D_W is an axial distance, in millimeters, from the object-side surface of the first lens unit of the objective optical system to the pupil-side surface of the third lens unit thereof at the wide-angle position of the finder. In this way, the real image mode variable magnification finder which is small in size, high in magnification, large in angle of emergence, and easy to observe can be provided.

Claims

1. A real image mode variable magnification finder comprising, in order from an object side:

an objective optical system with positive power, including a plurality of movable lens units;

an image erecting system; and

an ocular optical system with positive power,

wherein said finder satisfies the following conditions;

4. A real image mode variable magnification finder according to claim 1, 2 , or 3, wherein said objective optical system includes, in order from said object side, a first lens unit with negative power, a second lens unit with positive power, and a third lens unit with positive power, and each of lens units constituting said objective optical system is constructed with a single lens.

5. A real image mode variable magnification finder according to claim 1, 2, or 3, wherein said objective optical system includes, in order from said object side, a first lens unit, a second lens unit, and a third lens unit, and said finder further satisfies the following condition:

6. A real image mode variable magnification finder according to claim 5, wherein a prism whose entrance surface has a power is used and said entrance surface is configured to be aspherical.

7. A real image mode variable magnification finder according to claim 1, 2, or 3, wherein said ocular optical system is constructed with a single positive lens.

8. A real image mode variable magnification finder according to claim 1, 2, or 3, wherein said objective optical system includes, in order from said object side, a first lens unit with negative power, a second lens unit with positive power, and a third lens unit with negative power, and each of individual lens units constituting said objective optical system is constructed with a single lens.

9. A real image mode variable magnification finder according to claim 8, wherein said finder further satisfies the following condition:

 

−

0.3<

(r₄+r₃)/(r₄−

r₃)<

0.3

where r₃ is a radius of curvature of an object-side surface of said second lens unit of said objective optical system and r₄ is a radius of curvature of a pupil-side surface thereof.

10. A real image mode variable magnification finder according to claim 8, wherein an aspherical surface is used for a pupil-side surface of said third lens unit of said objective optical system.

11. A real image mode variable magnification finder according to claim 1, 2, or 3, wherein said objective optical system includes, in order from said object side, a first lens unit, a second lens unit, and a third lens unit, and said finder further satisfies the following condition:

12. A real image mode variable magnification finder according to claim 1, 2, or 3, wherein said objective optical system includes, in order from said object side, a first lens unit, a second lens unit, and a third lens unit, and said finder further satisfies the following condition:

13. A real image mode variable magnification finder according to claim 1, 2, or 3, wherein said objective optical system includes, in order from said object side, a first lens unit, a second lens unit, and a third lens unit, and said finder further satisfies the following condition:

 

2.5≧

L/f_W≧

1.72

where L is a distance from a pupil side surface of said third lens unit of said objective optical system to an intermediate imaging position at a wide-angle position of said finder, and f_W is a focal length of said objective optical system at the wide-angle position of said finder.

2. A real image mode variable magnification finder comprising, in order from an object side:

an objective optical system with positive power, including a plurality of movable lens units;

an image erecting system; and

an ocular optical system with positive power,

wherein said finder satisfies the following conditions;

3. A real image mode variable magnification finder comprising, in order from an object side:

an objective optical system with positive power, including a plurality of movable lens units;

an image erecting system; and

an ocular optical system with positive power,

wherein said finder satisfies the following conditions;