Real image mode variable magnification finder

• US 6,154,314 A
• Filed: 12/22/1998
• Issued: 11/28/2000
• Est. Priority Date: 12/26/1997
• Status: Expired due to Fees

• 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:
  US09/218,524
• Time in Patent Office: 707 Days
• Field of Search: 359/362, 359/420-422, 359/431-433, 359/676-678, 359/689, 359/784, 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.sub.W Z/D.sub.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 mode variable magnification finder comprising, in order from an object side:

an objective optical system with positive power, including at least three lens units;

an image erecting system; and

an ocular optical system with positive power, said finder satisfying the following conditions;

space="preserve" listing-type="equation">0.1≧

β

.sub.W Z/D.sub.W ≧

0.080

space="preserve" listing-type="equation">13.5 mm≦

f.sub.R ≦

17.3 mm

where β

_W is a magnification at a wide-angle position of said finder, Z is a variable magnification ratio of said finder, D_W is an axial distance, in millimeters from an object-side surface of a first lens unit of said objective optical system to a pupil-side surface of a third lens unit thereof at the wide-angle position of said finder, and f_R is a focal length of said ocular optical system of said finder.

5. A real image mode variable magnification finder according to any one of claims 1-4, 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.

6. A real image mode variable magnification finder according to claim 5, wherein at least said second lens unit and the third lens unit are movable when a magnification of said finder is changed.

7. A real image mode variable magnification finder according to claim 5, wherein said finder satisfies the following condition:

space="preserve" listing-type="equation">0.19<

E.sub.nW /D.sub.W <

0.43

where E_nW is an axial distance from an object-side surface of said first lens unit of said objective optical system at the wide-angle position of said finder to a position of an entrance pupil and D_W is an axial distance from an object-side surface of said first lens unit of said objective optical system to a pupil-side surface of said third lens unit thereof at the wide-angle position of said finder.

8. A real image mode variable magnification finder according to claim 7, wherein a prism whose entrance surface has a power is used and said entrance surface is configured to be aspherical.

9. A real image mode variable magnification finder according to any one of claims 1-4, wherein said ocular optical system is constructed with a single positive lens.

10. A real image mode variable magnification finder according to any one of claims 1-4, 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 unit constituting said objective optical system is constructed with a single lens.

11. A real image mode variable magnification finder according to claim 10, wherein said finder satisfies the following condition:

space="preserve" listing-type="equation">0.19<

E.sub.nW /D.sub.W <

0.43

where E_nW is an axial distance from an object-side surface of said first lens unit of said objective optical system at the wide-angle position of said finder to a position of an entrance pupil and D_W is an axial distance from an object-side surface of said first lens unit of said objective optical system to a pupil-side surface of said third lens unit thereof at the wide-angle position of said finder.

12. A real image mode variable magnification finder according to claim 11, wherein said finder satisfies the following condition:

space="preserve" listing-type="equation">-0.3<

(r.sub.4 +r.sub.3)/(r.sub.4 -r.sub.3)<

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.

13. A real image mode variable magnification finder according to claim 12, wherein an aspherical surface is used for a pupil-side surface of said third lens unit of said objective optical system.

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

an objective optical system with positive power, including at least three lens units;

an image erecting system; and

an ocular optical system with positive power,

said finder satisfying the following conditions;

space="preserve" listing-type="equation">0.1≧

β

.sub.W Z/D.sub.W ≧

0.071

space="preserve" listing-type="equation">14.5°

≧

ω

'"'"'≧

11.9°

space="preserve" listing-type="equation">13.5 mm≦

f.sub.R ≦

17.3 mm

where β

_W is a magnification at a wide-angle position of aid finder, Z is a variable magnification ratio of said finder, D_W is an axial distance, in millimeters, from an object-side surface of a first lens unit of said objective optical system to a pupil-side surface of a third lens unit thereof at the wide-angle position of said finder, ω

'"'"' is a half angle of view of emergence at a maximum angle or view of said finder, and f_R is a focal length of said ocular optical system of said finder.

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

an objective optical system with positive power, including at least three lens units;

an image erecting system; and

an ocular optical system with positive power,

said finder satisfying the following conditions;

space="preserve" listing-type="equation">0.1 ≧

β

.sub.W Z/D.sub.W ≧

0.071

space="preserve" listing-type="equation">2.5>

L/f.sub.W ≧

1.72

space="preserve" listing-type="equation">13.5 mm≦

f.sub.R ≦

17.3 mm

where β

_W is a magnification at a wide-angle position of said finder, Z is a variable magnification ratio of said finder, D_W is an axial distance, in millimeters, from an object-side surface of a first lens unit of said objective optical system a pupil-side surface of a third lens unit thereof at the wide-angle position of said finder, L is a distance from the pupil-side surface of the third lens unit of said objective optical system to an intermediate imaging position at the wide-angle position of said finder, f_W is a focal length of said objective optical system at the wide-angle position of said finder, and f_R is a focal length of said ocular optical system of said finder.

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

an objective optical system with positive power;

image erecting means; and

an ocular optical system with positive power,

said finder satisfying the following conditions;

space="preserve" listing-type="equation">14.5°

≧

ω

'"'"'≧

11.9°

space="preserve" listing-type="equation">13.5≦

f.sub.R ≦

17.3

space="preserve" listing-type="equation">0.59≧

β

.sub.W ≧

0.41

where ω

'"'"' is a half angle of view of emergence at a maximum angle of view of said finder, f_R is a focal length of said ocular optical system of said finder, and β

_W is a magnification at a wide-angle position of said finder.