Observation optical system, viewfinder equipped with observation optical system and method for manufacturing observation optical system

Patent metadata

Field	Value
Publication number	US-9454062-B2
Application number	US-201113237905-A
Country	US
Kind code	B2
Filing date	Sep 20, 2011
Priority date	Sep 21, 2010
Publication date	Sep 27, 2016
Grant date	Sep 27, 2016

Abstract

An observation optical system for observing an object includes, in order from the object side: a first lens having positive refractive power; a second lens having negative refractive power and a concave surface facing the object side; and a third lens having positive refractive power and a convex surface facing an eyepoint side. An aspherical surface is included on at least one lens surface, and given conditional expressions are satisfied, thereby providing a compact observation optical system having excellent optical performance, a viewfinder equipped with the observation optical system, and a method for manufacturing the observation optical system.

First claim

What is claimed is:

1. An optical system,
the optical system being configured as an observation optical system for observing an object and comprising, in order from the object side:
a first lens having positive refractive power;
a second lens having negative refractive power and a concave surface facing the object side; and
a third lens having positive refractive power and a convex surface on an optical axis and facing an eyepoint side,
an aspherical surface being included on at least one lens surface, and
the following conditional expressions being satisfied:
0.80<( R 22+ R 21)/( R 22− R 21)<2.00

1.534≦ f 1/(− f 2)<2.00

where R21 denotes a radius of curvature of the object side lens surface of the second lens, R22 denotes a radius of curvature of the eyepoint side lens surface of the second lens, f1 denotes a focal length of the first lens, and f2 denotes a focal length of the second lens.

2. The optical system according to claim 1 , wherein the following conditional expression is satisfied:
0.50<(−1)×(( R 32+ R 31)/( R 32− R 31))<1.00

where R31 denotes a radius of curvature of the object side lens surface of the third lens, and R32 denotes a radius of curvature of the eyepoint side lens surface of the third lens.

3. The optical system according to claim 1 , wherein the following conditional expression is satisfied:
0.05< d 12/ TL< 0.30
where d12 denotes a distance between the eyepoint side lens surface of the first lens and the object side lens surface of the second lens, and TL denotes a distance between the object plane and the most eyepoint side lens surface.

4. The optical system according to claim 1 , wherein the following conditional expression is satisfied:
0.90< f 1/ f 3<2.30
where f1 denotes a focal length of the first lens and f3 denotes a focal length of the third lens.

5. The optical system according to claim 1 , wherein all of the first lens, the second lens and the third lens are constructed by plastic lenses.

6. The optical system according to claim 1 , wherein an aspherical surface is disposed on the object side surface of the second lens.

7. The optical system according to claim 1 , wherein an aspherical surface is disposed on the eyepoint side surface of the third lens.

8. The optical system according to claim 1 , wherein the following conditional expression is satisfied:
0.20< h/TL< 0.35
where h denotes an object height, and TL denotes a distance between the object plane and the most eyepoint side lens surface.

9. The optical system according to claim 1 , wherein the following conditional expression is satisfied:
5.60< h< 12.00
where h denotes an object height.

10. A viewfinder equipped with an image display panel, and the optical system according to claim 1 .

11. The viewfinder according to claim 10 , wherein diopter adjustment is carried out by varying a distance between the image display panel and the object side lens surface of the first lens.

12. The viewfinder according to claim 11 , wherein distances between the first lens through the third lens are not varied upon adjusting diopter.

13. An optical apparatus equipped with the optical system according to claim 1 .

14. A viewfinder comprising:
an image display panel; and
an observation optical system configured for observing an image displayed on the image display panel,
the observation optical system comprising, in order from the image display panel side, a first lens having positive refractive power, a second lens having negative refractive power and a concave surface facing the image display panel side, and a third lens having positive refractive power and a convex surface on an optical axis and facing an eyepoint side,
an aspherical surface being formed on either one of the first lens and the third lens, and
the following conditional expression being satisfied:
0.20< h/TL< 0.26

where h denotes an object height, and TL denotes a distance between the object plane and the most eyepoint side lens surface.

15. The viewfinder according to claim 14 , wherein the following conditional expression is satisfied:
5.60< h< 12.00
where h denotes an object height.

16. An optical apparatus equipped with the viewfinder according to claim 14 .

17. A method for manufacturing an optical system including a first lens having positive refractive power, a second lens having negative refractive power, and a third lens having positive refractive power, the method configuring the optical system as an observation optical system for observing an object and comprising steps of:
disposing a concave surface on the object side lens surface of the second lens;
disposing a convex surface on an optical axis on an eyepoint side lens surface of the third lens;
disposing an aspherical surface on at least one of the first lens through the third lens; and
disposing each lens with satisfying the following conditional expressions:
0.80<( R 22+ R 21)/( R 22− R 21)<2.00

1.534≦ f 1/(− f 2)<2.00

where R21 denotes a radius of curvature of the object side lens surface of the second lens, R22 denotes a radius of curvature of the eyepoint side lens surface of the second lens, f1 denotes a focal length of the first lens, and f2 denotes a focal length of the second lens.

18. The method according to claim 17 , further comprising a step of:
disposing the third lens with satisfying the following conditional expression:
0.50<(−1)×(( R 32+ R 31)/( R 32− R 31))<1.00

where R31 denotes a radius of curvature of the object side lens surface of the third lens, and R32 denotes a radius of curvature of the eyepoint side lens surface of the third lens.

19. The method according to claim 17 , further comprising a step of:
disposing each lens with satisfying the following conditional expression:
0.05< d 12/ TL< 0.30

where d12 denotes a distance between the eyepoint side lens surface of the first lens and the object side lens surface of the second lens, and TL denotes a distance between the object plane and the most eyepoint side lens surface.

20. The method according to claim 17 , further comprising a step of:
disposing each lens with satisfying the following conditional expression:
0.90< f 1/ f 3<2.30

where f1 denotes a focal length of the first lens and f3 denotes a focal length of the third lens.

21. A method for manufacturing a viewfinder including an image display panel and an optical system, the method configuring the optical system as an observation optical system for observing an image displayed on the image display panel and comprising steps of:
disposing, in order from the image display panel side, a first lens having positive refractive power, a second lens having negative refractive power and a concave surface facing the image display panel side, and a third lens having positive refractive power and a convex surface on an optical axis and facing an eyepoint side, into the optical system;
disposing an aspherical surface on either one of the first lens and the third lens; and
disposing each lens with satisfying the following conditional expression:
0.20< h/TL< 0.26

where h denotes an object height, and TL denotes a distance between the object plane and the most eyepoint side lens surface.

22. The method according to claim 21 , further comprising a step of:
disposing each lens with satisfying the following conditional expression:
5.60< h< 12.00

where h denotes an object height.

23. A viewfinder comprising

Assignees

• Matsuo Taku
• Nikon Corp

Inventors

• Matsuo Taku

Classifications

• G02B9/16

  all the components being simple · CPC title

• G02B13/0035

  having three lenses · CPC title

• G03B13/00 Primary

  Viewfinders; Focusing aids for cameras; Means for focusing for cameras; Autofocus systems for cameras · CPC title

• Y10T29/49826

  Assembling or joining · CPC title