JP6071505B2 - Viewfinder optical system and imaging apparatus using the same - Google Patents

Description

  The present invention relates to a finder optical system and an imaging apparatus using the same, and is particularly suitable for an imaging apparatus such as a single-lens reflex camera, which can observe a finder image favorably with a large observation magnification of the finder optical system. .

  Conventionally, in a single-lens reflex camera, a subject image (finder image) formed on a focusing screen is observed through a finder optical system by a photographing lens. This viewfinder optical system is configured to view an object image formed on a focusing screen as an erect image through an image inverting means such as a penta roof mirror or a penta prism, and then to enlarge and observe the image with an eyepiece. . In this finder optical system for a single-lens reflex camera, the specifications of the finder such as observation magnification and eye relief are determined mainly by the optical path length from the focusing screen to the eyepiece, which depends on the size of the image inverting means.

  An eyepiece used in a finder optical system for a single lens reflex camera is required to have a high observation magnification, a sufficiently long eye relief, and a diopter adjustment function.

  By making the eye relief longer, sufficient image performance can be obtained even if the finder image is observed from a slightly separated position, instead of observing the finder image by pressing the face against the finder. For example, it becomes easy to look into the viewfinder while wearing glasses. That is, by making the eye relief longer, it is possible to obtain comfort when observing the viewfinder without stress.

  In the viewfinder optical system of such a single-lens reflex camera, various types of eyepiece optical systems having a large observation magnification and a sufficiently long eye relief have been conventionally proposed (Patent Documents 1 and 2).

Japanese Patent Laid-Open No. 2008-24195 JP 2009-271386 A

  However, in order to observe the finder image more comfortably, in addition to the long eye relief, it is important to increase the diameter of the eye relief. When the user of the camera holds the camera and the observation eye is well placed on the finder optical axis as an observer observing the finder, high optical performance can be obtained.

  However, when the observation eye and the viewfinder optical axis are greatly deviated, the image performance is deteriorated. In this case, the observer needs to set the camera again in order to find an easy-to-see finder image. Therefore, in order to obtain a finder that can be observed more comfortably, in addition to a long eye relief, an eye relief having a large diameter is required.

  An object of the present invention is to provide a finder optical system that can be used comfortably and has a large observation magnification while maintaining high optical performance, a sufficiently long eye relief, a sufficiently large eye relief diameter, and an imaging apparatus using the same Is to provide.

To achieve the above object, a finder optical system according to the present invention is a finder optical system for observing an object image formed on a predetermined surface, and is an erect image arranged in order from the object side to the observation side. , A first lens group having a negative refractive power, a second lens group having a positive refractive power that moves in the optical axis direction during diopter adjustment, and a third lens group having a positive or negative refractive power A finder optical system in which the distance between adjacent lens groups is changed during diopter adjustment,
The third lens group is composed of a 3a lens having positive refractive power and a 3b lens having a biconcave shape, which are arranged in order from the object side to the observation side.
The radius of curvature of the lens surface on the object side of the 3a lens is G3aRo, the radius of curvature of the lens surface on the observation side is G3aRe , and the diopter is −1 diopter, the first lens group, the second lens group, and the first lens group. When the combined focal length of the three lens groups is f, the focal length of the 3a lens is f3a, and the focal length of the 3b lens is f3b ,
-1.9 <(G3aRo + G3aRe) / (G3aRo-G3aRe) <-1.1
0.60 ≦ f3a / f <0.8
−2.1 <f3a / f3b <−1.5
It satisfies the following conditional expression.

  An imaging device using the above finder optical system also constitutes another aspect of the present invention.

  According to the present invention, a finder optical system capable of comfortable use with a large observation magnification while maintaining high optical performance, a sufficiently long eye relief, a sufficiently large eye relief diameter, and an imaging apparatus using the same Can be provided.

It is principal part sectional drawing when the finder optical system of this invention is applied to a single-lens reflex camera (imaging device). It is the optical path diagram which developed the optical path of the optical element from the mat surface of Numerical example 1 to an eye point as a finder optical system concerning an embodiment of the present invention. FIG. 5 is an aberration diagram of Numerical Example 1 as a finder optical system according to an embodiment of the present invention. It is the optical path figure which developed the optical path of the optical element from the mat | matte surface of Numerical Example 2 to an eye point as a finder optical system which concerns on embodiment of this invention. It is an aberration diagram of Numerical Example 2 as a finder optical system according to an embodiment of the present invention. It is the optical path figure which developed the optical path of the optical element from the mat | matte surface of Numerical Example 3 to an eye point as a finder optical system which concerns on embodiment of this invention. It is an aberration diagram of Numerical Example 3 as a finder optical system according to an embodiment of the present invention. It is the optical path figure which developed the optical path of the optical element from the mat surface of Numerical example 1 to an eye point as a finder optical system concerning the reference example 1 of the present invention. FIG. 6 is an aberration diagram of Numerical Example 1 as a finder optical system according to Reference Example 1 of the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Imaging device)
FIG. 1 is a cross-sectional view of a main part when a finder optical system according to an embodiment of the present invention is applied to a single-lens reflex camera. In FIG. 1, reference numeral 1 denotes a photographic lens as a photographic optical system, which is fixed to the camera body or detachably attached to the camera body. Reference numeral 2 denotes a quick return mirror (optical path bending mirror) which can be rotated around a rotation axis 2a. Reference numeral 3 denotes a focusing screen (focus plate), which is provided with a Fresnel lens on the surface on the quick return mirror 2 side and a mat surface 4 on the opposite surface, and a subject image (viewfinder) by the photographing lens 1 on the mat surface 4 (predetermined surface). Image, object image).

5 is a penta roof mirror as an image reversing member for forming erect (image inverting optical system), and the erect image of an object image formed on the matte surface 4. 6 represents an eyepiece lens system, and 7 represents the position of an eye point. The subject image formed on the mat surface 4 of the focusing screen 3 is made into an erect image by the penta roof mirror 5 and is observed at the eye point (observer's pupil position) 7 through the eyepiece lens system 6.

In addition, as an image corresponding to the subject image observed at the eye point 7, a subject image by the photographing lens 1 is formed on the imaging surface IP in a state where the quick return 2 is flipped up. On the imaging surface IP, a solid-state imaging device such as a CCD sensor or a CMOS sensor, or a photosensitive film is provided as imaging means for receiving an image.

(Finder optical system)
The finder optical system in the present embodiment includes the penta roof mirror 5 and the eyepiece lens system 6 in FIG. Eyepiece system 6, in order to observe the side, a first lens unit having a negative refractive power, a second lens unit having a positive refractive power and a third lens unit having a positive or negative refractive power. The first lens group is composed of a first lens 6a, the second lens group is composed of a second lens 6b, and the third lens group is disposed in order from the object side to the observation side and has a positive refractive power. 3 a lens 6c, are formed of a 3b-th lens 6 d having a negative refractive power.

The first lens 6a has a concave shape on both sides, and the second lens 6b has a convex shape on both sides. Also, the 3 a lens 6c is made the object side than the meniscus shape convex, the 3b-th lens 6d both sides is made from a concave shape. Diopter adjustment is performed by moving the second lens 6 b along the optical axis direction of the eyepiece lens 6 . In other words, in this embodiment, the distance between adjacent lens groups changes during diopter adjustment. In the optical path diagrams and aberration diagrams shown in FIG. 2 and subsequent figures, the viewfinder diopter is −1 diopter (standard diopter).

  In the optical path diagram, each reflecting surface of the penta roof mirror 5 is omitted, and an optical path from the mat surface 4 to the eye point 7 is shown. In the aberration diagrams, H is the height on the pupil plane, Y is the image height, ΔM is the meridional image plane, and ΔS is the sagittal image plane.

(Third lens shape of eyepiece system)
In the finder optical system according to the embodiment of the present invention, as the lens shape of the third a lens 6c of the eyepiece lens system, when the curvature radii of the object side surface and the observation side surface are G3 a Ro and G3 a Re, respectively, The following conditional expression (1) is satisfied.

-1.9 <(G3 a Ro + G3 a Re) / (G3 a Ro-G3 a Re) <- 1.1
(1)
Conditional expression (1) is for achieving a high observation magnification and maintaining high optical performance while having a long eye relief position and a large eye relief diameter. In a finder optical system having a long eye relief and a large diameter eye relief, spherical aberration and curvature of field are likely to occur. In order to correct this, it is desirable that the third a lens 6c has a meniscus shape with a convex surface facing the object side.

  Conditional expression (1) is a condition for ensuring high optical performance while maintaining a good balance at this time and realizing high observation magnification and comfortable observation conditions. If the lower limit of conditional expression (1) is exceeded, aberration correction is overcorrected, and if the upper limit is exceeded, correction of aberrations becomes difficult.

  More preferably, the numerical range of conditional expression (1) is set as follows.

−1.6 <(G3 a Ro + G3 a Re) / (G3 a Ro−G3 a Re) <− 1.1
(1a)
More preferably, the numerical range of conditional expression (1) is set as follows.

−1.4 <(G3 a Ro + G3 a Re) / (G3 a Ro−G3 a Re) <− 1.1
(1b)
According to these conditional expressions (1a) or (1b), further better aberration correction can be performed.

Further, the focal length of the third a lens 6c and f3 a, the first lens group when the diopter -1 diopter, the second lens group, the focal length of the synthesis of the third lens group is f More preferably, the following conditional expression (2) is satisfied.

0.60 ≦ f3a / f <0.8 (2)
Conditional expression (2) is for maintaining high optical performance while realizing high observation magnification. If the lower limit of conditional expression (2) is exceeded, the refractive power of the third-a lens 6c becomes too large, and various aberrations such as spherical aberration and curvature of field deteriorate. On the other hand, when the upper limit of conditional expression (2) is exceeded, the refractive power becomes weak, and the effect of increasing the magnification is reduced.

( 3b lens shape of eyepiece lens system)
In the finder optical system according to the embodiment of the present invention, it is desirable that the lens shape of the third b lens 6d of the eyepiece lens system is not a meniscus shape but a biconcave shape. This is because the 3b lens 6d arranged on the most observation side is preferably a negative lens having a strong power for ensuring curvature of field and long eye relief.

Further, the focal length of the 3 a lens 6c and f3 a, the focal length of the 3b lens 6d and f 3b, it is more preferable to satisfy the following conditional expression (3).

-2.1 <f3 a / f 3b < -1.5 ‥‥‥ (3)
Conditional expression (3) is for maintaining a sufficiently long eye relief while realizing a high observation magnification. When the lower limit of conditional expression (3) is exceeded, the effect of increasing the magnification by the third a lens 6c and the third b lens 6d is reduced. When the upper limit of conditional expression (3) is exceeded, the refractive power of the third b lens 6d with respect to the third a lens 6c becomes weak, and the effect of keeping the eye relief long is reduced.

Further, when the curvature radii of the object side surface and the observation side surface of the 3b lens 6d are respectively G 3b Ro and G 3b Re, it is more preferable that the following conditional expression (4) is satisfied.

0.6 <(G 3b Ro + G 3b Re) / (G 3b Ro−G 3b Re) <0.9
(4)
Conditional expression (4) is for maintaining a sufficiently long eye relief while realizing a high observation magnification. If the lower limit of conditional expression (4) is exceeded, the effects of correcting curvature of field and ensuring long eye relief will be weakened. When the upper limit of conditional expression (4) is exceeded, the power on the object plane side becomes weak and the power on the observation side becomes too strong, which is disadvantageous for aberration correction.

(Numerical example)
Hereinafter, as the finder optical system according to the embodiment of the present invention and the reference example , the numerical examples 1 to 3 and the reference example 1 are shown in FIG. 2, FIG. 4, FIG. 6, and FIG. FIG. 3, FIG. 5, FIG. 7, and FIG. 9 show aberration diagrams. In each numerical example and numerical example , the surface number indicates the order from the focusing screen 4 (surface number 1 corresponds to the mat surface 4 and surface number 2 is the radius of curvature of the virtual surface and is infinite). . r is the radius of curvature of each surface number, and d is the lens thickness and air spacing. n d and ν d are the refractive index and Abbe number of the material of each lens.

In each numerical example and numerical example , * represents an aspherical surface. The aspherical shape has an optical axis direction as an X axis, a direction perpendicular to the optical axis as a Y axis, a light traveling direction as positive, and R as a paraxial radius of curvature, and K, A4, A6, A8, and A10 as constants. It is defined as follows. Note that the display of “e-0X” means “10 ^−X ”.

Variable spacing as specifications of numerical example and numerical example illustrates the diopter and spacing change when the diopter adjustment by the second lens 6 b. Moreover, the approximate calculation result of the length of eye relief (shown as an eye point) is shown. Further, the image height of the finder image on the mat surface is shown as the maximum image height, and the pupil diameter at the eye point 7 is shown as the pupil diameter. Moreover, finder magnification at the time of realizing the finder optical system of each numerical example is shown as observation magnification. The viewfinder magnification is represented by an afocal angular magnification when a standard lens having a focal length of 50 mm is mounted as a photographing lens. Here, it is approximately represented by the ratio of the focal length of the taking lens and the focal length of the viewfinder optical system.

Table 1 shows the relationship between the conditional expressions (1), (2), (3), and (4) described above, numerical examples, and various numerical values in the numerical examples .

(Numerical example 1)
Surface data surface number rd nd ν d
1 ∞ 70.00
2 ∞ 0.00
3 -1000.000 1.00 1.58306 30.2
4 * 33.646 (variable)
5 * 24.504 4.54 1.53110 56.0
6 -33.391 (variable)
7 * 16.142 3.54 1.53110 56.0
8 101.127 3.55
9 -98.858 1.00 1.49171 57.4
10 * 11.376 19.89
11 (eye point)

Aspheric data 4th surface
K = 0.00000e + 000 A 4 = -1.09209e-005 A 6 = -3.83151e-008 A 8 = 3.06620e-010 A10 = -9.04082e-013
5th page
K = 0.00000e + 000 A 4 = -2.05180e-005 A 6 = -1.53176e-007 A 8 = 1.04471e-009 A10 = -3.01547e-012
7th page
K = 0.00000e + 000 A 4 = -1.32235e-005 A 6 = 2.22083e-007 A 8 = -1.91893e-009 A10 = 1.03031e-011
10th page
K = 0.00000e + 000 A 4 = -5.62846e-005 A 6 = 3.36526e-007 A 8 = -1.21407e-008 A10 = 9.27690e-011

Various data diopters -3.00 -1.00 +1.00
Focal length 62.22 59.69 57.39
Variable interval
d 4 0.50 1.92 3.37
d 6 3.37 1.95 0.50
Eye relief 19.9
Maximum image height 12.4
Pupil diameter 15
Observation magnification (-1 diopter) 0.87

(Numerical example 2)
Surface data surface number rd nd ν d
1 ∞ 70.00
2 ∞ 0.00
3 -1000.000 1.00 1.58306 30.2
4 * 30.576 (variable)
5 * 20.477 4.89 1.53110 56.0
6 -32.315 (variable)
7 * 16.812 3.36 1.53110 56.0
8 53.844 3.64
9 -63.288 1.00 1.49171 57.4
10 * 13.359 19.69
11 (eye point)

Aspheric data 4th surface
K = 0.00000e + 000 A 4 = -2.26836e-005 A 6 = 7.33389e-008 A 8 = -2.77080e-010 A10 = 2.25443e-013
5th page
K = 0.00000e + 000 A 4 = -6.00302e-005 A 6 = 1.60426e-007 A 8 = -7.72686e-010 A10 = 1.19057e-012
7th page
K = 0.00000e + 000 A 4 = 3.20505e-005 A 6 = 7.78836e-008 A 8 = -1.15445e-009 A10 = 1.71644e-011
10th page
K = 0.00000e + 000 A 4 = 2.88779e-005 A 6 = 2.89146e-009 A 8 = -3.36043e-009 A10 = 8.38562e-011

Various data diopters -3.00 -1.00 +1.00
Focal length 61.99 59.69 57.61
Variable interval
d 4 0.50 1.84 3.23
d 6 3.23 1.90 0.50
Eye relief 19.7
Maximum image height 12.4
Pupil diameter 15
Observation magnification (-1 diopter) 0.87

(Numerical Example 3)
Surface data surface number rd nd ν d
1 ∞ 70.00
2 ∞ 0.00
3 -1000.000 1.00 1.58306 30.2
4 * 31.603 (variable)
5 * 22.508 4.71 1.53110 56.0
6 -32.914 (variable)
7 * 16.373 3.48 1.53110 56.0
8 70.949 3.68
9 -65.635 1.00 1.49171 57.4
10 * 12.726 19.70
11 (eye point)

Aspheric data 4th surface
K = 0.00000e + 000 A 4 = -1.93000e-005 A 6 = 9.50400e-008 A 8 = -7.53971e-010 A10 = 2.15212e-012
5th page
K = 0.00000e + 000 A 4 = -4.05159e-005 A 6 = 9.80219e-008 A 8 = -7.60790e-010 A10 = 1.77666e-012
7th page
K = 0.00000e + 000 A 4 = 1.09027e-005 A 6 = 9.84207e-008 A 8 = -1.02674e-009 A10 = 1.30148e-011
10th page
K = 0.00000e + 000 A 4 = -2.67409e-006 A 6 = 8.64643e-008 A 8 = -4.76963e-009 A10 = 8.44778e-011

Various data diopters -3.00 -1.00 +1.00
Focal length 62.23 59.69 57.39
Variable interval
d 4 0.50 1.84 3.22
d 6 3.22 1.88 0.50
Eye relief 19.7
Maximum image height 12.4
Pupil diameter 15
Observation magnification (-1 diopter) 0.87

(Numerical example 1)
Surface data surface number rd nd ν d
1 ∞ 70.00
2 ∞ 0.00
3 -1000.000 1.00 1.58306 30.2
4 * 34.758 (variable)
5 * 25.513 4.40 1.53110 56.0
6 -35.234 (variable)
7 * 16.340 3.62 1.53110 56.0
8 197.257 3.56
9 -100.835 1.00 1.49171 57.4
10 * 11.077 20.20
11 (eye point)

Aspheric data 4th surface
K = 0.00000e + 000 A 4 = -8.63869e-006 A 6 = -5.77188e-008 A 8 = 4.27092e-010 A10 =
-1.09413e-012
5th page
K = 0.00000e + 000 A 4 = -1.14043e-005 A 6 = -2.29221e-007 A 8 = 1.51888e-009 A10 =
-4.05111e-012
7th page
K = 0.00000e + 000 A 4 = -2.44564e-005 A 6 = 2.65929e-007 A 8 = -2.11412e-009 A10 =
8.22949e-012
10th page
K = 0.00000e + 000 A 4 = -7.64643e-005 A 6 = 4.11103e-007 A 8 = -1.36794e-008 A10 =
7.84290e-011

Various data diopters -3.00 -1.00 +1.00
Focal length 62.33 59.69 57.31
Variable interval
d 4 0.50 1.95 3.42
d 6 3.42 1.97 0.50
Eye relief 20.2
Maximum image height 12.4
Pupil diameter 15
Observation magnification (-1 diopter) 0.87

(Modification)
As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to these embodiment, A various deformation | transformation and change are possible within the range of the summary. For example, a finder optical system that satisfies any one of conditional expressions (1), (1a), and (1b) and at least one of conditional expressions (2), (3), and (4) and a finder optical system that uses the same It is also possible to use a conventional imaging device.

In the above-described embodiment, the 3a lens is a meniscus lens having a convex surface on the object side and having a positive refractive power, but may be a lens having a positive refractive power in other shapes.

  In the embodiment described above, the penta roof mirror is used as the image inverting means, but a penta roof prism may be used.

1 .. Photography lens, 4 .. Focus plate (mat surface), 5 .. Penta-dah mirror (image reversal member), 6 a... First lens (negative), 6 b... Second lens (positive), 6 c. - the 3 a lens (positive), 6d ... 3b-th lens (negative), 7 .. eyepoint

Claims (4)

A finder optical system for observing an object image formed on a predetermined surface, which is arranged in order from the object side to the observation side, an image inverting member for forming an erect image, and a first lens having a negative refractive power And a second lens group having a positive refractive power that moves in the optical axis direction during diopter adjustment, and a third lens group having a positive or negative refractive power, and the distance between adjacent lens groups changes during diopter adjustment. A viewfinder optical system,
The third lens group is composed of a 3a lens having positive refractive power and a 3b lens having a biconcave shape, which are arranged in order from the object side to the observation side.
The radius of curvature of the lens surface on the object side of the 3a lens is G3aRo, the radius of curvature of the lens surface on the observation side is G3aRe , and the diopter is −1 diopter, the first lens group, the second lens group, and the first lens group. When the combined focal length of the three lens groups is f, the focal length of the 3a lens is f3a, and the focal length of the 3b lens is f3b ,
-1.9 <(G3aRo + G3aRe) / (G3aRo-G3aRe) <-1.1
0.60 ≦ f3a / f <0.8
−2.1 <f3a / f3b <−1.5
A finder optical system characterized by satisfying the following conditional expression:   The finder optical system according to claim 1, wherein the 3a lens is a meniscus lens having a convex surface facing the object side. When the radius of curvature of the lens surface on the object side of the 3b lens is G3bRo and the radius of curvature of the lens surface on the observation side is G3bRe,
0.6 <(G3bRo + G3bRe) / (G3bRo−G3bRe) <0.9
Finder optical system according to claim 1 or 2, characterized by satisfying the conditional expression. An imaging apparatus comprising: the finder optical system according to any one of claims 1 to 3 ; and an imaging unit that receives an image corresponding to a subject image observed by the finder optical system.