JP2021110827A - Observation device, and imaging apparatus having the same - Google Patents

Abstract

To provide an observation device capable of achieving high performance of finder optical system while providing a line-of-sight detection function, and an imaging apparatus having the same.SOLUTION: An observation device 100 includes: a finder optical system 50 that guides an image, which is to be displayed on an image display surface IP, to an eyeball EP of an observer; and an imaging unit 51 that captures the eyeball of the observer. The imaging unit picks up light branched by the first plane of the lens included in the finder optical system. The first plane is convex at the observer's side and transmits light from the image display surface and reflects the light from the eyeball of the observer and guides it to the imaging unit.SELECTED DRAWING: Figure 1

Description

The present invention relates to an observation device including a finder optical system for observing an image displayed on an image display element, and an imaging device having the same.

Conventionally, in order to observe an image displayed on an image display element such as a liquid crystal panel, an observation device including a finder optical system including a plurality of lenses is known. The finder optical system is required to have a sufficiently wide field of view, a long eye point, and satisfactorily corrected aberrations in order to improve visibility.

Further, conventionally, a finder optical system having a line-of-sight detection optical system that detects the direction of the photographer's line of sight for use in autofocus, automatic exposure setting, or the like is known. Patent Document 1 discloses a finder optical system that uses a prism to branch the optical path of the line-of-sight detection optical system. Further, Patent Document 2 discloses a finder optical system that uses a reflective optical system to branch the optical path of the line-of-sight detection optical system.

Japanese Unexamined Patent Publication No. 5-188430 Japanese Unexamined Patent Publication No. 2014-122941

However, in the finder optical systems of Patent Documents 1 and 2, it is necessary to increase the optical path length of the finder optical system, and the finder optical system has higher performance (correction of various aberrations, wider viewing angle, higher eye point). Is difficult.

An object of the present invention is to provide an observation device capable of improving the performance of a finder optical system while having a line-of-sight detection function, and an imaging device having the observation device.

The observation device as one aspect of the present invention includes a finder optical system that guides an image displayed on the image display surface to the observer's eyeball, and an image pickup unit that captures the observer's eyeball. The image pickup unit is a finder. The light branched by the first surface of the lens included in the optical system is imaged, and the first surface has a convex shape toward the observer side, and the light from the image display surface is transmitted and the observer's light is transmitted. It is characterized by reflecting the light from the eyeball and guiding it to the imaging unit.

According to the present invention, it is possible to provide an observation device capable of realizing high performance of a finder optical system while having a line-of-sight detection function, and an imaging device having the observation device.

It is the schematic of the observation apparatus of Example 1. FIG. It is the schematic of the observation apparatus of Example 2. It is the schematic of the observation apparatus of Example 3. FIG. FIG. 5 is a schematic view of a main part of an imaging device including the observation device according to any one of Examples 1 to 3.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In each figure, the same member is given the same reference number, and duplicate description is omitted.

1 to 3 are schematic views of the observation devices of Examples 1 to 3, respectively. FIG. 4 is a schematic view of a main part of an imaging device including the observation device according to any one of Examples 1 to 3.

The design values of the finder optical system of each embodiment are shown in Tables 1 to 3 below. In each embodiment, r represents the radius of curvature of each optical plane, and d represents the axial distance (distance on the optical axis) between the mth plane and the (m + 1) th plane. However, m is the number of the surface counted from the light incident side (the side of the image display surface). Further, nd and νd represent the refractive index and Abbe number of each optical member with respect to the d line, respectively.

Further, in each embodiment, the surface whose numerical value is described in the column of aspherical data has an aspherical shape defined by the following equation (1).

In equation (1), x is the amount of displacement from the surface apex in the optical axis direction, h is the height from the optical axis in the direction perpendicular to the optical axis, r is the paraxial curvature radius at the surface apex, and K is the conical constant. , A2, A4, A6, A8, A10 are paraxial coefficients.

The observation device 100 of this embodiment will be described with reference to FIG. The observation device 100 of this embodiment is a finder optical system 50 that guides an image displayed on an image display surface (object surface) IP of an image display element such as a liquid crystal display element or an organic EL to an observer's eyeball (eye point EP). , And an imaging unit 51 that images the observer's eyeball. That is, the observation device 100 of this embodiment has two optical paths. One is an optical path that guides light from the image display element to the eye point by the finder optical system 50. The other is an optical path that guides light from the eye point to the image sensor 21 described later of the image unit 51 by at least a part of the finder optical system 50 and the image pickup unit 51. The optical axis of the optical path that guides light from the image display element to the eye point is not bent. On the other hand, the optical axis of the optical path that guides light from the eye point to the image sensor 21 is bent. The effect of the present invention can also be obtained by bending the optical axis of the optical path that guides light from the image display element to the eye point.

The finder optical system 50 is arranged in order from the image display surface IP side to the observer side, with the first lens 1 having a positive refractive power, the second lens 2 having a negative refractive power, and the third lens having a positive refractive power. It has a lens 3, a fourth lens 4 having a positive refractive power, and a protective member 10. The diopter adjustment of the finder optical system 50 can be performed by integrally moving the first to fourth lenses 1-4 in the optical axis direction. The image pickup unit 51 includes an image pickup optical system 20 and an image pickup sensor 21. The image pickup optical system 20 includes at least one lens, and guides the reflected light from the first surface, which will be described later, to the image pickup sensor 21. The image sensor 21 images the observer's eyeball.

In the observation device 100 of this embodiment, in order to image the eyeball of the observer, the light reflected by the observer side surface (first surface) of the third lens 3 included in the finder optical system 50 is used. .. The surface of the third lens 3 on the observer side has a convex shape on the observer side, transmits light from the image display surface IP, and reflects light from the observer's eyeball to the image pickup unit 51. It is an optical lens surface to guide. The observer's eyeball imaged by the imaging unit 51 is mainly used to detect the direction of the observer's line of sight.

When the finder optical system and the imaging unit that captures the observer's eyeball are used in combination, a prism or a mirror is generally arranged in the optical path of the finder optical system to branch the optical path of the imaging optical system. However, arranging prisms and mirrors to increase the optical path length is a factor that hinders the high performance of the finder optical system (correction of various aberrations, wide viewing angle, high eye point). Further, when the finder optical system is used as an electronic viewfinder for magnifying and observing an image displayed on a relatively small image display element having a diagonal length of 20 mm or less, the magnification of the finder optical system becomes large. , The focal length of the viewfinder optical system becomes shorter. Therefore, even when the electronic viewfinder is used, the optical path length of the finder optical system increases, and it is difficult to improve the performance of the finder optical system.

In the observation device 100 of the present embodiment, the optical path of the imaging optical system 20 is set in the optical path of the finder optical system 50 by using the surface of the third lens 3 that acts as an optical lens surface in the optical path of the finder optical system 50. Branch from the optical path. As a result, the increase in the optical path length of the finder optical system 50 is suppressed.

If the optical path of the imaging optical system 20 is branched from the optical path of the finder optical system 50 using a concave surface on the observer side, the optical paths of the finder optical system 50 and the imaging optical system 20 physically interfere with each other. It becomes difficult to configure the observation device 100. In this embodiment, the optical path of the imaging optical system 20 can be appropriately branched from the optical path of the finder optical system 50 by using the surface of the third lens 3 on the observer side that is convex toward the observer. can. In addition, when the eyeball of the observer is imaged, a wide range can be imaged.

Further, in the observation device 100 of this embodiment, it is desirable that the surface of the third lens 3 acting as the reflection surface on the observer side satisfies the following conditional expression (2).

10 ° <θ <60 ° (2)
Here, θ is the angle of the tangent line perpendicular to the optical axis at a position 7 mm away from the optical axis of the finder optical system 50 in the direction perpendicular to the optical axis on the surface of the third lens 3 on the observer side. be.

The conditional expression (2) is a conditional expression for appropriately branching the optical path of the imaging optical system 20 from the optical path of the finder optical system 50. The position separated from the optical axis of the finder optical system 50 in the direction perpendicular to the optical axis by 7 mm is a position where the light from the observer's eyeball is reflected on the surface of the third lens 3 on the observer side. Since the size of the observer's eyeball is substantially constant regardless of the type of the finder optical system 50, the conditional expression (2) can be applied to any finder optical system. If it is less than the lower limit of the conditional expression (2), it becomes difficult to branch the optical path while avoiding interference between the finder optical system 50 and the imaging optical system 20, which is not preferable. On the other hand, if the upper limit value of the conditional expression (2) is exceeded, the curvature of the finder optical system 50 as a lens becomes too strong, and it becomes difficult to improve the performance of the finder optical system 50, which is not preferable.

It is desirable that the numerical range of the conditional expression (2) be the numerical range of the following conditional expression (2a).

20 ° <θ <60 ° (2a)
Further, it is more desirable that the numerical range of the conditional expression (2) is the numerical range of the following conditional expression (1b).

20 ° <θ <50 ° (2b)
Further, it is desirable that the observation device 100 of this embodiment satisfies the following conditional expression (3) when the diopter of the finder optical system 50 is -1 dpt.

0.2 <L / f <0.5 (3)
Here, L is the surface on the side of the image display surface IP of the lens closest to the image display surface IP of the finder optical system 50 from the image display surface IP (in this embodiment, the side of the image display surface IP of the first lens 1). The optical path length to the surface) and f are the focal lengths of the finder optical system 50.

The conditional expression (3) is a conditional expression for realizing high performance of the finder optical system 50, particularly wide viewing angle and high eye point. If it is less than the lower limit of the conditional expression (3), the power of the finder optical system 50 becomes too weak, and it becomes difficult to realize high performance of the finder optical system 50, which is not preferable. On the other hand, if the upper limit value of the conditional expression (3) is exceeded, the optical path length L becomes too long, and it becomes difficult to improve the performance of the finder optical system 50, which is not preferable.

It is desirable that the numerical range of the conditional expression (3) be the numerical range of the following conditional expression (3a).

0.25 <L / f <0.50 (3a)
Further, it is more desirable that the numerical range of the conditional expression (3) is set to the numerical range of the following conditional expression (3b).

0.3 <L / f <0.5 (3b)
Further, it is desirable that the observation device 100 of this embodiment satisfies the following conditional expression (4) when the maximum image height (diagonal length) of the image display surface IP is H.

0.5 <L / H <1.7 (4)
The conditional expression (4) is a conditional expression for realizing high performance of the finder optical system 50, particularly wide viewing angle and high eye point. If it is less than the lower limit of the conditional expression (4), the optical path length L becomes too short with respect to the maximum image height H of the image display surface IP, and it becomes difficult to improve the performance of the finder optical system 50, which is not preferable. On the other hand, if the upper limit of the conditional expression (4) is exceeded, the optical path length L becomes too long with respect to the maximum image height H of the image display surface IP, and it becomes difficult to improve the performance of the finder optical system 50, which is not preferable.

It is desirable that the numerical range of the conditional expression (4) be the numerical range of the following conditional expression (4a).

0.7 <L / H <1.7 (4a)
Further, it is more desirable that the numerical range of the conditional expression (4) is set to the numerical range of the following conditional expression (4b).

1.0 <L / H <1.7 (4b)
When illuminating the eyeball to image the observer's eyeball, illuminating the eyeball with visible region light hinders the observer from visually recognizing the finder optical system 50. Therefore, illuminate the eyeball with near-infrared region light. Is desirable. Therefore, in the observation device 100 of the present embodiment, it is desirable that the reflectance of the surface of the third lens 3 acting as the reflecting surface on the observer side with respect to the near-infrared region light is higher than the reflectance with respect to the visible region light. As a method of increasing the reflectance for near-infrared region light, for example, a dichroic that selectively increases the reflectance of a specific wavelength by applying a coating with a dielectric film to the surface of the surface of the third lens 3 on the observer side. There is a way to have the function of a mirror.

Further, the observer's eyeball may be imaged with visible region light using external light or light emission of the image display surface IP as a light source without illuminating the observer's eyeball. In this case, the lighting device becomes unnecessary and the cost can be reduced, but the lighting intensity changes greatly depending on the external environment, so that the imaging result may vary.

All the surfaces of the first to fourth lenses 1-4 are usually in the shape to be rotated, and there is a deviation between the center of the optical axis of the imaging optical system 20 and the center of the surface of the third lens 3 on the observer side. Occurs. Therefore, in the observation device 100 of this embodiment, it is desirable that at least one surface of the lens included in the imaging optical system 20 has a rotationally asymmetric shape. Thereby, the above-mentioned deviation can be corrected.

Further, in the observation device 100 of this embodiment, it is desirable that at least one surface of the lens included in the imaging optical system 20 is a free curved surface. As a result, the deviation between the center of the surface of the third lens 3 on the observer side and the center of the optical axis of the imaging optical system 20 can be completely corrected. However, a toric lens or the like may be used after taking into consideration the manufacturing difficulty and the required resolution of the image sensor 21.

Further, in the observation device 100 of this embodiment, it is desirable that the finder optical system 50 satisfies the following conditional expression (5).

0.20 <H / f <0.50 (5)
Conditional expression (5) defines the relationship between the maximum image height H of the image display surface IP and the focal length f of the finder optical system 50, and widens the viewing angle, spherical aberration, curvature of field, and astigmatism. It is a conditional expression for realizing the correction of various aberrations such as. If the upper limit of the conditional expression (5) is exceeded, the magnification of the finder optical system 50 becomes excessively large, and it becomes difficult to correct various aberrations such as spherical aberration, curvature of field, and astigmatism, which is not preferable. .. On the other hand, if it is less than the lower limit of the conditional expression (5), it becomes difficult to realize a wide magnification of the finder optical system 50, which is not preferable.

It is desirable that the numerical range of the conditional expression (5) be the numerical range of the following conditional expression (5a).

0.20 <H / f <0.45 (5a)
Further, it is more desirable that the numerical range of the conditional expression (4) is set to the numerical range of the following conditional expression (4b).

0.20 <H / f <0.40 (5b)
Further, it is desirable that the observation device 100 of this embodiment satisfies the following conditional expression (6).

0.5 <S / f <2.0 (6)
Here, S is the distance (total optical length) from the image display surface IP to the apex of the surface of the lens closest to the observer on the observer side when the diopter of the finder optical system 50 is -1 dpt. In this embodiment, the surface of the lens closest to the observer on the observer side is the surface of the fourth lens 4 on the observer side.

The conditional expression (6) defines the relationship between the total optical length S and the focal length f of the finder optical system 50. If it is less than the lower limit of the conditional expression (6), the total optical length S becomes too short with respect to the focal length f of the finder optical system 50, and each lens cannot select the required power arrangement, which is not preferable. On the other hand, if the upper limit value of the conditional expression (6) is exceeded, the total optical length S becomes too long, and it becomes difficult to improve the performance of the finder optical system 50, which is not preferable.

It is desirable that the numerical range of the conditional expression (6) be the numerical range of the following conditional expression (6a).

0.5 <S / f <1.6 (6a)
Further, it is more desirable that the numerical range of the conditional expression (6) is the numerical range of the following conditional expression (6b).

1.0 <S / f <1.6 (6b)

The observation device 100 of this embodiment will be described with reference to FIG. The configuration of the observation device 100 of this embodiment is basically the same as the configuration of the observation device 100 of the first embodiment. In this embodiment, a portion different from the configuration of the observation device 100 of the first embodiment will be described, and detailed description of the same portion will be omitted.

The observation device 100 of this embodiment uses the surface of the second lens 2 on the image display surface IP side as a surface that branches the optical path of the imaging optical system 20 from the optical path of the finder optical system 50 with the observation device 100 of the first embodiment. It differs in that it is used and that a plurality of image pickup units 51 are arranged.

In the observation device 100 of the present embodiment, in order to image the eyeball of the observer, the light reflected by the surface (first surface) on the image display surface IP side of the second lens 2 included in the finder optical system 50 is emitted. use. The surface of the second lens 2 on the image display surface IP side has a convex shape toward the observer side, transmits light from the image display surface IP, and reflects light from the observer's eyeball for imaging optics. Lead to system 20. The observer's eyeball imaged by the imaging unit 51 is mainly used to detect the direction of the observer's line of sight.

According to the configuration of this embodiment, by devising the design of the finder optical system 50 and the arrangement of the imaging optical system 20, the total reflection condition is set on the surface of the second lens 2 acting as the reflection surface on the image display surface IP side. The observer's eyeball can be imaged in a state where the above conditions are satisfied. However, in such a case, the total reflection condition may not be satisfied depending on the position of the observer's eyeball, and it is assumed that the exposure of the imaged result of the observer's eyeball varies greatly. In this embodiment, by using a plurality of imaging units 51 having different optical paths, it is possible to absorb variations in exposure of imaging results.

In this embodiment, two imaging units 51 are arranged, but more imaging units 51 may be arranged.

The observation device 100 of this embodiment will be described with reference to FIG. The configuration of the observation device 100 of this embodiment is basically the same as the configuration of the observation device 100 of the first embodiment. In this embodiment, a portion different from the configuration of the observation device 100 of the first embodiment will be described, and detailed description of the same portion will be omitted.

The observation device 100 of this embodiment is different from the observation device 100 of the first embodiment in that the configuration of the finder optical system 50 is three.

The finder optical system 50 includes a first lens 1 having a positive refractive power, a second lens 2 having a negative refractive power, and a third lens having a positive refractive power arranged in order from the image display element IP side to the observer side. 3 and a protective member 10. By appropriately arranging the third lens 3 that acts as a reflecting surface, it is possible to obtain a configuration capable of improving the performance of the finder optical system while having a line-of-sight detection function. Even when the finder optical system 50 is composed of the first lens 1 having a positive refractive power, the second lens 2 having a negative refractive power, and the third lens 3 having a positive refractive power, it will be described in the second embodiment. As described above, the surface of the second lens 2 on the image display element surface side may be used as the reflecting surface.

An imaging device such as a digital camera or a video camera including the observation device 100 according to any one of the first to third embodiments will be described with reference to FIG.

The object image formed by the photographing optical system 101 is converted into an electric signal by the image pickup element 102, which is a photoelectric conversion element. As the image sensor 102, a CCD sensor, a CMOS sensor, or the like is used.

The output signal from the image pickup device 102 is processed by the image processing circuit 103 to form an image. The formed image is recorded on a recording medium 104 such as a semiconductor memory, a magnetic tape, or an optical disk. Further, the image formed in the image processing circuit 103 is displayed in the observation device unit 105, which is the observation device 100 in any of the embodiments.

The observation device unit 105 includes an image display element 1051, a finder optical system 1052, an illumination system 1053, an image pickup optical system 1054, and an image pickup sensor 1055. The image display element 1051 is composed of a liquid crystal display element, an organic EL, or the like. The illumination system 1053 is composed of LEDs and the like, and illuminates the observer's eyeball 106. It is desirable to use near-infrared region light as the illumination light of the illumination system 1053 so that the observer does not feel uncomfortable. As the image pickup sensor 1055, a CCD sensor, a CMOS sensor, or the like is used.

The imaging unit that images the observer's eyeball is composed of an imaging optical system 1054 and an imaging sensor 1055. The image pickup unit may be placed at any position outside the optical path of the finder optical system 1052, but if it can be placed under the image pickup device while avoiding interference with other parts, the height of the image pickup device is high. It is preferable because it can prevent the increase in the optics.

By applying any of the observation devices 100 of each embodiment to the image pickup device in this way, it is possible to realize an image pickup device having a high-performance finder optical system while having a line-of-sight detection function.

[Table 1] Example 1
Unit mm
(Overall specifications)
Focal length f 18.707
Maximum image height of object surface H 6.45

(Surface data)
Surface number rd nd νd
1 (object surface) (variable) ---
2 293.271 4.22 1.7680 49.2
3 -10.650 2.47 ---
4 -6.287 2.20 1.6348 23.9
5 -35.477 0.35 ---
6 667.096 6.00 1.5350 55.7
7 -13.698 0.30 ---
8-83.497 3.60 1.5350 55.7
9 -18.473 (variable) ---
10 ∞ 0.80 1.4917 57.4
11 ∞ 23.00 ---
12 ∞ ----

(Aspherical data)

(Variable interval)
Diopter [dpt] -4 -1 +2
d1 6.64 7.50 8.54
d9 2.89 2.04 1.00

[Table 2] Example 2
Unit mm
(Overall specifications)
Focal length f 18.707
Maximum image height of object surface H 6.45

(Surface data)
Surface number rd nd νd
1 (Image display surface) (Variable) ---
2 293.271 4.22 1.7680 49.2
3 -10.650 2.47 ---
4 -6.287 2.20 1.6348 23.9
5 -35.477 0.35 ---
6 667.096 6.00 1.5350 55.7
7 -13.698 0.30 ---
8-83.497 3.60 1.5350 55.7
9 -18.473 (variable) ---
10 ∞ 0.80 1.4917 57.4
11 ∞ 23.00 ---
12 ∞ ----

(Aspherical data)

(Variable interval)
Diopter [dpt] -4 -1 +2
d1 6.64 7.50 8.54
d9 2.89 2.04 1.00

[Table 3] Example 3
Unit mm
(Overall specifications)
Focal length f 20.665
Maximum image height of object surface H 5.1

(Surface data)
Surface number rd nd νd
1 (Image display surface) (Variable) ---
2 40.000 3.24 1.5350 55.7
3 -11.486 2.09 ----
4 -6.800 1.65 1.6348 23.9
5 -100.000 3.38 ---
6 35.000 4.30 1.5350 55.7
7 -10.000 (variable) ---
8 ∞ 0.80 1.4917 57.4
9 ∞ 18.00 ---
10 ∞ ----

(Aspherical data)

(Variable interval)
Diopter [dpt] -3.5 -1 +1
d1 7.31 8.35 9.25
d9 3.28 2.24 1.34

The calculation results of the conditional expressions (2) to (6) in each embodiment are shown in Table (4).
[Table 4] Conditional expression

Although the preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and various combinations, modifications, and modifications can be made within the scope of the gist thereof.

EP eye point (eyeball)
IP image display surface 50 Finder optical system 51 Imaging unit 100 Observation device

Claims (16)

A finder optical system that guides the image displayed on the image display surface to the observer's eyeball,
It has an imaging unit that captures the eyeball of the observer.
The image pickup unit captures light branched by the first surface of the lens included in the viewfinder optical system.
The first surface has a convex shape toward the observer, and is characterized in that the light from the image display surface is transmitted and the light from the observer's eyeball is reflected and guided to the image pickup unit. Observation device. When the angle of the tangent line on the first surface at a position 7 mm away from the optical axis of the finder optical system in the direction perpendicular to the optical axis with respect to the direction perpendicular to the optical axis is θ.
10 ° <θ <60 °
The observation device according to claim 1, wherein the observation device satisfies the conditional expression. When the diopter of the finder optical system is -1 dpt, the optical path length from the image display surface to the surface of the finder optical system closest to the image display surface on the side of the image display surface is L, and the finder. When the focal length of the optical system is f,
0.2 <L / f <0.5
The observation device according to claim 1 or 2, wherein the conditional expression is satisfied. When the diopter of the finder optical system is -1 dpt, the optical path length from the image display surface to the surface of the finder optical system closest to the image display surface on the side of the image display surface is L, and the image. When the maximum image height of the display surface is H,
0.5 <L / H <1.7
The observation device according to any one of claims 1 to 3, wherein the observation device satisfies the conditional expression. The observation device according to any one of claims 1 to 4, wherein the reflectance of the first surface with respect to near-infrared region light is higher than the reflectance of the visible region light of the first surface. .. The imaging unit includes an imaging sensor for imaging the observer's eyeball, and an imaging optical system that guides the reflected light from the first surface to the imaging sensor.
The observation device according to any one of claims 1 to 5, wherein at least one surface of the lens included in the imaging optical system has a rotationally asymmetrical shape. The observation device according to claim 6, wherein at least one surface of the lens included in the imaging optical system is a free curved surface. The observation device according to claim 6, wherein the imaging optical system includes a toric lens. When the maximum image height of the image display surface is H and the focal length of the finder optical system is f,
0.20 <H / f <0.50
The observation device according to any one of claims 1 to 8, wherein the observation device satisfies the conditional expression. When the diopter of the finder optical system is -1 dpt, the distance from the image display surface to the apex of the surface of the lens closest to the observer on the side of the observer is S, and the focal length of the finder optical system is S. When f
0.5 <S / f <2.0
The observation device according to any one of claims 1 to 9, wherein the observation device satisfies the conditional expression. The observation device according to any one of claims 1 to 10, wherein in the finder optical system, the optical axis of the optical path that guides light from the image display surface to the eyeball of the observer is not bent. The finder optical system is a first lens having a positive refractive power, a second lens having a negative refractive power, and a third lens having a positive refractive power, which are arranged in order from the side of the image display surface to the side of the observer. The observation device according to any one of claims 1 to 11, further comprising a fourth lens having a positive refractive power. The finder optical system is a first lens having a positive refractive power, a second lens having a negative refractive power, and a third lens having a positive refractive power, which are arranged in order from the side of the image display surface to the side of the observer. The observation device according to any one of claims 1 to 11, wherein the observation device comprises. The observation device according to claim 12 or 13, wherein the first surface is a surface of the third lens on the side of the observer. The observation device according to claim 12, wherein the first surface is a surface of the second lens on the side of the image display surface. An image pickup apparatus according to any one of claims 1 to 15, which is used for observing an image output from an image pickup device.

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