JP7218472B2 - Observation device and imaging device having the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to an observation device and an imaging device having the same, and is suitable for observing an image displayed on an image display element in, for example, an electronic viewfinder used in a video camera, still camera, or broadcasting camera. .

2. Description of the Related Art Conventionally, an observation device using a finder optical system with a plurality of lenses is known for observing an image displayed on an image display device such as a liquid crystal panel. In order to improve visibility, these viewfinder optical systems have a sufficiently large field of view (high magnification), long eye relief (the distance from the lens surface on the observation side to the observation surface (eyepoint)), and excellent correction of various aberrations. It is required that

In particular, with the trend toward higher pixel counts in digital cameras, there is a demand for a high-magnification finder optical system in order to improve visibility.

As a high-magnification finder optical system, from the image display surface side (observation object side) to the eye point side (observer side), there is a positive refractive power lens, a negative refractive power lens, a positive refractive power lens, and a positive refractive power lens. A structure having three lenses is known (Patent Documents 1 to 3).

Patent Document 1 discloses an eyepiece optical system in which coma and distortion are well corrected. In Patent Document 1, it is composed of a first lens with positive refractive power, a second lens with negative refractive power with a concave surface facing the image display surface side, and a third lens with positive refractive power with a convex surface facing the eye point side. , the curvature of the lens surface of the third lens and the focal length of the entire eyepiece optical system are appropriately set.

Further, Japanese Patent Application Laid-Open No. 2002-200001 discloses an eyepiece optical system that has a large viewing angle and satisfactorily corrects various aberrations. Patent Document 2 has a first lens with a positive refractive power, a second lens with a negative refractive power, and a third lens with a biconvex shape with a positive refractive power. Set the distance properly.

Patent Document 3 discloses an eyepiece optical system that is compact, has a sufficiently wide viewing angle, and has high optical performance that can cope with an increase in the number of pixels. Patent Document 3 discloses that the optical system is composed of a positive refractive power first lens, a negative refractive power second lens, and a biconvex positive refractive power third lens, and that each lens is made of a high refractive power material. are doing.

JP 2014-074815 A JP 2014-228583 A JP 2015-135471 A

In order to ensure a wide viewing angle and a long eye relief in the viewfinder optical system used in observation equipment, it is important to appropriately set the lens configuration of the viewfinder optical system, the refractive power of each lens, and the lens shape. It's coming. In addition, when using an image display element having a small image display surface, it is important to appropriately set the ratio of the refractive power of the finder optical system to the size of the image display surface.

For example, it is difficult to obtain a wide viewing angle unless the refractive power of each lens is appropriately set. Also, if the radius of curvature of the lens surface of each lens is not appropriate, it will be difficult to increase the eye relief.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an observation apparatus that enables observation of an image on an image display surface at a wide viewing angle, satisfactorily corrects various aberrations, secures high optical performance, and secures a long eye point.

An observation apparatus according to the present invention is an observation apparatus having an image display element for displaying an image, and a finder optical system for observing an image displayed on the image display surface of the image display element, wherein the finder optical system comprises the image display device. The observation lens comprises a first lens with positive refractive power, a second lens with negative refractive power, a third lens with positive refractive power, and a fourth lens with positive refractive power, which are arranged in order from the surface to the observation side. The device has a cover glass closer to the image display surface than the first lens, and the optical axis between the cover glass and the image display surface is closer than the air gap on the optical axis between the cover glass and the first lens. is large, the lens closest to the observation side of the finder optical system is stationary during diopter adjustment, the focal length of the second lens is f2, the focal length of the finder optical system is f, The radius of curvature of the lens surface of the second lens on the image display surface side is R21, the radius of curvature of the lens surface of the second lens on the viewing side is R22, half the diagonal length of the image display surface is H, and the first lens R12 is the radius of curvature of the lens surface on the observation side , f1 is the focal length of the first lens, f3 is the focal length of the third lens, and R31 is the radius of curvature of the lens surface of the third lens on the screen display side. and when,
-0.70<f2/f<-0.20
0.7<(R22+R21)/(R22-R21) ≦ 1. 361
0.31<H/f<0.50
-8.5<(R21+R12)/(R21-R12)<-2.0
0.619≦f3/f1<3.10
-0.482≤(R31-R22)/(R31+R22)≤0.223
It is characterized by satisfying the following conditional expression:

According to the present invention, it is possible to obtain an observation apparatus that can observe an image on an image display surface at a wide viewing angle, satisfactorily correct various aberrations, ensure high optical performance, and ensure a long eye point.

FIG. 2 is a cross-sectional view of a finder optical system according to the observation apparatus of Example 1; FIG. 2 is an aberration diagram of a finder optical system according to the observation apparatus of Example 1; Sectional view of the finder optical system according to the observation apparatus of Example 2 Aberration diagram of the finder optical system according to the observation apparatus of Example 2 Sectional view of the finder optical system according to the observation apparatus of Example 3 Aberration diagram of the finder optical system according to the observation apparatus of Example 3 Sectional view of the finder optical system according to the observation apparatus of Example 4 Aberration diagram of the finder optical system according to the observation apparatus of Example 4 Sectional view of the finder optical system according to the observation apparatus of Example 5 Aberration diagram of the finder optical system according to the observation apparatus of Example 5 Sectional view of the finder optical system according to the observation apparatus of Example 6 Aberration diagram of the finder optical system according to the observation apparatus of Example 6 Sectional view of the finder optical system according to the observation apparatus of Example 7 Aberration diagram of the finder optical system according to the observation apparatus of Example 7 FIG. 1 is a schematic diagram of an essential part of an imaging device of the present invention;

An observation device having a finder optical system according to an embodiment will be described below. The observation device of the present invention has an image display element for displaying an image and a finder optical system for observing the image displayed on the image display surface of the image display element.

The finder optical system according to each embodiment observes an image displayed on the image display surface. The finder optical system has a first lens with positive refractive power, a second lens with negative refractive power, and a third lens with positive refractive power, which are arranged in order from the image display surface to the observation side. You may have the 4th lens of positive or negative refractive power on the observation side of the 3rd lens.

FIG. 1 is a cross-sectional view of the lens of the observation device of Example 1. FIG. FIG. 2 is an aberration diagram when the diopter of the finder optical system according to Example 1 of the present invention is -1.0 diopter (standard diopter).

FIG. 3 is a sectional view of the lens of the observation device of Example 2. FIG. FIG. 4 is an aberration diagram when the diopter of the finder optical system according to Example 2 is -1.0 diopter.

FIG. 5 is a cross-sectional view of the lens of the observation device of Example 3. FIG. FIG. 6 is an aberration diagram when the diopter of the finder optical system according to Example 3 is -1.0 diopter.

FIG. 7 is a sectional view of the lens of the observation device of Example 4. FIG. FIG. 8 is an aberration diagram when the diopter of the finder optical system according to Example 4 is -1.0 diopter.

FIG. 9 is a sectional view of the lens of the observation device of Example 5. FIG. FIG. 10 is an aberration diagram of the finder optical system according to Example 5 when the diopter is -1.0 diopter.

FIG. 11 is a sectional view of the lens of the observation device of Example 6. FIG. FIG. 12 is an aberration diagram of the finder optical system according to Example 6 when the diopter is -1.0 diopter.

FIG. 13 is a cross-sectional view of the lens of the observation device of Example 7. FIG. FIG. 14 is an aberration diagram of the finder optical system according to Example 7 when the diopter is -1.0 diopter.

FIG. 15 is a schematic diagram of a main part of an imaging apparatus having an observation device of the present invention.

The finder optical system of each embodiment is used in an observation device such as an electronic viewfinder of an imaging device such as a digital camera or a video camera. In the sectional view of the lens, the left side is the image display surface side, and the right side is the observation side (exit pupil side). In the lens sectional view, L0 is a finder optical system. Li is the i-th lens. IP is an image display surface of an image display element made of liquid crystal, organic EL, or the like. EP is an observation plane (eyepoint) (exit pupil) for observation. CG1 is a cover glass (protective member). In FIGS. 3 and 13, C1 is the reference position for calculating the viewing plane of the finder optical system L0.

In the spherical aberration diagrams among the aberration diagrams, the solid line d indicates the d-line (wavelength 587.6 nm), and the two-dot chain line F indicates the F-line (wavelength 486.1 nm). In the astigmatism diagrams, ΔS (solid line) indicates the sagittal image plane for the d-line, and ΔM (broken line) indicates the meridional image plane for the d-line. Distortion is shown for the d-line. Lateral chromatic aberration is shown for the F-line. H is half the diagonal length (maximum image height) of the image display surface.

In order to magnify and observe a compact image display surface (display panel) with a diagonal length of 20 mm or less at a viewing angle of 30 degrees or more, the finder optical system must have a strong positive refractive power (power )is necessary. For that purpose, each lens must have a strong positive refractive power or a strong negative refractive power.

In this case, more spherical aberration, curvature of field, astigmatism, and chromatic aberration are produced than in the finder optical system, making it difficult to correct these aberrations. At this time, residual aberrations such as spherical aberration, field curvature, astigmatism, and chromatic aberration deteriorate the optical performance when observing the image display surface. In order to improve various aberrations at this time, the finder optical system L0 according to each embodiment has the following configuration. A first lens L1 with positive refractive power, a second lens L2 with negative refractive power, and a second lens L2 with positive refractive power, which are arranged in order from the image display plane (object plane) IP to the observation plane (eye point) EP side. It has three lenses L3.

In each embodiment, preferably, a fourth lens having a positive refractive power may be provided on the viewing surface side of the third lens.

The finder optical system L0 in the observation apparatus of each embodiment includes a first lens with positive refractive power, a second lens with negative refractive power, and a It has a third lens. Let f2 be the focal length of the second lens L2, and f be the focal length of the finder optical system L0. Let R21 be the curvature radius of the lens surface of the second lens L2 on the image display surface IP side, R22 be the curvature radius of the observation EP side lens surface of the second lens L2, and H be half the diagonal length of the image display surface IP. At this time,
-0.70<f2/f<-0.20 (1)
0.7<(R22+R21)/(R22-R21)<1.4 (2)
0.31<H/f<0.50 (3)
satisfies the following conditional expression.

Next, the technical meaning of each of the above conditional expressions will be explained.

Conditional expression (1) defines the focal length of the second lens L2 and the finder optical system L0 as a whole. In the viewfinder optical system L0, in order to satisfactorily correct longitudinal chromatic aberration, the negative lens must have a certain or more strong negative power (refractive power). If the upper limit of conditional expression (1) is exceeded, it becomes difficult to correct axial chromatic aberration, which is not preferable. On the other hand, if the power is decreased below the lower limit, it becomes difficult to correct various aberrations in the finder optical system L0, and it becomes difficult to obtain good optical characteristics.

Conditional expression (2) defines the lens shape of the second lens L2. If the upper limit of conditional expression (2) is exceeded, the difference in the radius of curvature between the image display surface IP side and the observation surface EP side of the second lens L2 becomes too small, resulting in insufficient correction of chromatic aberration. . On the other hand, when the lower limit is not reached, the radius of curvature of the lens surface on the image display surface IP side of the second lens L2 becomes too small, which makes it difficult to correct various aberrations, which is not preferable.

Conditional expression (3) indicates a condition necessary to obtain a wide viewing angle using a small image display device. If the upper limit or the lower limit of conditional expression (3) is exceeded, it becomes difficult to obtain a large viewing angle with a small image display element, which is not preferable.

In each embodiment, it is preferable to satisfy one or more of the following conditional expressions.

Let R12 be the radius of curvature of the observation-side lens surface of the first lens L1. Let f1 be the focal length of the first lens L1. Let f3 be the focal length of the third lens L3. Let R31 be the radius of curvature of the lens surface of the third lens L3 on the screen display surface side. At least one surface of the second lens L2 has an aspherical shape. Let nd be the refractive index of the material of the second lens L2 at the d-line, and νd be the Abbe number of the material of the second lens L2 with respect to the d-line. Let dL be the length on the optical axis at diopter -1 diopter from the lens surface closest to the image display surface side of the finder optical system L0 to the lens surface closest to the observation surface EP side.

At this time, it is preferable to satisfy one or more of the following conditional expressions.
-8.5<(R21+R12)/(R21-R12)<-2.0 (4)
0.30<f1/f<1.00 (5)
0.50<f3/f1<3.10 (6)
-3.0<(R31-R22)/(R31+R22)<10.0 (7)
1.58<nd<1.95 (8)
15<νd<32 (9)
0.90<dL/f<1.65 (10)

Next, the technical meaning of each of the above conditional expressions will be explained.

Conditional expression (4) defines the shape of the air lens formed between the first lens L1 and the second lens L2. In order to satisfactorily correct the chromatic aberration of magnification, it is necessary to make the light ray incident on the lens surface of the second lens L2 on the image display surface IP side at a strong angle. preferably has a strong power above a certain level. If the upper limit of conditional expression (4) is exceeded, the power of the lens surface on the viewing plane EP side of the first lens L1 will be insufficient, making it difficult to correct lateral chromatic aberration. If the lower limit of conditional expression (4) is not reached, the power of the lens surface on the viewing plane EP side of the first lens L1 becomes too strong, making it difficult to correct various aberrations.

Conditional expression (5) defines the ratio of the focal length of the entire finder optical system L0 and the focal length of the first lens L1. If the lower limit of conditional expression (5) is not reached, it becomes difficult to achieve a wide viewing angle, which is not preferable. If the upper limit of conditional expression (5) is exceeded, the optical performance will deteriorate, which is not preferable.

Conditional expression (6) defines the ratio of the focal lengths of the first lens L1 and the third lens L3. If the lower limit of conditional expression (6) is not reached, it becomes difficult to achieve a wide viewing angle, which is not preferable. On the other hand, if the upper limit of conditional expression (6) is exceeded, chromatic aberration increases and optical performance deteriorates, which is not preferable.

Conditional expression (7) defines the shape of the air lens formed between the second lens L2 and the third lens L3. If the upper limit value or the lower limit value of conditional expression (7) is exceeded, the lens surface of the second lens L2 on the viewing plane EP side and the lens surface of the third lens L3 on the image display plane IP side become too far apart. If so, it is difficult to ensure a sufficient effective range of the third lens L3, and the eye relief is shortened, which is not preferable.

Conditional expression (8) defines the refractive index of the material of the second lens L2. If the lower limit of conditional expression (8) is not reached, the curvature of the lens surface becomes too strong, making molding difficult. Exceeding the upper limit of conditional expression (8) is not preferable because the Petzval sum of the finder optical system L0 increases, and curvature of field and astigmatism increase.

Conditional expression (9) defines the Abbe number of the material of the second lens L2. If the Abbe number νd of the material of the second lens L2 becomes so small that the lower limit of conditional expression (9) is exceeded, chromatic aberration is excessively corrected, which is undesirable. Moreover, if the upper limit of conditional expression (9) is exceeded, correction of chromatic aberration becomes insufficient, which is not preferable.

Conditional expression (10) defines the ratio of the total optical length of the finder optical system L0 to the focal length of the entire finder optical system L0. If the upper limit of conditional expression (10) is exceeded, the position of the principal point of the finder optical system L0 will be far from the image display plane IP, making it difficult to increase the viewing angle, which is not preferable. If the lower limit of conditional expression (10) is not reached, it becomes difficult to make the curvature of each lens sufficiently strong, making it difficult to increase the viewing angle, which is not preferable.

In this case, the lens surface means a surface having power, and an optical element having no refractive power, such as a flat plate, may be inserted between the front and rear of the finder optical system.

Further, the numerical ranges of the conditional expressions (1) to (10) are preferably within the numerical ranges of the following conditional expressions (1a) to (10a).
−0.64<f2/f<−0.30 (1a)
0.72<(R22+R21)/(R22-R21)<1.40 (2a)
0.31<H/f<0.45 (3a)
−8.0<(R21+R12)/(R21−R12)<−2.0 (4a)
0.35<f1/f<1.00 (5a)
0.50<f3/f1<3.08 (6a)
-3.0<(R31-R22)/(R31+R22)<9.0 (7a)
1.60<nd<1.94 (8a)
15<νd<25 (9a)
1.10<dL/f<1.55 (10a)

More preferably, it should be within the numerical range of the following conditional expressions (1b) to (10b).
-0.64<f2/f<-0.31 (1b)
0.74<(R22+R21)/(R22-R21)<1.38 (2b)
0.7<(R22+R21)/(R22-R21)≦1.361 (2b′)
0.31<H/f<0.40 (3b)
−7.8<(R21+R12)/(R21−R12)<−2.2 (4b)
0.40<f1/f<0.95 (5b)
0.60<f3/f1<3.06 (6b)
0.619≦f3/f1<3.10 (6b′)
-2.0<(R31-R22)/(R31+R22)<8.0 (7b)
−0.482≦(R31−R22)/(R31+R22)≦0.223 (7b′)
1.60<nd<1.93 (8b)
19<νd<24 (9b)
1.10<dL/f<1.50 (10b)

The finder optical system L0 of this embodiment has a diopter-adjustable mechanism. In Examples 1, 3, 4, 5, and 6, the first lens L1 to the third lens L3 are integrally moved in the optical axis direction, and the lens closest to the observation plane EP is kept stationary to adjust the diopter. Is going. Since the optical system of an electronic viewfinder normally adjusts the dioptric power by moving all the lenses in the optical axis direction, it is necessary to insert a protective glass on the viewing plane EP side of the final lens from the viewpoint of dust resistance. On the other hand, it is preferable to adjust the dioptric power while keeping the lens closest to the viewing plane EP stationary, because this eliminates the need for a protective glass and leads to downsizing of the finder optical system L0. In addition, by not inserting the protective glass, it is possible to eliminate the ghost generated by the reflection of the protective glass, which is also preferable from this point of view.

The finder optical system L0 of each embodiment includes, in order from the image display surface IP side to the image display surface IP side, a first lens L1 with positive refractive power, a second lens L2 with negative refractive power, and a second lens L2 with positive refractive power. It is preferable to use three lenses L3 and a fourth lens L4 having a positive refractive power. This is preferable because various aberrations can be satisfactorily corrected.

Next, an embodiment of an imaging device using the observation device shown in each example will be described with reference to FIG. 11 . An object image formed by the imaging optical system 101 is converted into an electric signal by the imaging element 102, which is a photoelectric conversion element. A CCD sensor, a CMOS sensor, or the like is used as the imaging device 102 .

An output signal from the imaging element 102 is processed in the image processing circuit 103 to form an image. The formed image is recorded on a recording medium 104 such as a semiconductor memory, magnetic tape, or optical disc. An image formed by the image processing circuit 103 is displayed on the finder optical system unit 105 . The finder optical system unit 105 includes an image display element 1051 and a finder optical system 1052 of each embodiment. The image display element 1051 is composed of a liquid crystal display element LCD, an organic EL element, or the like.

By applying the finder optical system of the present invention to an imaging device such as a digital camera or a video camera in this way, it is possible to obtain an imaging device with a wide viewing angle, a small size, and high optical performance.

Although preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and various modifications and changes are possible within the scope of the gist.

Numerical data for each example of the present invention are shown below. In the numerical data, "ri" indicates the paraxial radius of curvature of the i-th surface in order from the image display surface IP to the viewing side EP. r1 and r2 are the surfaces of the image display element, and r1 is the image display surface. r3 and r4 are surfaces of the protective member CG1. The last plane is the viewing plane EP. di indicates the axial top surface distance between the i-th surface and the (i+1)-th surface in order from the image display surface IP. Furthermore, ndi indicates the refractive index for the d-line (wavelength=578.6 nm) of the i-th material, and νdi indicates the Abbe number for the d-line of the i-th material.

In numerical data, [mm] is used as the unit of length unless otherwise specified. However, since the finder optical system can obtain the same optical performance even if it is proportionally enlarged or reduced, the unit is not limited to [mm], and other appropriate units can be used. In the numerical data, the surface with the suffix "*" written in the column of radius of curvature has an aspheric shape defined by the following formula (1).

In Equation 1, x is the distance in the direction of the optical axis from the vertex of the lens surface, h is the height in the direction perpendicular to the optical axis, R is the paraxial radius of curvature at the vertex of the lens surface, k is the conic constant, A4, A6, A8, A10 are polynomial coefficients. In the aspheric coefficients, "Ei" represents a base 10 exponential expression, ie, "10 ⁻ⁱ ". Table 8 shows the calculation results of each conditional expression for each numerical data.

Although preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and various modifications and changes are possible within the scope of the gist.

L0 finder optical system L1 first lens L2 second lens L3 third lens L4 fourth lens IP image display surface EP observation surface

Claims (5)

An observation device having an image display element for displaying an image and a finder optical system for observing the image displayed on the image display surface of the image display element,
The finder optical system includes a first lens with positive refractive power, a second lens with negative refractive power, a third lens with positive refractive power, and a positive refractive power, which are arranged in order from the image display surface to the observation side. consists of a fourth lens of
The observation device has a cover glass on the image display surface side of the first lens,
an air space on the optical axis between the cover glass and the image display surface is larger than an air space on the optical axis between the cover glass and the first lens;
When adjusting the dioptric power, the lens closest to the observation side of the finder optical system is stationary, the focal length of the second lens is f2, the focal length of the finder optical system is f, and the image of the second lens. The radius of curvature of the lens surface on the display surface side is R21, the radius of curvature of the lens surface on the observation side of the second lens is R22, the half of the diagonal length of the image display surface is H, and the lens surface on the observation side of the first lens. When the radius of curvature of R12 , the focal length of the first lens is f1, the focal length of the third lens is f3, and the radius of curvature of the lens surface of the third lens on the screen display surface side is R31 ,
-0.70<f2/f<-0.20
0.7<(R22+R21)/(R22-R21) ≦ 1. 361
0.31<H/f<0.50
-8.5<(R21+R12)/(R21-R12)<-2.0
0.619≦f3/f1<3.10
-0.482≤(R31-R22)/(R31+R22)≤0.223
An observation device characterized by satisfying the following conditional expression: 0.30<f1/f<1.00
2. The observation device according to claim 1, wherein the following conditional expression is satisfied. At least one surface of the second lens has an aspheric shape, and when nd is the refractive index of the material of the second lens at the d-line, and νd is the Abbe number of the material of the second lens with respect to the d-line,
1.58<nd<1.95
15<νd<32
3. The observation device according to claim 1, wherein the following conditional expression is satisfied. Let dL be the length on the optical axis at diopter of -1 diopter from the lens surface closest to the image display side of the finder optical system to the lens surface closest to the observation side,
0.90<dL/f<1.65
4. The observation device according to claim 1 , wherein the following conditional expression is satisfied. 2. An image pickup device, an image pickup optical system for forming an object image on said image pickup device, an image display device for displaying said object image, and an image displayed by said image display device. 5. An imaging apparatus comprising the viewing apparatus according to any one of items 1 through 4 .

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