JP2009003105A - Finder optical system and imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a finder optical system for achieving the reduction of weight of a lens and further having excellent performance over a larger visibility adjusting range in an electronic view finder using a little larger image display device of about 2.5 to 4 inches, and an imaging apparatus using the same. <P>SOLUTION: In the finder optical system, a first lens L<SB>1</SB>including a plastic concave aspherical lens, a second lens L<SB>2</SB>including a plastic convex aspherical lens, and a third lens L<SB>3</SB>including a plastic concave aspherical lens are arranged in order from an eye point EP side to an image surface 5, and a moving group 2 constituted of the first lens L<SB>1</SB>and the second lens L<SB>2</SB>and having positive power is constituted to integrally move along an optical axis (a) relative to a fixed group 3 constituted of the third lens L<SB>3</SB>. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a finder optical system used for an electronic viewfinder, for example, and an imaging apparatus using the finder optical system.

  Conventionally, in order to confirm an imaging range in an imaging apparatus such as a video camera, information obtained from an imaging element such as a CCD is copied as an image on an image display apparatus such as a liquid crystal panel, and the displayed image is displayed by an eyepiece system. An enlarged electronic viewfinder (EVF) is used. Patent Document 1 describes an image pickup apparatus that is made compact by reducing the size of the image display device of the electronic viewfinder, so that the optical system of the electronic viewfinder has a three-lens configuration. Yes. In the invention described in Patent Document 1, it is described that by using three lenses, it is possible to prevent steep refraction of the refracting surface and achieve both aberration correction and securing of a required viewing angle.

  By the way, in a conventional electronic viewfinder using a large image display device of about 2.5 inches, a moving group consisting of two glass spherical lenses, a concave lens and a convex lens, and a glass spherical lens consisting of one concave lens, A viewfinder optical system is configured by sequentially arranging the eyepoint side toward the image plane of the image display device. At this time, the moving group composed of two glass spherical lenses is configured such that the total power of the lenses becomes positive. In such a configuration, the diopter from the eye point side can be varied by changing the distance between the moving group and the fixed group.

In the above-described conventional configuration, when the large image display device is used, the viewfinder is divided into two groups of a moving group in which the total power of the two lenses is positive and a fixed group of concave lenses. This is because, since the focal length of the eyepiece group in the optical system is long, there is a problem that the diopter correction range cannot be expanded unless the two-group configuration is used.
JP 2002-303803 A

  However, in a conventional electronic viewfinder using a large image display device of about 2.5 inches, the finder optical system is composed of three glass lenses, so that its weight is heavy, and it is composed only of spherical glass. Therefore, there is a problem that only an optical design in which the diopter changes greatly between the center and the periphery of the screen is possible.

  In view of the above-described points, the present invention is an electronic viewfinder that uses a slightly larger image display device of about 2.5 inches to 4 inches, which reduces the weight of the lens and is excellent over a larger diopter adjustment range. A finder optical system having excellent performance and an imaging device using the same are provided.

  In order to solve the above problems and achieve the object of the present invention, a finder optical system according to the present invention includes a first lens made of a plastic concave aspheric lens, a second lens made of a plastic convex aspheric lens, and a plastic. A moving lens group having a positive power composed of a first lens and the second lens is arranged in order from the eye point side toward the image plane, and a third lens group consisting of a concave aspheric lens is a third lens. It is characterized in that it is configured to move integrally along the optical axis with respect to the fixed group constituted by the lenses.

  In the finder optical system of the present invention, the first, second and third lenses are all made of plastic aspheric lenses, so that it is possible to correct aberrations satisfactorily and to design an optical system with reduced weight. can do. Further, by configuring the moving group consisting of the first lens composed of the plastic concave aspheric lens and the second lens composed of the plastic convex aspheric lens so as to have a positive power, a slight movement of the moving group is achieved. The diopter can be greatly changed by the amount.

  The imaging device of the present invention is displayed on an imaging device, a signal processing unit that converts an optical signal obtained from the imaging device into an image signal, an image display device that displays information based on the image signal, and an image display device. A finder optical system capable of magnifying and viewing a magnified image. The finder optical system includes a first lens composed of a plastic concave aspheric lens, a second lens composed of a plastic convex aspheric lens, and a plastic concave A moving lens having a positive power, which is arranged in order from the eye point side toward the image plane of the image display device, and is composed of the first lens and the second lens. The fixed group constituted by the third lens is configured to move integrally along the optical axis.

  In the image pickup apparatus of the present invention, in the finder optical system, the moving group including the first lens including the plastic concave aspheric lens and the second lens including the plastic convex aspheric lens is configured to have positive power. By doing so, the diopter can be greatly changed with a small amount of movement of the moving group. Moreover, various aberrations are satisfactorily corrected by making all the first, second, and third lenses aspherical lenses.

  According to the finder optical system of the present invention, by using a plastic aspheric lens, it is possible to construct a high-performance optical system that is lightweight and has a wide diopter range and a wide viewing angle.

  Further, according to the imaging apparatus of the present invention, since a plastic aspheric lens is used in the finder optical system, a lightweight and high-performance optical system is configured over a wide diopter range and a wide viewing angle. The weight of the entire apparatus can be reduced, and even when a large image display apparatus is used for the finder, diopter uniformity within the field of view can be achieved.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 shows a schematic configuration of an embodiment of a finder optical system according to the present invention. The viewfinder optical system 1 of the present embodiment includes an eyepiece 4 used for an electronic viewfinder in an imaging apparatus such as a video camera, and uses a slightly larger image display device of about 2.5 inches to 4 inches for an electronic viewfinder. It is preferably used when

The eyepiece 4 of the finder optical system 1 in the present embodiment is configured on the optical path between the eye point EP and the image plane 5, and includes a first lens L ₁ , a second lens L ₂ , and a third lens. composed of a lens _{L 3.} In order from the eye point EP side, a first lens L ₁ , a second lens L ₂ , and a _third lens L ₃ are provided. The first lens L ₁ and the third lens L ₃ are plastic concave aspheric lenses, and the second lens L ₂ is a plastic convex aspheric lens. That is, the constituent lenses of the finder optical system 1 of this embodiment are all aspheric lenses made of plastic.

The first lens L ₁ and second lens L ₂ constitutes the moving group 2 move integrally. The third lens L ₃ constitutes the fixed group 3. The moving group 2 and the fixed group 3 constitute an eyepiece lens 4 of the finder optical system 1.

The lens power in the first lens L ₁ is L _1p , the lens power in the second lens L ₂ is L _2p , the lens power in the third lens L ₃ is L _3p , and the first lens L ₁ When the total lens power of the three lenses of the third lens L ₃ is L _ap , the following condition is satisfied.
(1) −3.05 <(L _1p / L _ap ) <− 0.89
(2) 3.50 <(L _2p / L _ap ) <5.07
(3) −3.51 <(L _3p / L _ap ) <− 1.76
The conditions (1) to (3) are conditions for relaxing each aberration.

Regarding the condition (1), when the lens power L _p1 of the first lens relative to the total lens power L _ap of the three lenses is smaller than −3.05 times, the peripheral image quality deteriorates, in particular, the chromatic aberration of magnification. Incurs an increase. On the other hand, if it is larger than −0.89 times, chromatic aberration and coma aberration on the positive side of the diopter increase.

In the condition (2), when the lens power L _p2 of the second lens with respect to the total lens power L _ap of the three lenses is smaller than 3.50 times, the diopter is positive on the plus side. Coma increases. On the other hand, when it is larger than 5.07 times, chromatic aberration and coma aberration at the periphery of the screen increase.

In the condition (3), when the lens power L _p3 of the third lens relative to the total lens power L _ap of the three lenses is smaller than −3.51 times, the diopter is a coma on the plus side. Aberration increases. On the other hand, when it is larger than -1.76 times, coma aberration on the plus side of the diopter increases.

Further, the moving group 2 is configured by two plastic aspherical lenses L ₁ and L ₂ such that the sum of the powers L _1p and L _2p of the lenses L ₁ and L ₂ becomes a positive power.

The refractive index L _2n in the second lens L ₂ and the Abbe number L _1v in the first lens L ₁ satisfy the following conditions.
(4) L _2n > 1.50
(5) 20 <L _1v <37

Regarding the condition (4), if the refractive index L _2n is lower than 1.50, the lens curvature becomes too steep when the lens is given power, which is disadvantageous for aberration correction and sufficient off-axis performance can be obtained. Absent.
As for the condition (5), if the Abbe number is less than 20, there is no suitable material. If the Abbe number is greater than 37, sufficient chromatic aberration correction cannot be performed.

In the finder optical system 1 configured under the above conditions, the diopter adjustment is performed by moving the moving group 2 in the direction of the arrow 6 along the optical axis a.
In the finder optical system 1 of the present embodiment, it is possible to cope with diopter +1 deopter (+ 1D) to -3 deopter (-3D). 2A and 2B show a schematic configuration of the finder optical system in + 1D and a schematic configuration of the finder optical system in -3D. As shown in FIGS. 2A and 2B, the diopter is adjusted by moving the moving group 2 and changing the angle of incident light incident on the eye point EP. By viewing the image plane 5 through the finder optical system 1 as described above, a virtual image can be visually recognized from the eye point EP.

Further, in the finder optical system 1 of the present embodiment, as seen from the eye point EP side, there is a moving group 2 in which the lens power is positive in the foreground, and there is a concave lens that becomes the fixed group 3 in the back thereof. full-length, i.e., the length from the image plane 5 to the first lens L ₁ side can be made shorter than the focal length. Therefore, when the image plane 5 becomes large, the focal length also becomes long. However, in the finder optical system 1 in the present embodiment, the total length of the finder optical system 1 can be shortened.

  Then, the moving group 2 can be configured as a moving group 2 with a small amount of aberration by configuring the moving group 2 with two concaves and convexes and using two plastic aspheric lenses. In addition, since both the moving groups 2 are made of aspherical plastic, the aberration correction capability can be increased even if the lens power is increased. Therefore, the moving group 2 has a strong convex power but generates a small amount of aberration. It can be an optical system. Since the power of the lens of the moving group 2 can be increased, the diopter can be changed greatly with a small amount of movement, and the diopter adjustment range can be expanded.

Furthermore, by making the fixed group 3 a plastic aspheric lens, it becomes possible to correct aberrations as a whole optical system. For this reason, it can be set as the finder which has favorable performance over a wide diopter adjustment range and a wide viewing angle, and a uniform resolution can be obtained. In addition, since the three lenses used are all aspherical lenses, even in the finder optical system using a larger image surface, it can be designed so that the diopter at the center and the periphery of the screen is uniform. It is possible to make the diopter uniform within the field of view.
Furthermore, the plastic lens is lightweight, and the lens weight of the finder optical system can be reduced.

  Next, examples in one embodiment of the finder optical system described above will be shown.

Table 1 shows specific values related to the example of the funder optical system 1 shown in FIG. The lens surfaces of the eyepiece lens group 4 shown in FIG. 1 are first to sixth surfaces from the eye point EP side.

Ｙは光軸ａからの距離、Ｚは光軸ａからの距離がＹにおける非球面上の点の非球面頂点からの距離、Ｃは曲率半径、Ｋはコーニック係数、Ａ_１、Ａ_２、Ａ_３、Ａ_４はそれぞれ４次、６次、８次、１０次の非球面係数である。 The aspherical shapes of the first to sixth surfaces of the lens in this embodiment are expressed by the following formula 1.

Y is the distance from the optical axis a, Z is the distance from the aspherical vertex of the point on the aspheric surface at the distance Y from the optical axis a, C is the radius of curvature, K is the conic coefficient, A ₁ , A ₂ , A ₃ and A ₄ are fourth-order, sixth-order, eighth-order, and tenth-order aspherical coefficients, respectively.

_R 1 ~r ₆ in Table 1 is the radius of curvature of each lens _surface, d 1 to d ₅ is the distance between the lens _surfaces, n 1 ~n ₃ is the refractive index of each _lens, v 1 to v ₃ are each lens Abbe number. The unit of the radius of curvature, the distance between the surfaces, and the effective radius is mm. K, A ₁ , A ₂ , A ₃ , and A ₄ are coefficients representing the aspherical shape of Equation 1 described above. In the present embodiment, the distance d ₀ from the sixth surface to the image display device is 103.1 mm.

  3A and 3B, spherical aberration (R, G, B) and astigmatism when the diopter is adjusted to -3D and when the diopter is adjusted to + 1D in the finder optical system 1 of this embodiment. And distortion aberration, respectively. In the spherical aberration, the vertical axis represents the ray height, and the horizontal axis represents the distance in the optical axis direction. Here, spherical aberrations due to typical wave numbers are illustrated. Astigmatism is the image height on the vertical axis and the amount of defocus on the horizontal axis. The broken line is the sagittal plane, and the solid line is the meridional plane. In the distortion aberration, the vertical axis represents the image height, and the horizontal axis represents the amount of image distortion.

3A and 3B, each aberration is a practically sufficient value in each diopter.
That is, in the finder optical system using the values of the present embodiment, different plastic materials are used for the lens L ₁ and the lens L ₂ in the combination of the _two plastic aspherical lenses L ₁ and L ₂ of the moving group 2. By selecting, practically sufficient chromatic aberration correction was made, and the fixed group was also made of a plastic aspherical lens, so that good aberration correction was made. Further, since the various aberrations are both good when the diopter is -3D and + 1D, it can be seen that the finder optical system has a high performance over a wide diopter range and a wide viewing angle.

Next, FIG. 4 shows a schematic configuration of a main part according to an embodiment of the imaging apparatus of the present invention.
The imaging apparatus according to the present embodiment is an example in which the above-described finder optical system 1 is used for an electronic view fan holder.

  The imaging device 10 shown in FIG. 4 shows only the imaging unit 11 and the electronic viewfinder 12. The imaging unit 11 includes, for example, an imaging device 13 such as a CCD imaging device or a CMOS imaging device and a signal processing unit 14, and the electronic viewfinder 12 includes an image display device 17 and a finder optical system 1. The image display device 17 used in the present embodiment is a large display device of about 2.5 inches to 4 inches.

  In the imaging device 10, the optical signal obtained by the imaging device 13 is converted into an electrical image signal 15 by the signal processing unit 14 in the imaging unit 11. The image signal 15 is sent to the electronic viewfinder 12 and is displayed on the image display device 17 such as a liquid crystal display panel via the driver 16. By viewing the image plane 5 of the image display device 17 on which the image is displayed from the eyepoint EP side through the eyepiece lens 4 of the finder optical system 1, an enlarged image can be viewed. Then, in the finder optical system 1 of the electronic viewfinder 12, the diopter can be adjusted by moving the moving group 2 of the eyepiece 4 along the optical axis a. That is, the diopter can be adjusted according to the visual acuity of the observer.

  In the imaging apparatus 10 according to the present embodiment, in the electronic viewfinder 12, the finder optical system 1 includes a moving lens group 2 having a positive lens and a concave lens and a convex lens, and a concave lens fixed group 3. . For this reason, even when the large image display device 17 is used, the overall length of the lens system can be made shorter than the focal length. Further, since the power of the lens of the moving group 2 can be designed to be large by using an aspheric lens, the diopter can be changed greatly with a small amount of movement of the moving group 2, and wide diopter adjustment is possible. A range can be obtained. Thereby, the electronic viewfinder can be made small.

  Furthermore, according to the imaging device 10 of the present embodiment, by using a plastic aspheric lens, it is possible to make the diopter uniform in the field of view even when the image display device 17 is enlarged. That is, the diopter at the center and the periphery of the screen of the image display device 17 can be made uniform. In addition, since all three lenses are made of plastic lenses, the imaging apparatus 10 can reduce the weight. In addition, since all three lenses are composed of aspherical lenses, aberration correction is excellent, and a uniform resolution can be obtained in the electronic viewfinder.

  As described above, according to the present invention, the moving group is configured by the plastic concave aspheric lens and the plastic convex aspheric lens, so that the lens group with low aberration is obtained while increasing the lens power by the two lenses. It can be. In addition, by combining this moving group and a fixed group with a plastic concave aspherical lens, the optical system can be made shorter than its focal length, and a high-performance finder optical system over a wide diopter adjustment range and wide viewing angle. Can be realized. Therefore, in the finder optical system of the present invention, even when a large image display device of about 2.5 inches to 4 inches is used in the image pickup device, the diopter uniformity within the visual field can be achieved.

It is a schematic block diagram of the finder optical system which concerns on one embodiment of this invention. A and B are schematic configuration diagrams of a finder optical system according to an embodiment of the present invention when the diopter is adjusted to -3D and + 1D. FIG. 6 is a diagram showing spherical aberration, non-surface aberration, and distortion when the diopter is adjusted to −3D and + 1D in the finder optical system in the example of the present invention. 1 is a schematic configuration diagram of an imaging apparatus according to an embodiment of the present invention.

Explanation of symbols

  1 .... finder optical system 2 .... moving group 3 .... fixed group 4 .... eyepiece 5 .... image plane 10 .... imaging device 11 .... shooting unit 12 .... electronic view finder, 13 .... Image sensor, 14 .... Signal processing unit, 15 .... Image signal, 16 .... Driver, 17 .... Image display device, EP ...

Claims (4)

A first lens comprising a plastic concave aspheric lens;
A second lens comprising a plastic convex aspheric lens;
A third lens composed of a plastic concave aspheric lens is arranged in order from the eye point side toward the image plane,
A moving group having a positive power constituted by the first lens and the second lens,
A viewfinder optical system configured to move integrally along the optical axis with respect to the fixed group constituted by the third lens. The first, second and third lenses have the following conditions:
(1) −3.05 <(L _1p / L _ap ) <− 0.89
(2) 3.50 <(L _2p / L _ap ) <5.07
(3) −3.51 <(L _3p / L _ap ) <− 1.76
(4) L _2n > 1.50
(5) 20 <L _1v <37
However,
L _1p : Lens power in the first lens L _2p : Lens power in the second lens L _3p : Lens power in the third lens L _ap : Lens power in the first, second and third lenses The finder optical system according to claim 1, wherein: L _2n : Refractive index of the second lens L _1v : Abbe number of the first lens is satisfied. An image sensor;
A signal processing unit that converts an optical signal obtained from the image sensor into an image signal;
An image display device for displaying information by the image signal;
A viewfinder optical system capable of enlarging and viewing the image displayed on the image display device,
The finder optical system includes a first lens made of a plastic concave aspheric lens,
A second lens comprising a plastic convex aspheric lens;
A third lens made of a plastic concave aspheric lens is sequentially arranged from the eye point side toward the image plane of the image display device,
A moving group having a positive power constituted by the first lens and the second lens,
An image pickup apparatus configured to move integrally along an optical axis with respect to a fixed group constituted by the third lens. The first, second and third lenses in the imaging device have the following conditions:
(1) −3.05 <(L _1p / L _ap ) <− 0.89
(2) 3.50 <(L _2p / L _ap ) <5.07
(3) −3.51 <(L _3p / L _ap ) <− 1.76
(4) L _2n > 1.50
(5) 20 <L _1v <37
However,
L _1p : Lens power in the first lens L _2p : Lens power in the second lens L _3p : Lens power in the third lens L _ap : Lens power in the first, second and third lenses _4. The imaging device according to claim 3, wherein: L _2n : Refractive index of the second lens L _1v : Abbe number of the first lens is satisfied.

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