JPH11211994A - Viewfinder optical system and optical equipment using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To secure a sufficient eye point even in a reference state and to satisfactorily correct the aberration of distortion even in a high eye point state by composing a system of a meniscus-shaped positive first lens turning its concave surface toward the side of an object and a positive second lens having both convex lens surfaces. SOLUTION: An optical finder system Fa is composed of a meniscus-shaped positive first lens L1 and a positive second lens L2 having both the convex lens surfaces. In the optical finder system Fa, two positive first and second lenses are integrally moved, diopter correction is performed, and the high eye point state is provided by moving a display plane A of a liquid crystal pixel or the like to observe an image to the side of observation. Therefore, the moving range of the lens group is reduced and the rigidity of the entire optical finder system is secured as well. In the optical finder system Fa, the positive first lens L1 on the side of an object is meniscus-shaped while turning its concave surface toward the side of the object. Thus, a wide emission pupil is maintained even in the reference state and further, the long eye point, to which the aberration correction is sufficiently performed, is achieved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a finder optical system and an optical apparatus using the same, for example, when observing an image on a small CRT surface of a video camera or the like or a display surface such as a liquid crystal screen, or a single lens reflex camera. This is suitable for magnifying and observing an object image formed on a reticle in a camera or the like. In particular, the present invention relates to a finder optical system which can observe a good finder image in which the various aberrations such as curvature of field are well corrected in an eye point state in which the eye point is lengthened with a simple configuration, and an optical apparatus using the same.

[0002]

2. Description of the Related Art Conventionally, so-called video cameras and the like have been described.
In the electronic viewfinder optical system (EVF),
A finder image displayed on a CRT surface or a liquid crystal screen provided in a video camera is formed by a finder optical system to form a virtual image of the finder image at a clear viewing distance and observed from an eye point.

Such an electronic viewfinder optical system is disclosed in, for example, Japanese Patent Publication No. Sho 61-40087 and Japanese Patent Publication No. Sho 63-87.
-58327, JP-A-2-186315,
JP-A-3-150515, JP-A-6-34893
JP, JP-A-6-222264 and Japanese Utility Model Application Laid-Open No. 63-222264.
-199217.

Japanese Patent Publication No. 63-58327 discloses a finder optical system having a two-group, two-lens structure comprising a first positive lens having a larger refractive power and a second positive lens having a smaller refractive power in order from the CRT surface. In the system, the first positive lens and the second positive lens are configured to be movable and retractable in the optical axis direction or out of the optical axis depending on a usage pattern.

Japanese Patent Publication No. 61-40087, Japanese Patent Application Laid-Open No. 3-150515, Japanese Patent Application Laid-Open No. 6-34893, and Japanese Patent Application Laid-Open No. 6-222264 disclose a finder optical system comprising two groups of a negative lens and a positive lens. Therefore, the overall length of the lens is reduced. 63-19921
Japanese Patent Application Laid-Open No. 7-186315 and Japanese Patent Application Laid-Open No. Hei 2-186315 describe a finder optical system having two groups and two lenses composed of two biconvex lenses, and achieve a high eye point state by moving two lenses.

[0006]

Conventionally, an electronic viewfinder optical system has required a large magnification in order to magnify and observe a finder image (image) displayed on a small CRT or a liquid crystal screen. In addition, since there are many occasions for photographing a low-angle photograph, a high-angle photograph, and a moving subject, take a long eye point (particularly, 30 cm).
Above) There is a demand for a viewfinder optical system that allows observation even when the user takes his / her eyes away from the camera. It is generally said that the pupil diameter of a human is about 5 mm to 7 mm at the time of finder observation, and the pupil at the time of observation is assumed to be "immobile" when observing in the standard state in the ordinary finder optical system specifications. Is designed, and aberration correction is performed on the light beam incident on the pupil.

However, as described above, there are many cases in which a moving subject or the like is observed in photographing. In such a case, if the eyes cannot be moved even one time from the viewfinder optical system, the eyes may become tired or hinder long-time photographing. I do. Therefore, in order to maintain a sufficient exit pupil diameter and suppress the occurrence of vignetting and distortion even if the observer's pupil moves slightly, it is necessary to design the pupil with a large pupil diameter from the beginning. In low-angle shooting and high-angle shooting, it is impossible to shoot with the pupil close to the viewfinder itself.
In the m-th position, it is desired to take an image away from the finder optical system to take an image. In a so-called business finder having a large CRT or the like, an image is taken by flipping up a lens unit and directly looking at the CRT. However, in viewfinder optical systems for consumer use, CRTs and liquid crystal screens are small in size to reduce the size and cost of the camera. It becomes impossible.

The aforementioned JP-B-61-40087, JP-A-3-150515, and JP-A-6-34893.
In the finder optical system composed of a negative lens and a positive lens proposed in Japanese Patent Application Laid-Open No. Hei 6-222264, it is possible to achieve a large magnification and a reduction in the overall length of the lens. To 30c
If it is more than m, only a part of the screen is observed, and it is difficult to secure a wide field of view. In addition, Japanese Patent Publication No. 63-583
In the viewfinder optical system proposed in Japanese Patent Publication No. 27, since the positive lens on the observer side is a positive meniscus lens with a strong concave surface facing the observer side, a large field of view can be obtained, but in order to achieve a high eye point. When the distance between the lens and the object is reduced and the observation is performed with the eyes separated from the finder optical system, distortion around the image is undesirably increased. JP-A-63-199217, JP-A-2-1
In the viewfinder optical system proposed in Japanese Patent No. 86315, the entire lens is moved to the object side to achieve a high eye point. However, the operating range of the moving lens group becomes large, and it becomes difficult to secure the rigidity of the viewfinder optical system itself. In addition, since the magnification at the time of the high eye point cannot be made large, the image becomes small, and it is difficult to observe the image with a wide field of view.

The present invention achieves good optical performance in a wide field of view while securing a sufficient eye point even in a reference state, and excellently corrects distortion even in a high eye point state, and facilitates optimal magnification for observation. It is an object of the present invention to provide a viewfinder optical system which can be secured in particular, and which is particularly suitable for an electronic viewfinder, and an optical apparatus using the same.

[0010]

The finder optical system according to the present invention comprises: (1-1) a meniscus positive first lens having a concave surface facing the object side in order from the object side and a positive first lens having both lens surfaces convex. It is characterized by comprising two lenses.

(1-2) A meniscus positive first lens having a concave surface facing the object side in order from the object side and a positive second lens having both lens surfaces convex, and the first lens having an object side. And when the radii of curvature of the lens surfaces on the observation side are R1 and R2, respectively, the condition 1.5 <R1 / R2 <5 is satisfied.

(1-3) A positive meniscus first lens having a concave surface facing the object side in order from the object side and a positive second lens having both lens surfaces convex, and the first and second lenses. The average value of the refractive indices of the above materials is defined as N, and at least one aspheric surface is applied to a lens in which N does not exceed 1.6.

An optical apparatus according to the present invention provides: (2-1) a finder image displayed on a display surface using the finder optical system according to any one of the constitutions (1-1) to (1-3). In the optical apparatus for observing, the diopter correction is performed by moving the entire finder optical system on the optical axis, and the observation state is switched between the reference state and the high eye point state by moving the display surface in the optical axis direction. Features.

(2-2) An optical apparatus for observing a finder image displayed on a display surface using the finder optical system according to any one of the constitutions (1-1) to (1-3), The entire viewfinder optical system is moved on the optical axis to perform diopter correction, and the display surface is moved in the optical axis direction to switch between observation in a reference state and a high eye point state. D is the movement amount of the finder optical system at the time, L is the distance between the display surface and the first lens at the time of the high eye point, and f is the focal length of the finder optical system.
It is characterized by satisfying the following condition: 0.15 <D / f <0.3 0.2 <L / f

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1 to 5 are cross-sectional views of essential parts of Embodiments 1 to 5 of an optical apparatus having a finder optical system according to the present invention. 6 and 7 are optical path diagrams in the reference state (diopter is −2 diopter (Diop)) and the high eye point state (diopter is −3.2 diopter (Diop)) according to the first embodiment of the present invention. .

FIGS. 8, 10, 12, 14, and 16 are aberration diagrams in the reference state of Numerical Examples 1 to 5, respectively.
11, 13, 15, and 17 show aberration diagrams in the high eye point state of Numerical Examples 1 to 5, respectively.

In the drawing, Fa is a finder optical system (finder system), G is a parallel flat protective glass on the front surface of a CRT or liquid crystal screen, A is a display surface, and a finder image is formed by the CRT or liquid crystal screen. ing. The finder optical system Fa is a meniscus first positive lens L1,
Both lens surfaces are composed of a positive second lens L2 having a convex surface. IP is the pupil position (eye point) of the observer.

In the finder optical system Fa of the present embodiment, the two positive first and second lenses move together to correct diopter, and a display surface A of a liquid crystal element or the like on which an image is to be observed. By moving the lens to the observation side to bring it into a high eye point state, the moving range of the lens group is reduced, and the rigidity of the entire finder optical system is also ensured.

In the finder optical system according to this embodiment, the positive first lens L1 on the object side has a meniscus shape with the concave surface facing the object side (the display surface A side), so that a wide exit is obtained as described above even in the reference state. The pupil is maintained, and a long eye point with sufficient aberration correction is achieved. Thereby, as shown by the light path of the first embodiment in FIGS. 6 and 7, the light beam emitted from the display surface A is gradually bent with a weak refractive power to obtain a desired refractive power, and a large exit pupil diameter is obtained. , While correcting distortion well.

Next, the lens configuration of the embodiment of the present invention will be specifically described. When the curvature radii of the positive meniscus first lens are R1 and R2 in order from the object side, 1.5 <R1 / R2 <5 The conditional expression (1) is satisfied.

This conditional expression determines the meniscus shape factor of the first lens, and R1 and R2 have the same sign and indicate a lens configuration with the concave surface facing the object side. If the lower limit of conditional expression (1) is exceeded, the refractive power of the concave surface on the object side becomes too strong, and the refractive power of the remaining lens surfaces becomes too strong to maintain the positive refractive power of the entire system. Correction becomes difficult, and it becomes difficult to secure a wide exit pupil. On the other hand, when the value exceeds the upper limit, it is difficult to correct the distortion when trying to achieve the high eye point, which is not preferable.

In this embodiment, in order to satisfactorily correct distortion as a high-performance finder system, the numerical range of conditional expression (1) is set to 1.6 <R1 / R2 <4.0 (1a). It is preferable that

In the present invention, in order to achieve a high eye point in a good aberration correction state, the amount of movement of the finder system Fa at the time of plus diopter correction from the reference state is D, as shown in FIGS. When the distance between the display surface A and the front surface of the first lens L1 in the high eye point mode is L and the focal length of the finder system is f, 0.15 <D / f <0.3 (2) 0 .2 <L / f ‥‥‥ (3).

That is, the conditional expressions (2) and (3) define the focal length f of the entire system that determines the finder magnification and the movement amount D of the finder system Fa at the time of diopter adjustment.
If the amount of movement is reduced beyond the lower limit of the equation (2), the plus diopter correction becomes insufficient, which is extremely inconvenient for a hyperopic observer, which is not preferable. If the upper limit is exceeded, the amount of lens movement for diopter correction becomes large. If the moving mechanism of the holding frame or the like is made as large as the conventional one, the strength of the finder frame cannot be maintained, which is not preferable. More preferably, in the present embodiment, the numerical range of the conditional expression (2) is set to 0.15 <D / f <0.25０．２ (2a).

Conditional expression (3) similarly defines the focal length f of the entire system for determining the finder magnification and the amount of movement of the object plane A at the time of the high eye point. If the lower limit value of the conditional expression (3) is exceeded, the magnification of the screen is too large, so that the periphery of the screen cannot be observed at the time of the high eye point, which is not preferable.
The object of the present invention can be sufficiently achieved by this conditional expression. However, when 0.25 <L / f ‥‥‥ (3a) is satisfied, it is possible to achieve a better image enlargement ratio and a high eye point state.

In Numerical Examples 1, 2, and 3 of the finder optical system of the present invention, the average refractive index of the first and second lens materials is set to a value exceeding 1.6, and all lens surfaces are spherical. Sufficient performance is achieved while configuring. In Numerical Examples 4 and 5, since the average refractive index of the material of the first and second lenses is 1.6 or less, the curvature increases to maintain the same magnification. The surface is made aspherical to achieve a finder system in which distortion is well corrected.

Next, numerical examples of the present invention will be described. In the numerical examples, Ri, Di, and Ni represent the i-th radius of curvature, lens thickness or air gap, and refractive index in order from the object side.
0 is the object plane, Ra and Rb are the CRT or the protective glass on the front of the liquid crystal screen, and RP is the pupil position of the observer. The above-mentioned reference state refers to a diopter state of -2 diopters, and the diopter at the time of the high eye point is -3.2 Diop.

The aspheric surface has an X axis in the optical axis direction, an H axis in a direction perpendicular to the optical axis, a positive traveling direction of light, R represents a paraxial radius of curvature, and B, C, D, E, and F represent When each is an aspheric coefficient

[0029]

(Equation 1) This is represented by Table 1 shows the relationship between the above-described conditional expressions and various numerical values in the numerical examples.

Numerical Example 1 f = 50.51 R0 = A-side D1 = 2.45 Ra = ∞D2 = 1.00 N1 = 1.51633 ν1 = 64.2 Rb = ∞ D3 = variable R1 = −90.176 D4 = 3.60 N2 = 1.80400 ν2 = 46.6 R2 = -40.863 D5 = 3.40 R3 = 344.319 D6 = 3.60 N3 = 1.80400 ν3 = 46.6 R4 = -119.776 D7 = variable RI = pupil position ＼ diopter -2.00 +5.00 high eye point variable interval ＼ D3 37.35 46.32 15.35 D7 40.00 31.03 362.20 Numerical Example 2 f = 50.53 R0 = A-side D1 = 2.45 Ra = ∞D2 = 1.00 N1 = 1.51633 ν1 = 64.2 Rb = ∞ D3 = variable R1 = −88.630 D4 = 3.70 N2 = 1.77250 ν2 = 49.6 R2 = -40.581 D5 = 3.50 R3 = 362.217 D6 = 3.50 N3 = 1.77250 ν3 = 49.6 R4 = -105.003 D7 = variable RI = pupil position ＼ diopter -2.00 +5.00 variable interval at high eye point D3 37.07 47.40 15.07 D 40.13 29.80 362.13 Numerical Example 3 f = 50.51 R0 = A-side D1 = 2.45 Ra = ∞D2 = 1.00 N1 = 1.51633 ν1 = 64.2 Rb = ∞D3 = variable R1 = −84.197 D4 = 4.10 N2 = 1.63854 ν2 = 55.4 R2 = -36.000 D5 = 5.83 R3 = 271.018 D6 = 4.30 N3 = 1.63854 ν3 = 55.4 R4 = -83.700 D7 = variable RI = pupil position ＼ diopter -2.00 +5.00 high eye point variable interval ＼ D3 37.11 45.44 13.11 D7 38.55 28.22 360.55 Numerical Example 4 f = 50.53 R0 = A-side D1 = 2.45 Ra = ∞D2 = 1.00 N1 = 1.51633 ν1 = 64.2 Rb = ∞ D3 = variable R1 = −85.707 D4 = 5.00 N2 = 1.49171 ν2 = 57.4 R2 = -32.248 D5 = 0.40 R3 = 97.461 D6 = 5.10 N3 = 1.49171 ν3 = 57.4 R4 = -97.461 D7 = variable RI = pupil position ＼ diopter -2.00 +5.00 variable interval at high eye point D3 37.09 46.06 15.09 D 7 40.00 31.03 362.00 Aspheric coefficient R2 k = -3.665570e-01 B = -5.75659e-07 C = 1.58684e-10 D = -2.04345e-12 E = 0.0e + 00 F = 0.0e + 00 Numerical examples 5 f = 51.14 R0 = A surface D1 = 2.45 Ra = ∞D2 = 1.00 N1 = 1.51633 ν1 = 64.2 Rb = ∞D3 = variable R1 = -118.226 D4 = 4.90 N2 = 1.49171 ν2 = 57.4 R2 = -37.009 D5 = 0.40 R3 = 109.599 D6 = 5.10 N3 = 1.49171 ν3 = 57.4 R4 = -82.847 D7 = variable RI = pupil position ＼ diopter -2.00 +5.00 high eye point variable interval ＼ D3 37.73 46.70 15.73 D7 40.00 31.03 362.00 aspheric coefficient R4 k = -1.35643e + 00 B = 3.31201e-07 C = 1.69139e-10 D = 4.75168e-13 E = 0.0e + 00 F = 0.0e + 00

[0031]

[Table 1]

[0032]

According to the present invention, by setting each element as described above, good optical performance can be achieved in a wide field of view while securing a sufficient eye point even in the reference state.
Further, it is possible to achieve a finder optical system particularly suitable for an electronic view finder and an optical apparatus using the same, in which distortion is well corrected even in a high eye point state, and an optimum magnification for observation can be easily secured. it can.

[Brief description of the drawings]

FIG. 1 is a sectional view of a principal part of a numerical example 1 of the present invention.

FIG. 2 is a sectional view of a main part of a lens according to a second numerical embodiment of the present invention;

FIG. 3 is a sectional view of a principal part of a numerical example 3 of the present invention.

FIG. 4 is a sectional view of an essential part of a numerical example 4 of the present invention.

FIG. 5 is a sectional view of a main part of a lens according to a fifth numerical embodiment of the present invention;

FIG. 6 is an optical path diagram in a reference state according to Numerical Embodiment 1 of the present invention.

FIG. 7 is an optical path diagram in a high eye point state according to Numerical Embodiment 1 of the present invention.

FIG. 8 is an optical path diagram in a reference state according to Numerical Embodiment 1 of the present invention.

FIG. 9 is an optical path diagram of a high eye point state according to Numerical Embodiment 1 of the present invention.

FIG. 10 is an optical path diagram of a reference state in Numerical Example 2 of the present invention.

FIG. 11 is an optical path diagram of a high eye point state according to Numerical Embodiment 2 of the present invention.

FIG. 12 is an optical path diagram in a reference state according to Numerical Embodiment 3 of the present invention.

FIG. 13 is an optical path diagram in a high eye point state according to Numerical Embodiment 3 of the present invention.

FIG. 14 is an optical path diagram of a reference state in Numerical Example 4 of the present invention.

FIG. 15 is an optical path diagram in a high eye point state according to Numerical Embodiment 4 of the present invention.

FIG. 16 is an optical path diagram in a reference state in Numerical Example 5 of the present invention.

FIG. 17 is an optical path diagram in a high eye point state according to Numerical Embodiment 5 of the present invention.

[Explanation of symbols]

 A Object surface G Protective glass Fa Finder system L1 First lens L2 Second lens IP Eye point d d line g g line ΔM Meridional image plane ΔS Sagittal image plane Y Image height (mm)

Claims (5)

[Claims] 1. A finder optical system comprising: a meniscus positive first lens having a concave surface facing the object side in order from the object side; and a positive second lens having both lens surfaces convex. 2. A meniscus positive first lens having a concave surface facing the object side in order from the object side and a positive second lens having both lens surfaces convex, and the first lens has an object side and an observation side. A finder optical system satisfying the following condition: 1.5 <R1 / R2 <5 when the radii of curvature of the lens surfaces are R1 and R2, respectively. 3. A meniscus positive first lens having a concave surface facing the object side in order from the object side, and a positive second lens having both lens surfaces convex, and the first and second lenses are made of a material. A finder optical system, wherein an average value of a refractive index is N, and at least one aspheric surface is provided on a lens in which N does not exceed 1.6. 4. An optical apparatus for observing a finder image displayed on a display surface using the finder optical system according to claim 1, wherein the entire finder optical system is moved on an optical axis. An optical device, wherein the diopter correction is performed in such a manner that the display surface is moved in the optical axis direction to switch between observation in a reference state and observation in a high eye point state. 5. An optical apparatus for observing a finder image displayed on a display surface using the finder optical system according to claim 1, wherein the entire finder optical system is moved on an optical axis. The diopter correction is performed, and the display surface is moved in the optical axis direction to switch the observation between the reference state and the high eye point state.
When the amount of movement of the finder optical system at the time of plus diopter correction is D, the distance between the display surface and the first lens at the time of a high eye point is L, and the focal length of the finder optical system is f 0.15 <D An optical apparatus satisfying the following condition: /f<0.3 0.2 <L / f.