JPH11160630A - Finder optical system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compact finder optical system small in size, simple in constitution, suitable for viewing a comparatively large liquid crystal display and low in manufacturing cost. SOLUTION: This finder optical system is constituted so that a picture displayed on the display surface of a display member I is observed from an eye point E through an observation optical system. The observation optical system is provided with a prism P and an eyepiece part LA guiding luminous flux emitted from the prism P to the point E in turn from the display member side. The eyepiece part LA is provided with a first lens L1 having negative refractive power and a second lens L2 having positive refractive power. When the optical axis of the eyepiece part LA is extended, the condition of 25 deg.<θL<35 deg. is satisfied by the angle of θL formed by the optical axis and the display surface of the display member.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a viewfinder optical system suitable for magnifying and observing an image (liquid crystal display) displayed on a display surface of a liquid crystal display member such as a video camera or a digital camera, and in particular, to a comparison. The present invention relates to a small and simple finder optical system capable of handling large liquid crystals.

[0002]

2. Description of the Related Art In recent years, home video cameras, digital cameras, and the like having a relatively large liquid crystal display (about 1.8 to 4 inches) have become widespread. However, in the case of only the liquid crystal display, there are problems that it is very difficult to see depending on the situation (usage form of the observer), and that the power consumption increases.

Recently, a finder provided separately from a liquid crystal has come out. One of them is an OVF viewfinder optical system. However, in the case of the OVF viewfinder optical system, there is a problem that it is very difficult to cope with a high magnification such as a recent home video camera.

Another example is an EVF viewfinder optical system. Various types of EVF finder optical systems have been proposed, for example, in JP-A-3-150515 and JP-A-5-45594.

Japanese Patent Application Laid-Open No. 3-150515 discloses a finder optical system having two lenses, a first lens having a negative refractive power and a second lens having a positive refractive power, in order from the object side.

JP-A-5-45594 discloses a finder optical system having two lenses, a first lens having a negative refractive power and a second lens having a positive refractive power, in order from the object side. According to the publication, a first lens having a negative refractive power closer to the object has a bilaterally symmetric aspherical shape in a sectional view, and a second lens having a positive refractive power farther from the object has a non-symmetrical non-symmetrical shape in a sectional view. A finder optical system for an EVF lens having a spherical shape is disclosed.

The above-mentioned EVF finder optical system can shorten the entire lens length as compared with a conventional finder optical system having only a positive lens. However, the problem that the viewfinder optical system becomes very large with the enlargement of the image display size occurs, and even if the refractive power of the lens is strengthened and the size is reduced, the viewfinder magnification becomes too large and the liquid crystal pixels are conspicuous. A point occurs.

Further, in the case of an EVF finder optical system,
Since a display member such as a liquid crystal is separately provided, there is a problem that the entire device is easily increased in size, and the manufacturing cost is significantly increased.

Therefore, conventionally, a finder optical system in which a prism is arranged in the optical path between the display member and the eyepiece optical system and the optical path is bent to reduce the size is disclosed in, for example, JP-A-5-232548. Proposed. In this publication, a display member that forms an image on a display surface, a prism having a reflecting surface that bends a light beam from the display surface in a predetermined direction, and an eyepiece that guides the light beam emitted from the prism to a pupil (eye point) A finder optical system is configured from the system, and the display member is inclined so that the viewing angle characteristics of the display surface match the optical axis of the eyepiece optical system.

[0010]

However, this publication does not show any specific numerical examples, and the angle formed by the display surface of the display member and the entrance surface of the eyepiece optical system is approximately 90 degrees.
°, it is necessary to arrange two reflectors in addition to the prism in the optical path between the display member and the eyepiece optical system, and as a result, the whole apparatus becomes complicated There is a problem. In addition, since the space between the display member and the eyepiece optical system must be increased in order to secure a space for disposing the two reflectors, there is a problem that the finder magnification is reduced.

The present invention comprises a prism as an observation optical system for observing an image (liquid crystal display) displayed on the display surface of a display member made of liquid crystal, and an eyepiece lens section made up of two appropriately arranged lenses. A small finder optical system that can observe a relatively large liquid crystal display with a simple configuration by forming the prism and the two lenses from a plastic material and appropriately setting the curvatures of the two lenses. The purpose is to provide a system.

[0012]

According to the present invention, there is provided a finder optical system comprising: (1) a finder optical system for observing an image displayed on a display surface of a display member from an eye point through an observation optical system; The optical system includes, in order from the display member side, a prism, and an eyepiece section for guiding a light beam emitted from the prism to the eye point. The eyepiece section includes a first lens having a negative refractive power and a positive lens. A second lens having a refractive power, and when the optical axis of the eyepiece is extended, the angle θ between the optical axis and the display surface of the display member
_L is characterized by satisfying a condition of 25 ° <θ _L <35 °.

In particular, (1-1) the prism has at least one specular reflection surface and at least one total reflection surface; and (1-2) the prism and the first and second lenses. And (1-3) that at least one of the first and second lenses has an aspherical surface, (1-4) When the radii of curvature on the display member side and the eye point side of the first lens are R5 and R6, respectively, and the radii of curvature on the display member side and the eye point side of the second lens are R7 and R8, respectively, 0 <(R5 + R6) ) / (R5−R6) <3−2 <(R7 + R8) / (R7−R8) <1 and (1-5) the display member is made of liquid crystal. .

[0014]

FIG. 1 is a sectional view of a principal part of a finder optical system according to Numerical Embodiment 1 of the present invention, and FIGS. 2 to 5 are aberration diagrams of Numerical Embodiments 1 to 4 of the present invention.

In the figure, I is a display member made of liquid crystal (hereinafter referred to as a display member).
Also referred to as “liquid crystal display member”. ), And its display surface Ia
An image (liquid crystal display) is displayed above. P is a prism, which is formed of a plastic material, and is an incident surface Pa parallel to the display surface Ia of the liquid crystal display member I, a specular reflecting surface Pb for specularly reflecting a light beam incident from the incident surface Pa, and the specular reflecting surface A total reflection surface Pc on the same plane as an incident surface Pa for totally reflecting the light flux specularly reflected by Pb, and a total reflection surface P
An emission surface Pd for emitting the light flux totally reflected by c to the eyepiece lens section LA described later.

Reference numeral LA denotes an eyepiece having a first lens L1 having a negative refractive power and a second lens L2 having a positive refractive power, and located behind the exit surface Pd of the prism P. They are arranged so as to satisfy conditional expression (1) described later. The materials of the first and second lenses L1 and L2 in this embodiment are both formed of a plastic material.
At least one of the second lenses L1 and L2 has an aspherical lens surface. E is an eye point, and S is the optical axis of the eyepiece LA.

The prism P and the eyepiece LA each constitute an element of the observation optical system.

In this embodiment, the display surface I of the liquid crystal display member I
a, a light beam based on the image displayed on the prism P is made incident on the incident surface Pa of the prism P, and the incident light beam is reflected on the specular reflection surface Pb.
, And the light beam that has been specularly reflected is totally reflected by the total reflection surface Pc on the same plane as the incident surface Pa, and the totally reflected light beam is emitted from the exit surface Pd. And the image (liquid crystal display) is observed from the eye point E.

In this embodiment, the first and second lenses L1 and L2 are made of a plastic material, as described above, to reduce the weight and cost of the entire apparatus. Further, among the first and second lenses L1 and L2, the second
By introducing an aspherical surface into the lens surface of the lens L2 on the first lens L1 side, various aberrations generated in the lens, particularly spherical aberration and coma, are satisfactorily corrected to improve optical performance. .

As described above, the observation optical system in this embodiment has the prism P in order from the liquid crystal display member I side, and the first and second lenses L1 and L2 for guiding the light beam emitted from the prism P to the eye point E. be more configuration as ocular LA, when the extension of the optical axis S of the eyepiece section LA, angle theta _L is 25 ° formed by the display surface Ia of the optical axis S and the liquid crystal display element I <θ _L < The condition of 35 ° １ (1) is satisfied.

Further, in the present embodiment, the radii of curvature of the first lens L1 on the liquid crystal display member I side and the eye point E side are R
5, R6, when the radii of curvature of the liquid crystal display member I side and the eye point E side of the second lens L2 are R7 and R8, respectively, 0 <(R5 + R6) / (R5-R6) <3３ (2) 2) <(R7 + R8) / (R7−R8) <1 (3)

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

Conditional expression (1) is for observing a displayed image well while reducing the size of the finder optical system. If conditional expression (1) is not satisfied, the size of the finder optical system becomes large, and the pixels of the liquid crystal are noticeably observed.

Conditional expression (2) relates to the lens shape of the first lens L1. If the lower limit of conditional expression (2) is exceeded, it will be difficult to correct coma. If the upper limit of conditional expression (2) is exceeded, the radius of curvature of lens surface R6 on the pupil side of first lens L1 will be small. Therefore, the change of the coma aberration with respect to the eccentricity becomes large, which is not preferable.

Conditional expression (3) relates to the lens shape of the second lens L2. Exceeding the lower limit of conditional expression (3) makes it difficult to satisfactorily correct mainly spherical aberration, while exceeding the upper limit of conditional expression (3) makes it difficult to satisfactorily correct coma. Absent.

In order to further reduce the size of the apparatus with better optical performance, the numerical range of the conditional expressions (2) and (3) is set to 0 <(R5 + R6) / (R5-R6) <2. (2a) It is better to set as follows: −1 <(R7 + R8) / (R7−R8) <1 ‥‥‥‥ (3a)

In this embodiment, the first and second lenses L1 and L2 made of a plastic material may be formed integrally with the lens barrel. This can further reduce the manufacturing cost.

When adjusting the diopter, the second lens L2 is moved on the optical axis and the position of the eye point E is moved at the same time, so that the first and second lenses L1 and L2 are moved.
2 can be downsized, and the manufacturing cost can be reduced.

In the present embodiment, a material called plastic is, for example, a light-transmitting and relatively inexpensive acrylic resin (for example, Polymethylmethacrylic).
rate: PMMA), polycarbonate (Polyc)
arbonete: PC), styrene resin (eg St)
yrene-Acrylonitriteresin:
SAN), polystyrene resin (for example, Polystyr)
ene: PSt) or amorphous polyolefin (for example, Amorphous-Polyolefin: APO)
And so on. An organic material may be used instead of plastic.

Next, numerical examples of the present invention will be described. In the numerical examples, Ri is the i-th radius of curvature in order from the object side, Di is the i-th lens thickness and air gap in order from the object side, and Ni and νi are the i-th lens in the order from the object side. The refractive index and Abbe number of glass.

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 aspherical shapes. Spherical coefficient

[0032]

(Equation 1) It is represented by the following equation.

Table 1 shows the relationship between the above-mentioned conditional expressions and various numerical values in the numerical examples. In the aberration diagram, the pupil diameter is φ7.

Numerical Example 1 f = 1.00 R1 = ∞ D1 = 0.01 N1 = 1.500000 ν1 = 60.0 R2 = ∞ D2 = 0.03 R3 = ∞ D3 = 0.46 N2 = 1.491710 ν2 = 57.4 R4 = ∞ D4 = 0.01 R5 = 0.714 D5 = 0.04 N3 = 1.491710 ν3 = 57.4 R6 = 0.148 D6 = 0.17 R7 = 0.376 D7 = 0.07 N4 = 1.491710 ν4 = 57.4 R8 = -0.415 D8 = 0.18 R9 = ∞ (eye point) Aspheric coefficient R7 K = -3.04992e- 01 B = 1.48581e + 01 C = -8.69326e + 01 D = 1.90215e + 04 E = 0.00000e + 00 Numerical example 2 f = 1.00 R1 = ∞ D1 = 0.01 N1 = 1.500000 ν1 = 60.0 R2 = ∞ D2 = 0.01 R3 = ∞ D3 = 0.32 N2 = 1.491710 ν2 = 57.4 R4 = ∞ D4 = 0.06 R5 = -1.046 D5 = 0.02 N3 = 1.491710 ν3 = 57.4 R6 = 0.089 D6 = 0.10 R7 = 0.225 D7 = 0.04 N4 = 1.491710 ν4 = 57.4 R8 = -0.235 D8 = 0.11 R9 = ∞ (eye point) Aspheric coefficient R7 K = -3.59368e-01 B = 4.85274e + 01 C = 5.53347e + 03 D = -4.90056e + 05 E = 0.00000e + 00 Numerical example 3 f = 1.00 R1 = ∞ D1 = 0.01 N1 = 1.500000 ν1 = 60.0 R2 = ∞ D2 = 0.02 R3 = ∞ D3 = 0.39 N2 = 1.491710 ν2 = 57.4 R4 = ∞ D4 = 0.02 R5 = -16.131 D5 = 0.03 N3 = 1.530410 ν3 = 55.5 R6 = 0.142 D6 = 0 .15 R7 = 0.362 D7 = 0.06 N4 = 1.530410 ν4 = 55.5 R8 = -0.344 D8 = 0.16 R9 = ∞ (eye point) Aspherical coefficient R7 K = -7.71636e-02 B = 1.41690e + 01 C = -9.85702e +02 D = 8.95538e + 04 E = 0.00000e + 00 Numerical example 4 f = 1.00 R1 = ∞ D1 = 0.01 N1 = 1.500000 ν1 = 60.0 R2 = ∞ D2 = 0.02 R3 = ∞ D3 = 0.32 N2 = 1.494710 ν2 = 57.4 R4 = ∞ D4 = 0.02 R5 = -1.910 D5 = 0.03 N3 = 1.530410 ν3 = 55.5 R6 = 0.117 D6 = 0.14 R7 = 0.351 D7 = 0.04 N4 = 1.530410 ν4 = 55.5 R8 = -0.285 D8 = 0.13 R9 = ∞ (Eye (Point) Aspheric coefficient R7 K = -5.23788e-02 B = 2.55519e + 01 C = -2.25345e + 03 D = 3.31023e + 05 E = 0.00000e + 00

[0035]

[Table 1]

[0036]

According to the present invention, as described above, the observation optical system for observing the image (liquid crystal display) displayed on the display member surface composed of liquid crystal is composed of a prism and two lenses appropriately arranged. A relatively large liquid crystal display can be observed with a simple configuration by composing the eyepiece section, forming the prism and the two lenses from a plastic material, and appropriately setting the curvatures of the two lenses. A small finder optical system can be achieved.

[Brief description of the drawings]

FIG. 1 is a sectional view of a lens according to a numerical example 1 of the present invention.

FIG. 2 is a diagram showing various aberrations of Numerical Embodiment 1 of the present invention.

FIG. 3 is a diagram showing various aberrations of Numerical Example 2 of the present invention.

FIG. 4 is a diagram showing various aberrations of Numerical Example 3 of the present invention.

FIG. 5 is a diagram showing various aberrations of Numerical Example 4 of the present invention.

[Explanation of symbols]

 P prism I display member LA eyepiece L1 first lens L2 second lens E eye point (pupil) d d line FF line CC line ΔM meridional image plane ΔS sagittal image plane

Claims (6)

[Claims] 1. A viewfinder optical system for observing an image displayed on a display surface of a display member from an eye point via an observation optical system, wherein the observation optical system includes a prism in order from the display member side, and a prism. An eyepiece for guiding the emitted light beam to the eye point; the eyepiece having a first lens having a negative refractive power and a second lens having a positive refractive power; A viewfinder optical system, wherein when the optical axis of the lens unit is extended, an angle θ _L formed between the optical axis and the display surface of the display member satisfies a condition of 25 ° <θ _L <35 °. 2. The finder optical system according to claim 1, wherein said prism has at least one specular reflection surface and at least one total reflection surface. 3. The finder optical system according to claim 1, wherein the prism and the first and second lenses are made of a plastic material. 4. The finder optical system according to claim 1, wherein at least one of the first and second lenses has an aspherical surface. 5. The curvature radii of the first lens on the display member side and the eye point side are R5 and R6, respectively, and the curvature radii of the second lens on the display member side and the eye point side are R.
7. The condition of 0, (R5 + R6) / (R5-R6) <3-2 <(R7 + R8) / (R7-R8) <1, when R8 is satisfied, wherein the following condition is satisfied. Viewfinder optical system as described. 6. The finder optical system according to claim 1, wherein said display member is made of a liquid crystal.