JP3190382B2 - Real image type zoom finder optical system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a real image type variable magnification finder optical system used for a photographic camera or a video camera.

[0002]

2. Description of the Related Art An inverted Galilean finder optical system is well known as a finder optical system in which an image pickup system and a finder system are separated. However, this finder optical system has drawbacks such as an unclear appearance of the field frame, a ghost generated by a half mirror for forming the field frame, and a poor view of the field itself due to flare. On the other hand, the Keplerian finder optical system observes the real image formed by the objective system through the eyepiece system, so that the disadvantages of the above-mentioned inverted Galileo finder optical system are almost eliminated, and a good-looking finder is obtained.

Further, as examples in which a Keplerian finder optical system is provided with a zooming function, there are a two-group zoom type objective system and a three-group zoom type objective system. As the former type, those described in JP-A-61-156018, JP-A-64-65519, and JP-A-1-257817 are known. Further, the latter type is known from Japanese Patent Application Laid-Open No. 1-131510.

[0004]

However, in the case of the former type, since the distance from the final surface of the objective lens to the intermediate image plane, that is, the back focus, is relatively long, the first reflection for image erecting is provided there. By arranging the surfaces and bending the optical path, the entire length of the finder portion can be shortened, but there is a disadvantage that the zoom ratio is small. On the other hand, it is easy for the latter type to have a zoom ratio of 2 or more. In addition, focusing only on the wide-angle end of this type, since the length from the first lens group to the third lens group is short and the back focus is long, the third lens is similar to the former type. It seems that the total length of the finder part can be shortened by installing the first reflecting surface between the group and the intermediate imaging surface and bending the optical path. However, in practice, at the telephoto end, the back focus becomes very short, so that it is impossible to provide a reflecting surface there, and the first reflecting surface must be provided after the intermediate image forming surface. Therefore, this type has a drawback that the length from the first lens group to the intermediate image plane is long, and as a result, the total length of the finder cannot be shortened.

SUMMARY OF THE INVENTION In view of the above problems, the present invention provides a real image type image forming apparatus which has a variable magnification ratio of about 3 or more, can shorten the entire length of a finder portion, can correct aberrations well, and can reduce manufacturing costs. It is intended to provide a variable magnification finder optical system.

[0006]

SUMMARY OF THE INVENTION One of the real image type variable magnification finder optical systems according to the present invention has an objective lens having a positive refractive power and a positive refractive power arranged in order from the object side. in real image type zoom finder optical system comprising an eyepiece, an objective lens, a third record with a second lens group and positive refractive power having a first lens group and positive refractive power having a negative refractive power A first reflecting surface for at least image erecting is provided between the third lens group and the intermediate image forming surface, and the first lens group is fixed, and the second lens group and the second lens group are fixed. The second lens group and the third lens group are moved in the direction of the optical axis such that the distance from the third lens group is maximized near the intermediate angle of view, so that zooming and diopter correction are performed, and the following condition is satisfied. It is characterized by doing so.

[0007] Here, r _1I is the radius of curvature of the most image side surface of the first lens unit,
r _1O is the radius of curvature of the surface closest to the object in the first lens group.

Also, in one of the real image type variable magnification finder optical systems according to the present invention, in addition to the above configuration, both the most object side surface and the most image side surface of the second lens unit are curved toward the object side. And satisfying the following conditions. Here, r ₂₁ is the radius of curvature of the most image side surface of the second lens group, r ₂₀ is the radius of curvature of the most object side surface of the second lens group, and r ₃₀ is the radius of curvature of the most object side surface of the third lens group. The radius of curvature. Also, a real image type zoom finder according to the present invention.
The optical system includes at least one surface of the second lens group and the
At least one surface of the third lens group is aspherical
It is characterized by. The real image type variable magnification finder optical system according to the present invention is characterized in that the second lens group includes a positive lens and a negative lens.

In the finder optical system according to the present invention, both the second lens unit and the third lens unit of the objective lens perform zooming and correct diopter. That is,
Since both the second lens unit and the third lens unit have a positive refractive power, by moving them from the eyepiece lens side to the object side, zooming from low magnification (wide angle) to high magnification (telephoto) is achieved. Done. Then, at the time of zooming, a deviation of the intermediate imaging position (a deviation of the diopter) occurs, so that the intermediate imaging position is kept constant by changing the distance between the second lens group and the third lens group, that is, diopter correction is performed. It has become.

If the combined magnification of the second lens unit and the third lens unit is β ₂₃ , the intermediate imaging position is shifted to the object side at the point where | β ₂₃ | = 1 at the time of zooming. In order to perform the correction, the distance between the second lens group and the third lens group is maximized. Therefore, when the magnification is changed within the range of | β ₂₃ | ≧ 1, the distance between the second lens group and the third lens group becomes maximum at low magnification, and the distance between the first lens group and the second lens group also becomes maximum. Between the third lens group and the intermediate image forming surface.
A sufficient back focus for installing the reflecting member cannot be secured, and the entire length of the finder becomes long. On the other hand, if the magnification is changed within the range of | β ₂₃ | ≦ 1, the shift of the intermediate imaging position becomes maximum at the time of high magnification, but the shift amount becomes larger than at the time of low magnification, so the second lens group for correction The amount of change in the distance between the lens and the third lens group also increases, and as a result,
The lens unit moves toward the eyepiece lens side at the time of low magnification, so that a sufficient back focus cannot be secured, and the entire length of the finder part becomes long.

Therefore, in the finder optical system according to the present invention, by setting | β ₂₃ | = 1 near the intermediate magnification (near the intermediate angle of view), the distance between the second lens unit and the third lens unit is maximized. Is set at an intermediate point between low magnification and high magnification. At low magnification, the distance between the second lens group and the third lens group is reduced to ensure a sufficient back focus, and the third lens group is also used at high magnification. Moves to the object side more than at low magnification, and a sufficient back focus is ensured. As a result, at least the first reflecting member can be installed between the third lens group and the intermediate imaging plane, and the finder section Can be shortened in length.

Incidentally, if a sufficient back focus can be secured for installing the first reflecting member, there is no problem even if the third lens group moves slightly toward the eyepiece lens at any intermediate magnification than at the low magnification. Needless to say. Also, if an optical element such as a mirror optical system or a Porro prism or an image rotator or a single imaging optical system for erecting an intermediately formed image after reflection is inserted between the objective system and the eyepiece system, An upright field image is obtained.

Further, in order to shorten the entire length of the finder section, it is desirable to make the second lens group as a whole a meniscus shape curved toward the object side, and to project its principal point to the first lens group side. This is because if the total length of the lens system is reduced while the principal point is in the lens group, the adjacent lens groups, especially the first
Interference between the lens group and the second lens group occurs. Therefore, if the principal point of the second lens group is shifted toward the first lens group to shift the position of the second lens group toward the eyepiece, the first
The air gap between the lens group and the second lens group can be secured.

The radii of curvature r _{1O and} r _1I of the entrance surface and the exit surface of the first lens unit, the radii of curvature r _2O and r _2I of the entrance surface and the exit surface of the second lens unit, and the radii of curvature of the third lens unit The radius of curvature r _3O of the entrance surface is determined by the above-mentioned conditional expressions (1), (2) and (3).
It is desirable to satisfy If the lower limit of conditional expression (1) is exceeded, the fluctuation of higher-order astigmatism will increase.
If the upper limit is exceeded, the distortion at the low magnification becomes large on the minus side. If the lower limit of conditional expression (2) is exceeded, the distortion at low magnification will become large on the negative side. If the upper limit is exceeded, fluctuations in spherical aberration and coma during zooming will increase, and the imaging performance will decrease. If the lower limit of conditional expression (3) is exceeded, the field curvature at the time of high magnification becomes large on the negative side. If the upper limit is exceeded, the fluctuation of distortion at the time of zooming will increase.

Also, at least one surface of the second lens unit and the third lens unit
Making at least one surface of the lens group aspherical respectively
It is preferable to reduce distortion at low and high magnifications and balance astigmatism and coma. Further, in the finder optical system according to the present invention, since the first lens group is fixed at the time of zooming, a cover glass for preventing dust from entering the optical system can be omitted, and as a result, costs can be reduced. At the same time, the overall length of the finder can be further reduced.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on illustrated embodiments. FIG. 1 is a perspective view of a first embodiment of a real image type variable magnification finder optical system according to the present invention. 1 is an objective lens, which is a fixed first lens group 2 composed of a negative lens, a movable second lens group 3 composed of a positive lens 3a and a negative lens 3b and having a positive refractive power as a whole, And a movable third lens group 4 having a positive refractive power. Then, the most object-side surface 3 of the second lens group 3
Both a 'and the most image-side surface 3b' are surfaces curved toward the object side.

5 is a first reflecting surface M₁And the second reflecting surface M_TwoTo
Prism 6 has a third reflecting surface M _ThreeAnd the fourth reflecting surface M
_FourPrisms, which constitute an image erecting system.
And a field frame 7 is provided on the exit surface of the prism 5.
Which is the intermediate image plane formed by the objective lens 1.
ing. That is, the third lens group 4 and the intermediate
1 reflection surface M₁And the second reflecting surface M_TwoIs provided. 8
Is an eyepiece provided behind the exit surface of the prism 6.
You.

FIG. 2 is a developed view of the first embodiment at wide-angle, intermediate, and telephoto, respectively. FIGS. 3, 4, and 5 show spherical aberration, astigmatism, and distortion at wide-angle, intermediate, and telephoto, respectively. It is each aberration curve figure. The data is shown below. Magnification 0.35 to 0.70 to 1.31, viewing angle (2ω) = 64.2 ° to 36.1 ° to 18.4 °

R ₁ = -233.8927 d ₁ = 1.028 n ₁ = 1.58362 ν ₁ = 30.37 r ₂ = 7.6021 (aspheric surface) d ₂ (variable) r ₃ = 5.3824 (aspheric surface) d ₃ = 2.100 n ₂ = 1.49260 ν ₂ = 58.02 r ₄ = 10.5496 d ₄ = 0.226 r ₅ = 7.5158 d ₅ = 1.000 n ₃ = 1.58362 ν ₃ = 30.37 r ₆ = 6.3475 d ₆ (variable) r ₇ = 10.2497 (aspherical surface) d ₇ = 2.687 n _{4 = 1.49260 ν 4 = 58.02 r 8} = -21.0421 d 8 ( _{variable) r 9 = 56.7539 d 9 =} 16.523 n 5 = 1.49260 ν 5 = 58.02 r 10 = ∞ d 10 = 1.0000 r 11 = 15.5302 d 11 = 28.862 n 6 = 1.49260 v ₆ = 58.02 r ₁₂ = ∞ d ₁₂ = 1.469 r ₁₃ = 9.9141 (aspherical surface) d ₁₃ = 3.539 n ₇ = 1.49260 v ₇ = 58.02 r ₁₄ = 111.0584 d ₁₄ = 15.0000 r ₁₅ (eye point)

Aspherical surface coefficient Second surface E = -0.60372 × 10 ^-3 , F = -0.34425 × 10 ^-5 , G = 0.48191 × 10 ^-8 Third surface E = -0.90093 × 10 ^-3 , F = -0.14004 × 10 ^-4 , G = -0.28893 × 10 ^-6 Surface 7 E = -0.33538 × 10 ^-3 , F = 0.76939 × 10 ^-5 , G = -0.32480 × 10 ^-6 Surface 3 E = -0.16996 × 10 ^-3 , F = 0.65951 x 10 ^-6 , G = -0.34414 x 10 ^-7

[0021]

Conditional expression (1) -0.937 Conditional expression (2) 0.082 Conditional expression (3) 0.235

Second Embodiment As shown in FIG. 6, this embodiment has a configuration similar to that of the first embodiment. FIGS. 6A, 6B, and 6C are developed views of the present embodiment at wide-angle, intermediate, and telephoto, respectively, and FIGS. 7, 8, and 9 are aberration curve diagrams at wide-angle, intermediate, and telephoto, respectively. is there. The data is shown below. Magnification 0.33 to 0.66 to 1.33 Viewing angle (2ω) = 54.6 ° to 29.2 ° to 14.1 °

R ₁ = −252.7357 d ₁ = 1.028 n ₁ = 1.58362 ν ₁ = 30.37 r ₂ = 7.6102 (aspherical surface) d ₂ (variable) r ₃ = 5.3054 (aspherical surface) d ₃ = 2.100 n ₂ = 1.49260 ν _{2 = 58.02 r 4 = 10.7043 d} 4 = 0.226 r 5 = 7.6077 d 5 = 1.000 n 3 = 1.58362 ν 3 = 30.37 r 6 = 6.2686 d 6 ( variable) r ₇ = 10.1823 (aspherical) d ₇ = 2.687 n ₄ = 1.49260 ν ₄ = 58.02 r ₈ = -23.2390 d ₈ (variable) r ₉ = 56.7539 d ₉ = 16.523 n ₅ = 1.49260 ν ₅ = 58.02 r ₁₀ = ∞ d ₁₀ = 1.000 r ₁₁ = 15.7130 d ₁₁ = 28.862 n ₆ = 1.49260ν ₆ = 58.02 r ₁₂ = ∞ d ₁₂ = 1.469 r ₁₃ = 9.8776 (aspherical surface) d ₁₃ = 3.539 n ₇ = 1.49260 ν ₇ = 58.02 r ₁₄ = 106.6582 d ₁₄ = 15.000 r ₁₅ (eye point)

Aspherical surface second surface E = −0.50783 × 10 ⁻³ , F = −0.14411 × 10 ⁻⁵ , G = 0.74277 × 10 ⁻⁷ Third surface E = −0.889026 × 10 ⁻³ , F = −0.12928 × 10 ^-4 , G = -0.21823 × 10 ^-8 7th surface E = -0.25178 × 10 ^-3 , F = 0.87013 × 10 ^-5 , G = -0.10582 × 10 ^-5 3rd surface E = -0.16611 × 10 ^-3 , F = 0.13393 x 10 ^-5 , G = -0.664768 x 10 ^-7

[0026]

Conditional expression (1) -0.942 Conditional expression (2) 0.083 Conditional expression (3) 0.238

[0028] This example third embodiment, as shown in FIG. 10, the prism 5 'having a first reflecting surface M _1, the second reflecting surface M _2, the third reflecting surface M ₃
And configure the image erecting system from the relay optical system 10 and having a fourth reflective surface M _4, between the prism 5 'and and between the relay optical system 10 and the eyepiece 8 the relay optical system 10, intermediate imaging The image planes are provided so as to exist.

FIGS. 10A, 10B, and 10C are developed views of the present embodiment at wide-angle, intermediate, and telephoto, respectively, and FIGS. 11 to 13 are aberration curves at wide-angle, intermediate, and telephoto, respectively. is there. The data is shown below. Magnification 0.35 to 0.68 to 1.31 Viewing angle (2ω) = 60.1 ° to 32.8 ° to 16.8 °

R ₁ = -44.3975 d ₁ = 1.000 n ₁ = 1.58362 ν ₁ = 30.37 r ₂ = 16.2878 (aspheric surface) d ₂ (variable) r ₃ = 5.8117 (aspheric surface) d ₃ = 3.300 n ₂ = 1.49241 ν ₂ = 57.66 r ₄ = -95.7654 d ₄ = 0.300 r ₅ = 13.5066 d ₅ = 1.505 n ₃ = 1.58362 ν ₃ = 30.37 r ₆ = 5.2183 d ₆ (variable) r ₇ = 11.5788 (aspherical surface) d ₇ = 1.907 n _{4 = 1.49241 ν 4 = 57.66 r} 8 = 159.4279 d 8 ( _{variable) r 9 = 12.2271 d 9 =} 9.019 n 5 = 1.49241 ν 5 = 57.66 r 10 = 68.4590 d 10 = 1.500 r 11 = 146.3630 d 11 = 27.227 n 6 = 1.49241 ν ₆ = 57.66 r ₁₂ = -30.9370 d ₁₂ = 0.300

R ₁₃ = 8.2425 (aspherical surface) d ₁₃ = 5.000 n ₇ = 1.49241 v ₇ = 57.66 r ₁₄ = -38.6987 d ₁₄ = 0.109 r ₁₅ = 5.4707 d ₁₅ = 3.741 n ₈ = 1.49241 v ₈ = 57.66 r _{16 = 11.2327 d 16 = 0.888 r 17} = -28.4658 d 17 = 1.500 n 9 = 1.80518 ν 9 = 25.43 r 18 = 3.0718 d 18 = 1.000 r 19 = 10.9769 d 19 = 8.889 n 10 = 1.49241 ν 10 = 57.66 r 20 = _{-4.9000 d 20 = 14.294 r 21 =} 9.8636 d 21 = 3.800 n 11 = 1.49241 ν 11 = 57.66 r 22 = -309.2520 d 22 = 20.501 r 23 = -28.5841 d 23 = 2.900 n 12 = 1.49241 ν 12 = 57.66 r 24 _{= -8.4475 d 24 = 15.000 r 25} ( eye point)

Aspheric surface second surface E = -0.16562 × 10 ^-3 , F = -0.27842 × 10 ^-5 , G = 0.19045 × 10 ^-6 H = -0.35490 × 10 ^-8 Third surface E = −0.667756 × 10 ^-3 , F = 0.57243 x 10 ^-5 , G = -0.73587 x 10 ^-6 H = -0.26009 x 10 ^-8 7th surface E = 0.20717 x 10 ^-3 , F = -0.62740 x 10 ^-4 , G = 0.30001 × 10 ⁻⁵ H = −0.30416 × 10 ⁻⁷ First 3rd surface E = −0.34821 × 10 ⁻³ , F = 0.30552 × 10 ⁻⁵ , G = −0.84034 × 10 ⁻⁷ H = −0.28550 × 10 ⁻⁹

[0033]

Conditional expression (1) -0.463 Conditional expression (2) -0.054 Conditional expression (3) 0.379

In each of the above embodiments, r ₁ , r ₂ ,
.... is the radius of curvature of each lens surface, d _1, d _2, ···· wall thickness and lens distance of each lens, n _1, n _2, ···· is the refractive index of each lens, [nu ₁ , ν ₂ ,... Are the Abbe numbers of each lens.

The aspherical shape in each of the above embodiments is represented by the following equation using an aspherical coefficient. However, the direction of the optical axis is X, and the direction perpendicular to the optical axis is S. Here, C is the curvature (= 1 / r) at the aspherical vertex.

Although the optical element of the objective lens in each of the above embodiments is made of plastic, glass may be used if the cost is appropriate.

[0038]

As described above, the real image type variable magnification finder optical system according to the present invention has a variable magnification ratio of about 3 or more and can shorten the entire length of the finder section. Further, aberration is also corrected well, and it is particularly effective to suppress astigmatism. In addition, it has an important practical advantage that the manufacturing cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a perspective view of a first embodiment of a real image type variable magnification finder optical system according to the present invention.

FIGS. 2A and 2B are configuration diagrams in which the optical system of the first embodiment shown in FIG. 1 is developed in the optical axis direction, wherein FIG.
(C) shows a telephoto state.

FIG. 3 is a diagram illustrating spherical aberration, astigmatism, and distortion in a wide angle state, respectively, for the first example.

FIG. 4 is a diagram illustrating spherical aberration, astigmatism, and distortion in an intermediate state, respectively, for the first example.

FIG. 5 is a diagram illustrating spherical aberration, astigmatism, and distortion in a telephoto state with respect to the first example, respectively.

FIGS. 6A and 6B are configuration diagrams in which the optical system of the second embodiment of the real image type variable magnification finder optical system according to the present invention is developed in the optical axis direction, where FIG. 6A is a wide angle, FIG. Represents the telephoto state.

FIG. 7 is a diagram illustrating spherical aberration, astigmatism, and distortion in a wide-angle state, respectively, for the second example.

FIG. 8 is a diagram illustrating a spherical aberration, an astigmatism, and a distortion in an intermediate state, respectively, in a second example.

FIG. 9 is a diagram illustrating spherical aberration, astigmatism, and distortion in a telephoto state, respectively, for the second example.

10A and 10B are configuration diagrams in which the optical system of the third embodiment of the real image type variable magnification finder optical system according to the present invention is developed in the optical axis direction, where FIG. 10A is a wide angle, FIG. Represents the telephoto state.

FIG. 11 shows the spherical aberration in the wide-angle state,
It is a figure which shows astigmatism and distortion respectively.

FIG. 12 shows the spherical aberration in the intermediate state,
It is a figure which shows astigmatism and distortion respectively.

FIG. 13 shows the spherical aberration in the telephoto state,
It is a figure which shows astigmatism and distortion respectively.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Objective lens 2 1st lens group 3 2nd lens group 4 3rd lens group 5, 5 'prism 6 Prism 7 Field frame 8 Eyepiece 10 Relay optical system.

Claims (4)

(57) [Claims] 1. A real image type variable magnification finder optical system comprising an objective lens having a positive refractive power and an eyepiece having a positive refractive power, which are arranged in order from the object side, wherein the objective lens has a negative refractive power. A first lens group having a refractive power, a second lens group having a positive refractive power, and a third lens group having a positive refractive power, wherein at least an image is formed between the third lens group and an intermediate image forming surface. Install the first reflective surface for erecting,
The first lens group is fixed, and the second lens group and the third lens group are moved in the optical axis direction such that the distance between the second lens group and the third lens group is maximized near the intermediate angle of view. A real-image variable-magnification finder optical system characterized by performing zooming and diopter correction thereby satisfying the following conditions. Here, r ₁₁ is the radius of curvature of the most image side surface of the first lens unit,
r ₁₀ is the radius of curvature of the most object side surface of the first lens group. 2. The apparatus according to claim 1, wherein both the most object-side surface and the most image-side surface of said second lens group are surfaces curved toward the object side, and satisfy the following conditions. 1
2. The real-image variable magnification finder optical system according to 1. Here, r ₂₁ is the radius of curvature of the most image side surface of the second lens group,
r ₂₀ is the radius of curvature of the surface closest to the object side of the second lens group, r ₃₀
Is the radius of curvature of the surface closest to the object side of the third lens group. 3. The apparatus according to claim 2, wherein at least one surface of said second lens group and
That the at least one surface of the third lens group, respectively aspherical
3. A real image type variable magnification file according to claim 1, wherein
Optical system. 4. The second lens group comprises a positive lens and a negative lens.
The real image according to claim 1, wherein the real image comprises:
Variable magnification finder optical system.