JP3038974B2 - Small wide-angle lens - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wide-angle lens suitable for use in a compact lens shutter camera of 35 mm format, a camera with a range finder, and the like.

[0002]

2. Description of the Related Art Conventionally, there are a biogon type, an aviogon type, and the like as target-type wide-angle lenses having a negative, positive, and negative refractive power distribution. The negative-positive-negative symmetric Biogon-type wide-angle lens can cover a wide angle of view and can reduce distortion. In addition, because of the distribution of negative, positive, and negative refractive power, there is an advantage that the amount of peripheral light can be increased as compared with a topogon-type wide-angle lens or an orthometer-type wide-angle lens. An example of developing these basic models and increasing the F-number is disclosed in
Japanese Patent Publication No. -70826 discloses an example of the minimum number
51-24886 and JP-A-56-140311.

[0003]

However, the biogon-type wide-angle lens has a large number of components, has a large total lens system thickness (thickness from the most object side surface to the most image side surface of the lens), and has a large F-number. It had the drawback of being dark.
Also, the lens system disclosed in Japanese Patent Application Laid-Open No. 54-70826 has a bright F-number, but has a large total thickness of the lens system, a large number of components, and is not sufficient in terms of compactness and low cost. Was. Also, JP-B-51-24886, JP-A-56-
The lens system disclosed in Japanese Patent Publication No. 140311 has six lenses, and this type of lens system has a minimum number of lenses. However, the overall length of the lens system was long and the F number was dark, which was not preferable.

The present invention solves such a conventional problem,
An object of the present invention is to provide a low-cost and compact symmetrical wide-angle lens which realizes a reduction in the total thickness of the lens system, a large aperture, and a reduced number of components.

[0005]

Means for Solving the Problems In order from the object side, a first lens component L _{1 of} a negative meniscus lens having a convex surface directed to the object side, a positive lens and a negative lens bonded together, and a junction having the convex surface directed to the object side. The second lens component L _{2 of} the positive lens, the third lens component L ₃ of the cemented positive lens formed by bonding a negative lens and a positive lens with the convex surface facing the image side, and the third lens component L _{3 of} the negative meniscus lens with the convex surface facing the image side It is constituted by four lens components L ₄ , has a diaphragm disposed between the second lens component L ₂ and the third lens component L ₃ , and satisfies the following conditions.

[0006]

(Equation 4)

T ₁ : On-axis air gap from the most image side surface of the first lens component L ₁ to the most object side surface of the second lens component L ₂ t ₃ : The third lens component L ₃ the most image side of the terms fourth lens component L ₄ most on-axis to the object side surface of the air space n _21: refractive index n ₂₂ at the d-line of the positive lens on the object side of the second lens in the component L ₂ : d of the negative lens on the image side of the second lens in the component L ₂
Refractive index n ₃₁ with respect to the line: the third lens component L ₃ in the object side of the negative lens refractive index at the d-line of the n _32: d of the positive lens on the image side of the third lens in the component L ₃
Refractive index f for line: Focal length of whole system

[0008]

[Action] In the present invention has a second lens component L ₂ third lens component L ₃ Tadashi Toga refractive power and has a refractive power arrangement of the negative polarity as a whole. The first lens component L ₁ and the fourth lens component
Each lens component L ₄ are, in order to sufficiently correct curvature of field and astigmatism, and a negative meniscus lens having a concave surface facing against the diaphragm. As described above, by using the negative meniscus lens, the angle of view can be further increased, which leads to an increase in the amount of peripheral light.

The second lens component L _{2 of} the cemented lens of the positive lens and the negative lens in order from the object side, and the third lens component L ₃ of the cemented lens of the negative lens and the positive lens in order from the object side are spherical aberrations, respectively. Is sufficiently corrected, and the shape is symmetrical with respect to the stop in consideration of correction of aberration such as distortion. If the second lens component L ₂ is replaced by a cemented lens of a negative lens and a positive lens in order from the object side, and the third lens component L ₃ is replaced by a cemented lens of a positive lens and a negative lens in order from the object side, correction of spherical aberration Becomes difficult,
This is disadvantageous for increasing the diameter. In the present invention, as shown in each condition, it is important to select the air gap of each lens and the thickness of each lens.

Next, each conditional expression will be described. Generally, in the case of a biogon-type lens having symmetry with respect to a negative / negative stop, a negative first lens unit (first lens component L
₁ ) and the negative lens group closest to the image side (the fourth lens component L
_The greater the air spacing (t ₁ and t ₃ ) between ₄ ) and the positive lens group therebetween, the greater the degree of freedom to keep the Petzval sum at an appropriate value. Then, it becomes possible to set a favorable Petzval sum even with a lens having a small number of components,
Astigmatism and curvature of field can also be reduced. However, if the air gaps t ₁ and t ₃ are too large, the total lens thickness is large, the front lens diameter and the rear lens diameter are large, and the entire lens system is undesirably enlarged. Conversely, when the air spacings t ₁ and t ₃ are very small, the Petzval sum is displaced in the positive direction, resulting in astigmatism,
Not only is it difficult to correct curvature of field, but also the separation of on-axis rays and off-axis rays is worse at lenses farther from the stop, so other on-axis aberrations must be properly balanced for off-axis aberration correction. Becomes difficult.

The Petzval sum causing these problems can be improved to some extent by setting appropriate refractive indices of the positive lens and the negative lens. In particular, the second lens component L ₂ and the third lens component L ₃ of the cemented positive lens
It is necessary to set an appropriate refractive index. Thus the positive lens in the second lens component L ₂ and the third lens in the component L ₃ of the cemented positive lens, than the negative lens using the glass of high refractive index, reducing the Petzval sum. In general, when a high refractive index glass is used for a positive lens and a low refractive index glass is used for a negative lens in a bonded lens having a positive refractive power, spherical aberration cannot be corrected and the F-number cannot be brightened. In the case of the present invention, the first lens component L
The air lens and the like present in the _first and second lens air spacing t ₁ and the third lens component L ₂ components L ₃ and the air gap t ₃ of the fourth lens component L _4, to correct the spherical aberration, the F-number Can be brightened. Therefore, at the same time as determining the air intervals t ₁ and t ₃ and the refractive index of each lens,
Must be an appropriate value. By maintaining an appropriate ratio between the air gap t and the refractive index n, the air gaps t ₁ and t ₃ can be reduced without deteriorating astigmatism and field curvature, and the total thickness of the lens can be reduced. Can be reduced.

The conditional expressions (1) and (2) are conditions relating to compactness of the lens and correction of off-axis aberrations, particularly, astigmatism and curvature of field. When the value falls below the lower limit of conditional expression (1), the following two cases can be considered. If the refractive index difference between the positive lens and the negative lens in the second lens in the component L ₂ is very small. When the air gap t ₁ between the first lens component L ₁ and the second lens component L ₂ is very large.

In the case (1), since the Petzval sum is large and takes a positive value, it is difficult to correct astigmatism and curvature of field. In the case of (1), the total thickness D of the lens becomes large, and the front lens diameter and the rear lens diameter of the lens also increase, which is not preferable. When the value exceeds the upper limit of conditional expression (1), the following two cases can be considered. If the refractive index difference between the positive lens and the negative lens in the second lens component L ₂ is very large. When the air gap t ₁ between the first lens component L ₁ and the second lens component L ₂ is very small.

In this case, the method is effective for Petzval sum, but as a result, the difference in dispersion between the cemented positive and negative lenses is reduced, and it is difficult to correct chromatic aberration. Further, it becomes difficult to correct spherical aberration, and the F number cannot be made bright. In the case of, the separation of the off-axis ray and the on-axis ray is deteriorated in the lens far from the stop, so that the balance of the correction of the off-axis aberration and the on-axis aberration is deteriorated, and especially the astigmatism and the field curvature are corrected. It becomes difficult, and the sagittal image plane is greatly curved. Therefore, good performance cannot be obtained. Therefore, this range is desirable. Good.

When the value falls below the lower limit of the condition (2), the following 2 is satisfied.
The case is as follows. Negative lens of the third lens in the component L _3, a third lens component L ₃ when the refractive index difference of the positive lens is very small fourth
If the air gap t ₃ between the lens component L ₄ is very large. In the case of (1), the Petzval sum takes a larger positive value, so that it becomes difficult to correct astigmatism and curvature of field.
In the case of (1), the total thickness of the lens becomes large, the front lens diameter and the rear lens diameter of the lens also increase, which leads to an increase in the size of the entire lens system, which is not preferable. Moreover, it leads to an increase in cost, which is not preferable.

When the value exceeds the upper limit of the condition (2), the following 2 is satisfied.
The case is as follows. If the refractive index difference of the third lens negative lens, positive lens in the component L ₃ is very large. The air gap t ₃ between the third lens component L ₃ and the fourth lens component L ₄ may be very small.

In the case of the above, it is effective for Petzval sum, but the difference in dispersion of the cemented negative lens is reduced, and it becomes difficult to correct chromatic aberration, which is not preferable. In addition, it becomes difficult to correct spherical aberration, and the F-number cannot be made bright. In the case of, the separation of the off-axis ray and the on-axis ray in the lens far from the stop becomes worse, the balance of the aberration correction between the off-axis aberration and the on-axis aberration is deteriorated, and in particular, astigmatism, and field curvature are reduced. Correction becomes difficult, and furthermore, the sagittal image surface becomes largely curved, and good performance cannot be obtained. In order to sufficiently exert the effects of the present invention, the lower limit is set to 0.
A value of 85 gives better results.

In the configuration of the present invention as described above, it is desirable to satisfy the following conditional expressions (3) and (4).

[0019]

(Equation 5)

D: axial distance from the most object-side surface to the most image-side surface of the lens t ₂ : the second lens of the cemented positive lens which is formed by bonding a positive lens and a negative lens and has a convex surface facing the object side the axial air space conditions to the surface on the most object side of the third lens component L ₃ of the cemented positive lens having a most image-side convex surface from the surface to be image side cemented together a negative lens and a positive lens component L ₂ equation (3) includes an air gap t ₃ between the first lens component L ₁ and the air gap t ₁ and the third lens component L ₃ between the second lens component L ₂ and the fourth lens component L ₄ Is a condition further defining the synthesized air space. When the value goes below the lower limit of conditional expression (3), the total thickness of the lens becomes small, but it becomes difficult to separate the on-axis ray and the off-axis ray, and the degree of freedom of aberration correction becomes insufficient. Point aberration and curvature of field deteriorate. Then, there is a possibility that each lens physically interferes, which is not preferable. Conversely, if the value exceeds the upper limit, the effect of the air lens used for correcting spherical aberration is weakened, which is not only unfavorable, but also the overall thickness of the lens is increased, which is unfavorable against compactness. In order to achieve the effects of the present invention, more favorable results can be obtained by setting the lower limit to 0.08 and the upper limit to 0.34.

Condition (4) defines the air gap t ₂ between the second lens component L ₂ and the third lens component L ₃ . The present invention, when used in compact lens shutter camera or a so-called compact camera or the like, it is necessary to put the shutter and stop S between the second lens component L ₂ and the third lens component L _3, or certain air An interval is needed. Therefore, when the value falls below the lower limit, the shutter and the aperture stop cannot enter the structure. Conversely, if the upper limit is exceeded, the position where the oblique rays having the maximum angle of view are incident becomes a portion of each lens surface farther from the optical axis, leading to a decrease in the amount of peripheral light. If the effective diameter is increased to compensate for this, the entire lens becomes larger, which is not preferable. In addition, since the angle of refraction of the peripheral oblique rays increases, high-order aberrations occur, and particularly off-axis aberrations are unfavorably deteriorated. Further, in order to exert the effect of the present invention, better results can be obtained by setting the lower limit to 0.1 and the upper limit to 0.35.

In the present invention, it is desirable to further satisfy the following conditional expressions (5) and (7).

[0023]

(Equation 6)

D ₂₁ : center thickness of the object-side positive lens in the second lens component L ₂ of the cemented positive lens which is formed by bonding a positive lens and a negative lens with the convex surface facing the object d ₃₂ : negative lens and positive lens total thickness D that is, the first lens component L third lens component L ₃ in the image side of the positive lens center thickness condition of the cemented positive lens having a convex surface on the result image side from the bonding (5) lenses
From the most object side surface of the ₁ sets forth the total thickness of up to the surface on the most image side of the fourth lens component L _4. The present invention has a longer back focus but a smaller total thickness D of the lens than a general symmetric lens. In other words, the entire length of the lens (the total thickness D of the lens + the back focus) is relatively large, and the total thickness of the lens is small. When the lens is incorporated in a compact lens shutter camera or a camera with a range finder, it can be stored compactly if it is retracted, and it is practically effective if the total thickness of the lens is small. When the value goes below the lower limit of conditional expression (5), the separation between the on-axis ray and the off-axis ray in a lens located farther from the stop becomes worse, and the correction balance of each aberration cannot be obtained.
It is difficult to widen the angle while achieving brightness of about 2.8. On the other hand, if the value exceeds the upper limit, the direction of aberration correction is advantageous, but the total thickness of the lens becomes large, which is not preferable from the object of the present invention. Further, in order to sufficiently exhibit the effects of the present invention, better results can be obtained by setting the lower limit to 0.55 and the upper limit to 1.2.

The conditional expressions (6) and (7) are conditions relating to the center thickness of the positive lens in the second lens component L ₂ and the third lens component L ₃ of the cemented positive lens. The center thickness of these positive lenses has an effect particularly on correcting spherical aberration.
In order to realize a lens having a large aperture ratio of about F2.8 as in the present invention as in the present invention, good correction of spherical aberration besides off-axis aberration is required.

[0026] Condition falls below the lower limit of (6) becomes difficult to correct spherical aberration, also resulting in manufacturing since the edge thickness of the positive lens in the bonded second lens component L ₂ is reduced preferably Absent. Conversely, if the upper limit is exceeded, the joined second
Central thickness of the positive lens in the lens component L ₂ becomes very large. Therefore, although it is good for correcting spherical aberration, the total thickness D of the lens is increased, and the diameter of each lens is increased. Therefore, this range is actually desirable.

When the value goes below the lower limit of conditional expression (7), it becomes difficult to properly correct spherical aberration. Also, as a result, the edge thickness of the positive lens in the cemented third lens component is reduced,
It is not preferable in production. Also, if exceed the upper limit on the contrary, the center thickness of the positive lens in the third lens component L ₃ which are joined is very large, the total lens thickness D is increased. Therefore, the diameter of each lens increases, and as a result, the size of the entire lens increases, which is not preferable. On the other hand, if the center thickness is too large, it becomes difficult to manufacture, which leads to an increase in cost, which is not preferable.

Furthermore, better results can be obtained by adding the following conditions to the present invention.

[0029]

(Equation 7)

Q ₁ : Shape factor of the first lens component L ₂ q ₄ : Shape factor of the fourth lens component L ₄ The equation of the shape factor q is shown below.

[0031]

(Equation 8)

R ₁ : radius of curvature of the object-side lens surface r ₂ : radius of curvature of the image-side lens surface The conditional expressions (8) and (9) relate to the shapes of the lens component closest to the object and the lens component closest to the image. It is an expression. And
(10) is an equation for obtaining the shape factor q.

[0033] When falls below the lower limit of condition (8), not only the curvature of the first lens surfaces of the components L ₁ radius becomes very production to become small difficulty, a first lens component L ₁ second The air gap t ₁ between the two lens components L ₂ is undesirably increased as a result. Conversely, when the value exceeds the upper limit, refraction of the off-axis ray on the first surface increases, and as a result, field curvature and astigmatism deteriorate.

When the value goes below the lower limit of the conditional expression (9), refraction of the fourth lens component L _{4 at} the last surface becomes extremely large with respect to off-axis rays, and as a result, field curvature and astigmatism are reduced. Getting worse. Conversely, if the value exceeds the upper limit, the radius of curvature of each surface of the fourth lens component becomes small, which makes it difficult to manufacture, and also results in a large air gap t ₃ between the third lens component L _3. Therefore, it is not preferable in spite of compactness. Therefore, this range is practically preferable.

[0035]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The first to sixth embodiments comprise a first lens component L _{1 of} a negative meniscus lens having a convex surface facing the object side in order from the object side, and a positive lens and a negative lens bonded together. Second lens component L of a cemented positive lens having a convex surface
_{2. A} third lens component L _{3 of} a cemented positive lens having a convex surface facing the image side, and a fourth lens component L _{4 of} a negative meniscus lens having a convex surface facing the image side.
It is constituted by, having arranged aperture between the second lens component L ₂ and the third lens component L _3.

The values of various embodiments of the present invention will be described below. The numbers at the left end in the specification table of the examples represent the order from the object side, r is the radius of curvature of the lens surface, d is the lens surface interval, the refractive index n and the Abbe number ν are the d-line (λ = 587.6 nm). )
Is the value for

[0037]

[Example 1] f = 28.6 F _NO = 2.90 2ω = 75.3 °

[0038]

(Equation 9)

[0039]

EXAMPLE 2 _{f = 28.6 F NO = 2.90 2ω} = 75.3 °

[0040]

(Equation 10)

[0041]

Example 3 _{f = 28.6 F NO = 2.83 2ω} = 75.1 °

[0042]

[Equation 11]

[0043]

Example 4 _{f = 28.6 F NO = 2.90 2ω} = 74.6 °

[0044]

(Equation 12)

[0045]

Example 5 _{f = 28.6 F NO = 2.90 2ω} = 74.9 °

[0046]

[Equation 13]

[0047]

Example 6 _{f = 28.6 F NO = 2.90 2ω} = 74.9 °

[0048]

[Equation 14]

When an aspherical lens is introduced into the first lens component L ₁ or the fourth lens component L ₄ of the present invention, astigmatism and field curvature can be further improved, and the angle of view can be further increased.
Further, by introducing an aspheric lens into the second lens component L ₂ or the third lens component L ₃ , it is possible to further correct the spherical aberration and to make the aperture larger, which is a general aspheric lens. Needless to say from how to use.

[0050]

As described above, according to the present invention, a bright wide-angle lens of about F2.8 can be realized with a very small number of lens components, and is applicable to a compact lens shutter camera, a camera with a range finder, and the like. it can. In addition, since the total thickness of the lens is small, if the system is retracted into the camera body, the total thickness of the lens becomes very thin. Further, the present invention is not limited to a 35 mm camera, but can also be used for a lens for a large camera.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a lens configuration according to a first embodiment of the present invention.

FIG. 2 is an aberration diagram of the first embodiment of the present invention.

FIG. 3 is a lens configuration diagram according to a second embodiment of the present invention.

FIG. 4 is an aberration diagram of a second embodiment of the present invention.

FIG. 5 is a lens configuration diagram according to a third embodiment of the present invention.

FIG. 6 is an aberration diagram of a third embodiment of the present invention.

FIG. 7 is a lens configuration diagram according to a fourth embodiment of the present invention.

FIG. 8 is an aberrational diagram of the fourth embodiment of the present invention.

FIG. 9 is a lens configuration diagram according to a fifth embodiment of the present invention.

FIG. 10 is an aberration diagram of a fifth embodiment of the present invention.

FIG. 11 is a lens configuration diagram of a sixth embodiment of the present invention.

FIG. 12 is an aberration diagram of a sixth embodiment of the present invention.

[Explanation of symbols]

_{L 1, L 2, L 3} , L 4 ··· each lens component S · · · aperture

Claims (3)

(57) [Claims] 1. A first lens component L _{1 of} a negative meniscus lens having a convex surface facing the object side in order from the object side, and a first lens component L _{1 of} a cemented positive lens having a convex surface facing the object side made by bonding a positive lens and a negative lens. A two-lens component L ₂ , a third lens component L _{3 of} a cemented positive lens composed of a negative lens and a positive lens bonded together with a convex surface facing the image side, and a fourth lens component L of a negative meniscus lens with a convex surface facing the image side is composed of _4, the second lens component L ₂ has arranged squeezed between the third lens component L _3, and compact wide-angle lens that satisfies the following conditions. (Equation 1) t ₁ : On-axis air gap from the most image side surface of the first lens component L ₁ to the most object side surface of the second lens component L ₂ t ₃ : The most image side of the third lens component L ₃ wherein the surface fourth lens component L on the axis to the most object-side surface of the ₄ air gap n _21: the second lens component L ₂ in the object side of the refractive index n ₂₂ at the d-line of the positive lens: the first D of the image-side negative lens in the two-lens component L ₂
Refractive index n ₃₁ with respect to the line: the third lens component L ₃ in the object side of the negative lens refractive index at the d-line of the n _32: d of the positive lens on the image side of the third lens in the component L ₃
Refractive index f for line: Focal length of whole system 2. The wide-angle lens according to claim 1, wherein the following conditions are satisfied. (Equation 2) D: axial distance from the most object side surface of the lens to the most image side surface t ₂ : the most object side surface of the third lens component L ₃ from the most image side surface of the second lens component L ₂ Axial air spacing up to 3. The wide-angle lens according to claim 2, wherein the following condition is satisfied. (Equation 3) d ₂₁ : center thickness of the object-side positive lens in the second lens component L ₂ d ₃₂ : center thickness of the image-side positive lens in the third lens component L ₃