JPH05127079A - Small-sized wide-angle lens - Google Patents

Abstract

PURPOSE:To obtain the wide-angle lens which is used suitably for a compact lens shutter of 35mm size, a camera with a range finder, etc. CONSTITUTION:This wide-angle lens consists of a 1st positive cemented lens element L1 which is constituted by cementing a positive lens L11 and a negative lens L12 and has a convex surface on the object side, a 2nd lens element L2 which is constituted by cementing a negative lens L21 and a positive lens L22 and has a convex surface on the image side, and a 3rd lens element L3 consisting of a negative meniscus lens which is convex to the image side in order from the object side; and a stop S is provided between the 1st lens element L1 and 2nd lens element L2 and various conditions are satisfied.

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 size, a camera with a range finder, and the like.

[0002]

2. Description of the Related Art As a conventional lens type including an angle of view of about 61 °, well-known symmetrical lenses such as a protter type, a Dagor type, an orthometer type, and a Gauss type are well known.
In addition, Japanese Patent Publication No. 29-3587 discloses an example in which a strong negative lens is arranged on the most image side of the lens system by sacrificing symmetry based on these symmetrical lenses. Furthermore, in recent years, an asymmetrical type (so-called telephoto type) wide-angle lens composed of four to five lenses using aspherical lenses has been shown, and examples thereof include JP-A-50-87322 and JP-A-61322. −
There is a publication No. 15114.

[0003]

However, the Protter type lens which has been known for a long time is the first Anastigsmart utilizing Rudolf's principle, and the number of lens components is small and the air contact surface of the lens is very small. Etc., but it is difficult to fundamentally brighten,
It has a drawback that the angle of view cannot be taken sufficiently.

Next, the Dagor type lens has two groups of six, and the number of groups is as small as the proter type lens, and the air contact surface of the lens is very small, which is advantageous in terms of ghost and baying glare. There are also manufacturing advantages such as a simple lens barrel. However, the optical performance was not good, and it was difficult to make it particularly bright. Moreover, the number of lens elements is relatively large, and is not preferable.

The orthometer type lens is advantageous in terms of the angle of view, and in particular, is a type capable of favorably correcting the curvature of field. However, it is difficult to make it bright, and the number of lens components is relatively large at six, which is not preferable. When a Gaussian lens is used with an angle of view of about 61 ° and a brightness of about F2.8, there are few problems with aberrations, but with an angle of view of about 61 °, there is a drawback that the amount of peripheral light is insufficient. In addition, the number of lens components is relatively large, which is 6, which is disadvantageous in terms of cost, and the total lens thickness is increased by the increase in the number of lenses, which is not preferable in terms of compactness.

Since the tesser type lens is disadvantageous to the angle of view, it is difficult to realize a lens having an angle of view of about 61 ° and an aperture of F2.8. Next, in the case of an asymmetrical lens, the characteristic of being able to relatively easily correct aberrations such as chromatic aberration of magnification and distortion, which is an advantage of a symmetrical lens, is lost. It is advantageous to correct aberrations.

The lens disclosed in Japanese Examined Patent Publication No. 29587/29 has a structure with strong asymmetry, and in particular, correction of lateral chromatic aberration, distortion, etc. was insufficient. Basically, this lens is designed to have a large angle of view by adding a negative lens to the rear of the zonal lens, which is advantageous for brightness. And angle of view 61 °
Although a lens with F2.8 is realized to some extent, the chromatic aberration and distortion of magnification are not so good due to the fundamentally strong asymmetry. Also, since the number of components is large and the total lens thickness is thick,
Overall, it was big and costly.

The telephoto type wide-angle lens disclosed in Japanese Unexamined Patent Publication No. 50-87322 has a field angle of about 61 °.
The number of constituent lenses is very small, from 4 to 5, and the total lens thickness is relatively small. However, since the F number is relatively dark at F4.5, there is no air lens that is advantageous for correcting spherical aberration, and there is only one cemented lens, correction of spherical aberration is insufficient even in correction of aberration, and curvature of field is also sufficient. It cannot be corrected. Therefore, it is difficult to increase the diameter with the shape as it is.

The lens disclosed in Japanese Patent Laid-Open No. 61-15114 is also a telephoto type wide-angle lens. This is a small-sized lens type having a configuration of 4 elements in 4 groups to 5 elements in 4 groups and a small number of elements. However, since the first lens and the second lens are separated, there is a drawback that they are extremely eccentric. Also, in terms of aberrations, the field curvature is relatively large, and the distortion aberration is also relatively large. In addition, the difference in chromatic aberration of magnification tends to increase depending on the angle of view, and the chromatic aberration of magnification may be reversed between a light beam having a low angle of view and a light beam having a high angle of view.
Further, the color difference due to coma aberration (hereinafter, referred to as chromatic coma aberration) is large, and in particular, the lower coma aberration has a large chromatic coma aberration. Moreover, since the air contact surface of the lens is relatively large, it is disadvantageous for ghosts and veiling glare,
The lens barrel was also complicated and was insufficient in terms of cost.

The present invention solves such conventional problems and provides a wide-angle lens which is low in cost, compact, and high in performance.

[0011]

A first lens component L _{1 of} a cemented positive lens having a convex surface facing the object side, which is formed by bonding a positive lens L ₁₁ and a negative lens L ₁₂ , and a negative lens L _{21 in} order from the object side. and the positive lens L attached second lens component of the cemented positive lens having a convex surface directed toward the image side consisting of combined L ₂ of _22, and a third lens component L ₃ Metropolitan negative meniscus lens having a convex surface directed toward the image side, aperture S is the first lens component L ₁ and the second lens component L
_It is installed between the _two and satisfies the following conditions.

N ₁₁ > n ₁₂ (1) n ₂₁ <n ₂₂ (2) d ₂₁ <d ₂₂ (3) 0.005 ≤ t _{2 /} f ≤ 0.1 (4) 0.03 ≤ n ₁₁ -n ₁₂ ≤ 0.35 ( 5) 0.05 ≤ n ₂₂ -n ₂₁ ≤ 0.3 (6) 0.1 ≤ t _{1 /} f ≤ 0.45 (7) 0.14 ≤ (d ₁₁ + d ₂₂ ) / f ≤ 0.5 (8) 0.9 ≤ (n ₂₂ -n ₂₁ ) / (T ₂ / f) ≦ 8 (9) 2.5 ≦ q ₃ ≦ 13 (10) where f: focal length of the entire system t ₁ : second lens component L from the surface closest to the image side of the first lens component L _{1 2} is an axial air distance from the surface closest to the object side (aperture distance) t ₂ : the axial air from the surface closest to the image side of the second lens component L ₂ to the surface closest to the object side of the third lens component L _3. Interval n ₁₁ : Refractive index of the positive lens on the object side in the first lens component L _{1 with} respect to d-line n ₁₂ : Refractive index of the negative lens on the image side in the first lens component L _{1 with} respect to d-line n ₂₁ : Second negative Les the object side in the lens component L ₂ d in FIG.
Refractive index for line n ₂₂ : Refractive index of the positive lens on the image side in the second lens component L ₂ for d line d ₂₁ : On-axis center thickness of the negative lens for the object side in the second lens component L ₂ d ₂₂ : axial center thickness of the image-side positive lens in the second lens component L ₂ d ₁₁ : axial center thickness of the object-side positive lens in the first lens component L ₁ q ₃ : third lens component Form factor of L ₃ Form factor q = (r ₂ + r ₁ ) / (r ₂ −r ₁ ) r ₁ : Radius of curvature of the surface of the lens on the object side (However, in the case of aspherical surface, paraxial radius of curvature is used instead. ) R ₂ : radius of curvature of the image-side surface of the lens (however, in the case of an aspherical surface, a paraxial radius of curvature is used instead)

[0013]

FIG. 1 shows an example of a lens configuration diagram of the present invention. object
Positive lens L in order from the body side₁₁And negative lens L₁₂Pasting with
The first lens component L of the cemented cemented positive lens₁And diaphragm
R and negative lens L_{twenty one}And positive lens L_{twenty two}From pasting with
The second lens component L of the cemented positive lens₂And the image surface is convex
The third lens component L of the negative meniscus lens directed toward ₃By
It is configured.

The reason why the first lens component L ₁ and the second lens component L ₂ of the present invention are cemented lenses is first that the chromatic aberration is favorably corrected, and secondly that the Petzval sum is set to an appropriate value. This is because. Normally, in the case of a symmetrical lens (so-called Proter type, Dagor type, etc.) in which there is a cemented lens with an aperture S interposed, the relationship between the refractive index of the positive lens and the refractive index of the negative lens in the cemented positive lens is Rudolf As shown in the principle of 1), when there are two positive cemented lenses, one of the positive cemented lenses is used as an old positive cemented achromatic lens, and the refractive index of the negative lens is made higher than that of the positive lens, and the other positive cemented lens is used. Cemented lens,
As a new positive cemented achromatic lens, the refractive index of the positive lens is usually higher than that of the negative lens.

Since the cemented surface of the old positive cemented achromatic lens has a diverging action, it is effective in correcting spherical aberration. However, the Petzval sum increased, the field curvature deteriorated, and it was not possible to achieve a large angle of view with the old positive cemented achromatic lens alone.
Therefore, as shown in Rudolf's principle, by making the other cemented lens a new positive cemented achromatic lens, since the cemented surface has a converging action, the Petzval sum is reduced and the field curvature is improved.

As a result, it becomes possible to widen the angle of view, but the correction of spherical aberration is deteriorated by the new positive cemented achromatic lens, making it difficult to increase the aperture. Therefore, with the conventional lens type, it is difficult to realize a bright wide-angle lens having an angle of view of more than 60 ° even with the Rudolf principle. Therefore, the present invention basically arranges the positive cemented lens symmetrically with the diaphragm S sandwiched in the same manner as in the proter type, the Dagor type, etc., so that both cemented surfaces of the first lens component L ₁ and the second lens component L ₂ are formed. With a converging surface, a large angle of view and a large aperture have been realized.

That is, a cemented positive lens in which the positive lenses L ₁₁ and L ₂₂ have a higher refractive index than the negative lenses L ₁₂ and L ₂₁ is used, and the Petzval sum is set to an appropriate value to correct the image plane curvature. Then, the positive lens L ₂₂ in the second lens component L _{2 is} made relatively thick to help spherical aberration correction. Then, the third lens component L ₃ of the negative meniscus lens is added, and the spherical aberration is corrected by the air gap t ₂ (so-called air lens) between the second lens component L ₂ and the third lens component L ₃ .

With the above structure, it is possible to realize a lens of F2.8 class with an angle of view of about 61 °. Further, according to the present invention, the air contact surface is small and the ghost and flare can be drastically reduced due to the simple structure of 5 elements in 3 groups. Therefore, the veiling glare is drastically reduced, an image with good contrast can be obtained, and the structure of the lens barrel of the lens is simplified, so that the assembling work becomes extremely simple, which is advantageous in manufacturing. Therefore, the cost can be remarkably reduced, and a lens with good cost performance can be realized.

Next, each conditional expression will be described. The conditional expressions (1) and (2) are conditions expressing the relationship between the refractive index of the negative lens and the refractive index of the positive lens in the cemented positive lens of the first lens component L ₁ or the second lens component L ₂ . If this conditional expression is not satisfied, that is, if the refractive index of the negative lens is larger than the refractive index of the positive lens in the first lens component L ₁ and the second lens component L ₂ of the cemented positive lens, then it is as simple as the present invention. With such a lens, the Petzval sum has a large value, so that it becomes difficult to correct the field curvature, and it becomes impossible to achieve a large angle of view.

Conditional expression (3) is a conditional expression showing the relationship between the axial center thicknesses of the positive lens L ₂₂ and the negative lens L ₂₁ in the second lens component L ₂ of the cemented positive lens. Second lens component L ₂
By increasing the thickness of the positive lens in the inside, spherical aberration is improved. Therefore, in the present invention, the center thickness d ₂₂ of the positive lens is made larger than the center thickness d ₂₁ of the negative lens in the cemented positive lens to make the correction of spherical aberration advantageous. If this conditional expression is not satisfied, correction of spherical aberration will be insufficient, which is not preferable.

The conditional expression (4) is the second lens component L.₂And negative
Third lens component L of the varnish lens ₃Determine the air space between
This is a conditional expression that determines. This conditional expression is the second lens component L
₂And the third lens component L₃Of the air lens that exists between
It shows the effect. As described above, the first aspect of the present invention
1 lens component L₁And the second lens component L₂The joint surface of the
Since it has a repulsive action, correction of spherical aberration is disadvantageous.

However, while satisfying the conditional expression (2), a meniscus having a convex surface directed to the image plane between the second lens component L ₂ and the third lens component L ₃ defined by the conditional expression (4). It is sufficient to correct spherical aberration with a shaped air lens. In this air lens, the quality of spherical aberration correction is determined by the magnitude of the refracting power and the magnitude of the effect on a ray at infinity (hereinafter referred to as a land ray).

Therefore, when the upper limit of conditional expression (4) is exceeded,
The air gap t ₂ between the second lens component L ₂ and the third lens component L ₃ becomes too large, and the effect as an air lens decreases. Further, since the third lens component L ₃ is arranged farther from the stop S, the land ray passes through a portion closer to the optical axis of the third lens component L ₃ , so that the spherical aberration correction effect is obtained. Decrease, and as a result it becomes difficult to increase the diameter,
Not preferable.

When the value is below the lower limit, the air gap t ₂ between the second lens component L ₂ and the third lens component L ₃ becomes too small, and the separation between the oblique ray and the land ray deteriorates, and as a result, It becomes difficult to correct off-axis aberrations such as upper coma. In addition, the second lens component L ₂ and the third lens component L ₃ are extremely close to each other, and contact at the peripheral portion of the lens, resulting in a decrease in peripheral light amount, and mechanical interference, which causes the maximum angle of view. This is not preferable because the light ray cannot enter.

When the upper limit is 0.098, the effect of the present invention can be further exerted. Condition (5) is a condition for setting a difference between the refractive index n ₁₁ and the refractive index n ₁₂ of the negative lens L ₁₂ of the first lens component L ₁ in the positive lens L ₁₁ of the cemented positive lens. If the lower limit of conditional expression (5) is exceeded, the positive lens L
_Since the difference in the refractive index between ₁₁ and the negative lens L ₁₂ is reduced, the Petzval sum is increased in the simple configuration as in the present invention.
The field curvature is displaced in the negative direction and deteriorates, which is not preferable. On the other hand, if the value exceeds the upper limit, correction of spherical aberration becomes difficult even if an effect of an air lens or the like is added, which is not preferable. As a result, the difference in dispersion tends to be small, and it becomes difficult to correct chromatic aberration.

Further, in order to exert the effect of the present invention, the lower limit is set.
It is desirable to set it to 0.04. Condition (6) has a refractive index n ₂₁ and the positive lens L ₂₂ of the negative lens L ₂₁ of the second lens in the component L ₂
This is a condition for setting the difference between the refractive index n ₂₂ and the refractive index n ₂₂ . When the value goes below the lower limit of the conditional expression (6), the difference in refractive index between the positive lens L ₂₂ and the negative lens L ₂₁ decreases as in the case of the conditional expression (5). Therefore, in the simple structure like the present invention. The Petzval sum becomes large, and the curvature of field is displaced in the negative direction and deteriorates, which is not preferable. On the other hand, if the value exceeds the upper limit, it becomes difficult to correct spherical aberration even if it has an effect of an air lens or the like, and it is not preferable because the aperture cannot be increased. As a result, the difference in variance also decreases,
It is not preferable because it becomes difficult to correct chromatic aberration.

Conditional expression (7) is expressed by the air gap between the first lens component L ₁ and the second lens component L _2, that is, the diaphragm gap t _1.
Is a conditional expression that defines. When the value goes below the lower limit of the conditional expression (7), not only the lens shutter and the program shutter for the compact camera are mechanically prevented from entering the aperture interval t ₁ , but also from the viewpoint of aberration, the balance between the axial aberration and the off-axis aberration. Is difficult to obtain. Further, it becomes difficult to correct axial chromatic aberration and lateral chromatic aberration, which is not preferable. On the other hand, when the value exceeds the upper limit, the aperture interval t ₁ becomes large and the total lens thickness also becomes large, and especially the lens diameter of the lens away from the aperture S becomes large, which is not preferable because the optical system becomes large. Further, forcibly reducing the lens diameter is not preferable because the amount of peripheral light decreases. Also in terms of aberrations, the third lens component L ₃ is farther from the diaphragm S than the third lens component L ₃
Also, the axial aberration of the air lens between the second lens component L ₂ and the third lens component L ₃ , particularly the effect of correcting spherical aberration is reduced, which is not preferable.

Conditional expression (8) is a conditional expression that determines the combined thickness of the central thicknesses of the positive lens L _{11 in} the first lens component L ₁ and the positive lens L ₂₂ in the second lens component L ₂ . In the case of a lens having a simple structure as in the present invention, it is important to satisfactorily correct spherical aberration in order to increase the aperture. Generally, the larger the center thickness of the positive lens in the cemented positive lens, the more advantageous the correction of spherical aberration. Therefore, if the value goes below the lower limit, not only is it difficult to correct spherical aberration, but also the edge thickness of the cemented positive lens is extremely small, which is difficult to manufacture and is not preferable. On the contrary, if the upper limit is exceeded, the total lens thickness increases and the lens diameter also increases, which is not preferable.

Conditional expression (9) is a condition relating to the compactness of the lens and the correction of off-axis aberrations, particularly astigmatism and field curvature. There are two possible cases: when the value is below the lower limit of the conditional expression. The positive lens L ₂₂ and the negative lens L in the second lens component L _2
When the difference in refractive index of ₂₁ is very small. When the air gap t ₂ between the second lens component L ₂ and the third lens component L ₃ is very large. In the case of, the Petzval sum becomes large, and it becomes difficult to correct the field curvature, which is not preferable. In that case, not only the effect of the air lens decreases and it becomes difficult to correct spherical aberration, but also the total thickness of the lens increases. Therefore, the lens diameter of the third lens component L ₃ becomes large, which is against the compactness.
It also leads to cost increase and is not preferable.

On the contrary, there are two cases where the upper limit is exceeded. The positive lens L ₂₂ and the negative lens L in the second lens component L _2
When the difference in the refractive index of ₂₁ is very large. When the air gap t ₂ between the second lens component L ₂ and the third lens component L ₃ is very small. In this case, not only is it difficult to correct spherical aberration, but also the difference in dispersion of the glass used is small, which makes correction of chromatic aberration difficult, which is not preferable. In that case, in the lens away from the stop S, the separation of the on-axis and off-axis rays deteriorates, so that the correction of the upper coma aberration, the astigmatism, the curvature of field, and the like deteriorates. Then, the second lens component L ₂ and the third lens component L ₃ are extremely close to each other and mechanically interfere with each other in the peripheral portion, which is not preferable. If the lower limit is set to 1.2, a better result will be obtained.

The condition (10) sets the shape factor q ₃ of the third lens component L ₃ . Below the lower limit, the third
Since the lens component L ₃ is a meniscus lens close to a plano-concave lens with a convex surface facing the image surface, it becomes difficult to correct off-axis aberrations, particularly upward coma aberration, astigmatism, and image plane curvature. On the other hand, when the value exceeds the upper limit, the third lens component L ₃ becomes a more curved meniscus lens, and higher-order aberrations occur with respect to off-axis rays. Therefore, the upper coma aberration becomes worse,
Furthermore, it also adversely affects spherical aberration. Further, the shape of the third lens component L ₃ is closer to a semicircle, which is not preferable in manufacturing.

Incidentally, in the case of the present invention, the total length is relatively large, but the total thickness (total axial thickness from the first surface of the first lens component L ₁ to the last surface of the third lens component L ₃ ) is made as short as possible. Making an effort. Therefore, it is completely different from a wide-angle lens having a strong asymmetry in which the back focus of the third lens component L ₃ is reduced and the overall length is shortened. By using a lens type with a strong asymmetry, the aberrational defects resulting from the compact size of the overall length are as described above, and especially the chromatic aberration of magnification and the color difference of coma aberration (chromatic coma aberration). However, there is a limit to the correction of distortion and the like, and it cannot be corrected well.

Therefore, it is disadvantageous and unfavorable to forcibly reduce the total length in terms of aberrations, and the total thickness (from the first surface of the first lens component L _{1 to} the third lens component L _{1) is} the same as in the present invention.
The total thickness up to the last surface of ₃ ) is made as small as possible to increase the back focus, and that part is retracted to make it compact, which is also advantageous in terms of aberrations. Further, if the following conditions are satisfied, the effect of the present invention can be more exerted.

0.6 ≦ | f ₃ / f | ≦ 7 (11) 0.2 ≦ f ₁ / f _R ≦ 1.2 (12) 35 ≦ νd ₁₁ ≦ 60 (13) 27 ≦ νd ₂₂ ≦ 49 (14) d ₁₁ > d ₁₂ (15) r ₂₂ > 0 (16) | r ₂₃ |> | r ₃₁ | (17) where f: focal length of the entire system f ₁ : focal length of the first lens component L ₁ f ₃ : third lens Focal length of component L ₃ f _R : Composite focal length of second lens component L ₂ and third lens component L ₃ νd ₁₁ : Abbe number of the positive lens on the object side in the first lens component L ₁ ν ₂₂ : Abbe number of the image-side positive lens in the two lens components L ₂ r ₂₂ : radius of curvature of the cemented surface of the second lens component r ₂₃ : radius of curvature of the most image-side surface of the second lens component L ₂ r ₃₁ : The radius of curvature closest to the object side of the third lens component L ₃ Conditional expression (11) is a conditional expression for setting the refractive power of the third lens component L ₃ . Below the lower limit, the third lens component L ₃
Correction of off-axis aberrations by weakening the negative refractive power of
In particular, not only is it difficult to correct upper coma and astigmatism, but it is also difficult to correct spherical aberration, which is not preferable. On the other hand, if the upper limit is exceeded, asymmetry will increase, and not only the difference due to chromatic aberration of magnification and coma aberration due to color (chromatic coma aberration) and distortion will worsen, but also the difference due to difference in image height of coma aberration will increase. Absent.

Conditional expression (12) is defined by the refractive power of the first lens component L ₁ of the front lens group and the second lens component L _{2 of} the rear lens group with the diaphragm S interposed therebetween.
And an appropriate balance of the combined refractive power of the third lens component L ₃ and the third lens component L ₃ . Below this lower limit, the symmetry becomes too strong, and as a result, it becomes difficult to correct spherical aberration with a lens having a simple structure as in the present invention. On the other hand, if the upper limit is exceeded, the asymmetry becomes stronger, and lateral chromatic aberration, chromatic coma aberration,
Distortion is worse, which is not preferable.

Conditional expressions (13) and (14) are conditional expressions that determine the Abbe number of the positive lens in the first lens component L ₁ and the second lens component L ₂ . If both of the conditional expressions are below the lower limits, it becomes difficult to correct axial chromatic aberration and lateral chromatic aberration. On the other hand, if the upper limit is exceeded, correction of chromatic aberration is good, but as a result, only glass with a low refractive index can be selected, so it becomes difficult to set the Petzval sum to an appropriate value, and if other conditions are satisfied, all Since the lens is made of glass having a low refractive index, it becomes difficult to correct spherical aberration.

Conditional expression (15) is a conditional expression that defines the center thicknesses of the positive lens L ₁₁ and the negative lens L ₁₂ in the first lens component L ₁ . If this conditional expression is not satisfied, spherical aberration will worsen, which is not preferable. Conditional expression (16) is a conditional expression that defines the radius of curvature of the cemented surface of the second lens component L ₂ . Radius of curvature r ₂₂
Is a condition that always takes a positive value, and if this condition is not satisfied, it becomes difficult to correct axial chromatic aberration.

The conditional expression (17) is the second lens component L ₂ and the third lens component L ₂ .
It is a conditional expression that defines the shape of an air lens between the lens component L _3. If this conditional expression is not satisfied, the air lens has a concave shape, so that the ability of the air lens to correct spherical aberration is reduced, and it becomes difficult to correct spherical aberration.

[0039]

EXAMPLES FIG. 1, FIG. 3, FIG. 5 are lens configuration diagrams of Example 1, Example 2, Example 3, Example 4, and Example 5 of the present invention.
This is shown in FIGS. In Examples 1 to 4, in order from the object side, the first lens component L ₁ of the cemented positive lens formed by bonding the positive lens L ₁₁ and the negative lens L ₁₂ together, and the diaphragm S.
And a second lens component L ₂ of a cemented positive lens which is formed by bonding a negative lens L ₂₁ and a positive lens L _22, and a third lens component L _{3 of} a negative meniscus lens having a convex surface facing the image plane. There is.

In the fifth embodiment, in order from the object side, the first lens component L ₁ of the cemented positive lens formed by bonding the positive lens L ₁₁ and the negative lens L ₁₂ together, the diaphragm S, and the negative lens L.
The second lens component L ₂ is a cemented positive lens that is formed by bonding ₂₁ and the positive lens L _22, and the third lens component L ₃ is a negative meniscus lens having a convex surface facing the image plane.
This is an example in which an aspherical plastic lens is used for the lens component L ₃ . By making an aspherical surface in the lens closest to the image side or the lens closest to the object side, correction of field curvature, distortion, and coma is performed, and further downsizing and cost reduction are made possible.

Needless to say, it is possible to further correct spherical aberration and increase the aperture by making the first lens component L ₁ and the second lens component L ₂ aspherical. The formula of the aspherical surface is shown below. The aspherical shape has an x-axis in the optical axis direction, a y-axis in the direction perpendicular to the optical axis, a positive light traveling direction, r is a paraxial radius of curvature, K is a conic constant, and C2, C
When C4, C6, C8 and C10 are aspherical coefficients,

[0042]

[Equation 1]

It is represented by

Tables 1 to 5 below show values of specifications of each example of the present invention. The leftmost number in the specifications table indicates the order from the object side, r is the radius of curvature of the lens surface, d is the lens surface interval, n is the refractive index, and ν is the Abbe number on the d line (λ = 5
87.6 nm), f is the focal length, F _NO is the F number, and 2ω is the angle of view. In each aberration diagram, d is d
The line (λ = 587.6 nm) and g indicate the aberration curve by the g line (λ = 435.8 nm). In the figure, the dotted line of astigmatism indicates the meridional image plane and the solid line indicates the sagittal image plane. In each aberration diagram of each example, various aberrations are extremely well corrected from the wide-angle end to the telephoto end, and excellent imaging performance is obtained.

[0045]

[Table 1] Data of specifications of Example 1 (Condition corresponding _{values) (4) t 2 /f=0.0417 (} 5) n 11 -n 12 = 0.0998 (6) n 22 -n 21 = 0.2016 (7) t 1 /f=0.178 (8) (d 11 + d _{22) /f=0.264 (9) (n} 22 -n 21) / (t 2 /f)=4.835 (10) q 3 = 5.59 (11) | f 3 /f|=1.648 (12) f 1 / f _R = 0.53 (13) νd ₁₁ = 52.3 (14) νd ₂₂ = 45.4

[0046]

[Table 2] Data of specifications of Example 2 (Condition corresponding _{values) (4) t 2 /f=0.0417 (} 5) n 11 -n 12 = 0.0998 (6) n 22 -n 21 = 0.2016 (7) t 1 /f=0.222 (8) (d 11 + d _{22) /f=0.194 (9) (n} 22 -n 21) / (t 2 /f)=4.835 (10) q 3 = 6.20 (11) | f 3 /f|=1.674 (12) f 1 / f _R = 0.493 (13) νd ₁₁ = 52.3 (14) νd ₂₂ = 45.4

[0047]

[Table 3] Data of specifications of Example 3 (Condition corresponding _{values) (4) t 2 /f=0.0375 (} 5) n 11 -n 12 = 0.0485 (6) n 22 -n 21 = 0.260 (7) t 1 /f=0.222 (8) (d 11 + d _{22) /f=0.192 (9) (n} 22 -n 21) / (t 2 /f)=6.93 (10) q 3 = 3.62 (11) | f 3 /f|=1.013 (12) f 1 / f _R = 0.389 (13) νd ₁₁ = 55.6 (14) νd ₂₂ = 38.1

[0048]

[Table 4] Data of specifications of Example 4 (Condition corresponding _{values) (4) t 2 /f=0.0806 (} 5) n 11 -n 12 = 0.1866 (6) n 22 -n 21 = 0.1929 (7) t 1 /f=0.128 (8) (d 11 + d _{22) /f=0.417 (9) (n} 22 -n 21) / (t 2 /f)=2.39 (10) q 3 = 9.91 (11) | f 3 /f|=3.16 (12) f 1 / f _R = 0.864 (13) νd ₁₁ = 46.5 (14) νd ₂₂ = 47.5

[0049]

[Table 5] Data of specifications of Example 5 (Condition corresponding _{values) (4) t 2 /f=0.0278 (} 5) n 11 -n 12 = 0.2229 (6) n 22 -n 21 = 0.1052 (7) t 1 /f=0.140 (8) (d 11 + d _{22) /f=0.245 (9) (n} 22 -n 21) / (t 2 /f)=3.78 (10) q 3 = 10.25 (11) | f 3 /f|=5.17 (12) f 1 / f _R = 0.751 (13) νd ₁₁ = 43.4 (14) νd ₂₂ = 49.5 (Eighth surface aspherical coefficient) k = 1.00 C2 = 0.00000 C4 = -5.30109 x 10 ^-5 C6 = -1.03543 x 10 ^-6 C8 = 2.16419 × 10 ^-8 C10 ＝ -4.45970 × 10 ^{-10 Since} the total thickness of the lens is small, the total thickness of the lens will be much thinner if it is retracted into the camera body.
Further, the present invention can be applied not only to 35 mm format cameras but also to large format lenses and the like, and by introducing an aspherical surface into the lens away from the diaphragm S, off-axis aberrations such as astigmatism and coma can be eliminated. Correction and further miniaturization are possible,
It is apparent from the examples of the present invention. Needless to say, by introducing an aspherical surface in the vicinity of the stop S, it is possible to further correct spherical aberration and increase the aperture in the same manner as a general method of using an aspherical surface.

[0050]

As described above, according to the present invention, it is possible to apply to a compact lens shutter type camera, a camera with a range finder, and the like, the number of lens elements is very small as 5 elements in 3 groups, and the air contact surface of the lens. It is possible to realize a bright wide-angle lens of about F2.8, which has very little image flare and ghost.

[Brief description of drawings]

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

FIG. 2 is an aberration diagram of Example 1 of the present invention.

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

FIG. 4 is an aberration diagram of Example 2 of the present invention.

FIG. 5 is a lens configuration diagram of Example 3 of the present invention.

FIG. 6 is an aberration diagram of Example 3 of the present invention.

FIG. 7 is a lens configuration diagram of Example 4 of the present invention.

FIG. 8 is an aberration diagram of Example 4 of the present invention.

FIG. 9 is a lens configuration diagram of Example 5 of the present invention.

FIG. 10 is an aberration diagram of Example 5 of the present invention.

[Explanation of symbols for main parts]

L ₁ ... First lens component L ₂ ... Second lens component L ₃ ... Third lens component S ... Aperture

Claims (3)

[Claims] 1. A first lens component L _{1 of} a cemented positive lens having a convex surface facing the object side, which is formed by bonding a positive lens L ₁₁ and a negative lens L _{12 in} order from the object side, a negative lens L ₂₁ and a positive lens L. ₂₂ a second lens component of the cemented positive lens having a convex surface directed toward the paste image side consisting combined with L _2, a third lens component L ₃ Metropolitan negative meniscus lens having a convex surface directed toward the image side, aperture stop S
Is provided between the first lens component L ₁ and the second lens component L _2, and the following conditions are satisfied, and a small wide-angle lens. n ₁₁ > n ₁₂ (1) n ₂₁ <n ₂₂ (2) d ₂₁ <d ₂₂ (3) 0.005 ≤ t ₂ / f ≤ 0.1 (4) where f: focal length of the entire system t ₂ : the first second lens component L from the surface on the most image side of the ₂ third lens component L ₃ of the most on the axis to the object side surface of the air gap n _11: the d-line of the object side of the positive lens of the first lens in the component L ₁ Refractive index n ₁₂ : Refractive index of the negative lens on the image side in the first lens component L _{1 with} respect to d-line n ₂₁ : d of the negative lens on the object side in the second lens component L ₂
Refractive index for line n ₂₂ : Refractive index of the positive lens on the image side in the second lens component L ₂ for d line d ₂₁ : On-axis center thickness of the negative lens for the object side in the second lens component L ₂ d ₂₂ : The axial center thickness of the image-side positive lens in the second lens component L _2. 2. The compact wide-angle lens according to claim 1, further satisfying the following condition. _{0.03 ≦ n 11 -n 12 ≦ 0.35} (5) 0.05 ≦ n 22 -n 21 ≦ 0.3 (6) 0.1 ≦ t 1 /f≦0.45 (7) where, t _1: the first lens closest to the image side of the component L ₁ From the surface of the second lens component L ₂ to the surface of the second lens component L ₂ closest to the object (axial distance) 3. The small wide-angle lens according to claim 2, further satisfying the following condition. _{0.14 ≦ (d 11 + d 22} ) /f≦0.5 (8) 0.9 ≦ (n 22 -n 21) / (t 2 / f) ≦ 8 (9) 2.5 ≦ q 3 ≦ 13 (10) However, d _11: the first lens component axial center thickness of the object side of the positive lens in the L ₁ q _3: third form factor shape factor of the lens component _{L 3 q = (r 2 +} r 1) / (r 2 -r 1) r ₁ : The radius of curvature of the object-side surface of the lens (however, in the case of an aspherical surface, the paraxial curvature radius is used for substitution) r ₂ : The radius of curvature of the image-side surface of the lens (however, if the surface is aspherical, the paraxial radius of curvature Substitute with)