JP3149481B2 - 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 As conventional lens types covering an angle of view of about 61 °, well-known symmetrical lenses include a Protar type, a Dagor type, an orthometer type and a Gauss type.
Japanese Patent Publication No. 29-3587 discloses an example in which a strong negative lens is disposed on the most image side of a lens system while sacrificing symmetry based on these symmetric lenses. In recent years, an asymmetrical type (so-called telephoto type) wide-angle lens composed of four to five lenses using an aspherical lens has been disclosed, and examples thereof are disclosed in JP-A-50-87322 and JP-A-61-1986. −
No. 15114.

[0003]

However, the Protar-type lens which has been known for a long time is the first anastig smart using the Rudolf's principle, and has a small number of lenses and a very small air contact surface of the lens. There are advantages such as, but it is fundamentally difficult to brighten,
There is a disadvantage that the angle of view cannot be sufficiently obtained.

Next, the Dagor type lens is composed of six elements in two groups, 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 veiling glare. There is also an advantage in manufacturing such as the lens barrel can be simplified. However, the optical performance was not good, and it was particularly difficult to make it bright. In addition, the number of lenses is relatively large in the configuration of six lenses, which is not preferable.

[0005] The orthometer type lens is advantageous for the angle of view, and is particularly of a type capable of favorably correcting field curvature. However, it is difficult to make the lens bright, and the number of lenses constituting the lens is relatively large at six, which is not preferable. When using a Gaussian lens with an angle of view of about 61 ° and a brightness of about F2.8, there is little problem with aberrations, but when using an angle of view of about 61 °, there is a disadvantage that the amount of peripheral light is insufficient. In addition, the number of lenses constituting the lens is relatively large at six, which is disadvantageous in terms of cost, and the total thickness of the lens is increased by the number of lenses.

[0006] Since the Tessar 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 F of about F2.8. Next, in the case of an asymmetric lens, the characteristic that aberrations such as chromatic aberration of magnification and distortion, which are advantages of the symmetric lens, can be relatively easily lost is lost. Therefore, the asymmetry is reduced as much as possible, and the symmetry is reduced as much as possible. Is advantageous for aberration correction.

[0007] The lens disclosed in Japanese Patent Publication No. 29-3587 has a structure with strong asymmetry, and in particular, insufficient correction of chromatic aberration of magnification, distortion, and the like. Basically, this lens has a large angle of view by adding a negative lens at the back of a zoner type lens which is advantageous for brightness. And angle of view 61 °
Although an F2.8 lens has been realized, the chromatic aberration and distortion of magnification are not very good because of fundamentally high asymmetry. Also, since the number of components is large and the total thickness of the lens is large,
The overall size was large and the cost was insufficient.

[0008] The telephoto type wide-angle lens disclosed in Japanese Patent Application Laid-Open No. 50-87322 encloses an angle of view of about 61 °,
The number of lenses is very small, four to five, and the total lens thickness is relatively small. However, the F-number is relatively dark at F4.5, there is no air lens that is advantageous for correcting spherical aberration, and since there is only one cemented lens, correction of spherical aberration is insufficient in aberration correction, and the curvature of field is sufficient. Cannot correct. Therefore, it is difficult to increase the diameter with the shape as it is.

The lens disclosed in Japanese Patent Application Laid-Open No. 61-15114 is also a telephoto type wide-angle lens. This is a lens type having a small size and a small number of components, with four elements in four groups and five elements in four groups. However, since the first lens and the second lens are separated, there is a disadvantage that the eccentricity is extremely weak. In terms of aberrations, the curvature of field is relatively large, and the distortion is also relatively large. The chromatic aberration of magnification also tends to increase depending on the angle of view, and the chromatic aberration of magnification may be inverted between a light ray having a low angle of view and a light ray having a high angle of view.
Further, there is a disadvantage that a color difference due to coma (hereinafter referred to as chromatic coma) is large, and in particular, a chromatic coma of lower coma is large. Also, since the air contact surface of the lens is relatively large, it is disadvantageous for ghost and bailing glare,
The lens barrel was also complicated and insufficient in terms of cost.

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

[0011]

A first lens component L ₁ and a negative lens L _{21 of} a cemented positive lens having a convex surface directed to the object side formed by bonding a positive lens L ₁₁ and a negative lens L ₁₂ 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 Let S be the first lens component L ₁ and the second lens component L
₂ and satisfy 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 most image-side surface of first lens component L _{1 2} on the most object side of the axial air distance to the surface (throttle interval) t _2: the on-axis air from the surface of the most image side of the second lens component L ₂ to the surface on the most 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 for d-line n ₁₂ : refractive index of the negative lens on the image side in the first lens component L ₁ for d-line n ₂₁ : second negative Les the object side in the lens component L ₂ d in FIG.
Refractive index n ₂₂ with respect to the line: a second lens component L refractive index at the d-line of the image side of the positive lens in the ₂ d _21: axial center thickness of the negative lens on the object side in the second lens component L ₂ d _22: second lens component L axial center thickness of the image-side positive lens in the ₂ d _11: axial center of the object side of the positive lens in the first lens component L ₁ thickness q _3: third lens component Shape factor of L ₃ Shape factor q = (r ₂ + r ₁ ) / (r ₂ -r ₁ ) r ₁ : radius of curvature of the object-side surface of the lens (however, in the case of an aspherical surface, the 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 aspheric surface, the paraxial radius of curvature is used instead)

[0013]

FIG. 1 shows an example of a lens configuration according to the present invention. object
In order from the body side, the positive lens L₁₁And negative lens L₁₂Bonding with
First lens component L of the cemented positive lens₁And aperture
R and negative lens L_{twenty one}And positive lens L_{twenty two}From pasting with
Second lens component L of the cemented positive lens_TwoAnd convex on the image surface
Third lens component L of negative meniscus lens _ThreeBy
It is constituted.

[0014] The first lens component L ₁ of the present invention, the reason for the second lens component L ₂ and the cemented lens is a good correction of the first chromatic aberration to set the second on Petzval sum to an appropriate value That's why. Usually, in the case of a symmetric lens having a cemented lens with a stop S interposed therebetween (a so-called Proter-type or Dagor-type), the relationship between the refractive index of the positive lens in the cemented positive lens and the refractive index of the negative lens is Rudolph's. As shown in the principle of the above, when there are two positive cemented lenses, one of the positive cemented lenses is used as an old positive cemented achromatic lens, the refractive index of the negative lens being higher than the refractive index of the positive lens, and the other positive cemented lens. The cemented lens,
As a new positive junction achromatic lens, it is usual to make the refractive index of the positive lens higher than that of the negative lens.

The former positive junction achromatism lens is effective in correcting spherical aberration because its junction surface has a diverging effect. However, the Petzval sum increased, the field curvature deteriorated, and a large angle of view could not be expected only with the old positive junction achromatic lens.
Therefore, as shown by Rudolph'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 is possible to widen the angle of view, but the correction of spherical aberration is deteriorated by the new positive junction achromatic lens, and it is difficult to increase the aperture. Therefore, it is difficult to realize a bright wide-angle lens exceeding an angle of view of 60 ° with the conventional lens type even based on Rudolph's principle. Therefore, the present invention basically arranges a positive junction lens symmetrically with respect to a stop S in the same manner as a Proter type, a Dagor type or the like, and makes both the junction surfaces of the first lens component L ₁ and the second lens component L ₂ A converging surface has been used to achieve a large angle of view and a large aperture.

That is, a positive lens L ₁₁ , L ₂₂ having a higher refractive index than the negative lenses L ₁₂ , L ₂₁ is used as a cemented positive lens, the Petzval sum is set to an appropriate value, and the field curvature is corrected. And it assists the spherical aberration corrected by relatively thickening the positive lens L ₂₂ of the second lens in the component L _2. Then, the third lens component L ₃ of the negative meniscus lens is added, and the spherical aberration is corrected by the air interval t ₂ (so-called air lens) between the second lens component L ₂ and the third lens component L ₃ .

With the above configuration, it is possible to realize an F2.8 class lens with an angle of view of about 61 °. Furthermore, according to the present invention, the air conditioner has a simple structure of three groups and five sheets, so that there are few air contact surfaces, and ghosts and flares can be drastically reduced. Accordingly, bailing glare is greatly reduced, an image with good contrast can be obtained, and the structure of the lens barrel is simplified, so that the assembling work is extremely simplified and the manufacturing is advantageous. Therefore, the cost is significantly reduced, and a lens with good cost performance can be realized.

Next, each conditional expression will be described. Condition (1) and (2) is a condition showing a refractive index of the relation between the refractive index and the positive lens of the negative lens in the cemented positive lens first lens component L ₁ and the second lens component L _2. When this conditional expression is not satisfied, that is, when 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, a simple lens as in the present invention is used. With a lens having such a configuration, since the Petzval sum becomes a large value, it becomes difficult to correct the field curvature, and it is impossible to increase the angle of view.

[0020] Condition (3) is a conditional expression representing the on-axis central thickness of the relationship between the second lens component L ₂ in the positive lens L ₂₂ and the negative lens L ₂₁ of the cemented positive lens. Second lens component L ₂
By increasing the thickness of the middle positive lens, spherical aberration is improved. Therefore, in the present invention has advantageous correction of the spherical aberration by increasing the center thickness d ₂₂ of the positive lens than the center thickness d ₂₁ of the negative lens in the cemented positive lens. If this conditional expression is not satisfied, spherical aberration is not sufficiently corrected, which is not preferable.

Conditional expression (4) represents the second lens component L_TwoAnd negative
Third lens component L of the varnish lens _ThreeDetermine the air gap with
Is a conditional expression to be defined. This condition is expressed as follows: the second lens component L
_TwoAnd the third lens component L_ThreeOf the air lens that exists between
The effect is shown. As described above, the present invention
One lens component L₁And the second lens component L_TwoThe joint surface is
Since it has a convergence effect, it is disadvantageous to correct spherical aberration.

However, the meniscus which satisfies the conditional expression (2) and further has 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) What is necessary is just to correct spherical aberration with a shaped air lens. In this air lens, the quality of the spherical aberration correction is determined by the magnitude of the refractive power and the magnitude of the effect on an axial infinite ray (hereinafter, referred to as a land ray).

Therefore, if the upper limit of conditional expression (4) is exceeded,
Too large an air gap t ₂ between the second lens component L ₂ and the third lens component L _3, reduces the effect of the air lens. Further, since the third lens component L ₃ is located farther from the stop S, the land ray passes through a portion of the third lens component L ₃ closer to the optical axis, so that the effect of spherical aberration correction is reduced. Decrease, and as a result, it becomes difficult to increase the diameter,
Not preferred.

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 oblique rays and land rays deteriorates. 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 remarkably approach each other and come into contact with each other at the peripheral portion of the lens, resulting in a decrease in peripheral light quantity, and furthermore, mechanical interference causes the main lens element to have a maximum angle of view. It is not preferable because light rays cannot enter.

When the upper limit is set to 0.098, the effect of the present invention can be further exhibited. 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. When falling below the lower limit of conditional expression (5), the positive lens L
The difference between the refractive index of ₁₁ and a negative lens L ₁₂ decreases, Petzval sum becomes large in a simple structure as in the present invention,
The curvature of field is displaced in the negative direction, which is not preferable because it deteriorates. Conversely, if the value exceeds the upper limit, it becomes difficult to correct the spherical aberration even if an effect of an air lens or the like is added. As a result, since the difference in dispersion tends to be small, it becomes difficult to correct chromatic aberration.

Further, the lower limit is required to exert the effect of the present invention.
Desirably 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
Is a condition for setting a difference from the refractive index n ₂₂ of the light emitting element. If the lower limit of conditional expression (6), to the difference of the conditional expression (5) as in the case positive lens L ₂₂ and the refractive index of the negative lens L ₂₁ of decreases, a simple structure as in the present invention The Petzval sum increases and the curvature of field is displaced in the negative direction, which is not preferable. Conversely, if the value exceeds the upper limit, correction of spherical aberration becomes difficult and the aperture cannot be increased even if the effect of an air lens or the like is obtained. As a result, the difference in variance also decreases,
It is not preferable because chromatic aberration correction becomes difficult.

Conditional expression (7) indicates that the air interval between the first lens component L ₁ and the second lens component L _2, that is, the aperture interval t _1.
Is a conditional expression that defines Balance falls below the lower limit of the condition (7), and only if, the axial aberration and off-axis aberrations even by aberrations equality program lens shutter or a compact camera aperture interval t ₁ the shutter can not enter the mechanical It becomes difficult to take. Further, it is difficult to correct axial chromatic aberration and magnification chromatic aberration, which is not preferable. Conversely, if the upper limit is exceeded, the aperture interval t ₁ becomes large, and the total thickness of the lens also becomes large. In particular, the lens diameter of the lens far 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 peripheral light amount is reduced. In terms of aberration, the third lens component L ₃ is separated from the stop S by the third lens component L _3.
In addition, the effect of correcting 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 the spherical aberration, is not preferable.

[0028] Conditional expression (8) is a conditional expression that defines the synthesis thickness of the central thickness of the positive lens L ₂₂ of the positive lens L ₁₁ of the first lens in the component L ₁ second lens in the component L _2. In the case of a lens having a simple configuration as in the present invention, it is important to properly 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 better the correction of spherical aberration. Therefore, when the value is below the lower limit, not only is it difficult to correct spherical aberration, but also the edge thickness of the cemented positive lens becomes extremely small, which makes the manufacturing difficult, which is not preferable. Conversely, when the value exceeds the upper limit, the total thickness of the lens increases and the lens diameter also increases, which is not preferable.

Conditional expression (9) is a condition relating to downsizing of the lens and correction of off-axis aberrations, particularly astigmatism and curvature of field. When the value falls below the lower limit of the conditional expression, there are two cases. Positive lens L ₂₂ and the negative lens L of the second lens in the component L _2
When the difference in the refractive index of ₂₁ is very small. If 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 (1), the Petzval sum becomes large and it becomes difficult to correct the curvature of field, which is not preferable. In such a case, the effect of the air lens is reduced and it becomes difficult to correct spherical aberration, and the total thickness of the lens is increased. That lens diameter of the third lens component L ₃ becomes large in size because, contrary to compactness.
It also leads to an increase in cost, which is not preferable.

Conversely, there are two cases of exceeding the upper limit. Positive lens L ₂₂ and the negative lens L of the second lens in the component L _2
When the difference between the refractive indices of ₂₁ is very large. If the air gap t ₂ between the second lens component L ₂ and the third lens component L ₃ is very small. In the case of (1), not only the correction of the spherical aberration becomes difficult, but also the difference in dispersion of the glass used becomes small, and the correction of the chromatic aberration becomes difficult. In such a case, the separation of on-axis and off-axis rays deteriorates in a lens farther from the stop S, and in particular, correction of upward coma, astigmatism, curvature of field, and the like deteriorates. The second lens component L ₂ and the third lens component L ₃ significantly closer, undesirable mutually mechanically interfere with the periphery. If the lower limit is set to 1.2, better results can be obtained.

[0031] Condition (10) is a condition set 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 the plano-concave lens having a convex surface facing the image plane, off-axis aberrations, particularly upper coma and astigmatism, to correct curvature of field becomes difficult. Conversely, when the value exceeds the upper limit when the third lens component L _3, becomes more curved meniscus lens, high-order aberration occurs for off-axis rays. For this reason, especially upper coma is deteriorated,
Furthermore, it also has an adverse effect on spherical aberration. Also the shape of the third lens component L ₃ is semicircular, Ki not a more proximal, manufacturing is not preferable.

[0032] Incidentally the present case, the length is relatively large, but the total thickness shorter as much as possible (axial Atsushi Kazusa from the first lens first surface of the component L ₁ to the last surface of the third lens component L ₃₎ Making an effort. Therefore, the back focus of the third lens component L ₃ is reduced, and strong wide-angle lens having asymmetric structure as to shorten the overall length, totally different. Aberrational drawbacks resulting from the use of a lens type having strong asymmetry to forcibly reduce the overall length as described above are as described above. In particular, chromatic aberration of magnification and color difference of coma (chromatic coma) However, there is a limit to the correction of distortion and the like, and good correction cannot be performed.

Therefore, it is disadvantageous and unfavorable to forcefully reduce the total length in terms of aberrations, and the entire thickness (from the first surface of the first lens component L ₁ to the third lens component L
_{The method of} reducing the total thickness up to the last surface of ( ₃ ) as much as possible to increase the back focus and collapsing that portion to make it compact is also advantageous in terms of aberration. Furthermore, when the following conditions are satisfied, the effects of the present invention can be further exhibited.

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 whole system f ₁ : focal length of the first lens component L ₁ f ₃ : third lens The focal length f _R of the component L ₃ : the composite focal length of the second lens component L ₂ and the third lens component L ₃ νd ₁₁ : the Abbe number of the positive lens on the object side in the first lens component L ₁ ν ₂₂ : the second lens component L ₂ in the image side of the positive lens Abbe number r _22: the second lens component of the joint surface of the radius of curvature r _23: the second lens component L of the most image-side surface of the ₂ radius of curvature r _31: the The radius of curvature of the three-lens component L ₃ closest to the object side Conditional expression (11) is a conditional expression that sets the refractive power of the third lens component L ₃ . When the value goes 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 upward coma and astigmatism, but also it becomes difficult to correct spherical aberration. Conversely, when the value exceeds the upper limit, the asymmetry becomes stronger, so that not only the chromatic aberration of magnification and the difference in color of coma (chromatic coma) and distortion become worse, but also the difference due to the difference in image height of coma increases, which is preferable. Absent.

Conditional expression (12) represents the refractive power of the first lens component L ₁ in the front group and the second lens component L _{2 in} the rear group with the stop S interposed therebetween.
When it is intended to set an appropriate balance of the refractive power of the combination of the third lens component L _3. Below the lower limit, the symmetry becomes too strong, and it becomes difficult to correct spherical aberration with a lens having a simple configuration as in the present invention. Conversely, when the value exceeds the upper limit, asymmetry becomes strong, and chromatic aberration of magnification, chromatic coma,
Distortion and the like are undesirably deteriorated.

The 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 conditional expressions are below the lower limits, it becomes difficult to correct axial chromatic aberration and lateral chromatic aberration. Conversely, if the value exceeds the upper limit, the correction of chromatic aberration is good, but as a result, only a glass having a low refractive index can be selected, so that it becomes difficult to set the Petzval sum to an appropriate value. Since the lens is made of glass having a low refractive index, it becomes difficult to correct spherical aberration.

[0037] Condition (15) is a conditional expression that defines the central thickness of the positive lens L ₁₁ of the first lens in the component L ₁ negative lens L _12. If this conditional expression is not satisfied, spherical aberration is undesirably deteriorated. Condition (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. If this condition is not satisfied, it becomes difficult to correct axial chromatic aberration.

Conditional expression (17) indicates that 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. When this conditional expression is not satisfied, the ability of the air lens to correct spherical aberration is reduced because the air lens has a concave shape, and it becomes difficult to correct spherical aberration.

[0039]

FIG. 1, FIG. 3, FIG. 5, and FIG.
FIG. 7 and FIG. Examples 1 to 4, in order from the object side, a first lens component L ₁ of the cemented positive lens consisting of bonding of the positive lens L ₁₁ and the negative lens L _12, stop S
When, a second lens component L ₂ of the cemented positive lens consisting of bonding between the negative lens L ₂₁ and the positive lens L _22, is constituted by the third lens component L ₃ of the negative meniscus lens having a convex surface directed toward the image surface I have.

In the fifth embodiment, in order from the object side, a first lens component L ₁ of a cemented positive lens formed by bonding a positive lens L ₁₁ and a negative lens L ₁₂ , an aperture S, and a negative lens L
₂₁ and bonded to the second lens component L ₂ of the cemented positive lens consisting of a combined with the positive lens L _22, is constituted by the third lens component L ₃ of the negative meniscus lens having a convex surface directed toward the image plane, the third
The lens component L ₃ is an example in which a non-spherical plastic lens. By adding an aspherical surface to the lens closest to the image side or the lens closest to the object side, curvature of field, distortion, and coma are corrected, and further downsizing and cost reduction are made possible.

It is needless to say that the spherical aberration can be further corrected by making the first lens component L _1, the second lens component L _{2, and the} like aspherical, thereby increasing the aperture. The formula of the aspheric surface is shown below. The aspherical shape has an x-axis in the optical axis direction, a y-axis in a direction perpendicular to the optical axis, a positive traveling direction of the light, r is a paraxial radius of curvature, K is a conic constant, C2, C
When each of 4, C6, C8, and C10 is an aspheric coefficient,

[0042]

(Equation 1)

Is represented by

Tables 1 to 5 below show values of various embodiments of the present invention. The leftmost numeral in the specification table represents 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, ν is the Abbe number, and 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 show the aberration curve by the g line (λ = 435.8 nm). In the figure, the dotted line of astigmatism shows the meridional image plane, and the solid line shows the sagittal image plane. Each of the aberration diagrams in each embodiment has excellent aberrations corrected over a wide range from the wide-angle end to the telephoto end, and has excellent imaging performance.

[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 = -5.350109 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 becomes very thin if the system is retracted in the camera body.
In addition, the present invention can be used not only for 35 mm format cameras but also for lenses for large format cameras, etc. By introducing an aspherical surface in a lens far from the stop S, astigmatism and off-axis aberrations such as coma can be reduced. Compensation and further downsizing are possible
It is clear from the embodiments of the present invention. In addition, by introducing an aspherical surface near the stop S, it is needless to say that the spherical aberration can be further corrected and the aperture can be made larger as in a general method of using an aspherical surface.

[0050]

As described above, according to the present invention, it is applicable to a compact lens shutter type camera or a camera with a range finder and the like. And a bright wide-angle lens of about F2.8 with very little flare and ghost can be realized.

[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.

[Description of Signs of Main Parts]

L _1: first lens component L _2: second lens component L _3: third lens component S: stop

Claims (3)

(57) [Claims] 1. A first lens component L ₁ of the cemented positive lens having a convex surface directed toward the object side paste consisting together with the positive lens L ₁₁ in order from the object side a negative lens L _12, a negative lens L ₂₁ and the positive lens L _A second lens component L _{2 of} a cemented positive lens having a convex surface facing the image side and a third lens component L _{3 of} a negative meniscus lens having a convex surface facing the image side.
Said first lens component L ₁ and provided between the second lens component L _2, a small wide-angle lens that 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) where f: focal length of the whole system t ₂ : 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 for the d-line of the image-side negative lens in the first lens component L ₁ n ₂₁ : d of the object-side negative lens in the second lens component L ₂
Refractive index n ₂₂ with respect to the line: a second lens component L refractive index at the d-line of the image side of the positive lens in the ₂ d _21: axial center thickness of the negative lens on the object side in the second lens component L ₂ d ₂₂ is an 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 axial air distance from the surface to the surface on the most object side in the second lens component L ₂ (stop interval) 3. The compact 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) where d ₁₁ : On-axis center thickness of the positive lens on the object side in the first lens component L ₁ q ₃ : shape factor of the third lens component L ₃ shape factor 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 aspheric surface, the paraxial radius of curvature is used instead) r ₂ : The radius of curvature of the image-side surface of the lens (however, in the case of an aspheric surface, the paraxial radius of curvature Substitute calculation)