JPH10133111A - Inner focal type zoom lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inner focal type zoom lens of high performance having a large view angle, a high variable power ratio exceeding 3.5 times, a large aperture whose F number is about 2.8 to 3.5. SOLUTION: This zoom lens is provided with a first lens group G1 of a positive refractive power, a second lens group G2 of a negative refractive power and a third lens group G3 of a positive refractive power. The second lens group G2 has a negative lens component L2A whose at least one surface is formed as an asphrical surface, a joined positive lens component L2B of a positive lens to a negative lens whose convex surface confronts the object side and a negative lens component whose concave surface confronts the object side. Focusing from an object an infinity to the close distance is performed by moving at least the third lens group G3 along the optical axis.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an in-focus type zoom lens, and more particularly to a large-aperture, high-magnification zoom lens having a relatively large angle of view and a relatively large aperture for focusing by a so-called in-focus method. is there.

[0002]

2. Description of the Related Art A large number of so-called standard zoom lenses have been proposed which start with a positive lens group, a negative lens group, and a positive lens group in order from the object side. In particular, JP-A-58-
JP-A-30709 and JP-A-58-179810 propose a small-sized standard zoom lens having a maximum angle of view of 62 ° and a zoom ratio of about 3 times.

Further, Japanese Patent Application Laid-Open No.
JP-A-208911 and JP-A-4-208912 propose a large-aperture high-magnification zoom lens. This high-magnification zoom lens has a maximum angle of view of 62 °, a zoom ratio of about 3 times, an F-number of 2.8 over the entire zoom range, and a large aperture as a standard zoom lens. Having. In this high-magnification zoom lens, focusing is performed by moving the second lens group and the third lens group.

[0004]

However, Japanese Patent Application Laid-Open Nos. 58-30709 and 58-17981 disclose the following.
The zoom lens disclosed in Japanese Patent Publication No. 0 has a relatively large aperture with an F-number of 3.5 (relatively bright).
However, the zoom ratio is about three times, and the maximum angle of view is only about 62 °. Also, from the viewpoint of aberrations, fluctuations in astigmatism due to spherical aberration and zooming are not satisfactorily corrected,
The fluctuation of coma remains. Therefore, based on the configuration and refractive power arrangement of this zoom lens, the angle of view is 7
It is difficult to realize a large-diameter high-magnification zoom lens exceeding 5 °. The above publication does not describe the focusing method in detail.

In the large-aperture zoom lens disclosed in Japanese Patent Application Laid-Open Nos. 4-208911 and 4-208912, aberration correction is favorably performed, and the F-number is as bright as 2.8. The ratio is about three times, and the maximum angle of view is only about 62 °. As described above, in the conventional zoom lens, further higher magnification and a larger angle of view are desired, and as for the focusing method, a method with a small change in aberration and focal length and a simple focusing mechanism is desired. It is rare.

The present invention has been made in view of the above problems, has a large angle of view, has a high zoom ratio exceeding 3.5 times, and has an F-number of 2.8 to 3.5. It is an object of the present invention to provide a high performance inner focus type zoom lens having a large aperture.

[0007]

According to the present invention, a first lens group G1 having a positive refractive power and a second lens group G1 having a negative refractive power are sequentially arranged from the object side. G2, and at least a third lens group G3 having a positive refractive power. The air gap between the first lens group G1 and the second lens group G2 and the second lens group G
In a zoom lens that performs zooming by changing the air spacing between the second lens group G3 and the third lens group G3, the second lens group G2 has at least one aspheric surface in order from the object side. The formed negative lens component L
2A, a cemented positive lens component L2B formed by bonding a positive lens and a negative lens with a convex surface facing the object side, and a negative lens component L2C with a concave surface facing the object side, and at least the third lens group. An in-focus type zoom lens is provided which focuses from an object at infinity to an object at a short distance by moving G3 along the optical axis.

According to a preferred aspect of the present invention, the paraxial radius of curvature of the most object side surface of the negative lens component L2A is Raf, and the paraxial radius of curvature of the most image side surface of the negative lens component L2A is Rar. Satisfies the following condition: (Rar + Raf) / (Rar−Raf) ≦ −1 (1) The on-axis air gap between the negative lens component L2A and the cemented positive lens component L2B is dAB, and the total axial thickness of the second lens group G2 from the most object side surface to the most image side surface is dAB. When d2, it is preferable to satisfy the following condition: 0.28 ≦ dAB / d2 ≦ 0.8 (2)

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the basic configuration of the present invention will be described. The present invention relates to a convex-leading type zoom lens in which a positive lens group is disposed closest to the object side, wherein a second lens group G2 capable of simultaneously satisfying three specifications of a large angle of view, a large aperture, and a high magnification. I found the configuration.

As described above, the second lens group G2 basically includes, in order from the object side, three lens components of a negative lens component, a positive lens component, and a negative lens component. Have. The intermediate positive lens component is composed of a cemented positive lens component L2B formed by bonding a positive lens with a convex surface facing the object side and a negative lens. The air gap between the cemented positive lens component L2B and the negative lens component L2A disposed on the object side is sufficiently large. By ensuring a sufficiently large air gap, the principal ray having a large angle of view in the vicinity of the wide-angle end can be pushed up in the optical axis direction, and the filter size can be reduced. Also, by keeping the air gap at an appropriate size, the dead space (variable air gap) between the first lens group G1 and the second lens group G2, which is problematic in downsizing the high-magnification zoom lens, is reduced. It becomes possible to secure.

However, in the negative / negative / negative type, the negative / negative / positive type, and the negative / negative / positive / negative type of the power arrangement of the second lens group G2 used in the conventional convex leading type zoom lens, the present invention is not applicable. To achieve the same effect as the above-described effect of the present invention, the total axial thickness of the second lens group becomes too large because the number of constituent lenses is large. Also, the second lens group G
The dead space between the second and subsequent lens groups is reduced, resulting in an increase in the overall length and an increase in the filter size due to an increase in the wall thickness.

In the present invention, it is important to form an intermediate positive lens component by a cemented positive lens component L2B formed by bonding a positive lens and a negative lens with the convex surface facing the object side. First, the concave surface having a strong curvature on the image side of the negative lens component L2A having a relatively strong refractive power and the convex surface on the object side of the cemented positive lens component L2B effectively contribute to the correction of downward coma mainly on the wide angle side. doing. In addition, on the telephoto side, in addition to the correction of the downward coma, similarly to the cemented surface of the cemented positive lens component L2B, it effectively contributes to the correction of the spherical aberration. In order to further enhance this effect, it is effective that the negative lens component L2A has an appropriate refractive power and has a concave surface having a strong curvature toward the image side.

In order to constitute the negative lens component L2A with one single lens, it is basically necessary to introduce an aspheric surface into the negative lens component L2A. By introducing an aspherical surface, distortion on the wide-angle side and downward coma over the entire area can be corrected well, and the negative lens component L2A and the cemented positive lens component L
Even if a sufficient air gap from 2B is ensured, the thickness is reduced and the diameter is reduced, as described above, without significant increase in thickness.

When an aspherical surface is introduced into the negative lens component L2A, it is preferable to introduce an aspherical surface into a concave surface having a strong curvature on the image side of the negative lens component L2A. By introducing an aspherical surface to the image-side surface of the negative lens component L2A, it is possible to reduce the number of components of the negative lens component L2A and to reduce the thickness thereof. The degree of freedom for correction is further increased. Also, the negative lens component L2A
Rand ray on the image side of the telephoto side (ray parallel to the optical axis)
Is large, and the introduction of an aspherical surface increases the degree of freedom for correcting spherical aberration on the telephoto side. Furthermore, it is desirable to introduce a conical coefficient κ when defining the shape of the aspherical surface, because it becomes possible to more finely control the amount of aspherical displacement from a low-order coefficient term to a high-order coefficient term of the aspherical coefficient.

The object-side surface of the negative lens component L2A is:
It is desirable that the convex surface is directed to the object side. When the negative lens component L2A has a concave surface facing the object side, correction of astigmatism and downward coma mainly on the wide-angle side deteriorates, and a large angle of view cannot be realized. In the cemented positive lens component L2B, setting the refractive index of the negative lens to be larger than that of the positive lens is advantageous for increasing the aperture. Also,
It is preferable that the most object side surface of the negative lens component L2C has a concave surface facing the object side, and a convex air lens is formed between the negative lens component L2C and the cemented positive lens component L2B. In this case, the convex air lens can favorably correct mainly the spherical aberration and the coma aberration on the telephoto side, which is advantageous for a larger aperture.

When the second lens group G2 is viewed as a whole, the intermediate cemented positive lens component L2B is sandwiched between the negative lens component L2A and the negative lens component L2C.
As described above, since the second lens group G2 is generally close to a symmetrical structure, various aberrations generated in the second lens group G2 can be reduced even when the second lens group G2 is small and has a relatively strong refractive power arrangement. It can be minimized. This configuration of the second lens group G2 is particularly suitable for a zoom lens that needs to satisfy both a large aperture and a large angle of view at the same time. further,
By introducing an aspheric surface to both the negative lens component L2A and the negative lens component L2C, it becomes possible to realize a second lens group G2 that is more compact and can withstand a relatively strong refractive power arrangement.

By employing the structure of the second lens group G2 as described above, even when focusing is performed in accordance with the inner focus method (inner focus method), it is possible to favorably suppress aberration fluctuations due to focusing. Will be possible. That is, by configuring the second lens group G2 having the most influence on the aberration variation during zooming according to the present invention, the second lens group G2
In particular, the third aberration can be minimized.
The degree of freedom of aberration correction of the lens group G3 can be used for correction of short-range fluctuation (aberration fluctuation generated due to focusing on a short-distance object). The third lens group G3 is the closest to the aperture stop, and has a small variation in curvature of field and astigmatism even when the third lens group G3 moves. Therefore, the third lens group G3 is preferable as a focusing lens group.

Hereinafter, the conditional expression of the present invention will be described.
In the present invention, it is preferable to satisfy the following conditional expression (1). (Rar + Raf) / (Rar-Raf) ≦ -1 (1) where, Raf: the paraxial radius of curvature of the surface closest to the object side of the negative lens component L2A Ra: the paraxial radius of the surface closest to the image of the negative lens component L2A curvature radius

Conditional expression (1) defines the shape factor of the negative lens component L2A. Exceeding the upper limit of conditional expression (1) means that the negative lens component L2A
Is a biconcave shape. When the shape of the negative lens component L2A is biconcave, as described above, it becomes difficult to correct mainly off-axis monochromatic aberrations such as astigmatism on the wide-angle side and downward coma, as well as correction of chromatic aberration of magnification. Will also be difficult. As a result, a zoom lens having a large angle of view cannot be realized. When an aspherical surface is introduced into the negative lens component L2A, the conditional expression (1) is calculated based on the paraxial radius of curvature of the aspherical surface. When the negative lens component L2A is composed of a cemented lens, conditional expression (1) is calculated by setting the radius of curvature of the surface closest to the object side to Raf and the radius of curvature of the surface closest to the image side to Rar.

In the present invention, it is preferable to satisfy the following conditional expression (2). 0.28 ≦ dAB / d2 ≦ 0.8 (2) where, dAB: the axial air gap between the negative lens component L2A and the cemented positive lens component L2B d2: the most object-side surface of the second lens group G2 Total axial thickness from to the image-side surface

Conditional expression (2) defines an appropriate range for the on-axis air gap dAB between the negative lens component L2A and the cemented positive lens component L2B. As described above, the axial air gap dAB between the negative lens component L2A and the cemented positive lens component L2B
Is sufficiently large, the principal ray having a large angle of view near the wide-angle end can be pushed up in the optical axis direction, and the filter size can be reduced. Further, it is possible to secure a dead space (variable air gap) between the first lens group G1 and the second lens group G2, which is a problem in downsizing the high-magnification zoom lens.

If the lower limit of conditional expression (2) is not reached, the axial air gap dAB becomes too small, and the effect of pushing up the principal ray having a large angle of view in the vicinity of the wide-angle end in the optical axis direction is significantly reduced. As a result, the filter size becomes large and the amount of peripheral light is insufficient, and it is impossible to achieve a large angle of view. Setting the lower limit of conditional expression (2) to 0.32 is more advantageous for miniaturization and diameter reduction. Further, when the lower limit of conditional expression (2) is set to 0.34,
The effects of the present invention can be maximized.

On the other hand, when the value exceeds the upper limit of conditional expression (2),
The on-axis air gap dAB becomes too large, and the second lens group G
It becomes difficult to secure a dead space (variable air gap) between the lens unit 2 and the lens group following the image side. As a result, the size of the zoom lens increases, and it is not possible to achieve high magnification. Also, other lens components are too thin,
It becomes difficult to correct important aberrations. In particular, in the case of a large-aperture zoom lens having a large angle of view as in the present invention, it becomes difficult to correct spherical aberration on the telephoto side, and it is not possible to achieve a large-aperture. Note that the upper limit of conditional expression (2) is set to 0.6.
If it is set to, it is possible to expect a larger diameter. If the upper limit of conditional expression (2) is set to 0.5, the effects of the present invention can be maximized.

In the present invention, it is preferable to satisfy the following conditional expression (3). n2p−n2n <0 (3) where, n2p: refractive index of the positive lens in the cemented positive lens component L2B with respect to the d-line n2n: refractive index of the negative lens in the cemented positive lens component L2B with respect to the d-line

Conditional expression (3) defines the magnitude relationship between the refractive index of the positive lens and the refractive index of the negative lens in the cemented positive lens component L2B. As described above, by setting the refractive index of the negative lens to be larger than that of the positive lens in the cemented positive lens component L2B, it becomes possible to favorably correct spherical aberration particularly on the telephoto side. This is advantageous for increasing the diameter. Incidentally, the cemented positive lens component L2B is a positive lens component in the second lens group G2 having a negative refractive power. Therefore, in order to set the Petzval sum to an appropriate value, it is necessary that the refractive index of the negative lens is larger than that of the positive lens. Thus, by satisfying conditional expression (3), it is possible to appropriately set the Petzval sum, and it is also possible to satisfactorily correct field curvature and astigmatism. It should be noted that the upper limit of conditional expression (3) is-
When it is set to 0.015, the effects of the present invention can be maximized.

In the present invention, it is preferable to satisfy the following conditional expression (4). 0.3 <f3 / fT <1 (4) where, f3: focal length of the third lens group G3, fT: focal length of the entire system at the telephoto end.

Conditional expression (4) defines an appropriate range for the focal length f3 of the third lens group G3. If the lower limit of conditional expression (4) is not reached, the refractive power of the third lens group G3 becomes too large, and an attempt to increase the aperture is not preferable because spherical aberration particularly on the telephoto side deteriorates. In addition, in order to perform satisfactory aberration correction, it is not preferable to avoid an increase in the number of constituent lenses, resulting in an increase in size.
If the lower limit of conditional expression (4) is set to 0.35,
The effects of the present invention can be maximized. on the other hand,
If the value exceeds the upper limit of conditional expression (4), the refractive power of the third lens group G3 becomes too small, so that the lens outer diameter becomes large, which is disadvantageous for downsizing and reducing the diameter of the entire lens system. When the upper limit of conditional expression (4) is set to 0.8, the effects of the present invention can be maximized.

In the present invention, the third lens group G
3 preferably has at least one cemented positive lens Lc formed by bonding a positive lens and a negative lens, and preferably satisfies the following conditional expression (5). n3p-n3n <0 (5) where n3p is the refractive index of the positive lens in the cemented positive lens Lc with respect to the d-line. n3n is the refractive index of the negative lens in the cemented positive lens Lc with respect to the d-line.

Condition (5) defines the magnitude relationship between the refractive index of the positive lens and the refractive index of the negative lens in the cemented positive lens Lc of the third lens group G3. Cemented positive lens Lc
By setting the refractive index of the negative lens to be larger than the refractive index of the positive lens, it is possible to favorably correct spherical aberration particularly on the telephoto side, which is advantageous for increasing the aperture. Further, in order to set the Petzval sum to an appropriate value, it is necessary that the refractive index of the negative lens is larger than that of the positive lens. As described above, by satisfying conditional expression (5), it is possible to appropriately set the Petzval sum, and it is also possible to appropriately correct field curvature and astigmatism. When the upper limit of conditional expression (5) is set to -0.1, the effects of the present invention can be maximized.

As described above, in the present invention, an aspheric surface is introduced into the second lens group G2. However, by introducing an aspheric surface to the third lens group G3 and the fourth lens group G4, correction of spherical aberration, upper coma aberration, and the like is burdened on the aspheric surface, and a large aperture, a high magnification, and a large angle of view are provided. It is possible to proceed further.

[0031]

Embodiments of the present invention will be described below with reference to the accompanying drawings. The zoom lens according to each embodiment of the present invention includes, in order from the object side, a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, and a second lens group G2 having a positive refractive power. The third lens group G3 includes a fourth lens group G4 having a positive refractive power. The second
The lens group G2 includes, in order from the object side, a negative lens component L2A having at least one surface formed in an aspherical shape, and a cemented positive lens component formed by bonding a positive lens having a convex surface facing the object side and a negative lens. L2B and a negative lens component L2C having a concave surface facing the object side.

In each of the embodiments, the aspheric surface has a height in a direction perpendicular to the optical axis of y and a displacement amount in the optical axis direction at the height y (along the optical axis from the tangent plane of the apex of each aspheric surface). When the distance (sag amount) is S (y), the reference radius of curvature is R, the conic coefficient is κ, and the nth order aspherical coefficient is Cn, the following equation (a) is used.

[Number 1] ^{S (y) = (y 2} / R) / {1+ (1-κ · y 2 / R 2) 1/2} + C 2 · y 2 + C 4 · y 4 + C 6 · y 6 + C 8 _{^{· y 8 + C 10 · y}} 10 + ··· (a) the paraxial curvature radius r of the aspherical surface is expressed by the following equation (b). r = 1 / (2 · C ₂ + 1 / R) (b) In each embodiment, the aspherical surface is marked with an asterisk on the right side of the surface number.

[First Embodiment] FIG. 1 is a diagram showing a lens configuration of a zoom lens according to a first embodiment of the present invention.
In the zoom lens of FIG. 1, the first lens group G1 includes, in order from the object side, a cemented positive lens L11 of a negative meniscus lens having a convex surface facing the object side and a biconvex lens, and a positive meniscus lens having a convex surface facing the object side. L12. The second lens group G2 includes, in order from the object side, a negative meniscus lens L2A having an aspherical surface on the image side and a convex surface facing the object side, a cemented positive lens L2B formed of a biconvex lens and a biconcave lens, and an object side. Is made up of a negative meniscus lens L2C having an aspheric surface and a concave surface facing the object side.

The third lens group G3 comprises, in order from the object side, a positive meniscus lens L31 having a concave surface facing the object side, and a cemented positive lens L32 of a biconvex lens and a negative meniscus lens having a concave surface facing the object side. ing. The fourth lens group G4 includes, in order from the object side, a positive meniscus lens L41 having a convex surface facing the object side, a cemented negative lens L42 having a biconvex lens and a biconcave lens, a negative meniscus lens and a biconvex lens having a convex surface facing the object side. A positive lens L43, a biconvex lens L44,
And a negative meniscus lens L45 having a concave surface facing the object side.

The second lens group G2 and the third lens group G
An aperture stop A is disposed between the zoom lens 3 and the aperture stop A, and upon zooming, the aperture stop A moves integrally with the third lens group G3. FIG.
Shows the lens arrangement at the wide-angle end. Upon zooming to the telephoto end, the first lens group G1 and the second lens group G2
Between the second lens group G2 and the third lens group G2 are increased.
All the lens groups move toward the object side so that the air gap between the lens groups G3 decreases. Further, when focusing from an object at infinity to an object at a short distance, the third lens group G3 and the aperture stop A move integrally to the image side along the optical axis.

Table 1 below summarizes the data values of the first embodiment of the present invention. In Table (1), f is the focal length,
FNO is the F number, 2ω is the angle of view, Bf is the back focus, β is the shooting magnification, and D0 is the object point distance (the distance along the optical axis between the most object side surface and the object). Represents. Further, the surface number indicates the order of the lens surfaces from the object side along the traveling direction of the light beam, d indicates the distance between the lens surfaces, r indicates the radius of curvature (the paraxial radius of curvature for an aspheric surface),
n is the refractive index for the d-line (λ = 587.6 nm), ν
Indicates Abbe numbers.

[0037]

Table 1 f = 29 to 102 FNO = 3.6 2ω = 76.2 to 23.2 ° Surface number rd ν n 1 209.1994 2.0000 25.50 1.804581 2 123.3916 8.0000 82.52 1.497820 3 -344.5143 0.1000 4 56.5074 5.4000 82.52 1.497820 5 93.2641 (d5 = variable) 6 109.1250 1.7000 49.45 1.772789 7 * 15.6692 10.6649 8 60.4809 7.0000 28.19 1.740000 9 -25.6142 1.4000 49.45 1.772789 10 115.3664 4.5000 11 * -26.1284 2.0000 49.45 1.772789 12 -37.3890 (d12 = variable) 13 Aperture stop 2.5000 14- 1254.9023 4.5000 58.90 1.518230 15 -47.1898 0.1000 16 62.0105 10.0000 61.09 1.589130 17 -30.8950 2.0000 28.56 1.795040 18 -89.4354 (d18 = variable) 19 47.1402 5.0000 58.90 1.518230 20 716.9156 1.0000 21 132.5979 4.5000 64.10 1.516800 22 -106.3722 1.6000 459.77 45.37 5.794 443.3049 1.7000 37.20 1.834000 25 39.5548 9.0000 48.97 1.531721 26 -38.1373 0.1000 27 74.7573 5.0000 64.10 1.516800 28 -164.5801 3.2000 29 -37.2162 2.0000 49.45 1.772789 30 -82.4474 (Bf) ( aspheric data) kappa C _{2 4} Surface 7 _{^{0.9234 0.0000 -6.92030 × 10 -6 C 6}} C 8 C 10 -7.94420 × 10 -9 -8.61250 × 10 -11 5.54370 × 10 -15 κ C 2 C 4 11 faces 0.2639 0.0000 1.59190 × 10 ^-6 C ₆ C ₈ C ₁₀ 1.20720 × 10 ^-8 4.25920 × 10 ^-11 7.42530 × 10 ^-14 (Variable interval in scaling) f 29.00000 50.00000 102.00000 D0 ∞ ∞ 5 d5 1.15591 21.97167 52.32140 d12 21.87071 9.69582 0.86248 d18 11.97487 3.33400 4.98721 Bf 37.9921761.345 (Variable interval in focusing operation) 37.99796 61.35165 88.38261 38.01177 61.40104 88.56586 (Conditional value) (1) (Rar + Raf) / (Rar-Raf) =-1.34 (2) dAB / d2 = 0.391 (3) n2p-n2n = -0.0328 4) f3 / fT = 0.448 (5) n3p-n3n = -0.2059

FIGS. 2 to 7 are graphs showing various aberrations of the first embodiment. That is, FIG. 2 is a diagram showing various aberrations at the infinity in-focus condition at the wide-angle end, FIG. 3 is a diagram showing various aberrations at the infinity-focus condition at the intermediate focal length, and FIG. The various aberration diagrams in the in-focus state are shown. FIG. 5 is a diagram showing various aberrations at a photographing magnification of 1/30 at the wide-angle end, and FIG. 6 is a photographing magnification of 1/30 at an intermediate focal length.
FIGS. 7A and 7B show various aberration diagrams at a magnification of 1/30 at the telephoto end, respectively. In each aberration diagram, FNO represents the F number, A represents the half angle of view, H0 represents the object height, and d represents the d-line (λ = 587.6n).
m) and g indicate the g-line (λ = 435.8 nm). In the aberration diagram showing astigmatism, a solid line indicates a sagittal image plane, and a broken line indicates a meridional image plane. Further, in the aberration diagram showing spherical aberration, a broken line indicates a sine condition (sine condition).

Referring to the aberration diagram of FIG. 2, it can be seen that the wide angle of view covers a sufficiently large angle of view at the wide angle end, and that various aberrations are satisfactorily corrected. Referring to the aberration diagrams of FIGS. 3 and 4, it can be seen that various aberrations are favorably corrected as in the case of the wide-angle end. On the other hand, referring to the aberration diagram of FIG. 5, it can be seen that the zoom lens covers a sufficiently large angle of view at the wide-angle end, has little short-range variation, and satisfactorily corrects aberrations. Referring to the aberration diagrams in FIGS. 6 and 7,
As in the case of the wide-angle end, it can be seen that the short-range variation is small, and various aberrations are corrected well. As described above, in the first embodiment, various aberrations are favorably corrected in each focal length state and each shooting distance state.

[Second Embodiment] FIG. 8 is a diagram showing a lens configuration of a zoom lens according to a second embodiment of the present invention.
In the zoom lens of FIG. 8, the first lens group G1 includes, in order from the object side, a cemented positive lens L11 of a negative meniscus lens having a convex surface facing the object side and a biconvex lens, and a positive meniscus lens having a convex surface facing the object side. L12. The second lens group G2 includes, in order from the object side, a negative meniscus lens L2A having an aspheric surface on the image side and a convex surface facing the object side, a biconvex lens, and a negative meniscus lens having a concave surface facing the object side. It is composed of a cemented positive lens L2B and a cemented negative lens L2C of a biconcave lens and a biconvex lens each having an aspherical object side surface.

The third lens group G3 comprises, in order from the object side, a biconvex lens L31 and a cemented positive lens L32 of a biconvex lens and a negative meniscus lens having a concave surface facing the object side. The fourth lens group G4 includes, in order from the object side, a positive meniscus lens L41 having a convex surface facing the object side, a cemented negative lens L42 having a biconvex lens and a biconcave lens, a negative meniscus lens and a biconvex lens having a convex surface facing the object side. , A double meniscus lens L45 having a concave surface facing the object side.

The second lens group G2 and the third lens group G
An aperture stop A is disposed between the zoom lens 3 and the aperture stop A, and upon zooming, the aperture stop A moves integrally with the third lens group G3. FIG.
Shows the lens arrangement at the wide-angle end. Upon zooming to the telephoto end, the first lens group G1 and the second lens group G2
Between the second lens group G2 and the third lens group G2 are increased.
All the lens groups move toward the object side so that the air gap between the lens groups G3 decreases. Further, when focusing from an object at infinity to an object at a short distance, the third lens group G3 and the aperture stop A move integrally to the image side along the optical axis.

Table 2 below summarizes data values of the second embodiment of the present invention. In Table (2), f is the focal length,
FNO is the F number, 2ω is the angle of view, Bf is the back focus, β is the shooting magnification, and D0 is the object point distance (the distance along the optical axis between the most object side surface and the object). Represents. Further, the surface number indicates the order of the lens surfaces from the object side along the traveling direction of the light beam, d indicates the distance between the lens surfaces, r indicates the radius of curvature (the paraxial radius of curvature for an aspheric surface),
n is the refractive index for the d-line (λ = 587.6 nm), ν
Indicates Abbe numbers.

[0044]

Table 2 f = 29 to 102 FNO = 2.9 to 3.6 2ω = 76.2 to 23.2 ° Surface number rd ν n 1 227.5952 2.0000 25.50 1.804581 2 128.3164 7.5000 82.52 1.497820 3 -327.5485 0.1000 4 57.1487 5.6000 82.52 1.497820 5 97.6515 (d5 = variable) 6 116.5721 1.7000 49.45 1.772789 7 * 15.3058 9.5846 8 66.3316 7.0000 28.19 1.740000 9 -21.6039 1.4000 49.45 1.772789 10 -306.6468 2.8000 11 * -28.1291 1.4000 49.45 1.772789 12 2082.5010 3.0000 64.1055616 130000 14 aperture stop 2.5000 15 260.8368 5.5000 58.90 1.518230 16 -49.6218 0.1000 17 62.8903 10.0000 61.09 1.589130 18 -32.3570 2.0000 28.56 1.795040 19 -117.0664 (d19 variable) 20 57.3096 3.8000 58.90 1.518230 21 118.3217 2.0000 22 92.3253 5.0000 64.10 1.516 800 98.6964 1.6000 45.37 1.796681 24 92.8815 9.0151 25 260.8967 1.7000 43.35 1.840421 26 42.1391 10.0000 54.55 1.514540 27 -36.8490 0.1000 28 81.0309 5.0000 64.10 1.516800 29 -149.2401 4.0000 30 -34.9712 2.0000 49.45 1.772789 31 -84.5986 ( f) (Aspherical Data) κ C ₂ C ₄ 7 surface _{^{0.9470 0.0000 -8.82590 × 10 -6 C 6}} C 8 C 10 -2.90580 × 10 -8 2.48060 × 10 -12 -5.62310 × 10 -13 κ C 2 C 4 11 faces 0.1111 0.0000 3.98310 × 10 ^-6 C ₆ C ₈ C ₁₀ 1.66440 × 10 ^-8 2.65860 × 10 ^-11 5.51280 × 10 ^-14 (variable interval in variable magnification) f 29.00000 50.00000 102.00000 D0 ∞ ∞ 5 d5 1.83627 22.72541 53.09288 d13 22.32971 10.19405 1.34451 d19 11.31896 3.03864 4.67401 Bf 37.98123 61.16613 88.18752 (Variable interval in focusing operation) β -0.03333 -0.03333 -0.03333 -0.06102 -0.10242 -0.18948 D0 811.7788 1405.1221 2864.7992 416.9342 393.2761 223.1288.29 231 629 331 629 314.288.231. 24.17644 12.26510 4.96317 d19 10.32256 2.36996 4.04106 9.47223 0.96759 1.05535 Bf 37.98702 61.17190 88.19330 38.00074 61.22108 88.37564 (Conditional value) (1) (Rar + Raf) / (Rar-Raf) =-1.30 (2) dAB / d2 = 0.357 3 ) N2p-n2n = -0.0328 (4) f3 / fT = 0.448 (5) n3p-n3n = -0.2059

FIGS. 9 to 14 show various aberration diagrams of the second embodiment. That is, FIG. 9 is a diagram showing various aberrations at the infinity in-focus condition at the wide angle end, FIG. 10 is a diagram showing various aberrations at the infinity in-focus condition at the intermediate focal length state, and FIG. The various aberration diagrams in the in-focus state are shown. FIG. 12 is a diagram showing various aberrations at a photographing magnification of 1/30 at the wide-angle end, FIG. 13 is a diagram showing various aberrations at a photographing magnification of 1/30 in the intermediate focal length state, and FIG. Various aberration diagrams are shown at a photographing magnification of 1/30 at the end. In each aberration diagram, FNO represents the F number, A represents the half angle of view, H0 represents the object height, and d represents the d-line (λ =
587.6 nm) and g is the g-line (λ = 435.8 nm).
Are respectively shown. In the aberration diagram showing astigmatism, a solid line indicates a sagittal image plane, and a broken line indicates a meridional image plane. Further, in the aberration diagram showing spherical aberration, a broken line indicates a sine condition (sine condition).

Referring to the aberration diagram of FIG. 9, it is understood that the wide angle of view covers a sufficiently large angle of view at the wide angle end, and that various aberrations are satisfactorily corrected. Also, referring to the aberration diagrams in FIGS. 10 and 11, it can be seen that various aberrations are favorably corrected as in the wide-angle end. On the other hand, referring to the aberration diagram of FIG. 12, it can be seen that the zoom lens system covers a sufficiently large angle of view at the wide-angle end, has little short-range variation, and satisfactorily corrects various aberrations. Referring to the aberration diagrams in FIGS. 13 and 14, it can be seen that short-range fluctuation is small and various aberrations are satisfactorily corrected, as in the wide-angle end. Thus, also in the second embodiment, various aberrations are favorably corrected in each focal length state and each shooting distance state.

In each of the embodiments described above, focusing is performed by moving the third lens group G3 and the aperture stop integrally. However, the third lens group G3
It is also possible to focus by moving the aperture stop and the aperture stop independently, or by moving only the third lens group G3 without moving the aperture stop. In this case, the focusing mechanism becomes complicated, but the movement of the aperture stop due to focusing reduces the interruption of the principal ray having a large angle of view, thereby making it possible to further shorten the minimum photographing distance.

[0048]

As described above, according to the present invention, 76.
A relatively small, high-performance, in-focus zoom lens that has a large angle of view of about 2 °, a large aperture with an F-number of about 2.8, and a high zoom ratio exceeding 3.5 times. Can be achieved.

[Brief description of the drawings]

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

FIG. 2 is a diagram illustrating various aberrations of the first embodiment at a wide-angle end and focused on infinity.

FIG. 3 is a diagram illustrating various aberrations of the first embodiment in an infinity in-focus state at an intermediate focal length state.

FIG. 4 is a diagram illustrating various aberrations of the first example at the telephoto end when focused on infinity;

FIG. 5 is a diagram illustrating various aberrations of the first example at a wide-angle end at a magnification of 1/30.

FIG. 6 is a photographing magnification 1 in the intermediate focal length state according to the first embodiment.
FIG. 7 is a diagram illustrating various aberrations in a state of / 30 times.

FIG. 7 is a diagram illustrating various aberrations of the first embodiment at a telephoto end at a magnification of 1/30.

FIG. 8 is a diagram illustrating a lens configuration of a zoom lens according to a second example of the present invention.

FIG. 9 is a diagram illustrating various aberrations of the second embodiment at a wide-angle end in a state of focusing on infinity.

FIG. 10 is a diagram illustrating various aberrations of the second example in an intermediate focal length state and focused on infinity.

FIG. 11 is a diagram illustrating various aberrations of the second embodiment at a telephoto end in an infinity in-focus state.

FIG. 12 is a diagram illustrating various aberrations of the second example at a wide-angle end at a magnification of 1/30.

FIG. 13 is a diagram illustrating various aberrations at a magnification of 1/30 in the intermediate focal length state according to the second example.

FIG. 14 is a diagram illustrating various aberrations of the second example at a telephoto end at a magnification of 1/30.

[Explanation of symbols]

 G1 First lens group G2 Second lens group G3 Third lens group G4 Fourth lens group L Each lens component A Aperture stop

Claims (6)

[Claims] 1. A first lens group G1 having a positive refractive power and a second lens group G having a negative refractive power in order from the object side.
2 and at least a third lens group G3 having a positive refractive power, wherein the first lens group G1 and the second lens group G
A zoom lens that performs zooming by changing the air gap between the second lens group G2 and the air gap between the second lens group G2 and the third lens group G3. In order from the side, a negative lens component L2A having at least one surface formed in an aspherical shape;
It has a cemented positive lens component L2B formed by bonding a positive lens and a negative lens with a convex surface facing the object side, and a negative lens component L2C with a concave surface facing the object side. An in-focus type zoom lens that focuses from an object at infinity to an object at a short distance by moving the lens along an axis. 2. When the paraxial radius of curvature of the most object side surface of the negative lens component L2A is Raf, and the paraxial radius of curvature of the most image side surface of the negative lens component L2A is Rar, (Rar + Raf) The inner focus zoom lens according to claim 1, wherein the following condition is satisfied: / (Rar-Raf) ≤-1. 3. An air gap on the axis between the negative lens component L2A and the cemented positive lens component L2B is defined as dAB.
When the total axial thickness from the most object side surface to the most image side surface of the lens group G2 is d2, the following condition is satisfied: 0.28 ≦ dAB / d2 ≦ 0.8 (2) An inner focus zoom lens according to claim 1. 4. The refractive index of the positive lens in the cemented positive lens component L2B for the d-line is n2p, and the refractive index of the negative lens in the cemented positive lens component L2B for the d-line is n
The inner focus type zoom lens according to any one of claims 1 to 3, wherein when 2n is satisfied, a condition of n2p-n2n <0 (3) is satisfied. 5. The focal length of the third lens group G3 is f3
The condition of 0.3 <f3 / fT <1 (4) is satisfied, where fT is the focal length of the entire system at the telephoto end. Inner focus zoom lens. 6. The third lens group G3 has at least one cemented positive lens Lc formed by bonding a positive lens and a negative lens, and refracts the positive lens in the cemented positive lens Lc with respect to the d-line. 6. The lens according to claim 1, wherein the following condition is satisfied: n3p-n3n <0 (5) where n3p is the refractive index and n3n is the refractive index of the negative lens in the cemented positive lens Lc with respect to the d-line. The inner focus type zoom lens according to any one of the above items.