JP4024747B2 - Zoom lens - Google Patents

Description

  The present invention relates to an optical system of a zoom lens, and more particularly to a zoom lens suitable as a small wide-angle zoom lens having telecentricity for a digital still camera and a video camera using a solid-state imaging device as a light receiving element.

In a so-called video camera that captures a moving image, a solid-state image sensor such as a CCD (Charge Coupled Device) or a MOS (Metal Oxide Semiconductor) is conventionally used as a light receiving element for imaging.
Further, in recent years, it is called a digital still camera or simply a digital camera, and a subject image is picked up by a solid-state imaging device to obtain image data of a still image (still image) of the subject, and an IC (integrated circuit) card or The type of camera that digitally records on a video flexible disk or the like is remarkably widespread. Some digital cameras can capture not only still images but also moving images (movie images).

Incidentally, an optical system of a camera using such a solid-state imaging device such as a CCD is required to have an exit pupil position sufficiently separated from an image plane. This is due to the following reason. Since the color filter of the solid-state imaging device is present at a position slightly away from the imaging surface, the substantial aperture efficiency is reduced when the light beam is incident obliquely. It is required that the effective thickness of the crystal filter for preventing the moire phenomenon due to the periodic structure of the solid-state imaging device does not vary much on and around the axis.
In particular, some recent high-sensitivity small solid-state image sensors have a microlens array immediately in front of the imaging surface. Even in this case, if the exit pupil is not sufficiently separated from the image surface, the aperture efficiency is high. Decrease around.

A first lens group having a negative refractive power and a second lens group having a positive refractive power are sequentially arranged from the object side to the image side. The first lens group and the second lens are arranged. A zoom lens that performs zooming by changing the distance between the groups is well known as so-called two-group zoom. Many of these two-group zooms are not suitable for application to a camera using a solid-state imaging device such as a CCD because the exit pupil position is close to the image plane.
Therefore, it is considered that the exit pupil position is moved away from the image plane by arranging a fixed lens unit or a moving lens unit having a positive refractive power behind the second lens unit, and many zoom lenses are proposed. Has been.
An example of a zoom lens in which a lens group having a positive refractive power is arranged behind the second lens group as described above is disclosed in, for example, Patent Document 1 (Japanese Patent Publication No. 3-20735) and Patent Document 2. (Japanese Patent Publication No. 7-52256) and Patent Document 3 (Japanese Patent Application Laid-Open No. 6-94996).

However, the zoom lenses described in Patent Document 1 and Patent Document 2 are designed mainly for single-lens reflex (single-lens reflex) still cameras.
For this reason, in the configurations described in Patent Document 1 and Patent Document 2, the positive refractive power of the third lens group is extremely weak, and the exit pupil cannot be sufficiently separated from the image plane. The zoom lens described in Patent Document 3 is fixed at an intermediate position between the first lens group and the second lens group without moving the aperture position during zooming in order to move the exit pupil position away from the image plane. It is arranged. For this reason, the zoom ratio is limited to a little less than twice due to restrictions on the movement of the first lens group and the second lens group.

In order to deal with the above-mentioned problem, the applicant can obtain a zoom ratio of about 3 times, and can sufficiently separate the exit pupil position from the image plane, which is suitable for a small digital still camera or the like. Wide-angle zoom lenses have been proposed so far.
For example, Patent Document 4 (Japanese Patent Application No. 9-14308) previously proposed describes an example of such a zoom lens.
However, these zoom lenses have large distortion, and distortion of about 6% occurs at the wide-angle end. Such distortion is larger than that of a conventional camera taking lens using a 35 mm plate, so-called Leica silver film, and it is difficult to obtain an accurate image.

On the other hand, recent digital still cameras tend to pursue higher image quality, and the small distortion of images is one of the important quality items in digital still cameras that are oriented toward higher image quality.
For this reason, the zoom lens described in Patent Document 4 described above is not sufficiently corrected for distortion, and is considered unsuitable for recent high-quality digital still cameras.
Therefore, the present applicant has proposed Patent Document 5 (Japanese Patent Application No. 9-269170) as a bright wide-angle zoom lens that is further suitable for a digital still camera or the like by further suppressing distortion.

However, in the current digital still camera market, it is most important to reduce costs while maintaining high image quality.
From this point of view, the zoom lens described in Patent Document 5 is composed of nine lenses, and it is difficult to say that the demand for cost reduction is sufficiently met by the number of lenses.

Japanese Patent Publication No. 3-20735 Japanese Patent Publication No. 7-52256 Japanese Patent Publication No. 6-94996 Japanese Patent Application No. 9-14308 Japanese Patent Application No. 9-26970

The present invention has been made in view of the above-mentioned circumstances, can obtain a zoom ratio of 3 times or more, can suppress distortion aberration while sufficiently separating the exit pupil position from the image plane, and An object of the present invention is to provide a zoom lens that can be configured as a bright wide-angle zoom lens that is small, has little aberration, and is suitable for a digital still camera or the like.
The first object of the present invention is, in particular, that the number of required lenses is small, the outer diameter of the lens is small, the aberration is corrected well, the exit pupil position can be sufficiently separated from the image plane , and the second lens. It is an object of the present invention to provide a zoom lens that can effectively correct aberrations occurring in a group .

The second object of the present invention is to obtain a zoom ratio of 3 times or more, to sufficiently separate the exit pupil position from the image plane, to suppress distortion, and to reduce the size of the aberration. The present invention is to provide a zoom lens that can be configured as a bright wide-angle zoom lens that is suitable for a digital still camera and the like, and in particular, requires a small number of lenses, is small, and has good aberration correction. .

In order to achieve the above-described object, particularly the first object, the zoom lens according to the present invention described in claim 1
A first group optical system having a negative refractive power, a second group optical system having a positive refractive power, and a third group optical system having a positive refractive power are sequentially arranged from the object side to the image side. ,
An aperture stop that moves integrally with the second group optical system during zooming is provided closer to the object side than the most object side lens of the second group optical system,
During zooming from the wide-angle end to the telephoto end, the first group optical system first moves to the image side on the optical axis, and moves in the shape of a convex arc on the image side by reversing the moving direction to the object side. Then, the variation in the focal position is corrected, the second group optical system moves monotonously on the optical axis and performs zooming,
The first group optical system has a negative lens provided with an aspheric surface, and the second group optical system has a positive lens provided with an aspheric surface,
The first group optical system includes a meniscus negative lens having a convex surface facing the object side and a meniscus positive lens having a convex surface facing the object side in order from the object side to the image side. The third group optical system is composed of a single positive lens,
Of the two lenses of the first group optical system, the meniscus negative lens located closest to the object side has an aspherical lens surface on the image side, and the aspherical surface is negatively refracted as the distance from the optical axis increases. and shape the force is weakened,
The second group optical system includes, in order from the object side to the image side, a positive lens, a meniscus positive lens having a convex surface facing the object side, a meniscus negative lens having a convex surface facing the object side, and the image side A positive lens having a strong refracting surface and a meniscus negative lens having a convex surface facing the object side are included.

The zoom lens according to the present invention described in claim 2 is, in particular, a first group optical system having negative refractive power sequentially from the object side to the image side in order to achieve the second object. A second group optical system having a positive refractive power and a third group optical system having a positive refractive power are disposed;
An aperture stop that moves integrally with the second group optical system during zooming is provided closer to the object side than the most object side lens of the second group optical system,
During zooming from the wide-angle end to the telephoto end, the first group optical system first moves to the image side on the optical axis, and moves in the shape of a convex arc on the image side by reversing the moving direction to the object side. Then, the variation in the focal position is corrected, the second group optical system moves monotonously on the optical axis and performs zooming,
The first group optical system has a negative lens provided with an aspheric surface, and the second group optical system has a positive lens provided with an aspheric surface,
The first group optical system includes a meniscus negative lens having a convex surface facing the object side and a meniscus positive lens having a convex surface facing the object side in order from the object side to the image side. The third group optical system is composed of a single positive lens,
Of the two lenses of the first group optical system, the meniscus negative lens located closest to the object side has an aspherical lens surface on the image side, and the aspherical surface is negatively refracted as the distance from the optical axis increases. The shape is weakened,
When the focal length of the M-th group optical system (M = 1 to 3) is f _M , and the combined focal length of the entire system at the wide angle end is f _W , these are conditions:
(1) 2.66 <| f ₁ | / f _W <2.80 (f ₁ <0)
(2) f ₃ / f _W <3.7
(3) 0.61 <f ₂ / f ₃ <0.68 (f ₂ > 0, f ₃ > 0)
It is characterized by satisfying .

[Action]
That is, the zoom lens according to the present invention has a first group optical system having a negative refractive power, a second group optical system having a positive refractive power, and a positive refractive power sequentially from the object side to the image side. A third-group optical system having an aperture stop that moves together with the second-group optical system during zooming on the object side of the second-group optical system closest to the object-side lens; During zooming from the telephoto end to the telephoto end, the first group optical system first moves to the image side on the optical axis, and moves in the form of a convex arc on the image side by reversing the moving direction to the object side. The variation in the focal position is corrected, and the second group optical system monotonously moves on the optical axis to perform zooming.

When the focal length of the M-th group optical system (M = 1 to 3) is f _M and the combined focal length of the entire system at the wide angle end is f _W , these are the conditions:
(1) 2.66 <| f ₁ | / f _W <2.80 (f ₁ <0)
(2) f ₃ / f _W <3.7
(3) 0.61 <f ₂ / f ₃ <0.68 (f ₂ > 0, f ₃ > 0)
It is configured to satisfy
With such a configuration, by reciprocating the third group optical system, the power of the second group optical system can be reduced while assisting zooming, and the amount of movement of the second group can be reduced and the size can be reduced. In addition, high zoom ratio can be realized.
In particular, by setting the range of the focal length of the first group optical system to the range of the condition (1), the zoom lens is reduced in size and aberration is reduced.

In addition, by setting the positive refractive power of the third group optical system within the range of the condition (2), the exit pupil position is separated from the image plane to have telecentricity.
Furthermore, by setting the positive refractive power distribution between the second group optical system and the third group optical system within the range of the condition (3), the lens is small and has good aberrations despite the small number of lenses. It can be corrected.
Therefore, with a small number of lenses, a zoom ratio of 3 times or more can be obtained, the exit pupil position can be sufficiently separated from the image plane, distortion can be suppressed, and the digital camera is small and has few aberrations. It can be configured as a bright wide-angle zoom lens suitable for a still camera or the like.

In the zoom lens according to the present invention, the first group optical system includes, in order from the object side to the image side, a meniscus negative lens having a convex surface directed toward the object side, and a meniscus shape having a convex surface directed toward the object side. And a second meniscus-shaped positive lens in which the second group optical system has a positive lens and a convex surface facing the object side in order from the object side to the image side. And a meniscus negative lens having a convex surface facing the object side, a positive lens having a strong refractive surface facing the image side, and a meniscus negative lens having a convex surface facing the object side.
With such a configuration, in particular, the zoom lens is configured with a small number of lenses, the lens outer diameter is reduced, and the aberration generated in the second lens group is effectively corrected.

In the zoom lens according to the present invention, an image side lens surface of a meniscus negative lens located closest to the object among the two lenses of the first group optical system has a negative refractive power as the distance from the optical axis increases. The aspherical surface is weakened.
With such a configuration, negative distortion that increases particularly on the short focal length side is effectively corrected.
The zoom lens according to the present invention has a shape in which the positive refractive power becomes weaker as the object side lens surface of the positive lens located closest to the object side among the five lenses of the second group optical system is separated from the optical axis. Aspherical.
Such a configuration prevents the spherical aberration from being insufficiently corrected.

According to the first aspect of the present invention, the first group optical system having a negative refractive power, the second group optical system having a positive refractive power, and the positive refractive power in order from the object side to the image side. A third group optical system having
An aperture stop that moves integrally with the second group optical system during zooming is provided closer to the object side than the most object side lens of the second group optical system,
During zooming from the wide-angle end to the telephoto end, the first group optical system first moves to the image side on the optical axis, and moves in the shape of a convex arc on the image side by reversing the moving direction to the object side. Then, the variation in the focal position is corrected, the second group optical system moves monotonously on the optical axis and performs zooming,
The first group optical system has a negative lens provided with an aspheric surface, and the second group optical system has a positive lens provided with an aspheric surface,
The first group optical system includes a meniscus negative lens having a convex surface facing the object side and a meniscus positive lens having a convex surface facing the object side in order from the object side to the image side. The third group optical system is composed of a single positive lens,
Of the two lenses of the first group optical system, the meniscus negative lens located closest to the object side has an aspherical lens surface on the image side, and the aspherical surface is negatively refracted as the distance from the optical axis increases. the force becomes weaker shape, the second group optical system includes, from the object side to the image side, in order, towards a positive lens, meniscus-shaped positive lens having a convex surface directed toward the object side, a convex surface on the object side Since it is configured to include a meniscus negative lens, a positive lens having a strong refracting surface facing the image side, and a meniscus negative lens having a convex surface facing the object side, the lens is tripled or As a bright wide-angle zoom lens suitable for digital still cameras and the like that can obtain a higher zoom ratio, sufficiently separate the exit pupil position from the image plane, suppress distortion, and is small in size and low in aberrations Can be composed In performance, in particular, small number of lenses that need, moreover can aberration lens diameter occurs in small and second group optical system to provide a well corrected zoom lens.

According to the zoom lens of claim 2 of the present invention, from the object side to the image side, the first group optical system having negative refractive power, the second group optical system having positive refractive power, and the positive A third optical system having refractive power is disposed;
An aperture stop that moves integrally with the second group optical system during zooming is provided closer to the object side than the most object side lens of the second group optical system,
During zooming from the wide-angle end to the telephoto end, the first group optical system first moves to the image side on the optical axis, and moves in the shape of a convex arc on the image side by reversing the moving direction to the object side. Then, the variation in the focal position is corrected, the second group optical system moves monotonously on the optical axis and performs zooming,
The first group optical system has a negative lens provided with an aspheric surface, and the second group optical system has a positive lens provided with an aspheric surface,
The first group optical system includes a meniscus negative lens having a convex surface facing the object side and a meniscus positive lens having a convex surface facing the object side in order from the object side to the image side. The third group optical system is composed of a single positive lens,
Of the two lenses of the first group optical system, the meniscus negative lens located closest to the object side has an aspherical lens surface on the image side, and the aspherical surface is negatively refracted as the distance from the optical axis increases. The shape is weakened,
When the focal length of the M-th group optical system (M = 1 to 3) is f _M and the combined focal length of the entire system at the wide-angle end is f _W , these are conditions:
(1) 2.66 <| f ₁ | / f _W <2.80 (f ₁ <0)
(2) f ₃ / f _W <3.7
(3) 0.61 <f ₂ / f ₃ <0.68 (f ₂ > 0, f ₃ > 0)
In particular, by setting the range of the focal length of the first group optical system to the range of the condition (1), the zoom lens can be reduced in size and aberration can be reduced. By setting the positive refractive power of the group optical system within the range of the condition (2), the exit pupil position can be separated from the image plane and telecentricity can be obtained, and the second group optical system and the third group optical system can be provided. By setting the positive refractive power distribution to the range of the condition (3), it is possible to correct the aberration satisfactorily with a small size despite the small number of lenses.
Therefore, with a small number of lenses, a zoom ratio of 3 times or more can be obtained, the exit pupil position can be sufficiently separated from the image plane, distortion can be suppressed, and the digital camera is small and has few aberrations. It can be configured as a bright wide-angle zoom lens suitable for a still camera or the like.

(1) -1 First Embodiment Hereinafter, a zoom lens according to the present invention will be described in detail with reference to the drawings based on an embodiment according to the present invention.
FIG. 1 shows a configuration of a main part of a zoom lens according to the first embodiment of the present invention.
FIG. 1A shows a lens configuration in a state where the zoom lens is set to the wide angle end of zooming, and FIG. 1B shows a lens configuration in a state where the zoom lens is set to the telephoto end of zooming. Show.

The zoom lens shown in FIG. 1 includes a first lens group G1 that is a first group optical system, a second lens group G2 that is a second group optical system, and a third lens sequentially from a subject, that is, from the object side to the image side. A third lens group G3, which is a group optical system, is disposed.
The first lens group G1 is composed of two lenses L1 and L2, the second lens group G2 is composed of five lenses L3, L4, L5, L6 and L7, and the third lens group G3 is It is composed of one lens L8.
An aperture stop S is disposed on the object side of the second lens group G2, that is, between the first lens group G1. A filter F in which a low-pass filter (LPF) L9 and an infrared light cut filter (IRCF) L10 are combined is provided between the third lens group G3 and the image plane. That is, the optical elements L1 to L8 are lenses, and the optical elements L9 and L10 are optical filters. r1 to r20 indicate optical surfaces, and in the examples, indicate curvature radii.
The first lens group G1 including the lenses L1 and L2 has a negative refractive power. The second lens group G2 including the lenses L3 to L7 has a positive refractive power. The third lens group G3 including the lens L8 has a positive refractive power.

During zooming from the wide-angle end to the telephoto end, the first lens group G1 first moves to the image side on the optical axis, and moves to the object side by reversing the moving direction from the middle. As described above, the first lens group G1 moves while drawing an arc-like locus convex toward the image side, thereby correcting the variation of the focal position during zooming from the wide-angle end to the telephoto end.
The second lens group G2 monotonously moves on the optical axis toward the object side during zooming from the wide-angle end to the telephoto end. When zooming from the wide-angle end to the telephoto end, the third lens group G3 first moves to the object side on the optical axis, and moves to the image side by reversing the moving direction from the middle. Thus, the third lens group G3 moves while drawing an arcuate locus convex toward the object side. Zooming from the wide-angle end to the telephoto end is performed by the zooming operation by the movement of the second lens group G2 and the third lens group G3.

In this way, by moving the third lens group G3 back and forth in a convex arc shape toward the object side, the second lens group G2 is provided with the assistance of zooming while reducing the power burden on the second lens group G2. Therefore, it is possible to realize a small size and a high zoom ratio.
The aperture stop S located on the object side of the second lens group G2 moves integrally with the second lens group G2. Accordingly, the movement of the second lens group G2 is not hindered by the aperture stop S.
In the first to third lens groups G1 to G3, the focal length of the first lens group G1 is f ₁ , the focal length of the second lens group G2 is f ₂ , and the focal length of the third lens group G3 is f ₃ , That is, when the focal length of the M-th lens group (M = 1 to 3) is f _M and the total focal length f _W of the entire system at the wide angle end is configured to satisfy the following conditions.

Condition (1):
2.66 <| f ₁ | / f _W <2.80 (f ₁ <0)
Condition (2)
f ₃ / f _W <3.7
Condition (3)
0.61 <f ₂ / f ₃ <0.68 (f ₂ > 0, f ₃ > 0)
Condition (1) is a zoom lens is downsized, a condition for restricting the range of the focal length f ₁ of the first lens group G1 to favorably correct aberrations. If the condition (1) is less than the lower limit, it is advantageous for miniaturization of the entire lens system, but the negative refractive power of the first lens group G1 becomes too strong, and various aberrations such as spherical aberration are deteriorated. Absent. If the upper limit of condition (1) is exceeded, aberrations can be corrected satisfactorily, but it is difficult to downsize the entire lens system.

Condition (2) is a condition for regulating the positive refractive power of the third lens group G3. When the upper limit of condition (2) is exceeded, the positive refractive power of the third lens group G3 becomes insufficient, the exit pupil position approaches the image plane, and telecentricity is lost.
Condition (3) is a condition that regulates the distribution of refractive power between the second lens group G2 and the third lens group G3, both of which have positive refractive power. This condition (3) is for making the second lens group G2 and the third lens group G3 small in number, facilitating miniaturization, and correcting aberrations satisfactorily.

If the condition (3) is less than the lower limit, the refractive power of the third lens group G3 becomes insufficient, the effect of the third lens group G3 is reduced, and the third lens group G3 is supplemented with the refractive power. Since the refractive power burden of the two lens group G2 is excessive, spherical aberration is deteriorated and the flatness of the image is also deteriorated.
If the upper limit of condition (3) is exceeded, the refractive power burden of the third lens group G3 is large, so the refractive power burden of the second lens group G2 group is reduced, the spherical aberration becomes good, and the flatness of the image is also good. However, both the negative refractive power of the first lens group G1 and the positive refractive power of the second lens group G2 tend to be weak, and it is difficult to achieve downsizing of the entire system.
As shown in FIG. 1, the first lens group G1 includes a meniscus negative lens L1 having a convex surface facing the object side, and a meniscus positive lens L2 having a convex surface facing the object side. The lenses L1 and L2 are arranged in order of L1-L2 from the object side to the image plane side.
The second lens group G2 has a positive lens L3, a meniscus positive lens L4 with a convex surface facing the object side, a meniscus negative lens L5 with a convex surface facing the object side, and a strong refracting surface facing the image side. The lens is composed of a positive lens L6 and a meniscus negative lens L7 having a convex surface facing the object side. The five lenses L3 to L7 are sequentially moved from the object side to the image side as L3-L4-L5-L6- Arranged in the order of L7.

In order to reduce the lens outer diameter, the negative lens L1 constituting the first lens group G1 is disposed on the object side. Then, in order to correct the spherical aberration, coma aberration, and astigmatism generated in the second lens group G2, first, the positive aberration as a whole is suppressed by suppressing the generation of spherical aberration as much as possible with the two positive lenses L3 and L4. Then, the negative lens L5 is overcorrected, and the subsequent positive lens L6 averages the field angle difference of each aberration.
The meniscus negative lens L1 disposed closest to the object side of the first lens group G1 has an image-side lens surface formed as an aspheric surface having a negative refractive power that decreases with increasing distance from the optical axis.
In this way, the image side lens surface of the meniscus negative lens L1 closest to the object side of the first lens group G1 forms an aspherical surface in which the negative refractive power decreases as the distance from the optical axis increases. In particular, negative distortion that increases on the short focal length side is corrected.

The positive lens L3 disposed closest to the object side of the second lens group G2 has an object-side lens surface formed as an aspheric surface whose positive refractive power becomes weaker as the distance from the optical axis increases.
In this way, the object-side lens surface of the positive lens L3 closest to the object side of the second lens group G2 forms an aspherical surface having a shape in which the positive refractive power decreases as the distance from the optical axis increases. Aberration is prevented from being undercorrected.

(1) -2 First Example Next, data of the first example of the zoom lens according to the first embodiment described above are shown in Tables 1 to 3.
Table 1 shows lens data of the optical system constituting the zoom lens, Table 2 shows aspherical data, and Table 3 shows variable amount data of the variable portion.
In this zoom lens, when the focal length of the entire system is f, the F number is F / No., The half angle of view is ω, and the image height is Y ′, f = 5.6 to 16.8 mm, F / No. = 2.8 to 5.0, ω = 32.3 to 11.7 deg, Y ′ = 3.47.
The surface number from the object side of the optical surface constituting the optical system is i, the radius of curvature of each optical surface is r _i , the distance between the subsequent optical surfaces (optical surfaces adjacent to the image side) is d _i , and the optical element The number is j (that is, each optical element is represented by L _j (j = 1 to 10)), the refractive index of the optical material of the optical element L _j is n _j , and the Abbe number of the optical material of the optical element L _j Table 1 shows lens data of the optical system constituting the zoom lens, where ν _j is ν _j .

In Table 1, the curvature radius r _i is expressed as “0.000”, which means that the curvature radius r _i is infinite (∞), indicating that the optical surface is a plane.
Accordingly, the surfaces r18, r19, r20 of the optical elements L9 and L10 constituting the filter F are flat surfaces, and both the optical elements L9 and L10 are closely joined.
The second optical surface r2 and the sixth optical surface r6 in Table 1, that is, the most image side lens surface r2 and second lens group G2 of the meniscus negative lens L1 disposed closest to the object side of the first lens group G1. The lens surface r6 on the object side of the positive lens L3 disposed on the object side is an aspherical surface.
As is well known, when the aspherical surface is made to coincide with the optical axis and the Z coordinate axis is orthogonal to the optical axis and the Y coordinate is taken, the radius of curvature on the optical axis is r, the conic constant is K, and the higher order aspherical coefficient is A curved surface obtained by rotating a curve represented by Equation 1 around the optical axis as A, B, and C.

In other words, the aspherical surface is defined by giving the aspherical surface equation of Formula 1 with parameters of the radius of curvature r on the optical axis, the conic constant K, and the higher-order aspherical coefficients A, B, and C. Identify the shape.
Therefore, the second optical surface r2 in Table 1, that is, the lens surface r2 on the image side of the meniscus negative lens L1 disposed closest to the object side of the first lens group G1, and the sixth optical surface r6 in Table 1, that is, The object-side lens surface r6 of the positive lens L3 arranged closest to the object side of the second lens group G2 has a radius of curvature r on the optical axis, a conic constant K, and a higher-order aspherical coefficient A shown in Table 2. It is formed on an aspheric surface defined by the parameters B and C.

In Table 1, the distance between the fourth optical surface r4, the fifteenth optical surface r15, and the seventeenth optical surface r17 (surface number) next to the optical surface (with the surface number) with the surface distance d _i being “variable” is It changes as shown in Table 3 at the wide-angle end where the focal length f is 5.60 mm, the intermediate focal length where the focal length f is 9.70 mm, and the telephoto end where the focal length f is 16.79 mm.

In this case, the total lens length at the wide-angle end, that is, the distance from the first optical surface of the optical system to the image plane is 40.06 mm.

2 to 4 show aberration diagrams in the first embodiment. 2 is an aberration diagram at the wide-angle end, FIG. 3 is an intermediate focal length, and FIG. 4 is an aberration diagram at the telephoto end.
In the aberration diagrams, SA is spherical aberration, SC is sinusoidal condition, As is astigmatism, and Dist is distortion.
In each aberration diagram, “d” indicates the aberration with respect to the d-line, and “g” indicates the aberration with respect to the g-line. In the spherical aberration diagram, the spherical aberration is indicated by a solid line, the sine condition is indicated by a broken line, and in the astigmatism diagram, the sagittal ray is indicated by a solid line and the meridional ray is indicated by a broken line.
2 to 4, it was confirmed that the aberration was corrected well at the wide-angle end, the intermediate focal length, and the telephoto end in the zoom range, and the performance was good.

(2) -1 Second Embodiment FIG. 5 shows a configuration of a main part of a zoom lens according to a second embodiment of the present invention.
FIG. 5A shows a lens configuration in a state where the zoom lens is set to the wide-angle end of zooming, and FIG. 5B shows a lens configuration in a state where the zoom lens is set to the telephoto end of zooming. Show.
The zoom lens shown in FIG. 5 includes a first lens group G1 ′ that is a first group optical system, a second lens group G2 ′ that is a second group optical system, in order from the subject, that is, the object side to the image side. A third lens group G3 ′, which is a third group optical system, is disposed.

  The first lens group G1 ′ is composed of two lenses L1 ′ and L2 ′, and the second lens group G2 ′ is composed of five lenses L3 ′, L4 ′, L5 ′, L6 ′ and L7 ′. The third lens group G3 ′ is composed of a single lens L8 ′.

An aperture stop S is disposed on the object side of the second lens group G2 ′, that is, between the first lens group G1 ′. On the further image side of the third lens group G3 ′, a filter F formed by combining a low-pass filter L9 ′ and an infrared light cut filter L10 ′ is provided between the third lens group G3 ′ and the image plane.
That is, the optical elements L1 ′ to L8 ′ are lenses, and the optical elements L9 ′ and L10 ′ are optical filters.
The first lens group G1 ′ including the lenses L1 ′ and L2 ′ has a negative refractive power. The second lens group G2 ′ including the lenses L3 ′ to L7 ′ has a positive refractive power. The third lens group G3 ′ including the lens L8 ′ has a positive refractive power.

The first lens group G1 ′ first moves on the optical axis to the image side during zooming from the wide-angle end to the telephoto end, and moves to the object side by reversing the moving direction from the middle. The first lens group G1 ′ thus moves along an image-side convex arcuate locus, thereby correcting the variation in the focal position during zooming from the wide-angle end to the telephoto end.
The second lens group G2 ′ moves monotonously on the optical axis toward the object side during zooming from the wide-angle end to the telephoto end. The third lens group G3 ′ first moves on the optical axis to the object side during zooming from the wide-angle end to the telephoto end, and moves to the image side by reversing the moving direction from the middle.
Thus, the third lens group G3 ′ moves along an arc-like locus convex toward the object side. Zooming from the wide-angle end to the telephoto end is performed by the zooming operation by the movement of the second lens group G2 ′ and the third lens group G3 ′.

In this way, the third lens group G3 ′ is reciprocated in a convex arc shape on the object side, thereby assisting the zooming while reducing the power burden on the second lens group G2 ′. The amount of movement of the group G2 ′ can be reduced to realize a small size and a high zoom ratio.
The aperture stop S located on the object side of the second lens group G2 ′ moves integrally with the second lens group G2 ′. Therefore, the movement of the second lens group G2 ′ is not hindered by the aperture stop S.

In the first to third lens groups G1 ′ to G3 ′, the focal length of the Mth lens group (M = 1 to 3) is f _M and the entire lens at the wide-angle end is the same as in the first embodiment. when the combined focal length f _W of the system, configured to satisfy the above conditions (1) to (3).
As shown in FIG. 5, the first lens group G1 ′ includes a meniscus negative lens L1 ′ having a convex surface facing the object side, and a meniscus positive lens L2 ′ having a convex surface facing the object side. Two lenses L1 'and L2' are arranged in order of L1'-L2 'from the object side to the image plane side.

  The second lens group G2 ′ includes a positive lens L3 ′, a meniscus positive lens L4 ′ having a convex surface facing the object side, a meniscus negative lens L5 ′ having a convex surface facing the object side, and strong refraction on the image side. A positive lens L6 'with its surface facing and a meniscus negative lens L7' with its convex surface facing the object side. These five lenses L3 'to L7' are sequentially moved from the object side to the image side. They are arranged in the order of L3'-L4'-L5'-L6'-L7 '.

The meniscus negative lens L1 ′ disposed closest to the object side of the first lens group G1 ′ is formed by forming the image side lens surface into an aspherical surface having a negative refractive power that decreases with increasing distance from the optical axis. Yes.
The positive lens L3 ′ disposed closest to the object side of the second lens group G2 ′ has an object-side lens surface formed as an aspheric surface having a shape in which the positive refractive power decreases as the distance from the optical axis increases.

(2) -2 Second Example Next, data of a second example of the zoom lens according to the second embodiment described above are shown in Tables 4 to 6. Table 4 shows lens data of the optical system constituting the zoom lens, Table 5 shows aspherical data, and Table 6 shows variable amount data of the variable portion.

  The second optical surface r2 'in Table 4, that is, the lens surface r2' on the image side of the meniscus negative lens L1 'disposed closest to the object side of the first lens group G1', and the sixth optical surface r6 in Table 4 ', That is, the object-side lens surface r6' of the positive lens L3 'arranged closest to the object side of the second lens group G2' has a curvature radius r on the optical axis, a conic constant K, and a higher order shown in Table 5. Are formed on the aspheric surface defined by the parameters of A, B, and C.

表４において、面間隔ｄ_ｉを「可変」とした第４光学面、第１５光学面および第１７光学面の次の（面番号の）光学面との面間隔は、全系の焦点距離ｆが５．６０mmの広角端、焦点距離ｆが９．７０mmの中間焦点距離および焦点距離ｆが１６．７８mmの望遠端において、表６に示されるように変化する。

In Table 4, the surface distance between the fourth optical surface, the fifteenth optical surface, and the seventeenth optical surface (with the surface number) next to the optical surface (with the surface number) having the surface distance d _i of “variable” is the focal length f of the entire system. Changes as shown in Table 6 at a wide angle end of 5.60 mm, an intermediate focal length of 9.70 mm and a telephoto end of 16.78 mm.

In this case, the total lens length at the wide-angle end, that is, the distance from the first optical surface of the optical system to the image surface is 39.06 mm.
6 to 8 show aberration diagrams in the second embodiment.
6 is an aberration diagram at the wide-angle end, FIG. 7 is an intermediate focal length, and FIG. 8 is an aberration diagram at the telephoto end.
6 to 8, it was confirmed that the aberration was corrected well at the wide-angle end, the intermediate focal length, and the telephoto end in the zoom range, and the performance was good.

(3) -1 Third Embodiment FIG. 9 shows a configuration of a main part of a zoom lens according to a third embodiment of the present invention.
FIG. 9A shows a lens configuration in a state where the zoom lens is set to the wide angle end of zooming, and FIG. 9B shows a lens configuration in a state where the zoom lens is set to the telephoto end of zooming. Show.
The zoom lens shown in FIG. 9 has a first lens group G1 ″ that is a first group optical system, a second lens group G2 ″ that is a second group optical system, and a second lens group sequentially from the subject, that is, the object side to the image side. A third lens group G3 ″ that is a three-group optical system is disposed.

The first lens group G1 ″ is composed of two lenses L1 ″ and L2 ″, and the second lens group G2 ″ is composed of five lenses L3 ″, L4 ″, L5 ″, L6 ″ and L7 ″. The third lens group G3 ″ is composed of a single lens L8 ″. An aperture stop S is disposed between the object side of the second lens group G2 ″, that is, between the first lens group G1 ″. On the further image side of the third lens group G3 ″, there is provided a filter F formed by combining a low-pass filter L9 ″ and an infrared light cut filter L10 ″ with the image plane. That is, the optical elements L1 "to L8" are lenses, and the optical elements L9 "and L10" are optical filters.
The first lens group G1 ″ including the lenses L1 ″ and L2 ″ has a negative refractive power. The second lens group G2 ″ including the lenses L3 ″ to L7 ″ has a positive refractive power. The third lens group G3 ″ including the lens L8 ″ has a positive refractive power.

During zooming from the wide-angle end to the telephoto end, the first lens group G1 ″ first moves on the optical axis to the image side, and in the middle, reverses the moving direction and moves to the object side. The first lens group G1 ″ moves. In this way, by moving along an image-side convex arcuate trajectory, the focal position variation during zooming from the wide-angle end to the telephoto end is corrected.
The second lens group G2 ″ monotonously moves on the optical axis toward the object side during zooming from the wide-angle end to the telephoto end. The third lens group G3 ″ is optical axis during zooming from the wide-angle end to the telephoto end. First, it moves to the object side, then moves in the reverse direction and moves to the image side. In this way, the third lens group G3 ″ moves while drawing an arc-like locus convex toward the object side. By the zooming operation by the movement of the second lens group G2 ″ and the third lens group G3 ″, the wide angle end is moved. Zooming from to the telephoto end.

In this manner, the third lens group G3 ″ is reciprocated in a convex arc shape on the object side, thereby assisting zooming while reducing the power burden on the second lens group G2 ″. The movement amount of the group G2 ″ is reduced, and it is possible to realize a small size and a high zoom ratio.
The aperture stop S located on the object side of the second lens group G2 ″ moves integrally with the second lens group G2 ″. Therefore, the movement of the second lens group G2 ″ is not hindered by the aperture stop S.
In the first to third lens groups G1 ″ to G3 ″, as in the first and second embodiments, the focal length of the Mth lens group (M = 1 to 3) is f _M and the wide angle is set. when the combined focal length f _W of the entire system at the end, configured so as to satisfy the above conditions (1) to (3).

As shown in FIG. 9, the first lens group G1 ″ includes a meniscus negative lens L1 ″ having a convex surface facing the object side, and a meniscus positive lens L2 ″ having a convex surface facing the object side. Two lenses L1 "and L2" are sequentially arranged from the object side to the image plane side in the order of L1 "-L2".
The second lens group G2 ″ includes a positive lens L3 ″, a meniscus positive lens L4 ″ with a convex surface facing the object side, a meniscus negative lens L5 ″ with a convex surface facing the object side, and strong refraction on the image side. The lens is composed of a meniscus positive lens L6 ″ having a surface and a meniscus negative lens L7 ″ having a convex surface on the object side. These five lenses L3 ″ to L7 ″ are directed from the object side to the image side. Are arranged in the order of L3 "-L4" -L5 "-L6" -L7 ".

The meniscus negative lens L1 ″ arranged closest to the object side of the first lens group G1 ″ is formed by forming the image side lens surface into an aspherical surface having a negative refractive power that decreases as the distance from the optical axis increases. Yes.
The positive lens L3 ″ disposed closest to the object side of the second lens group G2 ″ has an object-side lens surface formed as an aspherical surface having a positive refractive power that decreases with increasing distance from the optical axis.

(3) -2 Third Example Next, Tables 7 to 9 show data of a third example of the zoom lens according to the third embodiment described above. Table 7 shows lens data of the optical system constituting the zoom lens, Table 8 shows aspherical data, and Table 9 shows variable amount data of the variable portion.

  The second optical surface in Table 7, that is, the image-side lens surface r2 ″ of the meniscus negative lens L1 ″ disposed closest to the object side of the first lens group G1 ″, and the sixth optical surface in Table 7, that is, the The lens surface r6 ″ on the object side of the positive lens L3 ″ arranged closest to the object side of the two lens group G2 ″ has a curvature radius r on the optical axis, a conic constant K, and a higher-order aspherical coefficient shown in Table 8. An aspherical surface defined by the parameters A, B, and C is formed.

In Table 7, the distance between the fourth optical surface r4 ″, the fifteenth optical surface r15 ″ and the seventeenth optical surface r17 ″ with the surface distance d _i being “variable” is the next (surface number) optical surface. As shown in Table 9, the focal length f of the entire system changes at the wide-angle end where the focal length f is 5.60 mm, the intermediate focal length where the focal length f is 9.71 mm, and the telephoto end where the focal length f is 16.79 mm.

In this case, the total lens length at the wide-angle end, that is, the distance from the first optical surface of the optical system to the image surface is 40.07 mm.
10 to 12 show aberration diagrams according to the third embodiment. FIG. 10 is an aberration diagram at the wide-angle end, FIG. 11 is an intermediate focal length, and FIG. 12 is an aberration diagram at the telephoto end. 10 to 12, it was confirmed that the aberration was corrected well at the wide angle end, the intermediate focal length, and the telephoto end in the zoom range, and the performance was good. Each of the parameters | f ₁ | / f _W , f ₃ / f _W , f ₂ / f ₃ , and the image height ratio in the first to third embodiments described above, and the distortion aberration D _W at the wide angle end at 1.0. Table 10 shows (1.0).

  As described above, according to the first to third embodiments of the present invention, the zoom ratio is 3 times, the exit pupil position is sufficiently separated from the image plane, and the size is small and the aberration is corrected well. Furthermore, it is possible to provide a zoom lens with a small number of lenses with distortion being suppressed to 2% or less. Such a zoom lens can be configured as a bright wide-angle zoom lens suitable for a digital still camera or the like.

FIG. 2 is an optical system arrangement diagram schematically showing the arrangement configuration of the optical system of the zoom lens according to the first embodiment of the present invention. FIG. 3 is an aberration diagram showing spherical aberration, astigmatism, and distortion at the wide-angle end of the zoom lens according to the first example shown in FIG. 1. FIG. 3 is an aberration diagram showing spherical aberration, astigmatism, and distortion at the intermediate focal length of the zoom lens of the first example according to FIG. 1. FIG. 3 is an aberration diagram showing spherical aberration, astigmatism, and distortion at the telephoto end of the zoom lens according to the first embodiment shown in FIG. 1. FIG. 6 is an optical system arrangement diagram schematically showing an arrangement configuration of an optical system of a zoom lens according to a second embodiment of the present invention. FIG. 6 is an aberration diagram showing spherical aberration, astigmatism, and distortion at the wide-angle end of the zoom lens according to Example 2 in FIG. 5. FIG. 6 is an aberration diagram showing spherical aberration, astigmatism, and distortion at an intermediate focal length of the zoom lens according to the second example shown in FIG. 5. FIG. 6 is an aberration diagram showing spherical aberration, astigmatism, and distortion at the telephoto end of the zoom lens according to Example 2 in FIG. 5. FIG. 6 is an optical system arrangement diagram schematically showing an arrangement configuration of an optical system of a zoom lens according to a third embodiment of the present invention. FIG. 10 is an aberration diagram illustrating spherical aberration, astigmatism, and distortion at the wide-angle end of the zoom lens according to the third example illustrated in FIG. 9. FIG. 10 is an aberration diagram illustrating spherical aberration, astigmatism, and distortion at the intermediate focal length of the zoom lens according to the third example illustrated in FIG. 9. FIG. 10 is an aberration diagram illustrating spherical aberration, astigmatism, and distortion at the telephoto end of the zoom lens according to the third example illustrated in FIG. 9.

Explanation of symbols

G1, G1 ', G1 "First lens group G2, G2', G2" Second lens group G3, G3 ', G3 "Third lens group S Aperture F Filter L1-L10, L1'-L10', L1" ˜L10 ″ optical elements L1 to L8, L1 ′ to L8 ′, L1 ″ to L8 ″ lenses L9, L9 ′, L9 ″, L10, L10 ′, L10 ″ optical filters r1 to r20, r1 ′ to r20 ′, r1 ″ ~ R20 ″ optical surface

Claims (2)

A first group optical system having a negative refractive power, a second group optical system having a positive refractive power, and a third group optical system having a positive refractive power are sequentially arranged from the object side to the image side. ,
An aperture stop that moves integrally with the second group optical system during zooming is provided closer to the object side than the most object side lens of the second group optical system,
During zooming from the wide-angle end to the telephoto end, the first group optical system first moves to the image side on the optical axis, and moves in the shape of a convex arc on the image side by reversing the moving direction to the object side. Then, the variation in the focal position is corrected, the second group optical system moves monotonously on the optical axis and performs zooming,
The first group optical system has a negative lens provided with an aspheric surface, and the second group optical system has a positive lens provided with an aspheric surface,
The first group optical system includes a meniscus negative lens having a convex surface facing the object side and a meniscus positive lens having a convex surface facing the object side in order from the object side to the image side. The third group optical system is composed of a single positive lens,
Of the two lenses of the first group optical system, the meniscus negative lens located closest to the object side has an aspherical lens surface on the image side, and the aspherical surface is negatively refracted as the distance from the optical axis increases. and shape the force is weakened,
The second group optical system includes, in order from the object side to the image side, a positive lens, a meniscus positive lens having a convex surface facing the object side, a meniscus negative lens having a convex surface facing the object side, and the image side A zoom lens comprising: a positive lens having a strong refracting surface and a meniscus negative lens having a convex surface facing the object side . A first group optical system having a negative refractive power, a second group optical system having a positive refractive power, and a third group optical system having a positive refractive power are sequentially arranged from the object side to the image side. ,
An aperture stop that moves integrally with the second group optical system during zooming is provided closer to the object side than the most object side lens of the second group optical system,
During zooming from the wide-angle end to the telephoto end, the first group optical system first moves to the image side on the optical axis, and moves in the shape of a convex arc on the image side by reversing the moving direction to the object side. Then, the variation in the focal position is corrected, the second group optical system moves monotonously on the optical axis and performs zooming,
The first group optical system has a negative lens provided with an aspheric surface, and the second group optical system has a positive lens provided with an aspheric surface,
The first group optical system includes a meniscus negative lens having a convex surface facing the object side and a meniscus positive lens having a convex surface facing the object side in order from the object side to the image side. The third group optical system is composed of a single positive lens,
Of the two lenses of the first group optical system, the meniscus negative lens located closest to the object side has an aspherical lens surface on the image side, and the aspherical surface is negatively refracted as the distance from the optical axis increases. The shape is weakened,
When the focal length of the M-th group optical system (M = 1 to 3) is f _M , and the combined focal length of the entire system at the wide angle end is f _W , these are conditions:
(1) 2.66 <| f ₁ | / f _W <2.80 (f ₁ <0)
(2) f ₃ / f _W <3.7
(3) 0.61 <f ₂ / f ₃ <0.68 (f ₂ > 0, f ₃ > 0)
A zoom lens characterized by satisfying

Images