JPH05107474A - Zoom lens - Google Patents

Abstract

PURPOSE:To enable excellent imaging performance from a wide angle and to a telescopic and with the compact shape by constitute a zoom lens by a first lens group and a second lens group and specifying the constitution. CONSTITUTION:A first lens group G1 is constituted by a positive front lens group GF including a positive meniscus lens, a negative middle lens group GM including a junction lens and a positive rear lens group GR including a positive lens, and a second lens group G2 has a positive meniscus lens and a negative lens. The middle lens group GM has a concave lens surface on the article side and a convex lens surface on the image side and satisfies equations I to VII. In the equations I to VII, f1, f2 and fW are the focal distances of G1, G2 and a zoom lens wide angle end, respectively, rA and rB are radiuses of curvature of an article-side lens surface of GM and a joint surface of the junction lens, nF and nR are refractive indexes of a medium of the article side and the image side from the joint surface of the junction lens, nuF and nuR are Abbe numbers also of the medium on the article side and the image side and n11 and n21 are refractive indexes of the positive meniscus lens of GF and G2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom lens for a compact camera, and more particularly to a zoom lens of a short length having a zoom ratio of about 1.9 times including a wide angle range of 70 ° or more.

[0002]

2. Description of the Related Art Conventionally, as a zoom lens for a compact camera, a zoom lens having a positive / negative two-group structure has been mainly used. This type of zoom lens has a short overall length and a simple zoom lens barrel structure. It has an advantage in that the number of constituent elements can be relatively reduced. A zoom lens disclosed in JP-A-2-73322 is known as a zoom lens that makes full use of these advantages.

[0003]

However, in Japanese Patent Laid-Open No. 2-73322, the total angle of view at the wide-angle end is
It was about 60 °, and I could not fully respond to the voice that wanted a wider angle. Therefore, the present invention takes advantage of the positive / negative two-group zoom lens, which has a short overall length, a simple lens barrel structure, and a small number of components, while achieving a wide angle of view of up to about 70 °. It aims to provide a high-performance zoom lens.

[0004]

The zoom lens of the present invention has the following constitution in order to achieve the above object.
A zoom lens having a first lens group G ₁ having a positive refracting power and a second lens group G ₂ having a negative refracting power, and performing zooming by changing an air gap between the two lens groups. The group G ₁ includes, in order from the object side, a front lens group G _F having a positive refracting power as a whole including a positive meniscus lens having a convex surface directed toward the object side, a negative lens and a positive lens, and a convex surface facing the object side. The intermediate lens group G _M having a negative refractive power as a whole including at least a cemented lens having a cemented surface and the rear lens group G _R having a positive refractive power as a whole including a biconvex positive lens, The second lens group G ₂ is
In order from the object side, a positive lens formed in a meniscus shape having a convex surface facing the image side and a negative lens having a concave surface facing the object side are configured to be provided, and the intermediate lens group G _M is While having a concave lens surface on the most object side,
It is configured to have a convex lens surface on the most image side.

Further, in the present invention, the following conditions are satisfied based on the above configuration. _{(1) 0.7 <| f 1} / f 2 | <1.15 (2) 0.6 <| r A / f w | <1.0 r A <0 (3) 0.25 <r B / f w <0.5 (4) 0.2 <n _{F -n R (5) 15 <} ν R -ν F (6) 1.7 <n 11 (7) 1.7 <n 21 where, f _1: the focal length of the first lens group G _1, f _2: the second The focal length of the lens group G ₂ , f _w : the focal length of the zoom lens at the wide-angle end, r _A : the radius of curvature of the lens surface of the intermediate lens group G _M closest to the object side, r _B : the intermediate lens group G _M radius of curvature of the cemented surface of the cemented lens, n _F: bonding the cemented lens of the intermediate lens group G _M: the refractive index of the object-side medium from the junction surface of the intermediate lens group G _M in the cemented lens, n _R refractive index of the image side of the medium from the surface, [nu _F: the Abbe number of the object-side medium than the cemented surface of the cemented lens in said intermediate lens group G _M, ν _R: junction Len in the intermediate lens group G _M Abbe number of the image side of the medium than the junction surface of the, n _11: the refractive index of the front lens group positive meniscus lens in the G _F, n _21: refractive index of the positive meniscus lens in the second lens group G _2, in is there.

Further, it is preferable that the intermediate lens group G _M is composed of a cemented lens having a negative refracting power composed of a negative lens and a positive lens in order from the object side. Further, the intermediate lens group G _M may be composed of, in order from the object side, a negative lens and a cemented lens of a negative lens and a positive lens.

[0007]

In a zoom lens having a positive / negative two-group construction as in the present invention, when an attempt is made to widen the angle, the focal length of the first lens group G ₁ is disclosed in Japanese Patent Laid-Open No. 2-73322. It should be used shorter than the lens system. The reason for this is that in a positive / negative two-group zoom lens, the image from the first lens group is enlarged and formed by the second lens group in the entire zoom range, so the focus at the wide-angle end of the zoom lens This is because the distance becomes larger than the focal length of the first lens group.

As described above, when the focal length of the first lens group G ₁ is shortened to achieve a wider angle, a lens structure suitable for correction of spherical aberration, off-axis coma aberration, and curvature of field is obtained. There is a need. In particular, when the total lens length is shortened and the number of lens components is reduced for cost reduction, it becomes even more necessary to provide a lens configuration suitable for correction of the above-mentioned aberrations.

Therefore, in the zoom lens according to the present invention, the first lens group G ₁ is configured to have positive, negative and positive power arrangements in order from the object side, thereby achieving favorable correction of the aberrations. In the present invention, the first lens group G ₁ includes, in order from the object side, the front lens group G _F having a positive refractive power, the intermediate lens group G _M having a negative refractive power, and the rear lens group having a positive refractive power. And a lens group G _R. The positive lens in the front lens group G _F has a meniscus shape with a convex surface facing the object side to suppress the occurrence of coma and astigmatism due to off-axis rays. The intermediate lens group G _M includes a negative lens cemented with a negative lens and a positive lens, and the lens surface closest to the object side in this group has a shape with a concave surface facing the object side. As a result, the positive distortion aberration generated in the second lens group and the negative spherical aberration apt to occur in the first lens group are well balanced on the most object side lens surface of the intermediate lens group G _M. Correcting. Moreover, good correction of spherical aberration at the cemented surface of the cemented lens in the intermediate lens group G _M and well-balanced correction of axial chromatic aberration and lateral chromatic aberration are realized.

Further, in the present invention, since the most image-side lens surface in the intermediate lens group G _M is convex toward the image side, part of the positive refracting power of the first lens group G ₁ is shared and the rear lens This makes it possible to reduce the positive refractive power of the group G _R.
This is effective for correcting spherical aberration and reducing the number of rear lens groups G _R. Thereby, the rear lens group G
_R can be composed of one biconvex positive lens. Of course, the rear lens group G _R can be composed of a plurality of positive lenses, or can be composed of a negative and positive cemented lens, but in terms of size reduction, weight reduction, and cost reduction, a single lens is used. It is desirable to configure with.

The second lens group G ₂ is composed of, in order from the object side, a positive meniscus lens having a convex surface facing the image surface and at least one negative lens having a concave surface facing the object side. It is suitable for correction of spherical aberration, distortion surface aberration, and coma aberration, and is advantageous for ensuring a certain back focus. Even with a lens shutter type compact camera with few restrictions on the back focus, in order to simplify the lens barrel structure such as the zoom cam, in the 35 mm version,
It is desirable to secure a back focus of about 4 mm or more.

Each conditional expression of the present invention will be described in detail below. The condition (1) defines an optimum focal length ratio between the first lens group G ₁ and the second lens group G ₂ .
When the value goes below the lower limit of the condition (1), the focal length of the first lens group G ₁ becomes too short, which makes it difficult to correct spherical aberration and coma. Alternatively, the focal length of the second lens group G ₂ becomes long, and the zoom ratio of the zoom lens cannot be sufficiently obtained, which is not preferable.

On the contrary, if the upper limit of the condition (1) is exceeded, the first
The focal length of the lens group G ₁ becomes long, and it becomes difficult to obtain a wide angle of view of about 70 °. Alternatively, the focal length of the second lens group G ₂ becomes too short, and aberration fluctuations due to zooming such as spherical aberration and distortion become large, which is not preferable. The condition (2) defines the optimum radius of curvature of the most object-side lens surface of the intermediate lens group G _M having a negative refractive power in the first lens group G ₁ .

The most object-side lens surface of the intermediate lens group G _M has a concave surface facing the object side, which causes large negative distortion with respect to off-axis rays. This allows
The positive distortion that occurs in the second lens group G ₂ is balanced out. Further, the positive spherical aberration is generated for the axial ray, so that the negative spherical aberration generated in the entire first lens group G ₁ is corrected well.

When the value exceeds the upper limit of the condition (2), the curvature of the lens surface of the intermediate lens group G _M closest to the object side becomes gentle, so that the negative distortion aberration generated on this surface becomes small. Therefore, it is not preferable because the positive distortion that occurs in the second lens group G ₂ cannot be corrected. On the contrary, condition (2)
Beyond the lower limit of, the curvature of the lens surface of the intermediate lens group G _M closest to the object side becomes too tight, and the coma aberration on this lens surface becomes remarkable and cannot be corrected.

The condition (3) defines the optimum radius of curvature of the cemented surface of the cemented lens in the intermediate lens group G _M. By arranging a cemented lens including a negative lens and a positive lens in order from the object side in the intermediate lens group G _M , it is possible to correct spherical aberration well and to correct axial chromatic aberration and lateral chromatic aberration in a well-balanced manner. Become. When the value exceeds the upper limit of the condition (3), the curvature of the cemented surface in the intermediate lens group G _M becomes loose, so that both spherical aberration and axial chromatic aberration are insufficiently corrected, which is not preferable. On the other hand, if the value goes below the lower limit of the condition (3), the curvature of the cemented surface of the cemented lens in the intermediate lens group G _M becomes too tight, and therefore both spherical aberration and axial chromatic aberration are overcorrected, which is not preferable. The condition (4) defines the difference in the refractive index of the medium before and after the cemented surface of the cemented lens in the intermediate lens group G _M.

If the lower limit of the condition (4) is exceeded, spherical aberration will be undercorrected, which is not preferable. By the way, the first lens group G
_In order to suppress the fluctuation of the chromatic aberration when zooming is performed by changing the air gap between the first lens group G ₂ and the first lens group G ₂ , it is desirable that the first lens group G ₁ alone corrects the chromatic aberration. The chromatic aberration generated in the first lens group G ₁ is determined by the condition (5) by defining the optimum Abbe number difference between the media before and after the cemented surface of the cemented lens in the intermediate lens group G _M. G ₁ is corrected by itself.

When the value goes below the lower limit of the condition (5), axial chromatic aberration is insufficiently corrected, which is not preferable. Condition (6) defines an appropriate refractive index of the positive meniscus lens in the front lens group G _F in the first lens group G _{1 with} respect to Petzval sum and spherical aberration correction. In the zoom lens of the present invention, since the positive first lens group G ₁ is used with relatively strong power, the Petzval sum tends to be positively large. Therefore, the positive meniscus lens located closest to the object side in the front lens group G _F is used with a high refractive index to prevent the Petzval sum from becoming excessively large. At the same time, it is effective for correcting spherical aberration. If the lower limit of condition (6) is exceeded, the Petzval sum will be too large, which is not preferable. The condition (7) also relates to the correction of Petzval sum, and defines the refractive index of the positive meniscus lens located closest to the object side in the second lens group G ₂ . If the lower limit of condition (7) is exceeded, the Petzval sum will be too large, which is not preferable.

If the intermediate lens group G _M is composed of, in order from the object side, a negative lens and a negative and positive cemented lens, a better correction of spherical aberration can be achieved.

[0020]

EXAMPLES Examples of the present invention will be described below. FIG. 1 and FIG. 5 respectively show lens configuration diagrams of the first and second embodiments of the present invention. And, in each of the embodiments,
It has a first lens group G ₁ having a positive refractive power and a second lens group G ₂ having a negative refractive power. Zooming from the wide-angle end to the telephoto end is performed by the first lens group G ₁ and the second lens group G ₂
The first lens group G ₁ and the second lens group G ₂ move toward the object side so that the group distance between the first lens group G ₁ and the second lens group G ₂ decreases.

The first lens group G ₁ is composed of a front lens group G _F having a positive refractive power, an intermediate lens group G _M having a negative refractive power, and a rear lens group G _R having a positive refractive power. There is. Further, as shown in FIG. 1, in the first embodiment, the positive front lens group G _F is composed of one positive meniscus lens L ₁₁ having a convex surface directed toward the object side. The negative intermediate lens group G _M comprises, in order from the object side, a biconcave negative lens L ₁₂ with a stronger concave surface facing the object side, and a cemented positive lens having a biconvex shape as a whole. In order from the object side, a negative meniscus lens L ₁₃ with a concave surface facing the image side and a biconvex positive lens L ₁₄ with a stronger convex surface facing the object side are formed. The positive rear lens group G _R is composed of one biconvex positive lens L ₁₅ .

The second lens group G ₂ includes, in order from the object side, a positive meniscus lens L ₂₁ having a concave surface facing the object side,
The negative meniscus lens L ₂₂ has a concave surface facing the object side, and the negative meniscus lens L ₂₃ has a concave surface facing the object side.
As shown in FIG. 5, in the second embodiment, the positive front lens group G
_F is a positive meniscus lens L with a convex surface facing the object side
_It consists of ₁₁ . The negative intermediate lens group G _M is composed of a meniscus-shaped cemented negative lens whose concave surface faces the object side as a whole. This cemented negative lens has, in order from the object side, a biconcave negative lens L ₁₂ and a convex surface stronger on the object side. It is composed of a biconvex positive lens L ₁₃ which is directed to The positive rear lens group G _R comprises one biconvex lens L ₁₄ .

The second lens group G ₂ comprises, in order from the object side, a positive meniscus lens L ₂₁ having a concave surface facing the object side and a negative meniscus lens L ₂₂ having a concave surface facing the object side. The object-side lens surface of ₂₂ is composed of an aspherical surface. In this way, since the lens surfaces in the second lens group G ₂ are aspherical surfaces, the number of constituent elements is reduced,
And the improvement of the imaging performance is achieved. It goes without saying that any one of the lens surfaces in the first lens group G ₁ can be made an aspherical surface to improve the imaging performance.

[0024] Incidentally, in each embodiment, the aperture S is adjacent to the G ₁ the first lens group, located on the first object side of the lens group G _1, during zooming, the first lens group G ₁ and the integral And move. The values of specifications of each example are listed below. In Tables 1 and 2, f is the focal length, F _NO is the F number, 2 ω is the angle of view, the leftmost number is the order from the object side, r is the radius of curvature of the lens surface, and d is the lens. Surface spacing,
ν is the Abbe number, and n is the refractive index for the d-line (λ = 587.6 nm).

As for the aspherical surface shape, considering a tangential plane at the aspherical vertex, the displacement in the optical axis direction from the optical axis at the position of height y on the tangent plane is defined as x with reference to the aspherical vertex. When
It is represented by the following formula. ^{x = (y 2 / r)} / [1+ {1-k (y / r) 2} 1/2 ] _{^{+ C 2 y 2 + C 4}} y 4 + C 6 y 6 + C 8 y 8 + C 10 y 10 , however, C ₂ , C ₄ , C ₆ , C ₈ , C ₁₀ , Is an aspherical coefficient.

[0026]

[Example 1] f = 28.8 to 54.5, F _NO = 3.7 to 7.0,
2 ω = 72.8 ° ~ 44.0 ° The values corresponding to the conditions according to this embodiment are shown below. _{| F 1 / f 2 | =} 1.000, | r A / f w | = 0.791, r
_{B / f w = 0.314, n} F -n R = 0.2893, ν R -ν F = 2
0.7, n ₁₁ = 1.74400, n ₂₁ = 1.78797

[0027]

[Embodiment 2] f = 28.8 to 54.5, F _NO = 4.0 to 7.6
, 2 ω = 72.4 ° ~ 44.2 ° 10th surface aspherical coefficient k = 0.6 C ₂ = 0.0 C ₄ = -0.2317 × 10 ^-4 C ₆ = -0.3727 × 10 ^-6 C ₈ = 0.1997 × 10 ^-8 C ₁₀ = -0.2266 × 10 ^-10 The values corresponding to the conditions by example are shown below. _{| F 1 / f 2 | =} 0.857, r A / f w = 0.841, r B /
f _w = 0.348, n _F −n _R = 0.28631, ν _R −ν _F = 19.
4, n ₁₁ = 1.80684, n ₂₁ = 1.74810, FIGS. 2, 3 and 4 show various aberration diagrams of the first embodiment of the present invention, and FIGS. 6, 7 and 8 show various aberration diagrams of the second embodiment of the present invention. Indicates. 2 and 6 are various aberration diagrams at the wide-angle end, FIGS. 3 and 7 are various aberration diagrams at the intermediate focal length state, and FIGS. 4 and 8 are various aberration diagrams at the telephoto end.

Incidentally, in the astigmatism diagrams in each aberration diagram,
The meridional image plane is shown by a broken line, and the sagittal image plane is shown by a solid line. From comparison of each aberration diagram, it can be seen that the present invention has an excellent imaging performance from the wide-angle end to the telephoto end while maintaining a compact shape.

[0029]

According to the present invention, with a small number of constituent elements, a compact shape is maintained, a wide angle of view of about 70 ° is included, and an excellent imaging performance is obtained from the wide-angle end to the telephoto end. Achieve a zoom lens.

[Brief description of drawings]

FIG. 1 is a lens configuration diagram of a first embodiment.

FIG. 2 is a diagram of various types of aberration at the wide-angle end according to the first example.

FIG. 3 is a diagram of various types of aberration in the intermediate focal length state of the first example.

FIG. 4 is a diagram of various types of aberration at the telephoto end of the first example.

FIG. 5 is a lens configuration diagram of a second embodiment.

FIG. 6 is a diagram of various types of aberration at the wide-angle end according to the second example.

FIG. 7 is a diagram of various types of aberration in the intermediate focal length state of the second example.

FIG. 8 is a diagram of various types of aberration at the telephoto end of the second example.

[Explanation of symbols for main parts]

G ₁ ‥‥ first lens group G _F ‥‥ first lens front lens group in the group G _M ‥‥ first lens intermediate lens group in the group G _R ‥‥ rear lens group in the first lens group G ₂ ‥ Second lens group S ... Aperture

Claims (3)

[Claims] 1. A zoom lens having a first lens group G ₁ having a positive refracting power and a second lens group G ₂ having a negative refracting power, and performing zooming by changing an air gap between both lens groups. In the above, the first lens group G ₁ has, in order from the object side, a front lens group G _F having a positive refracting power as a whole including a positive meniscus lens having a convex surface facing the object side, and a negative lens and a positive lens. And an intermediate lens group G _M having a negative refractive power as a whole, including at least a cemented lens having a convex cemented surface on the object side,
And a rear lens group G _R having a positive refracting power as a whole including a biconvex positive lens, and the second lens group G ₂ is a positive meniscus lens having a convex surface directed toward the image side in order from the object side. , A negative lens formed of a shape with a concave surface facing the object side, and the intermediate lens group G _M has a concave lens surface on the most object side and a convex lens surface on the most image side. The zoom lens is characterized by satisfying the following conditions. (1) 0.7 <| f ₁ / f ₂ | <1.15, f ₂ <0 (2) 0.6 <| r _A / f _w | <1.0, r _A <0 (3) 0.25 <r _B / f _w <0.5 _{(4) 0.2 <n F -n} R (5) 15 <ν R -ν F (6) 1.7 <n 11 (7) 1.7 <n 21 where, f _1: the focal length of the first lens group G _1, f ₂ : focal length of the second lens group G ₂ , f _w : focal length of the zoom lens at the wide-angle end, r _A : radius of curvature of the lens surface of the intermediate lens group G _M closest to the object side, r _B : the focal length radius of curvature of the cemented surface of the cemented lens in the intermediate lens group G _M, n _F: refractive index of the object-side medium than the cemented surface of the cemented lens in said intermediate lens group G _M, n _R: said intermediate lens group G _M refractive index of the image side of the medium than the cemented surface of the cemented lens in, [nu _F: the Abbe number of the object-side medium than the cemented surface of the cemented lens in said intermediate lens group G _M, ν _R: said intermediate lens group G _M Abbe number of the image side of the medium than the cemented surface of the cemented lens, n _11: refractive index of the positive meniscus lens of the front lens group G _F, n _21: refraction of the positive meniscus lens in the second lens group G ₂ The rate is. 2. The zoom lens according to claim 1, wherein the intermediate lens group G _M is composed of only a cemented lens having a negative refractive power and composed of a negative lens and a positive lens in order from the object side. .. 3. The zoom lens according to claim 1, wherein the intermediate lens group G _M has a negative lens on the object side of the cemented lens.