JP3466385B2 - Small zoom lens - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a compact zoom lens.

[0002]

2. Description of the Related Art In addition to a conventional video camera using a solid-state image pickup device such as a CCD, a digital still camera has recently become popular. Many solid-state image pickup devices used in these video cameras and digital still cameras are provided with color filters for color separation in the same light receiving surface so as to capture a full-color image.

In such a solid-state image pickup device for a color image, as represented by a CCD, there is a gap between the light-receiving surface and the color filter. May be eclipsed by the filter and the aperture efficiency may be substantially reduced, or the correspondence between the filter pixel and the light receiving element may be displaced, causing “color shift”.

Therefore, in such a lens system which forms an image on a solid-state image pickup device for color images, it is necessary to enhance the telecentricity by sufficiently separating the exit pupil position from the image plane.

A two-group zoom lens, which has been widely known from the past, is constructed by arranging a first group having a negative refractive power on the object side and a second group having a positive refractive power on the image side. Many of these have an exit pupil position close to the image plane and are not preferable as a lens for forming an image of a subject on a solid-state image sensor for color images.

It is conceivable to dispose the exit pupil position away from the image plane by arranging the third group having a positive refractive power on the image side of the above-mentioned two-group zoom lens. Although such a three-group zoom lens is known for a single-lens reflex still camera (Japanese Patent Laid-Open No. 62-87925, etc.), these are generally the third lens.
Since the refractive power of the group is extremely weak, the exit pupil position cannot be largely separated from the image plane.

Further, as a three-group zoom lens in which the exit pupil position is largely separated from the image plane, Japanese Patent Laid-Open No. 6-
Although the one disclosed in Japanese Patent No. 94996 is known, in this lens, an aperture is used to keep the exit pupil position away from the image plane.
Since it is fixed between the first and second groups, the movement of the first and second groups is restricted by the diaphragm, and the variable power ratio remains about a little less than twice. Of course, it is desirable that the zoom lens is small.

[0008]

In view of the above-mentioned circumstances, the present invention is capable of sufficiently separating the exit pupil position from the image plane, is bright with a wide angle of view, is compact, and has good performance.
Furthermore, it is an object to realize a small zoom lens that is capable of a large zoom ratio and is suitable as a shooting lens for digital still cameras and video cameras.

[0009]

As shown in FIG. 1, a compact zoom lens according to the present invention has first to third groups arranged in order from the object side (left side in the figure) toward the image side. Become. The first group GI has a "negative refractive power", the second group GII has a "positive refractive power", and the third group GIII has a "positive refractive power".
The aperture stop S provided on the object side of the second group GII moves integrally with the second group GII during zooming. Also, the third group G
III is a "fixed group for zooming".

From the wide-angle end (FIG. 1A) to the telephoto end (FIG. 1)
During zooming to (b)), the first group GI first moves to the image side on the optical axis, and then "moves in a convex arc shape convex to the image side" by reversing the moving direction to the object side. The second group GII performs "monotonic movement toward the object side" on the optical axis to perform zooming by correcting variations in the focal position.

Since the aperture stop S moves together with the second lens group GII during zooming, the second aperture group GII is moved by the aperture diaphragm.
Movement is not hindered.

The focal length of the I-th group (I = 1 to 3) is f _I ,
Assuming that the combined focal length of the entire system at the telephoto end is f _T and the imaging magnification of the second lens unit at the telephoto end is m (2T), these conditions are: (1) 0.74 <| f ₁ | / f _T <0.9 (2) 0.46 <f 2 / f 3 <0.62 (f 2> 0, f 3>
0) (3) 1.6 <| m (2T) | <1.9 (m (2T) <0) is satisfied.

The above-mentioned "imaging magnification of the second lens unit at the telephoto end:
“M (2T)” is the group arrangement at the telephoto end, and refers to the image forming magnification of the second group having the image point of the first group as the object point. In FIG. 1, reference numeral CG indicates a cover glass of the solid-state image sensor located between the third group GIII and the image plane, and the light-receiving surface of the solid-state image sensor is located at the image plane.

The above condition (1) is a condition for restricting the range of the focal length: f ₁ of the first lens unit in order to downsize the entire system and satisfactorily correct aberrations. The negative refracting power of is too strong, which is advantageous for downsizing of the entire lens system, but it is not preferable because various aberrations such as spherical aberration are deteriorated. If the upper limit of the condition (1) is exceeded, the aberration will be good, but it will be difficult to downsize the entire lens system.

The condition (2) is a condition for restricting the distribution of the refracting powers of the second and third groups, both having a positive refracting power, and keeping the number of constituent lenses of the second and third groups small to reduce the size. This is a condition for facilitating the correction of aberrations and satisfactorily correcting aberrations.
When the value goes below the lower limit of the condition (2), the refractive power of the third lens group is insufficient, the exit pupil position approaches the image plane, and the telecentricity is lost. Further, the burden of refracting power of the second group becomes excessive, spherical aberration is deteriorated, and flatness of the image is also deteriorated. If the upper limit of the condition (2) is exceeded, the refractive power load of the third lens unit will be large, the refractive power load of the second lens unit will be alleviated, the aberration will be good, and the flatness of the image will be good, but the negative first This also matches the tendency that the refractive powers of both the group and the positive second group become weak, and it becomes difficult to downsize the entire lens system.

The condition (3) is a condition relating to the total length of the lens. When the upper limit is exceeded, the total length becomes too long at the telephoto end, which is disadvantageous for downsizing, and when the lower limit is exceeded, the total length becomes short at the telephoto end. , Along with this, the refractive power of the first lens unit becomes weaker in order to secure a predetermined focal length for the entire system at the telephoto end,
The movement amount of the first group increases.

In the compact zoom lens according to claim 1, the first group GI includes, in order from the object side to the image side,
A negative meniscus lens with a convex surface facing the object side, a negative lens with a strong refractive surface facing the image surface, and a biconvex lens are arranged.
The second group GII is composed of a biconvex lens, a positive meniscus lens having a convex surface facing the object side, a negative meniscus lens having a convex surface facing the object side, and a biconvex lens arranged in this order from the object side to the image side. (Claim 2)

As described above, by disposing the negative lens on the object side in the first group GI, it is possible to reduce the lens outer diameter of the compact zoom lens. Further, in order to correct the spherical aberration, the coma aberration, and the astigmatism generated in the second group GII, the spherical aberration is generated by the two object-side positive lenses (the biconvex lens and the positive meniscus lens) in the second group GII. Is suppressed as much as possible to obtain a positive refracting power, and then the negative meniscus lens is overcorrected, and the subsequent biconvex lens averages the angle of view difference of each aberration.

In the compact zoom lens according to the second aspect, the object-side lens surface of the biconvex lens, which is the positive lens of the first group, has an aspherical surface having a shape in which the positive refracting power becomes stronger as the distance from the optical axis increases. Can be set (Claim 3). By adopting such an aspherical surface, it becomes easy to correct the negative distortion which increases particularly on the short focus side.

Further, in the compact zoom lens according to claim 2 or 3, the object side surface of the object side biconvex lens of the second group is an aspherical surface having a shape in which the positive refracting power becomes weaker as the distance from the optical axis increases. It can be set to (Claim 4). By adopting such an aspherical surface, it becomes possible to satisfactorily correct spherical aberration that tends to be undercorrected.

Further, in the compact zoom lens according to claim 2 or 3 or 4, the third group GIII can be a "biconvex lens having a surface having a strong refractive power on the object side" (claim 5). That is, in order to reduce the number of constituent lenses of the zoom lens, it is desirable that the number of lenses of the third group GIII, which is a fixed group, be as small as possible. As in the invention of claim 5, the third group is a single lens. With the configuration, the addition of the third group can be prevented from hindering miniaturization. In that case, by making the lens form of the third lens group GIII a “biconvex lens”, the strong positive refractive power required for the third lens group can be distributed to both surfaces, and the convex surface having a strong refractive power should be directed to the object side. As a result, the telecentricity can be improved.

Further, in the above-mentioned claim 2 or 3 or 4 or 5, the "negative lens having a strong refracting surface facing the image plane" of the second lens from the object side of the first group GI has the negative meniscus It can be a lens or a biconcave lens (claim 6).

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION Specific embodiments will be described below. FIG. 1 shows an embodiment of a compact zoom lens according to claims 2 and 5, wherein the first group GI is a negative meniscus lens having a convex surface facing the object side, and a strong refracting surface facing the image surface. The second lens group GII
Consists of a biconvex lens, a positive meniscus lens with a convex surface facing the object side, a negative meniscus lens with a convex surface facing the object side, and a biconvex lens in this order from the object side to the image side.
The third group GIII is a biconvex lens with the surface having a strong refractive power facing the object side.

[0024]

[Examples] Three specific examples of the embodiment shown in FIG. 1 will be given below. Counted from the object side, the i-th surface (the surface of the diaphragm S and the cover glass C of the solid-state image sensor)
The included) the face of the _{G r i (i = 1~19)} , the i-th surface counted from the object side and the surface spacing on the optical axis of the i + 1 th surface _d i (i = 1 to 18) , The refractive index and Abbe number of the jth lens or cover glass counted from the object side,
Let n _j and ν _j (j = 1 to 9), respectively. Also,
f is “focal length of the entire system”, ω is “half angle of view” F / No. Is “brightness”, Y ′ is “image height”, f _I (I = 1 to 3) is “focal length of I-th group”, f _T is “composite focal length of entire system at telephoto end”, m ( 2T) is the "magnification of the second group at the telephoto end".

In each of Examples 1 to 3, "aspherical surface" is adopted for the fifth surface (i = 5) and the eighth surface (i = 8) (claims 3 and 4). As is well known, when an aspherical surface has a Z axis in the optical axis direction and a Y axis in a direction orthogonal to the optical axis, a known aspherical surface formula: Z = (Y ² / r) / [1 + √ {1- (1 + K) ( Y / r)
² }] + A · Y ⁴ + B · Y ⁶ + C · Y ⁸ + D · Y ¹⁰ +. ． A curved surface obtained by rotating the curve given by in the direction of the optical axis, and the shape is specified by giving paraxial radius of curvature: r, conical constant: K, and higher-order aspherical coefficients: A, B, C, D To do. In addition, in the notation of the high-order aspherical coefficient, "E and the number following it"
Represents "10 to the power of power". For example, "E-9" means 10 to ⁹ , and this numerical value multiplies the numerical value immediately before it.

Example 1 f = 4.6 to 14.0 mm, F / No. = 2.5 to 4.4, ω = 36.3 to 12.8 degrees, Y ′ = 3.15 i r _i d _i j _{j j j} v _j 1 13.169 2.50 1 1.74400 44. 90 2 5.718 2.09 3 379.395 0.80 2 1.69680 55.46 4 8.086 2.02 5 19.723 1.32 3 1.80518 25.46 6 158.315 Variable 7 ∞ (aperture) 0.50 8 13.065 1.21 4 1.69350 53.209 9-37.766 0.10 10 5.310 1.17 5 1.69680 55.46 11 6.626 0.65 12 21.207 1.91 6 1.846666 23.78 13 5.232 0.58 14 11.603 1.47 7 1.48749 70.44 15 -11.189 Variable 16 14.064 1.33 8 1 .48749 70. 4 17 -51.027 1.00 18 ∞ 3.10 9 1.51680 64.20 19 ∞.

[0027]   Aspherical surface   Fifth surface:   K = 4.03478, A = 2.743354E-4,   B = -1.06833E-5, C = 8.56489E-7,   D = -2.05438E-8   8th surface:   K = -2.51053, A = -2.23827E-5,   B = -1.60847E-6, C = 6.58013E-8.

Variable amount: f 4.6 8.0 14.0 d ₆ 14.85 6.46 1.60 d ₁₅ 3.40 8.15 16.54.

Value of parameter of conditional expression: | f ₁ | / f _T = 0.79, f ₂ / f ₃ = 0.49, | m (2T) | = 1.74.

Example 2 f = 4.6 to 14.0 mm, F / No. = 2.4 to 4.3, ω = 36.3 to 12.8 degrees, Y ′ = 3.15 i r _i d _i j n _j ν _j 1 13.221 1.86 1 1.69680 55. 46 2 6.025 2.27 3 168.650 0.80 2 1.69680 55.46 4 8.485 1.92 5 18.013 1.41 3 1.82027 29.70 6 217.214 Variable 7 ∞ (aperture) 0.50 8 15.437 1.24 4 1.69350 53.20 9 -24.215 0.10 10 5.435 1.31 5 1.65160 58.40 11 9.588 0. 47 12 21.919 2.07 6 1.84666 23.78 13 4.726 0.82 14 32.830 1.18 7 1.56384 60.83 15 -13.147 Variable 16 13.629 1.41 8 1.48749 70 44 17 -27.945 1.00 18 ∞ 3.10 9 1.51680 64.20 19 ∞.

[0031]   Aspherical surface   Fifth surface:   K = 2.47732, A = 2.24428E-4,   B = -7.9929E-6, C = 5.09709E-7,   D = -1.02881E-8   8th surface:   K = -2.78904, A = -3.17852E-5,   B = -7.98743E-7, C = 4.41065E-8.

Variable amount: f 4.6 8.0 14.0 d ₆ 15.63 6.75 1.60 d ₁₅ 2.91 7.40 15.34.

Value of parameter of conditional expression: | f ₁ | / f _T = 0.87, f ₂ / f ₃ = 0.59, | m (2T) | = 1.64.

Example 3 f = 4.5 to 15.0 mm, F / No. = 2.5 to 4.8, ω = 36.9 to 11.9 degrees, Y ′ = 3.15 i r _i d _i j _{j j j} v _j 1 12.748 0.94 1 1.69680 55. 46 2 5.771 2.09 3 -428.071 0.80 2 1.69680 55.46 4 8.093 1.90 5 18.674 1.37 3 1.82027 29.70 6 -108.177 Variable 7 ∞ (aperture) 0.50 8 15.160 1.20 4 1.69350 53.20 9 −32.440 0.10 10 6.007 1.31 5 1.65160 58.40 11 12.964 0. 42 12 23.503 2.54 6 1.84666 23.78 13 4.832 0.77 14 26.130 1.187 7 1.56384 60.83 15 -14.405 Variable 16 13.996 1.39 98 1.48749 7 .44 17 -30.891 1.00 18 ∞ 3.10 9 1.51680 64.20 19 ∞.

[0035]   Aspherical surface   Fifth surface:   K = 3.477729, A = 2.57066E-4,   B = -1.01953E-5, C = 7.996988E-7,   D = -1.866637E-8   8th surface:   K = -2.23816, A = -1.44192E-5,   B = -1.87950E-6, C = 1.09630E-7.

Variables: f 4.6 8.0 15.0 d ₆ 16.18 6.78 1.60 d ₁₅ 3.22 8.36 17.80.

Value of parameter of conditional expression: | f ₁ | / f _T = 0.77, f ₂ / f ₃ = 0.57, | m (2T) | = 1.82.

Aberration diagrams relating to Example 1 are sequentially shown in FIGS. 2 is for the wide-angle end, FIG. 3 is for the intermediate focal length, and FIG. 4 is for the telephoto end. Aberration diagrams relating to Example 2 are sequentially shown in FIGS. 5 is for the wide-angle end, FIG. 6 is for the intermediate focal length, and FIG. 7 is for the telephoto end. 8 to 1
Aberration diagrams related to Example 3 are sequentially shown in 0. 8 is for the wide-angle end, FIG. 9 is for the intermediate focal length, and FIG. 10 is for the telephoto end.

In each aberration diagram, "SA" is spherical aberration,
“SC” is a sine condition, “Ast” is astigmatism, and “Dis”
“T” indicates distortion. [D and g] in the aberration diagrams are
It shows that the aberrations are for d and g lines.
In the figure of spherical aberration and sine conditions, the solid line is spherical aberration,
The broken line is the sine condition. In the diagram of astigmatism, the solid line shows the sagittal ray and the broken line shows the meridional ray.

In each of the examples, aberrations are corrected well, performance is good, bright, and wide angle of view is obtained in any of wide angle, intermediate, and telephoto.

[0041]

As described above, according to the present invention, a novel compact zoom lens can be provided. Small zoom lens of the present invention, as described above, excellent telecentricity order to be able to release sufficiently the exit pupil position of the image plane, off for color separation in the solid-state imaging device for color image
Kera Re and due to the filter, it is possible to effectively reduce the color shift.

Further, since the aperture stop does not limit the movement of the moving group, a zoom ratio of 3 times or more is possible as seen in each of the above embodiments. The total lens length at the telephoto end is the first embodiment.
42.4 mm, Example 2 40.38 mm, Example 3
It is 42.02 mm and is compact.

Further, as seen in each of the embodiments, good performance can be realized with a bright and wide angle of view. Since the small-sized zoom lens of the present invention has such effects, it is suitable as a zoom lens for photographing a digital still camera or a video camera.

[Brief description of drawings]

FIG. 1 is a diagram for explaining a lens configuration and a zooming operation of a compact zoom lens according to the present invention.

FIG. 2 is an aberration diagram at a wide-angle end according to Example 1.

FIG. 3 is an aberration diagram of an intermediate focal length according to Example 1.

FIG. 4 is an aberration diagram for Example 1 at the telephoto end.

FIG. 5 is an aberration diagram for Example 2 at the wide-angle end.

FIG. 6 is an aberration diagram of an intermediate focal length according to Example 2.

FIG. 7 is an aberration diagram for Example 2 at the telephoto end.

FIG. 8 is an aberration diagram at a wide-angle end according to Example 3;

FIG. 9 is an aberration diagram of intermediate focal lengths according to Example 3;

FIG. 10 is an aberration diagram for Example 3 at the telephoto end.

[Explanation of symbols]

GI first group GII second group GIII Third group S aperture stop

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Claims (6)

(57) [Claims] 1. A first lens unit to a third lens unit are arranged in this order from the object side to the image side, the first group having a negative refractive power, and the second group having a positive refractive power. The third lens unit has a positive refracting power, has an aperture stop on the object side of the second lens unit, which moves integrally with the second lens unit during zooming, and the third lens unit is a fixed lens unit for zooming. When zooming from the wide-angle end to the telephoto end, the first group first moves to the image side on the optical axis, and then reverses the moving direction to the object side, forming a convex arc shape convex to the image side. moving by correcting the variation of the focal position, the second group performs zooming monotonously moved on the optical axis toward the object side, the focal distance f _I group I (I = 1 to _3), the telephoto When the combined focal length of the entire system at the end is f _T and the imaging magnification of the second lens unit at the telephoto end is m (2T), these are the conditions: (1) 0.74 <| f ₁ | / F _T <0.9 (2) 0.46 <f ₂ /f3<0.62 (f ₂ > 0, f
₃ > 0) (3) A small zoom lens characterized by satisfying 1.6 <| m (2T) | <1.9. 2. The compact zoom lens according to claim 1, wherein the first lens group has, in order from the object side to the image side, a negative meniscus lens having a convex surface facing the object side and a strong refracting surface facing the image surface. A negative lens and a biconvex lens are arranged, and the second lens group in order from the object side to the image side is a biconvex lens, a positive meniscus lens with a convex surface facing the object side, and a negative meniscus lens with a convex surface facing the object side. A compact zoom lens characterized by comprising a biconvex lens. 3. The compact zoom lens according to claim 2, wherein the object-side lens surface of the biconvex lens, which is a positive lens, in the first lens group has a shape in which the positive refracting power becomes stronger as the distance from the optical axis increases. A compact zoom lens that is spherical. 4. A compact zoom lens according to claim 2 or 3, wherein the object-side surface of the object-side biconvex lens in the second group has a shape in which the positive refracting power becomes weaker as the distance from the optical axis increases. A compact zoom lens. 5. The compact zoom lens according to claim 2, 3 or 4, wherein the third group is a biconvex lens having a surface having a strong refractive power on the object side. 6. The compact zoom lens according to claim 2, 3 or 4 or 5, wherein the second lens from the object side in the first lens group, which is a negative lens having a strong refracting surface facing the image surface, is a negative meniscus lens. Or a small zoom lens that is a biconcave lens.