JP2006023679A - Zoom lens and image pickup device equipped with same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a zoom lens which has few number of constituting lenses, which is compact, and which has superior optical performance, and to provide an imaging device that has the same. <P>SOLUTION: A zoom lens has a first lens group L1 of negative refractive power and a second lens group L2 of positive refractive power, in this order starting from the object side to an image side, and its spacing of both of the lens groups changes in zooming. The first lens group L1 consists of an eleventh lens G11 of negative refracting power and a twelfth lens G12 of a positive refracting power. The second lens group L2 consists of a twenty-first lens G21 of positive refractive power and a twenty-second lens G22 of negative refractive power. When the Abbe number of the materials of the twenty-first lens G21 and the twenty-second lens G22 is given as ν21 and ν22 respectively, it is so constituted as to satisfy the condition 45<ν21-ν22<50. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a zoom lens, and is suitable for an imaging apparatus using a solid-state imaging device such as a digital still camera, a video camera, or a surveillance camera.

  In recent years, imaging devices such as digital still cameras and video cameras have higher optical performance, and have become smaller and thinner due to remarkable technological progress of solid-state imaging devices such as CCDs used therein and downsizing of imaging devices. Therefore, there is a demand for a photographic lens that has been reduced in weight.

  Relatively high optical performance is obtained, and the entire lens system is a small zoom lens, and in order from the object side to the image side, the first lens unit L1 having a negative refractive power and the second lens unit having a positive refractive power. Thus, there is a two-group zoom lens that performs zooming by changing the air gap between the two lens groups.

  Since this two-group zoom lens can be configured with a relatively small number of lenses, it is often used for a zoom type lens system aiming at miniaturization.

  As a two-group zoom lens, a small two-group zoom lens is known in which a first lens group includes a negative lens and a positive lens, and a second lens group includes a positive lens and a negative lens (Patent Documents 1 to 3).

  Further, in the two-group zoom lens, there is known a two-group zoom lens in which the second lens group includes a second-a lens group having a positive refractive power and a second-b lens group having a positive refractive power, and focusing is performed by the second-b lens group. (Patent Document 4).

  On the other hand, as a zoom lens compatible with a small image pickup apparatus equipped with a high-resolution image pickup device with higher image quality, a three-group zoom lens made up of lens groups having negative, positive, and positive refractive powers is known ( Patent Documents 5 and 6).

In the three-group zoom lens, there is known a small three-group zoom lens in which the second lens group includes a positive lens and a negative lens (Patent Document 7).
JP-A-6-273670 JP 9-033810 A Japanese Patent Laid-Open No. 11-052235 JP 2000-9777 A JP 2000-147381 A JP 2000-284177 A JP 2000-9999 A

  The two-group zoom lens and the three-group zoom lens proposed in each of the above-described patent documents have room for improvement in optical performance for a small and high-resolution imaging device.

  An object of the present invention is to provide a compact zoom lens having excellent optical performance, which is suitable for an imaging system using a solid-state image sensor, for example.

The zoom lens of the present invention includes a first lens unit having a negative refractive power and a second lens group having a positive refractive power in order from the object side to the image side, and the distance between both lens groups changes during zooming. In the zoom lens, the first lens group includes an eleventh lens having a negative refractive power and a twelfth lens having a positive refractive power, and the second lens group includes a twenty-first lens having a positive refractive power and a negative refraction. When the Abbe numbers of the materials of the 21st lens and the 22nd lens are ν21 and ν22, respectively,
45 <ν21−ν22 <50
It is characterized by satisfying the following conditions.

  According to the present invention, a zoom lens that is compact and has excellent optical performance can be obtained.

  Embodiments of the zoom lens of the present invention and an image pickup apparatus having the same will be described below.

  FIGS. 1A, 1B, and 1C are cross-sectional views of the zoom lens of Embodiment 1 of the present invention at the wide-angle end (short focal length end), the intermediate zoom position, and the telephoto end (long focal length). It is. 2, 3, and 4 are aberration diagrams of the zoom lens of Example 1 at the wide-angle end, the intermediate zoom position, and the telephoto end, respectively. Example 1 is a zoom lens having a zoom ratio of 1.91 and an aperture ratio of about 3.28 to 4.69.

  5A, 5B, and 5C are lens cross-sectional views at the wide-angle end (short focal length end), the intermediate zoom position, and the telephoto end (long focal length) of the zoom lens according to Embodiment 2 of the present invention. It is. 6, 7, and 8 are aberration diagrams of the zoom lens of Example 2 at the wide-angle end, the intermediate zoom position, and the telephoto end, respectively. The second exemplary embodiment is a zoom lens having a zoom ratio of 1.91 and an aperture ratio of about 3.28 to 4.67.

  FIGS. 9A, 9B, and 9C are lens cross-sectional views at the wide-angle end (short focal length end), the intermediate zoom position, and the telephoto end (long focal length) of the zoom lens according to Embodiment 3 of the present invention. It is. FIGS. 10, 11, and 12 are aberration diagrams of the zoom lens of Example 3 at the wide-angle end, the intermediate zoom position, and the telephoto end, respectively. The third embodiment is a zoom lens having a zoom ratio of 1.96 and an aperture ratio of about 3.28 to 4.54.

  FIGS. 13A, 13B, and 13C are lens cross-sectional views at the wide-angle end (short focal length end), the intermediate zoom position, and the telephoto end (long focal length) of the zoom lens according to the fourth exemplary embodiment of the present invention. It is. FIGS. 14, 15, and 16 are aberration diagrams of the zoom lens of Example 4 at the wide-angle end, the intermediate zoom position, and the telephoto end, respectively. The fourth embodiment is a zoom lens having a zoom ratio of 1.91 and an aperture ratio of about 3.28 to 4.83.

  FIGS. 17A, 17B, and 17C are lens cross-sectional views at the wide-angle end (short focal length end), the intermediate zoom position, and the telephoto end (long focal length) of the zoom lens according to Embodiment 5 of the present invention. It is. 18, 19 and 20 are aberration diagrams of the zoom lens of Example 5 at the wide-angle end, the intermediate zoom position, and the telephoto end, respectively. The fifth embodiment is a zoom lens having a zoom ratio of 1.91 and an aperture ratio of about 2.88 to 4.07.

  FIG. 21 is a schematic diagram of a main part of a digital still camera (imaging device) including the zoom lens of the present invention.

  The zoom lens of each embodiment is a photographic lens system used in an imaging apparatus, and in the lens cross-sectional view, the left side is the object side and the right side is the image side.

  In the lens cross-sectional views of FIGS. 1, 5, 9, 13, and 17, L1 is a first lens unit having a negative refractive power (optical power = reciprocal of focal length), and L2 is a positive refractive power. The second lens group, L3, is a third lens group having a positive refractive power. SP is an aperture stop, and Examples 1 to 3 and 5 are located on the object side of the second lens unit L2, and Example 4 is located on the image side.

  G is an optical block provided for optical design corresponding to an optical filter, a face plate, a crystal low-pass filter, an infrared cut filter, and the like. IP is an image plane, which is placed on an imaging plane of a solid-state imaging device (photoelectric conversion device) such as a CCD sensor or a CMOS sensor when used as a photographing optical system of a video camera or a digital still camera.

  In the aberration diagrams, d and g are represented by d-line and g-line, respectively, ΔM and ΔS are represented by meridional image surface, sagittal image surface, and lateral chromatic aberration are represented by g-line.

  OBJ is an object distance measured from the image plane.

  In the following embodiments, the zoom positions at the wide-angle end and the telephoto end are zoom positions when the zoom lens unit (second lens unit) is positioned at both ends of a range that moves on the optical axis due to the mechanism.

  In the zoom lenses of Embodiments 1 to 4 in FIGS. 1, 5, 9, and 13, the first lens unit L1 has a locus convex to the image side during zooming from the wide-angle end to the telephoto end zoom position. The second lens unit L2 moves to the object side.

  In the zoom lens of Example 5 in FIG. 17, during zooming from the wide-angle end to the telephoto end, the first lens unit L1 moves so as to draw a part of a convex locus toward the image side, and the second lens unit L2 Is moved to the object side so that the distance from the first lens group L1 is small, and the third lens group L3 is moved to the object side so that the distance from the second lens group L2 is large.

  In any of the embodiments, the aperture stop SP moves together with the second lens unit L2 during zooming.

  In the zoom lens of each embodiment, main zooming is performed by moving the second lens unit L2, and movement of the image point accompanying zooming is corrected by moving the first lens unit L1.

  In Examples 1 to 4, focusing is performed by the first lens unit L1. In the fifth embodiment, focusing is performed by the third lens unit L3.

  At this time, the focusing by the first lens unit L1 may form a zooming cam locus in a step shape and use an extended locus for zooming.

  In general, in a 2 group zoom lens or a 3 group zoom lens, an aspherical surface is used in the lens system in order to achieve a good optical performance over the entire zoom range and to reduce the number of lenses to reduce the thickness of the lens system. It is effective to use it at an appropriate place.

  Further, by appropriately setting the lens configuration of the second lens group, in which the amount of movement during zooming is relatively large, and the lens configuration of the first lens group that corrects image plane variation due to zooming, aberration variation during zooming is suppressed as much as possible. There is a need.

  Therefore, in each embodiment, the first lens unit L1 has a meniscus negative eleventh lens G11 having an aspheric surface on the image side and a convex surface on the object side, and a meniscus shape having a convex surface on the object side. The twelfth lens G12 has a positive refractive power.

  A material having a high refractive index and high resolution is used for the twelfth lens G12.

  The second lens unit L2 has a positive refractive power in which the absolute value of the refractive power is larger than the image-side surface, the object-side surface is large, the object-side surface is aspherical, and both lens surfaces are convex. The twenty-first lens G21 is composed of a twenty-second lens G22 having a negative refractive power in which the absolute value of refractive power is larger on the image side than on the object-side surface, and the image-side surface is aspherical and meniscus. .

  A low refractive index and low resolution material is used for the twenty-first lens G21, and a high refractive index and high resolution material is used for the twenty-second lens G22.

  This corrects axial chromatic aberration well.

  In the fifth embodiment, the third lens unit L3 includes one positive refractive power 31st lens.

  In each embodiment, one or more of the following conditional expressions are satisfied, thereby obtaining an effect corresponding to each conditional expression.

The Abbe numbers of the materials of the 21st lens and the 22nd lens are ν21 and ν22, respectively, and the radii of curvature of the object side and image side surfaces of the 21st lens G21 are R21a and R21b, respectively, and the object side and image side of the 22nd lens G22. When the curvature radii of the surfaces of R22a and R22b are respectively
45 <ν21−ν22 <50 (1)

The following conditional expression is satisfied.

  In conditional expression (1), the Abbe number is based on the d line, and the Abbe number νd is expressed by the following expression.

νd = (Nd−1) / (NF−NC)
Nd: Refractive index of the material with respect to d-line
NF: Refractive index of the material with respect to F-line
Next, the technical meaning of each conditional expression will be described.

  Conditional expression (1) relates to the Abbe number of the materials of the 21st lens G21 and the 22nd lens G22 in the second lens unit L2. If the upper limit or lower limit of conditional expression (1) is exceeded and the Abbe number difference is not appropriate, it is difficult to correct axial chromatic aberration in the telephoto range.

  Conditional expression (2) relates to the shape factor of the twenty-second lens G22 in the second lens unit L2. When the upper limit value or lower limit value of conditional expression (2) is exceeded, it becomes difficult to correct coma flare around the screen in the telephoto range.

  Conditional expression (3) relates to the shape factor of the twenty-first lens G21 in the second lens unit L2. If the upper limit value or lower limit value of conditional expression (3) is exceeded, it will be difficult to correct coma flare in the periphery of the screen over the entire zoom range.

  More preferably, the numerical range of each conditional expression is set as follows.

It is good to satisfy the condition.

  In each embodiment, more preferably, one or more of the following conditional expressions should be satisfied.

  As a result, an effect corresponding to each conditional expression is obtained.

  The focal lengths of the eleventh lens G11 and the twelfth lens G12 are f11 and f12, the focal length of the first lens unit L1 is f1, the focal length of the entire system at the zoom position at the wide angle end is fw, and the material of the eleventh lens G11 Abbe number with respect to the d line is ν11, refractive index and Abbe number with respect to the d line of the material of the twelfth lens G12 are N12 and ν12, respectively, Abbe number with respect to the d line of the materials of the 21st lens G21 and the 22nd lens G22 is ν21, respectively. ν22, when the length from the first lens surface (most object side surface) of the first lens unit L1 to the final lens surface (most image side surface) of the first lens unit L1 is Da,

7 <ν11−ν12 <15 (5)
1.8 <N12 (6)
26 <ν12 (7)
−0.39 <Da / f1 <−0.3 (8)
-2.4 <f1 / fw <-1.5 (9)
The following conditional expression is satisfied.

  Next, the technical meaning of each conditional expression will be described.

  Conditional expression (4) relates to the focal lengths of the eleventh lens G11 and the twelfth lens G12 constituting the first lens unit L1. Conditional expression (5) relates to the Abbe number of the materials of the eleventh lens G11 and the twelfth lens G12 constituting the first lens unit L1.

  In order to achieve both correction of coma flare and chromatic aberration in the entire zoom range, it is preferable to satisfy the conditional expressions (4) and (5) at the same time.

  In conditional expressions (4) and (5), in order to maintain the balance of chromatic aberration in a state where the refractive powers of the two lenses constituting the first lens unit L1 are moderately strengthened and the power of each lens is strong to some extent. The difference between the Abbe numbers of the materials of the two lenses constituting the first lens unit L1 needs to be kept moderate, and the conditions for this are expressed in mathematical formulas.

  If the refractive power of each lens becomes too strong beyond the upper limit of conditional expression (4), it will be difficult to satisfactorily correct off-axis aberrations in the wide-angle range. If the lower limit of conditional expression (4) is exceeded and the refractive power of each lens becomes too weak, the entire lens system will become large, which is not good.

  In a power arrangement within the range of conditional expression (4), if the upper limit or lower limit of conditional expression (5) is exceeded, it will be difficult to correct lateral chromatic aberration in the entire lens system.

  When the upper limit value of conditional expression (5) is exceeded, it is necessary to weaken the refractive power of each lens constituting the first lens unit L1 in order to maintain the balance of lateral chromatic aberration, and as a result, the numerical range of conditional expression (4) is reduced. By deviating, coma flare increases in the entire zoom range.

  When the lower limit of conditional expression (5) is exceeded, it is necessary to increase the refractive power of each lens constituting the first lens unit L1, and it is difficult to secure the edge of the twelfth lens G12 in the first lens unit L1. It becomes.

  Conditional expression (6) relates to the refractive index of the material of the twelfth lens G12 in the first lens unit L1. When the refractive index is lowered beyond the lower limit of conditional expression (6), the lens diameter of the first lens unit L1 increases, and it becomes difficult to correct coma flare in a wide angle region.

  Conditional expression (7) relates to the Abbe number of the material of the twelfth lens G12 in the first lens unit L1. Exceeding the lower limit of conditional expression (7) makes it difficult to correct lateral chromatic aberration in the entire lens system.

  Conditional expression (8) relates to the total thickness of the lenses in the first lens unit L1 and the distance between the lenses. If the upper limit of conditional expression (8) is exceeded, the thickness of the first lens unit L1 increases, so the front lens diameter increases and the entire lens system increases in size.

If the thickness of the first lens unit L1 is reduced beyond the lower limit of the conditional expression (8), the lens fixing holder that should exist between the eleventh lens G11 and the twelfth lens G12 becomes thin, so that the strength is insufficient. It's not good because it comes.
Conditional expression (9) relates to the focal length of the first lens unit L1. Exceeding the upper limit of conditional expression (9) makes it difficult to correct curvature of field in the entire zoom range. If the lower limit of conditional expression (9) is exceeded, the total lens length at the wide-angle end tends to increase, which is not good.

  More preferably, the numerical range of each conditional expression is set as follows.

It is good to satisfy the following conditional expression.

  In each of the above embodiments, a filter and a converter lens are provided on the object side of the first lens unit L1, and / or a field lens or the like having a small refractive power is provided on the image side of the second lens unit L2 or the third lens unit L3. A lens group may be added.

As described above, according to each embodiment, in order from the object side to the image side, the first lens unit having the negative refractive power and the second lens group having the positive refractive power are provided. In the zoom lens in which the interval changes, as described above, the lens configuration of each lens group, the position of the aspheric surface, the moving method during zooming, and the like are optimally set, and the focusing method is optimally set. This makes it possible to reduce the number of lenses and achieve a reduction in the overall length of the lens, but with a zoom ratio of about 2 times, a zoom that is bright and has high optical performance, suitable for digital still cameras. Has achieved the lens.

  Next, an embodiment of a digital still camera (imaging device) using the zoom lens of the present invention as a photographing optical system will be described with reference to FIG.

  In FIG. 21, reference numeral 20 denotes a video camera body, 21 denotes a photographing optical system constituted by the zoom lens of the present invention, 22 denotes a solid-state image pickup device (photoelectric conversion) such as a CCD sensor or a CCMOS sensor that receives a subject image by the photographing optical system 21. Element) 23, a memory for recording a subject image received by the image sensor 22, and a viewfinder 24 for observing the subject image displayed on a display element (not shown).

The display element is constituted by a liquid crystal panel or the like, and a subject image formed on the image sensor 22 is displayed.

  Thus, by applying the zoom lens of the present invention to an image pickup apparatus such as a digital still camera, a small image pickup apparatus having high optical performance is realized.

Next, numerical examples of the present invention will be shown. In each numerical example, i indicates the order of the surfaces from the object side, Ri is the radius of curvature of the lens surface, Di is the lens thickness and interval between the i-th surface and the i + 1-th surface, and Ni and νi are respectively The refractive index and Abbe number with respect to the d-line are shown.

  The two surfaces closest to the image side are glass materials such as face plates.

When the aspherical shape is x with the displacement in the optical axis direction at the position of the height h from the optical axis as the reference to the surface vertex,
x = (h ² / R) / [1+ {1− (1 + k) (h / R) ² } ^1/2 ]
+ Ah ² + Bh ⁴ + Ch ⁶ + Dh ⁸ + Eh ¹⁰
It is represented by However, k is a conic constant, A, B, C, D, and E are aspherical coefficients, and R is a paraxial curvature radius.

“E-0x” means “× 10 ^−x ”. f indicates a focal length, Fno indicates an F number, and ω indicates a half angle of view.

Lens cross-sectional view of the zoom lens of Example 1 Aberration diagrams at the zoom position at the wide-angle end of the zoom lens of Example 1. FIG. Aberration diagram at the intermediate focal position of the zoom lens of Example 1 Aberration diagram at the zoom position at the telephoto end of the zoom lens of Example 1 Lens sectional view of the zoom lens of Example 2 Aberration diagrams at the zoom position at the wide-angle end of the zoom lens of Example 2. Aberration diagram at the intermediate focal position of the zoom lens of Example 2 Aberration diagram at the zoom position at the telephoto end of the zoom lens of Example 2 Lens sectional view of the zoom lens of Example 3 Aberration diagrams at the zoom position at the wide-angle end of the zoom lens according to Embodiment 3 Aberration diagrams at the intermediate focal position of the zoom lens of Example 3 Aberration diagram at the zoom position at the telephoto end of the zoom lens of Example 3 Lens sectional view of the zoom lens of Example 4 Aberration diagrams at the zoom position at the wide-angle end of the zoom lens according to Example 4 Aberration diagrams at the intermediate focal position of the zoom lens of Example 4 Aberration diagram at the zoom position at the telephoto end of the zoom lens of Example 4 Lens sectional view of the zoom lens of Example 5 Aberration diagrams at the zoom position at the wide-angle end of the zoom lens according to Example 5 Aberration diagrams at the intermediate focal position of the zoom lens of Example 5 Aberration diagrams at the zoom position at the telephoto end of the zoom lens of Example 5 Schematic diagram of the main part of a digital still camera

Explanation of symbols

L1: First lens group L2: Second lens group L3: Third lens group SP: Aperture IP: Image plane G: Glass block d: d line g: g line ΔS: Sagittal image plane ΔM: Meridional image plane

Claims (7)

In the zoom lens having a first lens unit having a negative refractive power and a second lens unit having a positive refractive power in order from the object side to the image side, the distance between the two lens units changes during zooming. The lens group includes an eleventh lens having a negative refractive power and a twelfth lens having a positive refractive power, and the second lens group includes a twenty-first lens having a positive refractive power and a twenty-second lens having a negative refractive power. When the Abbe numbers of the materials of the 21st lens and the 22nd lens are ν21 and ν22, respectively,
45 <ν21−ν22 <50
A zoom lens characterized by satisfying the following conditions: When the curvature radii of the object side surface and the image side surface of the 22nd lens are R22a and R22b, respectively.

The zoom lens according to claim 1, wherein the following condition is satisfied.   The eleventh lens has a larger absolute value of the refractive power of the image side surface than the absolute value of the refractive power of the object side surface, and at least one surface has an aspherical shape. 3. The zoom lens according to claim 1, wherein the zoom lens has a convex meniscus shape.   4. The zoom lens according to claim 1, wherein an aperture stop is provided on the object side or the image side of the second lens group, and the twenty-first lens and the twenty-second lens are independent lenses. When the curvature radii of the object side surface and the image side surface of the 21st lens are R21a and R21b, respectively.

The zoom lens according to claim 1, wherein the following condition is satisfied.   6. The zoom lens according to claim 1, wherein the zoom lens is an optical system for forming an image on a solid-state image sensor.   An image pickup apparatus comprising: the zoom lens according to claim 1; and a solid-state image pickup device that receives an image formed by the zoom lens.

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