JP2011028144A - Zoom lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make resolution and magnification higher without making an aperture ratio smaller, in a zoom lens. <P>SOLUTION: The zoom lens includes, in order from an object side, a first group G1 having positive refractive power, a second group G2 having negative refractive power, and a lens group GK following the second group G2. The second group G2 includes, in order from the object side, a negative lens L5 whose concave surface faces an image side, and a double-sided aspherical lens L6, and is configured such that the lens surface R10 on the object side of the double-sided aspherical lens L6 satisfies an expression (1): sagM-sagZ<0, and an expression (2): sagM/sagZ>2.3, and in the zoom lens, when the setting of zooming is changed from the wide angle end to a telephoto end, the first group G1 is fixed, and the second group G2 is moved to the image side to vary magnification. In this case, in the two expressions, sagM and sagZ is lens depth at a position of an effective diameter on the lens surface R10 when being set to a wide angle end, and is lens depth at a position of the diameter of 80% of the effective diameter, respectively. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a zoom lens, and more particularly to a zoom lens in which a first group is fixed and a second group is moved when changing zoom settings.

  2. Description of the Related Art Conventionally, a high-magnification zoom lens with a high resolution and a zoom ratio of 30 or more, for example, used for a video camera or an electronic still camera is known. The zoom lens having such a large zoom ratio includes, for example, a first group having a positive refractive power, a second group having a negative refractive power, a third group having a positive refractive power, a stop, and a positive refraction. A zoom lens having a fourth group having power in this order is known.

  As such a zoom lens, there is known a zoom lens that performs zooming by fixing the first group and moving the second group when changing the zoom setting to the wide-angle side or the telephoto side. (See Patent Document 1).

JP 2007-148340 A

  By the way, as the number of pixels of an image sensor increases and the application range of video cameras and electronic still cameras expands, zoom lenses with higher resolution and higher magnification are used as zoom lenses applied to such video cameras and electronic still cameras. It has been demanded.

  Here, it is relatively easy to reduce the aperture ratio and increase the magnification, but in such a case, there may be a shortage of light quantity in photographing in a dark place. In addition, if the aperture ratio is increased so that the light quantity is not insufficient, the apparatus size may be increased.

  Therefore, for example, there is a demand for realizing a zoom lens with higher resolution and higher magnification while maintaining an aperture ratio and apparatus size that can be applied to a small surveillance camera or the like.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a compact zoom lens with high resolution and high magnification without reducing the aperture ratio.

  The zoom lens of the present invention includes, in order from the object side, a first group having a positive refractive power, a second group having a negative refractive power, and a lens group following the second group, and zooms from the wide-angle end to the telephoto end. When changing the ratio, the zoom lens is configured to perform zooming by fixing the first group and moving the second group to the image side along the optical axis. The second group is sequentially moved from the object side. , A negative lens having a concave surface facing the image side, a double-sided aspheric lens, and the object-side lens surface of the double-sided aspherical lens is expressed by the following equation (1): sagM−sagZ <0, and (2) : SagM / sagZ> 2.3 is satisfied.

  Here, sagM is the lens depth at the position of the effective diameter on the object-side lens surface of the double-sided aspheric lens when the zoom lens is set at the wide-angle end, and sagZ is the zoom lens at the wide-angle end. This is the lens depth at a position of a diameter of 80% of the effective diameter on the object-side lens surface of the aspherical lens when set.

  The lens depth at the position of the effective diameter of the lens surface means the distance in the optical axis direction from the position of the intersection that intersects the optical axis on the lens surface to the position of the effective diameter on the lens surface. . Further, the lens depth at a position having a diameter of 80% of the effective diameter of the lens surface is the light from the position of the intersection intersecting the optical axis on the lens surface to a position having a diameter of 80% of the effective diameter on the lens surface. It means the distance in the axial direction.

  The value of the lens depth is negative when the effective diameter position on the lens surface or the position of 80% of the effective diameter exists on the object side relative to the position of the intersection point intersecting the optical axis on the lens surface. A positive value is obtained when the position of the effective diameter on the lens surface or the position of the diameter of 80% of the effective diameter is present on the image side from the position of the intersection intersecting the optical axis on the lens surface.

  The second group includes, in order from the object side, only four lenses, a negative lens having a concave surface directed toward the image side, a double-sided aspheric lens, a negative lens, and a positive lens. The negative lens and the positive lens are both It is desirable to form a cemented lens in which are mutually joined.

  The zoom lens includes a stop between the second group and the subsequent lens group. The subsequent lens group includes, in order from the object side, a third group having a positive refractive power and a fourth group having a positive refractive power. When the zoom setting is changed from the wide-angle end to the telephoto end, the first group and the third group are fixed, and the second group moves to the image side along the optical axis. It is desirable that the image plane is corrected and focused by moving along the optical axis of the fourth group while zooming.

  The third group includes, in order from the object side, only a positive double-sided aspheric lens, a positive meniscus lens having a concave surface facing the object side, and three negative lenses having a concave surface facing the object side. Can do.

  The fourth group includes, in order from the object side, only a positive double-sided aspheric lens, a positive lens, and a negative lens, and the positive lens and the negative lens are cemented with each other. It can be made.

  The second group of double-sided aspheric lenses may be plastic lenses.

  The zoom lens according to the present invention includes, in order from the object side, a first group having a positive refractive power, a second group having a negative refractive power, and a lens group subsequent to the second group. When changing from the telephoto end to the telephoto end, a zoom lens in which the first lens group is fixed and the second lens group is moved to the image side along the optical axis, and zooming is performed. In order from the negative lens having a concave surface facing the image side and a double-sided aspheric lens, and the object-side lens surface of the double-sided aspheric lens is expressed by the following equation (1): sagM-sagZ <0, Since both sagM / sagZ> 2.3 are satisfied, it is possible to obtain a small zoom lens with high resolution and high magnification without reducing the aperture ratio. Compact, high resolution, high magnification suitable for use in video cameras It can be realized Murenzu.

  If the lens surface on the object side of the double-sided aspherical lens in the second group does not satisfy the expressions (1) and (2), the curvature of field and the coma will increase, and the zoom range will be reduced. It becomes difficult to perform correction so as to suppress aberration over the entire area.

Sectional drawing which shows schematic structure in the state set to the wide-angle end of the zoom lens by embodiment of this invention with the optical path of the light ray which passes along this zoom lens The figure which expands and shows the optical path of the light ray which passes along 2nd group of the said zoom lens set to the wide-angle end Sectional drawing which shows schematic structure of the said zoom lens set to a telephoto end with the optical path of the light ray which passes along this zoom lens FIG. 3 is a diagram illustrating a schematic configuration in a state where the zoom lens according to the first embodiment is set at a wide angle end. The figure which shows the longitudinal aberration of the zoom lens of Example 1 set to the wide-angle end The figure which shows the longitudinal aberration of the zoom lens of Example 1 set to the telephoto end The figure which shows the lateral aberration of the zoom lens of Example 1 set to the wide-angle end The figure which shows the lateral aberration of the zoom lens of Example 1 set to the telephoto end The figure which shows schematic structure in the state set to the wide-angle end of the zoom lens of Example 2. The figure which shows the longitudinal aberration of the zoom lens of Example 2 set to the wide-angle end The figure which shows the longitudinal aberration of the zoom lens of Example 2 set to the telephoto end The figure which shows the lateral aberration of the zoom lens of Example 2 set to the wide-angle end The figure which shows the lateral aberration of the zoom lens of Example 2 set to the telephoto end FIG. 6 is a diagram illustrating a schematic configuration in a state where the zoom lens according to Embodiment 3 is set at a wide angle end. The figure which shows the longitudinal aberration of the zoom lens of Example 3 set to the wide-angle end The figure which shows the longitudinal aberration of the zoom lens of Example 3 set to the telephoto end The figure which shows the lateral aberration of the zoom lens of Example 3 set to the wide-angle end The figure which shows the lateral aberration of the zoom lens of Example 3 set to the telephoto end FIG. 6 is a diagram illustrating a schematic configuration in a state where the zoom lens according to Embodiment 4 is set at a wide angle end. The figure which shows the longitudinal aberration of the zoom lens of Example 4 set to the wide-angle end The figure which shows the longitudinal aberration of the zoom lens of Example 4 set to the telephoto end The figure which shows the lateral aberration of the zoom lens of Example 4 set to the wide-angle end The figure which shows the lateral aberration of the zoom lens of Example 4 set to the telephoto end FIG. 10 is a diagram illustrating a schematic configuration in a state where the zoom lens according to Embodiment 5 is set at a wide angle end. The figure which shows the longitudinal aberration of the zoom lens of Example 5 set to the wide-angle end The figure which shows the longitudinal aberration of the zoom lens of Example 5 set to the telephoto end The figure which shows the lateral aberration of the zoom lens of Example 5 set to the wide-angle end The figure which shows the lateral aberration of the zoom lens of Example 5 set to the telephoto end FIG. 10 is a diagram illustrating a schematic configuration in a state where the zoom lens according to Embodiment 6 is set at a wide angle end. The figure which shows the longitudinal aberration of the zoom lens of Example 6 set to the wide-angle end The figure which shows the longitudinal aberration of the zoom lens of Example 6 set to the telephoto end The figure which shows the lateral aberration of the zoom lens of Example 6 set to the wide-angle end The figure which shows the lateral aberration of the zoom lens of Example 6 set to the telephoto end The figure which shows the video camera comprised using the zoom lens of this invention

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing a schematic configuration of a zoom lens according to an embodiment of the present invention together with an optical path of a light beam passing through the zoom lens. FIG. 1 shows a state where the zoom lens is set at the wide angle end. 2 is an enlarged cross-sectional view showing the optical path of a light beam passing through the second group of the zoom lens set at the wide-angle end, and FIG. 3 is a cross-sectional view showing a schematic configuration of the zoom lens set at the telephoto end. It is.

  The illustrated zoom lens 100 is a lens following the first group G1 having a positive refractive power, the second group G2 having a negative refractive power, and the second group G2 in order from the object side (the −Z side in the drawing). When the zoom setting is changed from the wide-angle end to the telephoto end, the first group G1 is fixed and the second group G2 is positioned along the optical axis Z1 on the image side (+ Z in the figure). The zooming is performed by moving to the side).

  In the zoom lens 100, the second group G2 includes, in order from the object side, a negative lens L5 having a concave surface facing the image side, and a double-sided aspheric lens L6, and an object-side lens of the double-sided aspheric lens L6. The surface R10 satisfies the formula (1) sagM-sagZ <0 and the formula (2) sagM / sagZ> 2.3.

  As shown in FIG. 2, sagM is the lens depth De100 at the effective diameter position E100 on the object-side lens surface R10 of the double-sided aspheric lens L6 when the zoom lens 100 is set at the wide-angle end. Value.

  As shown in FIG. 2, sagZ is a diameter of 80% of the effective diameter on the object-side lens surface R10 of the aspherical lens L6 of the second group G2 when the zoom lens 100 is set at the wide-angle end. This is the value of the lens depth De80 at the position E80.

  The lens depth De100 is a distance in the optical axis direction (Z direction) from an intersection position P10 where the lens surface R10 and the optical axis Z1 intersect to an effective diameter position E100 on the lens surface R10, and the position P10. Is a negative value when the effective diameter position E100 exists on the object side, and a positive value when the effective diameter position E100 exists on the image side with reference to the position P10. Accordingly, the value of sagM indicating the lens depth in FIG. 2 is a negative value because the effective diameter position E100 exists on the object side with respect to the position P10, and its magnitude (absolute value) is the position P10. To the effective diameter position E100 in the optical axis direction (Z direction).

  Further, the value of sagZ indicating the lens depth De80 at the position E80 of the diameter 80% of the effective diameter on the lens surface R10 is also determined in the same manner as in the case of sagM.

  The position of the effective diameter of the lens surface constituting the lens that is the shape to be rotated has a constant distance from the optical axis Z1 of the lens.

  Hereinafter, a desirable configuration in the present invention will be described although it is not an essential configuration in the present invention. The zoom lens 100 has these configurations.

  1 and 3, lenses L1 to L15 constituting the zoom lens 100 are shown in this order from the object side (−Z direction in the figure) to the image side (+ Z direction in the figure), and the lenses in the lenses L1 to L15 are shown. The surfaces R1 to R27 are shown in order from the object side to the image side.

  Here, the lens surface R2 is a cemented surface between the lenses L1 and L2, the lens surface R13 is a cemented surface between the lenses L7 and L8, and the lens surface R24 is a cemented surface between the lenses L13 and L14.

  The lens surface R2 indicates the image side lens surface of the lens L1 and the object side lens surface of the lens L2 with a common reference R2. The same applies to the lens surface R13 and the lens surface R24, which are other cemented surfaces.

  The plane parallel plate L15 is a filter for blocking unnecessary light incident on the imaging surface.

  Further, light incident on the zoom lens 100 from the object side passes through the zoom lens 100 and forms an image on the image plane Jk.

  The aperture stop St is disposed between the second group G2 and the lens group GK.

  The first group 1G includes a lens L1, a lens L2, a lens L3, and a lens L4 in order from the object side. The lens L1 and the lens L2 form a cemented lens S12 in which both are cemented. .

  The second group G2 includes, in order from the object side, only a negative lens L5 having a concave surface directed toward the image side, a double-sided aspheric lens L6, a negative lens L7, and a positive lens L8. The positive lens L8 forms a cemented lens S78 in which both are cemented. If the second group G2 is configured in this way, aberrations can be corrected well over the entire zoom range of the zoom lens 100.

  The lens group GK following the second group G2 includes, in order from the object side, a third group having a positive refractive power and a fourth group having a positive refractive power. When changing the zoom setting from the wide-angle end to the telephoto end, the first group G1 and the third group G3 are fixed with respect to the image plane Jk, and the second group G2 is moved along the optical axis Z1. The image plane is corrected and focused by moving the fourth group G4 along the optical axis Z1 while moving to the image side and changing the magnification. If the subsequent lens group GK is configured in this manner, the zoom lens 100 can be further downsized.

  Note that the fixing and movement of the position when setting the zoom in the zoom lens 100 is fixing and moving the position of each group with respect to the position of the imaging plane Jk.

  The correction of the image point position (image plane correction) is performed by changing the magnification by moving the second group along the optical axis, and correcting the change in the image point position due to the magnification change in the fourth group. The focusing is adjustment of the image formation position so that the image formed through the zoom lens is positioned on the image formation plane Jk.

  The third group G3 includes, in order from the object side, only a positive double-sided aspheric lens L9, a positive meniscus lens L10 with a concave surface facing the object side, and a negative lens L11 with a concave surface facing the object side. Is. If the third group G3 is configured in this way, the zoom lens 100 can be further reduced in size.

  The fourth group G4 includes, in order from the object side, only three lenses including a positive double-sided aspheric lens L12, a positive lens L13, and a negative lens L4. The positive lens L13 and the negative lens L4 are joined together. The cemented lens S1314 is formed. If the fourth group G4 is configured in this way, it is possible to reduce the distance fluctuation during focusing.

  Note that the double-sided aspheric lens L6 of the second group G2 may be a plastic lens. By doing so, the cost of the lens member necessary for suppressing various aberrations can be reduced, and the device cost can be reduced.

<Specific Examples>
Next, FIG. 4 (FIGS. 4A, 4B, 4C, 4D, 4E) to FIG. 9 (FIGS. 9A, 9B, 9C, 9D, 9E) and Table 1 (Table 1a, Table 1b, Table 1c) to Table 6 ( With reference to Tables 6a, 6b, and 6c), numerical data and the like related to the zoom lenses of Examples 1 to 6 will be described together.

  The values of sagM-sagZ and the values of sagM / sagZ when the zoom lenses of Examples 1 to 6 are set at the wide angle end are shown below.

Example 1: value of sagM-sagZ = -0.010, value of sagM / sagZ = 2.70
Example 2: value of sagM-sagZ = −0.009, value of sagM / sagZ = 8.20
Example 3: value of sagM-sagZ = −0.008, value of sagM / sagZ = 4.57
Example 4: value of sagM-sagZ = −0.007, value of sagM / sagZ = 3.04
Example 5: value of sagM-sagZ = -0.010, value of sagM / sagZ = 2.84
Example 6: value of sagM-sagZ = -0.010, value of sagM / sagZ = 2.76
Tables 1 to 6 are tables showing basic data of the zoom lenses of Examples 1 to 6, respectively.

  Tables 1a to 6a show lens data, and Tables 1b to 6b show the difference between the wide-angle end setting and the telephoto end setting. Further, Table 1c to Table 6c show respective coefficients of the aspheric surface expression representing the shape of the aspheric surface adopted for each zoom lens.

  In the lens data in Tables 1a to 6a, the surface number of the lens is shown as the i-th (i = 1, 2, 3,...) Surface number that sequentially increases from the object side to the image side. These lens data do not include the surface numbers of the aperture stop St and the imaging surface Jk, but the surface numbers of the object-side surface and the image-side surface of the parallel flat plate L15 (i = 26, 27). ) Is included.

  Ri represents the paraxial radius of curvature of the i-th (i = 1, 2, 3,...) Surface, and Di (i = 1, 2, 3,...) Represents the i-th surface and the i + 1-th surface. The space | interval on the optical axis Z1 with a surface is shown. Note that a symbol Ri indicating the paraxial radius of curvature of the lens data corresponds to a symbol Ri (i = 1, 2, 3,...) Indicating the lens surface in FIG.

  Here, the lens surface R2, which is a cemented surface, indicates the lens surface on the image side of the lens L1 and the lens surface on the object side of the lens L2 with a common reference R2. The lens surface R13, which is a cemented surface, indicates the image side lens surface of the lens L7 and the object side lens surface of the lens L8 with a common reference R13. Further, the lens surface R24, which is a cemented surface, indicates the image side lens surface of the lens L13 and the object side lens surface of the lens L14 with a common reference R13.

  Nej represents the refractive index with respect to the e-line (wavelength 546.1 nm) of the j-th (j = 1, 2, 3,...) Optical element that sequentially increases from the object side to the image side, and νdj represents The Abbe number of the j-th optical element with respect to the d-line (wavelength wavelength: 587.6 nm) is shown.

  The unit of the paraxial radius of curvature and the surface interval is mm, and the paraxial radius of curvature is positive when convex on the object side and negative when convex on the image side.

  Comparison between the setting at the wide-angle end and the setting at the telephoto end shown in Tables 1b to 6b shows the difference between the distances D7, D14, D20, D25, and the focal length f ′.

The aspherical coefficients KA, B3, B4, B5... Shown in Tables 1c to 6c are applied to the following aspherical expressions.

  4A, 5A,... 9A are cross-sectional views showing a schematic configuration in a state in which each of the zoom lenses of Examples 1 to 6 is set at the wide-angle end, and the reference numerals in FIGS. 4A to 9A that coincide with each other indicate parts corresponding to each other.

  4B, 5B,... 9B are diagrams showing longitudinal aberrations at the wide-angle end of the zoom lenses of Examples 1 to 6, respectively.

  4C, 5C,... 9C are diagrams showing longitudinal aberrations at the telephoto end of the zoom lenses of Examples 1 to 6, respectively.

  4D, 5D,... 9D are diagrams showing lateral aberrations at the wide-angle end of the zoom lenses of Examples 1 to 6, respectively.

  4E, 5E,... 9E are diagrams showing lateral aberrations at the telephoto end of the zoom lenses of Examples 1 to 6, respectively.

  Each diagram showing the aberration shows the aberration for each of the wavelength 546.1 nm (e-line), the wavelength 460.0 nm, and the wavelength 615.0 nm.

  In each graph showing aberrations, the wavelength 546.1 nm (e-line) is indicated by a solid line, the wavelength 460.0 nm is indicated by a broken line, and the wavelength 615.0 nm is indicated by a one-dot chain line.

  Each diagram showing transverse aberration shows coma aberration, and the coma aberration in the tangential direction and the coma aberration in the sagittal direction are shown corresponding to each other in the left-right direction.

  In addition, the angle shown on the vertical axis of the figure relating to astigmatism and distortion in the figure representing longitudinal aberration is a half angle of view. When this half angle of view is ω, the distortion in the figure uses the focal length f of the entire zoom lens system and the angle of view θ (variable treatment, 0 ≦ θ ≦ ω), and the ideal image height is f × tan θ. The amount of deviation in the image height direction from the ideal image height is expressed as a percentage.

  The astigmatism in the figure represents the amount of deviation in the optical axis direction from the paraxial image plane using the angle of view θ (variable treatment, 0 ≦ θ ≦ ω).

  As can be seen from the basic data of Examples 1 to 6 and diagrams showing various aberrations, the zoom lens of the present invention reduces the aperture ratio by optimizing the shape and material of each lens. Thus, a small zoom lens with high resolution and high magnification can be obtained.

  FIG. 10 illustrates a configuration of a video camera 101 configured using the zoom lens 100 according to the embodiment of the present invention as an example of the imaging device according to the embodiment of the present invention. 10 schematically shows the first group G1, the second group G2, the aperture stop St, the third group G3, and the fourth group G4 included in the zoom lens 100, and the second group G2 that moves during zooming and A double arrow is attached to the moving direction of the fourth group G4.

  The video camera 101 includes a zoom lens 100, a filter 2 having a function such as a low-pass filter and an infrared cut filter disposed on the image side of the zoom lens 100, an image sensor 4 disposed on the image side of the filter 2, And a signal processing circuit 5. Here, the position of the light receiving surface of the image sensor 4 coincides with the position of the image plane Jk of the zoom lens 100.

  An image of a subject is formed on the light receiving surface of the image sensor 4 by the zoom lens 100, and an image signal carrying the image output from the image sensor 4 is processed by the signal processing circuit 5, and the image is displayed on the display device 6. A visible image is displayed.

  In addition, this invention is not limited to the said embodiment and each Example, A various deformation | transformation implementation is possible. For example, the radius of curvature, the refractive index, the dispersion, or the surface interval between the lenses is not limited to the above numerical values, and can take other values.

G1 First group G2 Second group GK Subsequent lens group L5 Negative lens,
L6 Double-sided aspheric lens R10 Double-sided aspherical lens L6 object side lens surface Z1 Optical axis

Claims (6)

When changing the zoom setting from the wide angle end to the telephoto end, in order from the object side, a first group having a positive refractive power, a second group having a negative refractive power, and a lens group following the second group. In the zoom lens, the first lens unit is fixed, and zooming is performed by moving the second lens unit toward the image side.
The second group includes, in order from the object side, a negative lens having a concave surface facing the image side, a double-sided aspheric lens, and the lens surface on the object side of the double-sided aspheric lens has the following formula (1): And a zoom lens satisfying the expression (2).
sagM-sagZ <0 (1)
sagM / sagZ> 2.3 (2)
here,
sagM: the lens depth at the position of the effective diameter on the object-side lens surface of the double-sided aspheric lens when the zoom lens is set at the wide-angle end. sagZ: the lens depth when the zoom lens is set at the wide-angle end. Lens depth at a position of 80% of the effective diameter on the object-side lens surface of an aspheric lens   The second group includes, in order from the object side, a negative lens having a concave surface directed to the image side, the double-sided aspheric lens, a negative lens, and a positive lens, and the negative lens and the positive lens are 2. The zoom lens according to claim 1, wherein the zoom lens forms a cemented lens that is cemented with each other. A diaphragm between the second group and the subsequent lens group;
The subsequent lens group includes, in order from the object side, a third group having a positive refractive power and a fourth group having a positive refractive power.
When changing the zoom setting from the wide-angle end to the telephoto end, the first group and the third group are fixed, and the fourth group is zoomed while moving by moving the second group toward the image side. The zoom lens according to claim 1 or 2, wherein the image plane is corrected and focused by moving the lens in the optical axis direction.   The third group includes, in order from the object side, a positive double-sided aspheric lens, a positive meniscus lens having a concave surface facing the object side, and a negative lens having a concave surface facing the object side. The zoom lens according to claim 3.   The fourth group includes, in order from the object side, only a positive double-sided aspheric lens, a positive lens, and a negative lens, and the positive lens and the negative lens form a cemented lens joined together. The zoom lens according to claim 3, wherein the zoom lens is provided.   An imaging apparatus comprising the zoom lens according to claim 1.

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