JP5290902B2 - 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 positive first group G1, a negative second group G2, a diaphragm St, a positive third group G3, and a positive fourth group G4. The third group G3 includes, in order from the object side, only a positive double-sided aspherical lens L9, a positive meniscus lens L10 whose concave surface faces the object side, and a negative lens L11 whose concave surface faces the object side, and is configured such that the meniscus lens L10 satisfies an expression (1): 4.8&lt;(Ra+Rb)/(Ra-Rb)&lt;9.0. When the setting of zoom is changed from a wide angle end to a telephoto end, the first group G1 and the third group G3 are fixed, and the fourth group G4 is moved to perform the correction of an image surface and focusing, while moving the second group G2 to an image side to vary magnification. In the expressions, Ra and Rb is the curvature radius of the lens surface R17 on the object side of the meniscus lens L10, and is the curvature radius of the lens surface R18 on the image side of the meniscus lens L10. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a zoom lens, and more particularly to a zoom lens in which a first group and a third group are fixed and a second group and a fourth group are 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.

  Further, in such a zoom lens, when changing the zoom setting to the wide-angle side or the telephoto side, the first group and the third group are fixed, and the second group and the fourth group are moved to perform zooming. A zoom lens to perform is known (see Patent Document 1).

JP 2007-148340 A

  By the way, as the number of pixels of the 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 has, in order from the object side, a first group having a positive refractive power, a second group having a negative refractive power, a stop, a third group having a positive refractive power, and a positive refractive power. the fourth consists of a group, when changing the setting of the zoom from a wide-angle end to the telephoto end, the first and third lens groups are fixed, variable by the movement of the image side along the optical axis of the second group The image plane is corrected and focused by moving along the optical axis of the fourth group while doubling, and the third group is a positive double-sided aspheric lens in order from the object side. , 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 meniscus lens has the formula (1): 4.8 <(Ra + Rb) / (Ra− Rb) <9.0 is satisfied.

  Here, Ra is the radius of curvature of the object-side lens surface of the meniscus lens, and Rb is the radius of curvature of the image-side lens surface of the meniscus lens.

  The radius of curvature of the lens surface is the radius of curvature in the paraxial region when the lens surface is aspheric.

  The fourth group includes, in order from the object side, only a positive double-sided aspherical lens, a positive lens, and a negative lens, and the positive lens and the negative lens are cemented lenses that are joined together. It is desirable that

  The second group may include at least one aspheric lens.

  The zoom lens of the present invention has, in order from the object side, a first group having a positive refractive power, a second group having a negative refractive power, a stop, a third group having a positive refractive power, and 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 change by moving toward the image side along the optical axis of the second group. It is assumed that the image plane is corrected and focused by moving along the optical axis of the fourth group while being doubled. The third group is a positive double-sided aspheric lens in order from the object side, It is assumed that there are only three meniscus lenses, a positive meniscus lens having a concave surface facing the object side and a negative lens having a concave surface facing the object side, and the meniscus lens has the formula (1): 4.8 <( Ra + Rb) / (Ra−Rb) <9.0 is satisfied, so it is small without reducing the aperture ratio. It can realize high resolution and high magnification of the zoom lens.

  If the meniscus lens has a shape that does not satisfy Expression (1), coma increases, and it is difficult to perform correction so as to suppress aberration over the entire zoom range.

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 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 exemplary 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 of the state in which the zoom lens of Example 2 was set to the wide-angle end 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 the fourth exemplary embodiment 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 the fifth exemplary embodiment 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 The figure which shows schematic structure of the state by which the zoom lens of Example 6 was set to the 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 schematic structure of the state by which the zoom lens of Example 7 was set to the wide-angle end The figure which shows the longitudinal aberration of the zoom lens of Example 7 set to the wide-angle end The figure which shows the longitudinal aberration of the zoom lens of Example 7 set to the telephoto end The figure which shows the lateral aberration of the zoom lens of Example 7 set to the wide-angle end The figure which shows the lateral aberration of the zoom lens of Example 7 set to the telephoto end The figure which shows schematic structure of the state by which the zoom lens of Example 8 was set to the wide-angle end. The figure which shows the longitudinal aberration of the zoom lens of Example 8 set to the wide-angle end The figure which shows the longitudinal aberration of the zoom lens of Example 8 set to the telephoto end The figure which shows the lateral aberration of the zoom lens of Example 8 set to the wide-angle end The figure which shows the lateral aberration of the zoom lens of Example 8 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. FIG. 2 is a sectional view showing a schematic configuration of the zoom lens set at the telephoto end.

  The illustrated zoom lens 100 includes, in order from the object side (the −Z side in the figure), a first group G1 having a positive refractive power, a second group 2G having a negative refractive power, an aperture stop St, and a positive refractive power. When the zoom setting is changed from the wide angle end to the telephoto end, the first group G1 and the third group G3 are fixed. While performing zooming by moving the position of the second group G2 along the optical axis to the image side, the image plane is corrected and focused by moving the position of the fourth group G4 along the optical axis. It is comprised as follows.

  In the zoom lens 100, the third group G3 includes, in order from the object side, a positive double-sided aspheric lens L9, a positive meniscus lens L10 having a concave surface facing the object side, and a negative lens L11 having a concave surface facing the object side. What is provided with only three lenses and the meniscus lens L10 is configured to satisfy the formula (1): 4.8 <(Ra + Rb) / (Ra−Rb) <9.0 It is.

  The symbol Ra represents the radius of curvature of the object-side lens surface R17 of the meniscus lens L10, and the symbol Rb represents the radius of curvature of the image-side lens surface R18 of the meniscus lens L10.

  The correction of the image point position (image plane correction) is performed by moving the second group G2 along the optical axis, and the variation of the image point position due to the magnification change is corrected by the fourth group G4. The focus is adjustment of the image formation position so that the image formed through the zoom lens 100 is positioned on the image formation plane Jk.

  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.

  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.

  In FIGS. 1 and 2, the 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 this order from the object side (−Z direction in the figure) to the image side (+ Z direction in the figure).

  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. In the lens surface R2, the lens surface on the image side of the lens L1 and the lens surface on the object side of the lens L2 are indicated by 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.

  When changing the zoom setting, the positions of the first group G1 and the third group G3 are fixed with respect to the imaging plane Jk, and the position of the second group G2 is moved with respect to the imaging plane Jk. The fourth group G4 is moved with respect to the image plane Jk while zooming, and the image plane is corrected and focused.

  The first group G1 having a positive refractive power includes a lens L1, a lens L2, a lens L3, and a lens L4 arranged in this order from the object side. The lens L1 and the lens L2 are joined to each other. The lens S12 is configured.

  The second group G2 having a negative refractive power has at least one aspheric lens, and includes a negative lens L5 having a concave surface facing the image side, a double-sided aspheric lens L6, a negative lens L7, a positive lens The lens L8 is arranged in this order from the object side, and the negative lens L7 and the positive lens L8 form a cemented lens S78 in which both are cemented with each other.

  The fourth group G4 having positive refractive power 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 L14. The lens L14 constitutes a cemented lens S1314 that is cemented with each other. By configuring the fourth group G4 in such a manner, it is possible to reduce the distance fluctuation when focusing.

  Further, by adopting aspheric lenses for the second group G2, the third group G3, and the fourth group G4 as described above, various aberrations can be favorably corrected over the entire zoom range, so that the aperture ratio is reduced. A small zoom lens with high resolution and high magnification can be realized without this.

<Specific Examples>
Next, FIG. 3 (FIGS. 3A, 3B, 3C, 3D, 3E) to FIG. 10 (FIGS. 10A, 10B, 10C, 10D, 10E) and Table 1 (Table 1a, Table 1b, Table 1c) to Table 8 ( With reference to Table 8a, Table 8b, and Table 8c), numerical data relating to the zoom lenses of Examples 1 to 8 will be described together.

  The values of (Ra + Rb) / (Ra−Rb), which are variables included in the expression (1), for each zoom lens of Example 1 to Example 8 are shown below.

Example 1: Value of (Ra + Rb) / (Ra−Rb) = 7.55
Example 2: Value of (Ra + Rb) / (Ra-Rb) = 7.41
Example 3: (Ra + Rb) / (Ra-Rb) value = 7.53
Example 4: Value of (Ra + Rb) / (Ra-Rb) = 7.24
Example 5: (Ra + Rb) / (Ra-Rb) value = 4.50
Example 6: (Ra + Rb) / (Ra-Rb) value = 8.50
Example 7: (Ra + Rb) / (Ra-Rb) value = 5.22
Example 8: (Ra + Rb) / (Ra-Rb) value = 6.06
Tables 1 to 8 are tables showing basic data of the zoom lenses of Examples 1 to 8, respectively.

  Tables 1a to 8a show lens data, and Tables 1b to 8b show differences between the setting at the wide-angle end and the setting at the telephoto end. Further, Table 1c to Table 8c show the coefficients of the aspheric surface expression representing the shape of the aspheric surface employed in each zoom lens.

  In the lens data of Table 1a to Table 8a, 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 8b 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 8c are applied to the following aspherical expressions.

  FIGS. 3A, 4A,... 10A are cross-sectional views showing a schematic configuration in a state in which each of the zoom lenses of Examples 1 to 8 is set at the wide angle end, and the reference numerals in FIGS. 3A to 10A that coincide with each other indicate parts corresponding to each other.

  3B, 4B,... 10B are diagrams showing longitudinal aberrations at the wide-angle end of the zoom lenses of Examples 1 to 8, respectively.

  3C, 4C,... 10C are diagrams showing longitudinal aberrations at the telephoto end of the zoom lenses of Examples 1 to 8, respectively.

  3D, 4D,... 10D are diagrams showing lateral aberrations at the wide-angle end of the zoom lenses of Examples 1 to 8, respectively.

  3E, 4E,... 10E are diagrams showing lateral aberrations at the telephoto end of the zoom lenses of Examples 1 to 8, 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 8 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. 11 shows a configuration of a video camera 101 configured by using the zoom lens 100 according to the embodiment of the present invention as an example of the imaging apparatus according to the embodiment of the present invention. 11 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 1st group G2 2nd group St Aperture stop G3 3rd group G4 4th group L9 Double-sided aspherical lens L10 Meniscus lens R17 Lens surface on the object side of the meniscus lens L10 R18 Lens surface on the image side of the meniscus lens L10 Z1 Optical axis

Claims (4)

In order from the object side, a first lens unit having a positive refractive power, a second group having a negative refractive power, a stop, a third group having a positive refractive power, and a fourth group having a positive refractive power, wide When changing the zoom ratio from the end to the telephoto end, the first group and the third group are fixed, and the optical axis of the fourth group is changed while zooming by moving the second group toward the image side. The image plane is corrected and focused by moving in the direction, and
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, a negative lens having a concave surface facing the object side, and the meniscus lens A zoom lens satisfying the following expression (1):
4.8 <(Ra + Rb) / (Ra−Rb) <9.0 (1)
here,
Ra: radius of curvature of the lens surface on the object side of the meniscus lens Rb: radius of curvature of the lens surface on the image side of the meniscus lens   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 in which both are cemented with each other The zoom lens according to claim 1, wherein:   The zoom lens according to claim 2, wherein the second group includes at least one aspheric lens.   An imaging apparatus comprising the zoom lens according to claim 1.

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