JP2019066701A - Zoom lens and imaging apparatus having the same - Google Patents

Abstract

To provide a zoom lens small in size and having high optical performance.SOLUTION: The zoom lens has a first lens group L1 disposed closest to an object side and having a negative refractive power, a final lens group Lk disposed closest to an image side, and an intermediate group Lp having a positive refractive power and comprising lens groups disposed between the first lens group L1 and the final lens group Lk. An interval between adjoining lens groups varies upon zooming. Upon zooming from a wide angle end to a telephoto end, an interval between the first lens group L1 and a lens group disposed adjoining to the first lens group L1 decreases, while the final lens group Lk moves toward the object side. The first lens group L1 includes a negative lens G1 disposed closest to the object side and having a lens surface on the object side that is aspheric with a positive aspheric departure. The final lens group Lk includes a lens Gk having an aspheric surface with a positive aspheric departure. The zoom lens satisfies a predetermined conditional expression.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a zoom lens, and is suitable for an imaging device such as a digital video camera, a digital still camera, a broadcast camera, a silver halide film camera, and a surveillance camera.

  With the recent increase in functions and miniaturization of imaging devices, there is a demand for realizing a compact zoom lens while having high optical performance.

  Patent Document 1 discloses a wide-angle zoom lens in which an aspheric surface is introduced for the purpose of obtaining high optical performance.

JP, 2015-206976, A

  Since the wide-angle zoom lens of Patent Document 1 is premised to be used for a single-lens reflex camera, the back focus is relatively long. On the other hand, in the zoom lens for a mirrorless camera which can make the flange back shorter than a single-lens reflex camera, since the back focus can be shortened, the lens can be disposed at a position closer to the image plane. For this reason, further downsizing and high performance of the zoom lens can be expected by finding an arrangement and a shape of the lens suitable for shortening the back focus.

  An object of the present invention is to provide a zoom lens which is compact and has high optical performance.

The zoom lens according to the present invention has a first lens group of negative refractive power disposed closest to the object side, a final lens group disposed closest to the image side, and a position between the first lens group and the final lens group. A zoom lens having a middle group of positive refractive power, which is a lens group disposed, wherein the distance between adjacent lens groups changes during zooming, and the first lens during zooming from the wide-angle end to the telephoto end. The distance between the lens group and the lens group disposed adjacent to the first lens group narrows, the final lens group moves toward the object side, and the first lens group is the lens disposed closest to the object side and the object side The final lens group includes a positive aspheric surface aspheric negative lens G1, the final lens group includes a positive aspheric surface aspheric surface, and a skw back focus at the wide-angle end and the zoom lens at the wide-angle end The focal length is fw When,
0.25 <skw / fw <2.0
It is characterized by satisfying the following conditional expression.

  According to the present invention, a zoom lens having a small size and high optical performance can be realized.

FIG. 2 is a cross-sectional view of the zoom lens of Example 1; 5 is an aberration diagram of the zoom lens of Example 1. FIG. FIG. 7 is a cross-sectional view of the zoom lens of Example 2; 5 is an aberration diagram of a zoom lens of Example 2. FIG. It is a figure explaining the aspheric amount. It is the schematic of an imaging device.

  Hereinafter, embodiments of a zoom lens according to the present invention and an imaging apparatus having the same will be described based on the attached drawings. The zoom lens of each embodiment includes a first lens unit L1 of negative refractive power disposed closest to the object side, a final lens unit Lk disposed closest to the image side, a first lens unit L1, and a final lens unit Lk. And an intermediate group Lp of positive refractive power, which is composed of a lens group disposed between them. The intermediate group Lp includes at least one lens group. In the zoom lens of each embodiment, the distance between adjacent lens groups changes during zooming.

  1 and 3 are cross-sectional views of the zoom lenses of the first and second embodiments. The zoom lens in each embodiment is a zoom lens used in an imaging device such as a video camera, a digital camera, a silver halide film camera, and a television camera.

  In each sectional view, the left side is the object side (front), and the right side is the image side (rear). Further, SP denotes an aperture stop, VSP denotes a sub-stop, and IP denotes an image plane. The aperture stop SP is used to set the F-number of the zoom lens to a desired value. The sub-aperture VSP is a variable stop whose diameter changes during zooming, and is used to determine the beam diameter at the open F-number (Fno) at each zoom position. When the zoom lens of each embodiment is used in an imaging device, a solid-state imaging device such as a CCD or a CMOS sensor or a film is disposed on the image plane IP.

  The zoom lens of Example 1 has a first lens unit L1 of negative refractive power, a second lens unit L2 of positive refractive power, a third lens unit L3 of positive refractive power, and a fourth lens unit L4 of positive refractive power. The fifth lens unit L5 has a negative refractive power, and the sixth lens unit L6 has a positive refractive power. The second lens unit L2, the third lens unit L3, the fourth lens unit L4, and the fifth lens unit L5 as a whole have positive refractive power, and correspond to the intermediate group Lp. The sixth lens unit L6 corresponds to the final lens unit Lk.

  The zoom lens of Example 2 includes a first lens unit L1 of negative refractive power, a second lens unit L2 of positive refractive power, a third lens unit L3 of positive refractive power, and a fourth lens unit L4 of negative refractive power. The fifth lens unit L5 has a positive refractive power, and the sixth lens unit L6 has a negative refractive power. The second lens unit L2, the third lens unit L3, the fourth lens unit L4, and the fifth lens unit L5 as a whole have positive refractive power, and correspond to the intermediate group Lp. The sixth lens unit L6 corresponds to the final lens unit Lk.

  Further, arrows shown in the respective cross-sectional views represent movement loci of the respective lens units in zooming from the wide-angle end to the telephoto end. In the present specification, the wide-angle end and the telephoto end mean that the lens unit which moves during zooming is located at both ends of the movable range of the mechanism.

  In the zoom lens of each embodiment, the first lens unit L1 moves monotonically to the image side during zooming from the wide-angle end to the telephoto end. The lens unit included in the intermediate lens unit Lp monotonously moves to the object side. Further, the final lens unit Lk monotonously moves to the object side. Further, during zooming from the wide-angle end to the telephoto end, the distance between the first lens unit L1 and the second lens unit L2 is narrowed.

  The zoom lens of Embodiment 1 performs focusing by moving the second lens unit L2 to the image side.

  In the zoom lens of Example 2, the second lens unit L2 is moved to the image side to perform main focusing, and the fourth lens unit L4 is auxiliaryly moved to reduce aberration fluctuation associated with focusing. The fourth lens unit L4 moves to the image side in focusing at the wide angle end, and moves to the object side in focusing at the telephoto end.

  FIGS. 2A and 2B are aberration diagrams of the zoom lens of Example 1 when focusing at infinity at the wide angle end and at the telephoto end. Further, FIGS. 4A and 4B are aberration diagrams of the zoom lens of Embodiment 2 when the zoom lens is focused at infinity at the wide-angle end and the telephoto end.

  In each aberration diagram, Fno is an F number, and ω is a half angle of view (degree). In the spherical aberration diagram, d (solid line) is d-line (wavelength 587.6 nm) and g (two-dot chain line) is g-line (wavelength 435.8 nm). In the astigmatism diagram, S (solid line) indicates the d-line on the sagittal image plane, and M (broken line) indicates the d-line on the meridional image plane. The distortion is shown for d-line. The chromatic aberration of magnification is based on the d-line and is shown for the g-line.

  Here, prior to the description of the characteristics of each lens group in the zoom lens of each embodiment, the definition of the "aspheric amount" in the present specification will be described with reference to FIG.

  FIG. 5 is a cross-sectional view of a negative lens having an aspheric surface. As shown in FIG. 5, the aspheric amount Ar represents the maximum value of the amount of deviation of the aspheric surface Ra from the reference spherical surface Rref. The reference spherical surface Rref is a spherical surface that passes through the surface vertex R0 of the aspheric surface and the outermost periphery of the light beam effective diameter (hereinafter, referred to as effective diameter) Dr. That is, the radius (curvature radius) of the reference spherical surface Rref is the radius of the spherical surface determined by the surface vertex R0 and the effective diameter Dr of the reference spherical surface Rref.

  The aspheric amount is positive when the deviation direction of the aspheric surface Ra from the reference spherical surface Rref is the direction in which the medium is placed on the reference spherical surface Rref (the lens thickness is increased) We define spherical amount as negative.

  For example, since the aspheric surface Ra shown in FIG. 5 deviates from the reference spherical surface Rref in the direction in which the medium is filled, it has a positive aspheric amount.

  First, a method of determining the positive / negative value of the aspheric amount from lens data of a known document or a method of calculating the aspheric amount will be described.

  In order to determine the sign of the aspheric amount of the aspheric surface and to calculate the aspheric amount, it is necessary to determine the radius (curvature radius) of the aspheric reference sphere. In order to obtain the radius of the reference spherical surface, it is necessary to obtain the effective diameter of the aspheric surface. If the lens diameter of known literature describes the effective diameter of the aspheric surface, that value can be used.

  When the effective diameter is not described in the lens data, the drawing magnification is calculated from the actual lens length of the lens cross section and the known lens total length indicated by the numerical data, and the drawing magnification is calculated to the actual size of the curved surface of each lens. The effective diameter can be obtained by multiplying. Although the diameter of the curved surface may be set slightly larger than the actual effective diameter depending on the optical tool used when drawing the lens sectional view, discrimination of the positive / negative value of the aspheric amount or rough It is sufficient for the calculation of the aspheric amount.

  As a method of obtaining the effective diameter with higher accuracy, there is a method of calculating from a portion in which the marginal contact is performed in the first lens group of negative refractive power, or a biconvex lens. As the first lens unit having a negative refractive power of a wide angle of view photographing lens narrows the lens interval of the plurality of negative lenses, it becomes easier to miniaturize the entire system and correct the curvature of field. For this reason, in general, in a wide-angle shooting lens, so-called marginal contact is performed in which the lens peripheral portions of negative lenses adjacent to each other are brought into contact with each other. Further, also in the lens periphery of the biconvex lens, usually, the lens peripheral thickness is made as thin as possible, so that downsizing of the whole system and correction of curvature of field become easy.

  From this fact, ray tracing is performed after setting the position where the lens surfaces intersect with each other as a temporary effective diameter on all the lens surfaces of the first lens group. As a result, the outermost peripheral ray is determined at any one of the provisional effective diameters. The effective diameter can be obtained with higher accuracy by setting the height of each of the outermost peripheral rays thus determined on each lens surface as the effective diameter.

  By determining the aspheric reference surface using the effective diameter obtained from the lens data in this manner, it is possible to determine the sign of the aspheric amount or calculate the aspheric amount.

  Next, a method of calculating the effective diameter of an aspheric surface from the actual lens will be described. The simplest way to obtain an effective diameter from actual lenses is to measure the diameter of the polished surface of each lens. In many lenses, in order to reduce the weight of the main body, the margin to the diameter of the outermost periphery of the polishing surface with respect to the effective diameter is made as small as possible. Therefore, if the diameter of the polishing surface is measured, the effective diameter can be obtained with sufficient accuracy for the determination of the positive / negative value of the aspheric amount and the rough calculation of the aspheric amount.

  As a method of more accurately knowing the effective diameter, there is a method of measuring the inner diameter of the light shielding member provided on the lens in the first lens group of negative refractive power. Usually, when light strikes the boundary between the polished surface and the rough rubbing surface of the lens, the light is irregularly reflected to generate ghost light. For this reason, the light blocking member may be provided in accordance with the effective diameter so that light incident on the boundary between the polishing surface and the rough rubbing surface is not irregularly reflected. For this reason, ray tracing is performed with the inner diameter of the light blocking member provided for each lens as the temporary effective diameter. As a result, the outermost peripheral ray is determined at any one of the provisional effective diameters. The effective diameter can be obtained with higher accuracy by setting the height of each of the outermost peripheral rays thus determined on each lens surface as the effective diameter.

  As another method, there is a method of applying a light shielding member to the surface closest to the object side of the optical system. A light shielding member from the periphery to the center of the lens surface closest to the object side of the optical system while projecting light onto the optical system using the projection device or mounting the optical system on the imaging device and capturing an image Move The position of the light shielding member immediately before the start of shadowing in the photographed image or the projected image is taken as the effective diameter of the lens surface closest to the object. By performing ray tracing using the effective diameter thus determined, it is possible to obtain an effective diameter other than the lens surface closest to the object.

  By determining the aspheric reference sphere using the effective diameter obtained from the actual lens, it is possible to determine the sign of the aspheric amount or calculate the aspheric amount.

  As mentioned above, although the method of calculating | requiring the aspheric amount by various methods was demonstrated, when calculating | requiring an aspheric amount, you may use any method.

  Next, features of each lens unit in the zoom lens of each embodiment will be described.

  In a conventional wide-angle zoom lens, in order to correct distortion, a negative lens A having an aspheric surface with a positive aspheric amount is disposed at a position (most object side) where the incident height of the off-axis principal ray is the highest. It was The aspheric surface having a positive aspheric amount is, as described above, an aspheric surface formed by filling the medium with respect to the reference spherical surface (thickening the thickness).

  Although the distortion is corrected by the negative lens A having an aspheric surface with a positive aspheric amount, the curvature of field at the wide angle end shifts to the under side. In order to correct the field curvature at the wide angle end, it is necessary to shift the field curvature to the over side by a lens disposed on the image side of the negative lens A. However, at the telephoto end, the incident height of the off-axis principal ray of the negative lens A becomes low, so that the contribution of the negative lens A to the curvature of field is significantly reduced. Therefore, when attempting to correct the field curvature as described above, the field curvature at the telephoto end tends to be over.

  Such curvature of field at the telephoto end is corrected by further providing the lens B having an aspheric surface with a positive aspheric amount so that the contribution to the curvature of field is small at the wide-angle end and increases at the telephoto end. can do. However, since it is necessary to secure a certain degree of back focus in the zoom lens for a single-lens reflex camera, it is difficult to arrange the lens B at such a position.

  On the other hand, by shortening the back focus, the lens can be disposed at a position closer to the image plane. At a position closer to the image plane, the incident height of the axial ray is lower. The correction effect of the curvature of field increases when both the incident height of the off-axis chief ray and the incident height of the on-axis light are high. By providing the lens B at such a position, the lens against the curvature of field at the wide angle end The contribution of B can be reduced. Further, by moving the lens B toward the object side during zooming from the wide-angle end to the telephoto end, it is possible to increase the incident height of the on-axis ray while maintaining the incident height of the off-axis chief ray large to some extent. Therefore, with the zooming from the wide-angle end to the telephoto end, it is possible to gradually intensify the effect of correcting the field curvature by the lens B to the under side.

  In the zoom lens of each embodiment, based on the concept as described above, the first lens unit L1 and the final lens unit Lk are each provided with an aspheric surface having a positive aspheric amount. In the zoom lens of each embodiment, the object-side surface of the negative lens G1 disposed closest to the object is an aspheric surface with a positive aspheric amount. In addition, the final lens unit Lk has a lens Gk having an aspheric surface with a positive aspheric amount.

Furthermore, the zoom lens of each embodiment satisfies the following conditional expression (1).
0.25 <skw / fw <2.0 (1)

  In equation (1), skw is the back focus at the wide angle end. The back focus is the distance on the optical axis from the surface closest to the image of the zoom lens to the image plane. Also, fw is the focal length of the zoom lens at the wide angle end.

  By satisfying the equation (1), it is possible to reduce the contribution to the curvature of field of the lens Gk at the wide angle end. If the value of skw / fw becomes larger than the upper limit value of the expression (1), the contribution to the field curvature of the lens Gk at the wide angle end becomes too large, and the field curvature becomes under at the wide angle end. On the other hand, if the value of skw / fw becomes so small that it falls below the lower limit value of equation (1), the amount of extension of the final lens unit Lk during zooming from the wide-angle end to the telephoto end becomes too large, and the zoom lens becomes large. I will.

Moreover, it is preferable that the zoom lens of each embodiment satisfies at least one of the following conditional expressions (2) to (8). In the following conditional expression, skt is a back focus at the telephoto end. DG1G2 is a distance on the optical axis between the negative lens G1 and the lens G2 having a negative aspheric surface aspheric amount disposed adjacent to the image side of the negative lens G1 in the first lens unit L1. f1 is the focal length of the first lens unit L1. DGk2w is the distance on the optical axis from the image-side surface of the lens Gk2 having a negative aspheric amount located closer to the object than the lens Gk at the wide-angle end to the image plane. EAGk is an effective diameter of the lens Gk. ICmax is the maximum value of the image circle diameter from the wide angle end to the telephoto end. EAGk2 is an effective diameter of a lens Gk2 having a negative aspheric amount disposed closer to the object than the lens Gk. G1R1ref is the radius of curvature of the reference spherical surface on the object side surface of the negative lens G1.
0.25 <(skt-skw) / fw <4.0 (2)
0.20 <−DG1G2 / f1 <0.80 (3)
0.80 <DGk2w / fw <4.0 (4)
0.50 <EAGk / ICmax <1.0 (5)
1.1 <EAGk / EAGk2 <2.0 (6)
1.0 <−f1 / fw <2.5 (7)
0.10 <−f1 / G1R1ref <0.80 (8)

  The equation (2) relates to a condition for making the correction effect of the curvature of field by the lens Gk favorable while appropriately moving the final lens unit Lk during zooming from the wide angle end to the telephoto end.

  If the upper limit value of equation (2) is exceeded, the amount of movement of the final lens unit Lk becomes too large, and the incident height of the off-axis chief ray at the lens Gk at the telephoto end becomes low. It is difficult to obtain a sufficient correction effect.

  Below the lower limit of conditional expression (2), the amount of movement of the final lens unit Lk becomes too small, and the incident height of the on-axis ray at the lens Gk at the telephoto end becomes low. It will be difficult to get enough.

  As described above, in the zoom lens of each embodiment, the distortion is corrected by the negative lens G1, and therefore the curvature of field is shifted to the under side at the wide angle end. Therefore, in the first lens unit L1, it is preferable to dispose a lens G2 having a negative aspheric amount on the image side of the negative lens G1. The incidence height of the off-axis ray at the lens G2 is lower than that of the negative lens G1, and the incidence height of the on-axis ray at the lens G2 is higher than that of the negative lens G1. The correction can be made better compatible. More preferably, the lens G2 is disposed adjacent to the negative lens G1.

  Equation (3) relates to the positional relationship between the negative lens G1 and the lens G2 when the lens G2 having a negative aspheric amount is disposed adjacent to the image side of the negative lens G1 in the first lens unit L1.

  If the upper limit value of the expression (3) is exceeded, the lens G2 is too far from the negative lens G1, and the incident height of the off-axis chief ray at the lens G2 is too low.

  Below the lower limit value of the expression (3), the lens G2 comes too close to the negative lens G1, and the incident height of the off-axis chief ray and the incident height of the on-axis ray at the negative lens G1 and the lens G2 become approximately equal. It will As a result, it is difficult to satisfactorily correct both distortion and curvature of field.

  Further, it is preferable that the intermediate group LP or the final lens group Lk have a lens Gk2 having a negative aspheric surface aspheric surface disposed closer to the object side than the lens Gk. That is, it is preferable that a lens Gk2 having an aspheric surface with a negative aspheric amount be disposed on the image side of the first lens unit L1 and the object side of the lens Gk. This makes it possible to better correct curvature of field at the wide angle end.

  The equation (4) relates to the arrangement of the lens Gk2 in the case where the lens Gk2 having an aspheric surface with a negative aspheric amount is provided on the object side of the lens Gk.

  If the upper limit value of Expression (4) is exceeded, the incident height of the off-axis chief ray at the lens Gk2 becomes too low, and the correction effect of the field curvature by the lens Gk2 becomes small.

  If the lower limit value of Expression (4) is not reached, the incident height of the on-axis ray at the lens Gk2 becomes too low, and the correction effect of the curvature of field by the lens Gk2 becomes small.

  Further, equation (5) relates to the size of the lens Gk. Satisfying the equation (5) means that the incident height of the off-axis chief ray in the lens Gk becomes high.

  If the upper limit value of Expression (5) is exceeded, the telecentricity of the zoom lens becomes too large, and the mount for mounting the zoom lens on the imaging device becomes too large. As a result, it is difficult to sufficiently miniaturize the entire imaging apparatus including the camera body and the zoom lens.

  If the lower limit value of Expression (5) is exceeded, the incident height of the off-axis chief ray at the lens Gk becomes too low, and the correction effect of the curvature of field by the lens Gk becomes small.

  Equation (6) relates to the ratio of the effective diameter of the lens Gk to the lens Gk2 when the lens Gk2 having an aspheric surface with a negative aspheric amount is provided on the object side of the lens Gk.

  If the upper limit value of equation (6) is exceeded, the diameter of the lens Gk2 becomes too small, and the incident height of the off-axis ray at the lens Gk2 becomes too low. As a result, it is difficult to sufficiently obtain the correction effect of the curvature of field by the lens Gk2.

  Below the lower limit value of the expression (6), the correction effects of the curvature of field by the lens Gk and the lens Gk2 cancel each other out, which makes it difficult to sufficiently correct the curvature of field, which is not preferable.

  Equation (7) relates to the focal length of the first lens unit L1.

  The negative refractive power of the first lens unit L1 exceeding the upper limit value of the expression (7) is too weak, and it is not preferable because it becomes difficult to make the zoom lens compact enough.

  Below the lower limit value of the expression (7), the negative refractive power of the first lens unit L1 becomes too strong, which makes it difficult to simultaneously correct curvature of field and distortion, which is not preferable.

  Expression (8) relates to the shape of the object-side surface of the negative lens G1.

  If the upper limit value of Expression (8) is exceeded, the radius of curvature of the object-side surface of the negative lens G1 becomes too large, and distortion at the wide angle end occurs in the negative lens G1, which is not preferable.

  Below the lower limit value of the expression (8), the curvature radius of the object-side surface of the negative lens G1 becomes too small, and the peripheral light flux is easily broken when an ND filter or a protector is attached to the object side of the negative lens G1. Unfavorable.

In addition, it is more preferable to make the numerical range of Formula (1) to Formula (8) mentioned above into the range of following formula (1a) to Formula (8a).
0.50 <skw / fw <1.5 (1a)
0.75 <(skt−skw) / fw <3.5 (2a)
0.25 <−DG1G2 / f1 <0.70 (3a)
1.0 <DGk2w / fw <3.0 (4a)
0.55 <EAGk / ICmax <0.90 (5a)
1.2 <EAGk / EAGk2 <1.8 (6a)
1.1 <−f1 / fw <2.0 (7a)
0.15 <−f1 / G1R1ref <0.60 (8a)

Further, it is more preferable to set the numerical ranges of the above-mentioned formulas (1) to (8) into the ranges of the following formulas (1b) to (8b).
0.70 <skw / fw <1.0 (1b)
1.0 <(skt-skw) / fw <3.0 (2b)
0.30 <−DG1G2 / f1 <0.60 (3b)
1.2 <DGk2w / fw <2.0 (4b)
0.60 <EAGk / ICmax <0.85 (5b)
1.3 <EAGk / EAGk2 <1.7 (6b)
1.2 <-f1 / fw <1.50 (7b)
0.20 <−f1 / G1Rref <0.40 (8 b)

In the zoom lens of each embodiment, it is preferable that the aspheric amount of a lens having an aspheric surface be within the range of the following formula (9).
0.0020 <| Ar / Ea × Nd | <0.10 (9)

  Here, Ar in the equation (9) is an aspheric amount of any aspheric surface, Ea is an effective diameter of the aspheric surface, and Nd is a refractive index to the d-line of a lens having the aspheric surface.

  Below the lower limit value of the expression (9), while the aspherical surface molding process becomes difficult, the optical effect by the aspherical surface decreases, which is not preferable. When the value exceeds the upper limit value of the expression (9), the rate of change of the surface inclination angle of the aspheric surface becomes too large, which is not preferable because it becomes difficult to form the aspheric surface.

  Next, the zoom lens of each embodiment will be described in detail.

  The zoom lens according to the first embodiment is a zoom lens including six lens groups, and the photographing full angle of view at the wide angle end is 109 degrees, and the variable power ratio is 2.2.

  The first lens unit L1 includes a negative lens G1 disposed closest to the object side and a lens G2 disposed adjacent to the negative lens G1. The object-side surface of the negative lens G1 is an aspheric surface with a positive aspheric amount. The lens G2 has a meniscus shape with a convex surface facing the object side, and has negative refractive power. Also, the lens G2 has an aspheric surface with a negative aspheric amount.

  The final lens unit Lk has a lens Gk disposed closest to the image. The lens Gk has negative refractive power. The surface on the image side of the lens Gk is an aspheric surface with a positive aspheric amount.

  The surface on the image side of the lens Gk2 on the most image side of the fifth lens unit L5 is an aspheric surface with a negative aspheric amount.

  The zoom lens according to the second embodiment is a zoom lens including six lens groups, and the photographing full angle of view at the wide-angle end is 103 degrees, and the variable power ratio is 3.9.

  The first lens unit L1 includes a negative lens G1 disposed closest to the object side and a lens G2 disposed adjacent to the negative lens G1. The object-side surface of the negative lens G1 is an aspheric surface with a positive aspheric amount. The lens G2 has a biconcave shape and has negative refractive power. Also, the lens G2 has an aspheric surface with a negative aspheric amount.

  The final lens unit Lk has a lens Gk disposed closest to the image. The lens Gk has positive refractive power. The surface on the image side of the lens Gk is an aspheric surface with a positive aspheric amount.

  The final lens unit Lk has a lens Gk2 disposed adjacent to the object side of the lens Gk. The lens Gk2 has positive refractive power. Further, the surface on the image side of the lens Gk2 is an aspheric surface with a negative aspheric amount.

  Next, Numerical Embodiments 1 and 2 corresponding to Embodiments 1 and 2 will be shown.

In the surface data of each numerical example, r represents the radius of curvature of each optical surface, and d represents the axial distance (distance on the optical axis) between the ith surface and the (i + 1) surface. Where i is the number of the surface counted from the light incident side. Further, nd represents the refractive index of each optical member to the d-line, and νd represents the Abbe number of the optical member to the d-line. The Abbe number dd is a value defined by the following equation (10), where n, nF, nd, and nC are refractive indices for Fraunhofer line g, F, d, and C, respectively. is there.
d d = (nd-1) / (nF-nC) (10)

Further, in the surface data of each numerical example, the sign of * (asterisk) is added after the surface number for the lens surface of the aspherical shape. Further, the aspheric surface data indicates the aspheric coefficients of each aspheric surface. “E ± B” in the aspheric coefficient means “× 10 ^{± B} ”. The aspheric shape of the lens surface is the displacement amount from the surface vertex in the optical axis direction X, the height from the optical axis in the direction perpendicular to the optical axis H, the paraxial radius of curvature R, the conic constant K, When the aspheric coefficients are A4, A6, A8, A10, and A12, they are expressed by the following equation (11).

  In each numerical example, the back focus BF is the distance from the final lens surface to the image plane. The total lens length is a value obtained by adding back focus to the distance from the first lens surface to the final lens surface.

  Further, a portion where the distance d of each optical surface is (variable) changes during zooming, and the surface distance according to the focal length is shown separately from the surface data.

Numerical Embodiment 1
Unit mm

Surface data surface number rd nd dd effective diameter
1 * 775.303 2.80 1.58313 59.4 52.19
2 * 16.599 7.46 35.56
3 * 48.891 2.00 1.85400 40.4 35.14
4 * 37.855 6.95 30.04
5-47.730 1.60 1.49700 81.5 30.03
6 30.607 4.09 1.90366 31.3 27.94
7 119.063 (variable) 27.35
8 (F-stop) ∞ (Variable) 16.29
9 45.906 2.94 1.85025 30.1 23.63
10 730.786 0.40 23.73
11 33.651 1.20 1.90366 31.3 24.10
12 18.201 4.19 1.51742 52.4 23.21
13 43.525 (variable) 23.29
14 26.359 7.29 1.49700 81.5 25.58
15 -68.154 1.30 1.90366 31.3 25.22
16 -1372.759 1.00 25.18
17 ((variable) 21.74
18 28.484 1.20 1.91082 35.3 25.00
19 17.033 6.98 1.49700 81.5 23.55
20 -116 2.106 0.15 23.27
21 30.858 5.85 1.58313 59.4 23.69
22 -53.140 (variable) 23.32
23 -118.452 3.60 1.95906 17.5 22.73
24-25.319 1.00 1.90366 31.3 22.56
25 30.348 4.05 21.74
26 -48.803 1.40 1.85400 40.4 22.07
27 *-96.787 (variable) 23.46
28 52.256 11.15 1.43875 94.7 28.52
29-21.569 0.15 30.46
30 -44.466 1.70 1.58313 59.4 31.85
31 * ((variable) 33.98
32 (image plane) ∞

Aspheric data first surface
K = 0.00000e + 000A 4 = 2.13932e-005 A 6 =-3.34859e-008 A 8 = 4.04582e-011 A10 =-3.50291e-014 A12 = 1.41487e-017

Second side
K = -4.24699e-001 A4 = -2.13746e-006 A6 = 9.96232e-009 A 8 = 7.58799e-011 A10 = -9.37010e-013 A12 = 4.63210e-016

Third side
K = 0.00000e + 000A 4 = -2. 11375e-005 A 6 = 1.10913e-008 A 8 = 3.94107e-010 A10 =-6.84198e-013 A12 =-1.21842e-016

Fourth side
K = 0.00000e + 000A 4 =-2.63939e-006 A 6 = 2. 11808e-008 A 8 = 5.77157e-010 A10 =-1.29435e-012 A12 = 4.34715e-015

27th
K = 0.00000e + 000 A 4 = 4.49350e-005 A 6 = 1.09562e-007 A 8 = 1.66409e-010 A10 =-1.74596e-012

Face 31
K = 0.00000e + 000 A 4 = -8.41484e-006 A 6 = 1.43969e-008 A 8 =-1.02187e-010 A10 = 3.45505e-013 A12 =-4.23113e-016

Various data Zoom ratio 2.22

Wide-angle Intermediate telephoto focal length 15.30 24.20 34.00
F number 2.91 2.91 2.91
Angle of view 54.73 41.80 32.47
Image height 21.64 21.64 21.64
Lens total length 135.05 125.84 125.33
BF 13.00 22.20 32.26

d 7 28.21 11.19 3.03
d13 9.23 6.28 4.22
d17 2.36 0.98-0.40
d22 0.60 1.98 3.36
d27 0.68 2.24 1.89
d31 13.00 22.20 32.26

Entrance pupil position 18.59 16.10 14.12
Exit pupil position -70.53 -63.81 -54.94
Front principal point position 31.09 33.50 34.86
Rear principal point position -2.30 -2.00 -1.74

Zoom lens group data group Start surface Focal length Lens configuration length Front principal point position Rear side principal point position
1 1-20.58 24.90 4.73-14.23
2 8 76.71 8.73 -5.14 -9.84
3 14 71.29 9.59 -1.81 -8.20
4 18 28.09 14.19 5.30 -4.41
5 23 -21.78 10.05 2.54-4.51
6 28 65.76 13.00 3.57 -5.62

Numerical Embodiment 2
Unit mm

Surface data surface number rd nd dd effective diameter
1 * 191.254 2.50 1.76450 49.1 53.22
2 * 21.055 13.57 38.08
3 * -125.637 1.90 1.49700 81.5 37.92
4 39.479 3.46 1.85478 24.8 35.33
5 72.471 (variable) 34.71
6 30.489 2.78 1.76385 48.5 19.24
7 252.345 0.15 19.19
8 24.986 1.10 1.85478 24.8 19.28
9 19.571 (variable) 18.73
10 (stop) 絞 り 0.30 16.04
11 22.723 4.28 1.49700 81.5 20.93
12 -155.703 (variable) 20.69
13 -46.000 0.80 1.72047 34.7 19.58
14 66.172 1.81 1.89286 20.4 19.58
15 150.134 (variable) 19.54
16 ((variable) 13.08
17 46.101 3.93 1.43875 94.9 19.68
18-33.354 0.15 19.56
19 26.908 4.49 1.56732 42.8 18.23
20 -26.246 0.90 1.88300 40.8 17.52
21 -327.694 (variable) 17.04
22 1017.684 4.26 1.49700 81.5 16.54
23-17.914 1.30 1.90043 37.4 16.59
24 14.142 4.48 1.58313 59.4 18.19
25 * 47.463 5.33 20.04
26-225.274 5.86 1.85478 24.8 28.99
27 * -38.228 (variable) 31.24
28 (image plane) ∞

Aspheric data first surface
K = 0.00000e + 000A 4 = 1.999693e-005 A 6 =-4.53191e-008 A 8 = 5.09223e-011 A10 =-3.22262e-014 A12 = 1.15859e-017

Second side
K = 0.00000e + 000A 4 = 1.51305e-005 A 6 = -3.32242e-009 A 8 = -1.10279e-010 A10 = -8.59596e-014

Third side
K = 0.00000e + 000 A 4 = -3.47986e-006 A 6 = 1.32198e-008 A 8 =-5.54342e-011 A10 = 4.28993e-014

25th
K = 0.00000e + 000A 4 = 2.45420e-005 A 6 = -9.11000e-009 A 8 = -6.77756e-010 A10 =-1.16115e-012

27th
K = 0.00000e + 000A 4 = -6.61029e-006 A 6 =-2.65244e-008 A 8 = 5.51274e-011 A10 =-2.38486e-013

Various data zoom ratio 3.93

Wide-angle Intermediate telephoto focal length 17.30 35.00 68.00
F number 3.58 4.18 5.85
Angle of view 51.35 31.72 17.65
Image height 21.64 21.64 21.64
Lens total length 142.70 138.53 143.42
BF 13.32 29.60 57.62

d 5 46.71 6.92 1.00
d 9 5.66 25.00 7.79
d12 3.06 2.02 4.11
d15 2.80 3.19 1.50
d16 7.13 1.70 0.15
d21 0.66 6.74 7.89
d27 13.32 29.60 57.62

Zoom lens group data group Start surface Focal length Lens configuration length Front principal point position Rear side principal point position
1 1-23.62 21.44 4.28 -12.37
2 6 68.94 4.03-3.14-5.20
3 10 40.22 4.58 0.67-2.51
4 13 -52.35 2.61 0.38 -1.03
5 17 28.70 9.47 1.34-4.81
6 22-36.72 21.23-4.04-24.09

  Various values in each example are summarized in Table 1. In Table 1, G1R1ASP is the aspheric amount of the object side surface of the negative lens G1, G1R2ASP is the aspheric amount of the image side surface of the negative lens G1, G1ASP is the object side surface of the negative lens G1 and the image side surface Is the sum of the aspheric amounts of G1R1ref is the radius of curvature of the reference spherical surface of the object-side surface of the negative lens G1, and G1R2ref is the radius of curvature of the reference spherical surface of the image-side surface of the negative lens G1.

  G2R1ASP is the aspheric amount of the object side surface of the negative lens G2, G2R2ASP is the aspheric amount of the image side surface of the negative lens G2, G2ASP is the aspheric surface of the object side surface of the negative lens G2 and the image side It is the sum of quantities. G2R1ref is the radius of curvature of the reference spherical surface of the object-side surface of the negative lens G2, and G2R2ref is the radius of curvature of the reference spherical surface of the image-side surface of the negative lens G2.

  Gk2R1ASP is the aspheric amount of the object-side surface of the lens Gk2, Gk2R2ASP is the aspheric amount of the image-side surface of the lens Gk2, and Gk2ASP is the sum of the aspheric amounts of the object-side surface and the image-side surface of the lens Gk2. It is. Gk2R1ref is the radius of curvature of the reference spherical surface of the object-side surface of the lens Gk2, and Gk2R2ref is the radius of curvature of the reference spherical surface of the image-side surface of the lens Gk2.

  GkR1ASP is the sum of the aspheric amounts of the object-side surface of the lens Gk, GkR2ASP is the aspheric amount of the image-side surface of the lens Gk, and GkASP is the sum of the aspheric amounts of the object-side surface and the image side of the lens Gk It is. GkR1ref is the radius of curvature of the reference spherical surface of the object-side surface of the lens Gk, and GkR2ref is the radius of curvature of the reference spherical surface of the image-side surface of the lens Gk.

[Imaging device]
Next, an embodiment of the imaging apparatus of the present invention will be described. FIG. 6 is a schematic view of an imaging apparatus (digital still camera) 100 according to this embodiment. The imaging apparatus 100 includes a camera body 70, a zoom lens 71 similar to that of the first or second embodiment described above, and a light receiving element (imaging element) 72 that photoelectrically converts an image formed by the zoom lens 71.

  The imaging apparatus 100 according to the present embodiment can obtain a high quality image formed by the zoom lens 71 having high optical performance. In addition, the imaging device 100 can be configured in a small size.

  As the light receiving element 72, an imaging element such as a CCD sensor or a CMOS sensor can be used. At this time, by electrically correcting various aberrations such as distortion aberration and chromatic aberration of the image acquired by the light receiving element 72, it is possible to make the output image have high image quality.

  The zoom lens according to each of the embodiments described above can be applied not only to the digital still camera shown in FIG. 6 but also to various optical devices such as cameras for silver halide films, video cameras, telescopes and the like.

  Although the preferred embodiments and examples of the present invention have been described above, the present invention is not limited to these embodiments and examples, and various combinations, modifications, and changes are possible within the scope of the present invention.

L1 first lens group Lk final lens group Lp middle group G1 negative lens G1
Gk lens Gk

Claims (13)

It consists of a first lens group of negative refractive power arranged closest to the object side, a final lens group arranged closest to the image side, and a lens group arranged between the first lens group and the final lens group A zoom lens having a positive refractive power intermediate group, and a distance between adjacent lens groups being changed during zooming,
During zooming from the wide-angle end to the telephoto end, the distance between the first lens group and the lens group disposed adjacent to the first lens group narrows, and the final lens group moves toward the object side,
The first lens group includes a negative lens G1 which is disposed closest to the object side and the lens surface on the object side is an aspheric surface with a positive aspheric amount,
The final lens group includes a lens Gk having an aspheric surface with a positive aspheric amount,
When the back focus at the wide angle end is skw and the focal length of the zoom lens at the wide angle end is fw,
0.25 <skw / fw <2.0
A zoom lens characterized by satisfying the following conditional expression. Assuming that the back focus at the telephoto end is skt,
0.25 <(skt−skw) / fw <4.0
The zoom lens according to claim 1, which satisfies the following conditional expression.   3. The zoom lens according to claim 1, wherein the first lens group includes a negative lens G 2 having an aspheric surface with a negative aspheric amount.   The zoom lens according to claim 3, wherein the negative lens G2 is disposed adjacent to the negative lens G1. Assuming that the distance between the negative lens G1 and the negative lens G2 on the optical axis is DG1G2 and the focal distance of the first lens group is f1:
0.20 <−DG1G2 / f1 <0.80
5. A zoom lens according to claim 4, wherein the following conditional expression is satisfied.   The lens according to any one of claims 1 to 5, further comprising: a lens Gk2 having an aspheric surface with a negative aspheric amount, disposed on the image side of the first lens group and on the object side of the lens Gk. The zoom lens according to any one of the items. Assuming that the distance on the optical axis from the lens surface on the image side of the lens Gk2 to the image plane at the wide angle end is DGk2w,
0.80 <DGk2w / fw <4.0
The zoom lens according to claim 6, satisfying the following conditional expression. When the effective diameter of the lens Gk is EAGk and the effective diameter of the lens Gk2 is EAGk2,
1.1 <EAGk / EAGk2 <2.0
The zoom lens according to claim 6, wherein the zoom lens satisfies the following conditional expression. Assuming that the effective diameter of the lens Gk is EAGk, and the maximum value of the image circle diameter from the wide-angle end to the telephoto end is ICmax,
0.50 <EAGk / ICmax <1.0
The zoom lens according to any one of claims 1 to 8, satisfying the following conditional expression. Assuming that the focal length of the first lens group is f1, 1.0 <−f1 / fw <2.5
The zoom lens according to any one of claims 1 to 9, satisfying the following conditional expression. Assuming that the radius of curvature of the aspheric reference sphere on the object side of the negative lens G1 is G1R1ref, and the focal length of the first lens group is f1:
0.10 <−f1 / G1R1ref <0.80
The zoom lens according to any one of claims 1 to 10, wherein the following conditional expression is satisfied.   The zoom lens according to any one of claims 1 to 11, wherein the negative lens G1 is a meniscus lens having a convex surface facing the object side.   An image pickup apparatus comprising: the zoom lens according to any one of claims 1 to 12; and an image pickup element that photoelectrically converts an image formed by the zoom lens.

Images