JP2009053326A - Zoom lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a zoom lens that has a small lens-diameter, is thin in the forward and backward directions, corrects a color aberration satisfactorily at a high zoom ratio, and has a satisfactory optical performance over the entire zoom range. <P>SOLUTION: The zoom lens includes, in order from the object side to the image side: a first lens group of negative refractive power; a second lens group of negative refractive power; a third lens group of positive refractive power; and a fourth lens group of positive refractive power. For zooming from the wide angle end to the telephoto end, the intervals between the lens groups of the zoom lens vary. In this zoom lens, the first lens group is not moved for zooming. The first lens group has a positive lens, a negative lens, and an optical element for bending an optical path. The imaging transverse magnification, β3W, of the third lens group at the wide angle end during an infinity object focusing is appropriately set. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a zoom lens suitable for an imaging apparatus such as a still camera, a video camera, and a digital still camera.

  Recently, it is demanded that an image pickup apparatus such as a video camera or a digital still camera using a solid-state image pickup device (image pickup device) is small in size and a zoom lens used for the image pickup device has a high zoom ratio.

  In an imaging apparatus using an imaging element, various optical members such as a low-pass filter and a color correction filter are disposed between the last lens part and the imaging element. For this reason, the zoom lens used therefor is required to have a long back focus.

  Further, in the case of a color camera (color imaging apparatus) using an image sensor for color images, the image side is required to be telecentric so that color shading does not occur due to an incident angle characteristic to the image sensor. .

  As a zoom lens having a long back focus and good telecentricity on the image side, a negative lead type zoom lens preceded by a lens unit having a negative refractive power is known.

  As a negative lead type zoom lens, in order from the object side to the image side, a first lens group having a negative refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a positive refractive power There is known a 4-group zoom lens composed of the fourth lens group (Patent Document 1).

  In the four-group zoom lens disclosed in Patent Document 1, zooming is performed by moving the second to fourth lens groups. In this negative lead type four-group zoom lens, when an optical path bending member such as a mirror or a prism is inserted in the optical path and the optical system and the optical path are bent and used in an imaging apparatus, the apparatus is thinned in the front-rear direction. Such zoom lenses are known (Patent Documents 2 and 3).

In Patent Documents 2 and 3, an optical path bending prism is arranged in the first lens group. A zoom lens having a zoom ratio of about 2 to 3 times in which the second to fourth lens units are moved during zooming is disclosed.
JP 2001-343588 A JP 2004-163477 A JP 2004-348082 A

  If an optical path bending member is disposed in the lens group of the zoom lens and the optical path is bent, it becomes easy to reduce the thickness of the zoom lens in the front-rear direction. For this reason, when a zoom lens having an optical path bending member is used in an imaging apparatus (camera), it is easy to reduce the thickness direction (front-rear direction) of the imaging apparatus.

  However, the zoom lens having the optical path bending member disclosed in Patent Documents 2 and 3 has a zoom ratio of about 2 to 3 times, and the zoom ratio is not always sufficient.

  In the negative lead type four-group zoom lens of Patent Documents 2 and 3, the absolute value of the imaging lateral magnification at the wide-angle end when the third lens group is focused on an object at infinity is about 0.6.

  In order to achieve a high zoom ratio in the four-group zoom lens, if the image forming magnification at the wide-angle end of the third lens group is kept within this range, a high zoom ratio (for example, a zoom ratio of 5 times or more) is used. The lens group is configured to be closest to the first lens group at the telephoto end.

  On the other hand, at the wide angle end, the first lens group and the second lens group are arranged with a large group interval. As a result, the effective diameter (front lens diameter) of the first lens group increases.

  Further, along with the high zoom ratio, axial chromatic aberration increases on the telephoto side, and the optical performance deteriorates over the entire zoom range.

  Thus, in the negative lead type four-group zoom lens in which the optical element for bending the optical path is arranged in the first lens group, when an attempt is made to increase the zoom ratio, the effective diameter of the first lens group increases. However, the optical performance tends to decrease on the telephoto side.

  For this reason, in a negative lead type four-group zoom lens in which an optical path bending member is disposed in the optical path, the optical diameter of the first lens group (front lens diameter) is reduced, and a high optical ratio and a high optical ratio in the entire zoom range are achieved. Obtaining performance is a major issue.

  For this purpose, the lens configuration of the first lens group including the optical path bending member and the positive refractive power first arranged on the image side for correcting various aberrations generated in the first and second lens groups having negative refractive power. It is important to appropriately set the lens configuration of the three lens groups.

  If these configurations are inappropriate, it is difficult to correct various aberrations, particularly chromatic aberration in each lens group, and it is difficult to obtain high optical performance.

  The present invention provides a zoom lens having a small front lens diameter, a thin thickness in the front-rear direction, a good correction of chromatic aberration with a high zoom ratio, and an excellent optical performance over the entire zoom range, and an imaging apparatus using the same For the purpose of provision.

The zoom lens according to the present invention includes, in order from the object side to the image side, a first lens group having a negative refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a positive lens having a positive refractive power. Consists of a fourth lens group,
In zoom lenses in which the distance between lens groups changes during zooming from the wide-angle end to the telephoto end,
The first lens group does not move during zooming,
The first lens group includes an optical element for bending an optical path, a positive lens, and a negative lens.
When the imaging lateral magnification of the third lens group at the wide-angle end when focusing on an object at infinity is β3W,
0.3 <| β3W | <0.5
It satisfies the following conditional expression.

  According to the present invention, it is possible to obtain a zoom lens having a small front lens diameter, a small thickness in the front-rear direction, excellent correction of chromatic aberration with a high zoom ratio, and excellent optical performance over the entire zoom range.

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

  The zoom lens of each embodiment includes, in order from the object side to the image side, a first lens group having a negative refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a positive refractive power. This zoom lens has a fourth lens group, and the lens group interval of each lens group changes during zooming (magnification).

  The first lens unit L1 includes a negative component lens (negative lens), an optical element for bending an optical path, and a positive component lens (positive lens), and does not move during zooming (for zooming). is there.

The third lens group has a plurality of lenses and moves during zooming. The third lens group is configured to satisfy a conditional expression (1) described later.
FIG. 1 is a lens cross-sectional view at the wide-angle end (short focal length end) when the optical path is bent 90 degrees in the zoom lens of Example 1 of the present invention.

  Hereinafter, the lens data and lens cross-sectional views of each example are shown in a state where the optical path of the optical element (prism) for bending the optical path is developed so that the optical axis is in a straight line.

  FIG. 2 is a lens cross-sectional view at the wide-angle end of the zoom lens according to the first exemplary embodiment of the present invention. 3, 4 and 5 are aberration diagrams of the first embodiment of the present invention at the wide-angle end, the intermediate zoom position, and the telephoto end (long focal length end).

  Example 1 is a zoom lens having a zoom ratio (magnification ratio) of 7 and an aperture ratio of about 2.8 to 5.8.

  FIG. 6 is a lens cross-sectional view at the wide-angle end of the zoom lens according to Embodiment 2 of the present invention.

  7, 8 and 9 are aberration diagrams of the second embodiment of the present invention at the wide angle end, at the intermediate zoom position, and at the telephoto end. Example 2 is a zoom lens having a zoom ratio (magnification ratio) of 5 and an aperture ratio of about 2.8 to 5.6.

  FIG. 10 is a lens cross-sectional view at the wide-angle end of the zoom lens according to Example 3 of the present invention. 11, 12 and 13 are aberration diagrams of the third embodiment of the present invention at the wide angle end, at the intermediate zoom position, and at the telephoto end. The third embodiment is a zoom lens having a zoom ratio (magnification ratio) of 6 and an aperture ratio of about 3.2 to 5.6.

  FIG. 14 is a lens cross-sectional view at the wide-angle end of the zoom lens according to a fourth embodiment of the present invention. FIGS. 15, 16, and 17 are aberration diagrams of the fourth embodiment of the present invention at the wide-angle end, the intermediate zoom position, and the telephoto end. Example 4 is a zoom lens having a zoom ratio (magnification ratio) of 5 and an aperture ratio of about 2.8 to 5.6.

  FIG. 18 is a lens cross-sectional view at the wide-angle end of the zoom lens according to Embodiment 5 of the present invention. 19, 20, and 21 are aberration diagrams of the fifth embodiment of the present invention at the wide-angle end, the intermediate zoom position, and the telephoto end. The fifth embodiment is a zoom lens having a zoom ratio (magnification ratio) of 8 and an aperture ratio of about 2.8 to 5.8.

  FIG. 22 is a schematic view of the main part of the imaging apparatus of the present invention.

  The zoom lens of each embodiment is an imaging lens system used in an imaging apparatus. In each lens cross-sectional view, the left side is a subject (object) side (front), and the right side is an image side (rear).

  In the lens cross-sectional view, L1 is a first lens group having negative refractive power (optical power = reciprocal of focal length), L2 is a second lens group having negative refractive power, and L3 is a third lens group having positive refractive power. , L4 is a fourth lens unit having a positive refractive power. SP is an aperture stop, which is located on the object side of the third lens unit L3.

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

  In the aberration diagrams, d, g, and C are d-line, g-line, and C-line, respectively. ΔM and ΔS are a meridional image surface and a sagittal image surface, respectively, and lateral chromatic aberration is represented by g-line and C-line. Fno is the F number, and ω is the half angle of view.

In each embodiment, the wide-angle end and the telephoto end are zoom positions when the zooming lens unit (third lens unit L3) is positioned at both ends of the range in which the mechanism can move on the optical axis.
In each embodiment, the zoom lens moves from the wide-angle end to the telephoto end as indicated by arrows in the lens cross-sectional view.

  Specifically, in the zoom lens of Example 1, the first lens unit L1 does not move during zooming from the wide-angle end to the telephoto end. The second lens unit L2 reciprocates or substantially reciprocates along a locus convex toward the image side. The third lens unit L3 moves to the object side. The fourth lens unit L4 moves along a locus convex toward the object side.

  In the zoom lenses of Examples 2 to 5, the first lens unit L1 does not move during zooming from the wide-angle end to the telephoto end. The second lens unit L2 reciprocates or substantially reciprocates along a locus convex toward the image side. The third lens unit L3 moves to the object side. The fourth lens unit L4 moves to the image side.

  In the zoom lens of each embodiment, the main zooming is performed by the movement of the third lens unit L3, and the fluctuation of the image plane due to the zooming is corrected by the reciprocating or substantially reciprocating movement of the second lens unit L2.

  The aperture stop SP is adjusted by adjusting means (not shown) so that the aperture diameter, that is, the aperture area, is different between the wide-angle end and the telephoto end.

  In each embodiment, the first lens unit L1 that is stationary during zooming and has a negative refractive power includes a negative component lens (negative lens), an optical element for bending an optical path, and a positive component lens (positive lens).

  Although the optical element for bending the optical path is shown as a prism, it may be a mirror.

  The first lens unit L1 is fixed during zooming, and an optical element for bending the optical path is arranged in the lens unit, so that the thickness direction of the image pickup apparatus is reduced both during shooting and during non-shooting. Further, by providing a negative lens and a positive lens in the first lens unit L1, achromaticity in the lens unit is eliminated, and chromatic aberrations that occur particularly when the zoom ratio is increased are favorably corrected.

  Focusing is performed by the fourth lens unit L4.

  In each embodiment, the imaging lateral magnification of the third lens unit L3 at the wide-angle end when focusing on an object at infinity is β3W.

At this time, 0.3 <| β3W | <0.5 (1)
The following conditional expression is satisfied.

  Next, the technical meaning of conditional expression (1) will be described.

  Conditional expression (1) shows a desired zoom ratio (for example, a zoom ratio of 5 times or more) in a four-group zoom lens composed of lens groups having negative, negative, positive, and positive refractive power in order from the object side to the image side. When it is going to obtain, it is a conditional expression for the locus | trajectory of the 2nd lens group L2 which corrects an image surface fluctuation | variation to become substantially reciprocation.

  When an upper limit of conditional expression (1) is exceeded, when a desired zoom ratio is to be obtained, the second lens unit L2 approaches the first lens unit L1 that does not move during zooming at the telephoto end rather than at the wide angle end. At this time, if it is ensured that the distance between the first lens group and the second lens group does not interfere at the telephoto end, the group distance between the first lens group L1 and the second lens group L2 at the wide angle end becomes larger. The ball diameter (effective diameter of the first lens unit L1) increases.

  Further, when a desired zoom ratio is obtained when the lower limit is exceeded, the group interval between the first lens unit L1 and the second lens unit L2 becomes large at the telephoto end, and the total length (from the first lens surface to the image plane) is increased. This is not good because the length is longer.

More preferably, the numerical range of the conditional expression (1) is set to the following range.
0.34 <| β3W | <0.48 (1a)
More preferably, the numerical range of the conditional expression (1a) is set to the following range.
0.36 <| β3W | <0.46 (1b)
As described above, according to each embodiment, a zoom lens having a large zoom ratio and a compact zoom lens can be obtained.

  In the zoom lens of each embodiment, in order to obtain better optical performance or to reduce the size of the entire lens system, one or more of the following conditional expressions should be satisfied. According to this, the effect equivalent to each condition is acquired.

  The Abbe number of the material of the positive lens constituting the first lens unit L1 is ν1p, and the Abbe number of the material of the negative lens is ν1n.

  The combined focal length of the first lens unit L1 and the second lens unit L2 at the wide angle end is f12W, and the focal length of the entire system at the wide angle end is fW.

  The fourth lens unit L4 moves on the optical axis for focusing, and the radius of curvature of the object side surface of the positive lens included in the fourth lens unit L4 is denoted by ra, and the radius of curvature of the image side surface is denoted by rb.

  The Abbe number of the material of at least one positive lens among the positive lenses included in the third lens unit L3 is νd3p, and the partial dispersion ratio is θgF3p.

  The third lens unit L3 has a negative lens. Among these, the Abbe number of the material of at least one negative lens is νd3n, and the partial dispersion ratio is θgF3n.

At this time,
5 <| ν1p−ν1n | <30 (2)
2.6 <| f12W | / fW <4.0 (3)
−5.0 <(r4a + r4b) / (r4a−r4b) <1.0 (4)
−0.00168 * νd3p + 0.644 <θgF3p (5)
θgF3n <−0.00168 * νd3n + 0.644 (6)
It is preferable to satisfy one or more of the following conditions.

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

  Conditional expression (2) is a conditional expression for achromatic in the lens group of the first lens group L1.

  If the upper limit of conditional expression (2) is exceeded, the refractive index of the material of the lens constituting the first lens unit L1 will be low, and it will be difficult to correct curvature of field.

  Further, if the lower limit is exceeded, achromaticity in the lens group becomes insufficient, and particularly when the zoom ratio is increased, it is difficult to correct chromatic aberration in the entire optical system.

  More preferably, the numerical range of the conditional expression (2) is set to the following range.

5 <| ν1p−ν1n | <25 (2a)
Conditional expression (3) is a conditional expression for appropriately defining the imaging lateral magnification β3W of the third lens unit L3 at the wide-angle end.

  Even if the imaging lateral magnification β3W is defined by the conditional expression (1), if the upper limit of the conditional expression (3) is exceeded, the imaging lateral magnification at the wide-angle end of the fourth lens unit L4 that is the focus lens group becomes small.

  At this time, the refractive power of the fourth lens unit L4 becomes too large, making it difficult to correct curvature of field, and the combined refractive power of the first lens unit L1 and the second lens unit L2 becomes too weak at the wide angle end. The front lens diameter will increase. Even if the imaging lateral magnification β3W is defined by the conditional expression (1), if the lower limit of the conditional expression (3) is exceeded, the imaging lateral magnification at the wide angle end of the fourth lens unit L4 increases.

  At this time, the focusing sensitivity of the fourth lens unit L4 is reduced and the distance variation is increased, and the combined refractive power of the first lens unit L1 and the second lens unit L2 at the wide-angle end is increased, and distortion aberration is generated at the wide-angle end. It is not good because correction of various aberrations becomes difficult.

  More preferably, the numerical range of the conditional expression (3) is set to the following range.

2.8 <| f12W | / fW <3.8 (3a)
More preferably, the numerical range of the conditional expression (3a) is set to the following range.

3.0 <| f12W | / fW <3.6 (3b)
Conditional expression (4) relates to the lens shape of the positive lens constituting the fourth lens unit L4 for focusing.

  When the zoom lens has a high zoom ratio, especially when the focal length at the telephoto end increases, the amount of movement of the fourth lens unit L4 for focusing increases. For this reason, the lens shape of the fourth lens unit L4 is important in order to appropriately correct the distance variation. Conditional expression (4) is a conditional expression for appropriately defining the lens shape of the positive lens included in the fourth lens group for focusing and obtaining good optical performance.

  When the upper limit of conditional expression (4) is exceeded, the positive lens included in the fourth lens group is convex on the image side and has a meniscus shape, and it becomes difficult to correct distance fluctuations particularly in the telephoto range. If the lower limit is exceeded, the shape of the positive lens included in the fourth lens group becomes a meniscus shape with a strong convex on the object side, and it becomes difficult to correct distance variation in the telephoto range.

  More preferably, the numerical range of the conditional expression (4) is set to the following range.

−3.0 <(r4a + r4b) / (r4a−r4b) <1.0 (4a)
More preferably, the numerical range of the conditional expression (5a) is set to the following range.

−2.0 <(r4a + r4b) / (r4a−r4b) <0.9 (4b)
Conditional expression (5) defines the material of the positive lens included in the third lens unit L3 for main variable magnification in Examples 1 to 3.

  Here, the Abbe number νd and the partial dispersion ratio θgF are as follows.

The refractive indices of the materials for the Fraunhofer g-line (wavelength 435.8 nm), F-line (486.1 nm), d-line (587.6 nm), and C-line (656.3 nm) are Ng, NF, and Nd, respectively. , NC. At this time,
νd = (Nd−1) / (NF−NC)
θgF = (Ng−NF) / (NF−NC)
It is represented by

  If the zoom ratio is increased in a negative lead type zoom lens preceded by a lens unit having negative refractive power, axial chromatic aberration on the short wavelength side tends to be difficult to correct particularly in the telephoto range.

  Conditional expression (5) is a conditional expression for appropriately defining the anomalous dispersibility of the third lens unit L3 for main variable magnification in the vicinity of the stop, and for correcting axial chromatic aberration well even in the telephoto range.

  The range of conditional expression (5) indicates that the partial dispersion ratio θgF is larger than that of a general glass material. By using a material having a partial dispersion ratio in this range for the positive lens of the third lens unit L3 for main magnification, it becomes easy to satisfactorily correct axial chromatic aberration on the short wavelength side in the telephoto range.

  As a material that satisfies the conditional expression (5), UV curable resin (optical constant is (Table 1)) is used for the fourth positive lens G34 counted from the object side of the third lens unit L3 in Example 1. .

  In Example 2, N-polyvinylcarbazole (optical constant is (Table 1)) is used for the fourth positive lens G34 of the third lens unit L3.

  In Example 3, a material in which TiO2 (titanium dioxide) with a volume fraction of 5% is dispersed in PMMA (Polymethylmethacrylate) in the fourth positive lens G34 of the third lens unit L3 (optical constant is (Table 2)). ) Is used.

  Here, the dispersion characteristic N (λ) of the mixture in which the nanoparticles are dispersed can be easily calculated by the following equation derived from the well-known Durde equation.

N (λ) = [1 + V {N _TiO2 ² (λ) -1} + (1-V) {N _p ² (λ) -1}] ^1/2
Here, lambda is an arbitrary _{wavelength, N TiO2} is the refractive index of TiO _2, the _{N p} the refractive index of PMMA, V is the fraction of the total volume of the TiO ₂ particles to the PMMA volume.

  A material suitable for use in the positive lens of the third lens unit L3 is not limited to the above material.

  Conditional expression (6) defines the material of the negative lens included in the third lens unit L3 for main magnification in Examples 4 and 5.

  Conditional expression (6), like conditional expression (5), appropriately defines the anomalous dispersion of the third lens unit L3 in the vicinity of the stop, and is a condition for satisfactorily correcting axial chromatic aberration even in the telephoto range. It is a formula.

  The range of conditional expression (6) represents that the partial dispersion ratio θgF is smaller than that of a general glass material. By using a material having a partial dispersion ratio in this range for the negative lens of the third lens unit L3 for main zooming, it becomes easy to satisfactorily correct axial chromatic aberration on the short wavelength side in the telephoto range.

  As a material satisfying conditional expression (6), a ceramic material is used for the third negative lens G33 of the third lens unit L3 in Example 4 (optical constant is (Table 1)). In Example 5, the third negative lens G33 of the third lens unit L3 is made of a material in which ITO (Indium-Tin Oxide, indium tin oxide) having a volume fraction of 5% is dispersed in PMMA (optical constant is ( Table 3)) is used.

  A material suitable for use in the negative lens of the third lens unit L3 is not limited to the above material.

  Next, specific features of the lens configuration in each embodiment will be described.

  In each embodiment, the first lens unit L1 includes, in order from the object side to the image side, a negative lens, an optical path bending prism, and a positive lens.

  Specifically, in Example 1, the first lens unit L1 includes, in order from the object side to the image side, a meniscus negative lens G11 having a convex surface facing the object side, an optical path bending prism PR, and a biconvex positive lens. It is composed of G12.

  In Examples 2 to 5, the first lens unit L1 includes, in order from the object side to the image side, a meniscus negative lens G11 having a convex surface facing the object side, an optical path bending prism PR, and a meniscus having a convex surface facing the object side. A positive lens G12 having a shape is used.

  By adopting such a lens configuration for the first lens unit L1, the achromaticity in the first lens unit L1 is eliminated, and aberrations are generated in reverse by the combination of the negative lens and the positive lens, thereby improving various aberrations. It is corrected. Further, the concave surface on the image side of the negative lens G11 has an aspherical shape in which the negative refractive power becomes weaker from the lens center to the lens periphery.

  As a result, astigmatism and distortion are corrected in a balanced manner. The aspheric surface provided in the negative lens G11 may be a lens surface on the object side. The aspherical shape in this case may be a shape in which the curvature gradually increases from the lens center toward the lens periphery.

  In each embodiment, the second lens unit L2 includes a negative lens and a positive lens.

  Specifically, in each embodiment, the second lens unit L2 is composed of two independent lenses, a biconcave negative lens G21 and a positive lens G22 having a convex surface on the object side, in order from the object side to the image side. Yes. In Example 5, the negative lens G21 and the positive lens G22 are cemented lenses.

  The second lens unit L2 plays the role of a compensator. By adopting such a lens configuration for the second lens unit L2, the refractive power necessary for correcting various aberrations in the entire zoom range is realized with a small number of lenses, and fluctuations in chromatic aberration during zooming are suppressed. .

  In each embodiment, the third lens unit L3 includes one or more cemented lenses including a positive lens and a negative lens.

  Specifically, in Examples 1 to 3, the third lens unit L3 includes, in order from the object side to the image side, a cemented lens in which the positive lens G31 and the negative lens G32 are cemented, a negative lens G33, a positive lens G34, and a positive lens G35. It consists of a cemented cemented lens.

  In Example 4, the third lens unit L3 includes, in order from the object side to the image side, a cemented lens in which the positive lens G31 and the negative lens G32 are cemented, and a cemented lens in which the negative lens G33 and the positive lens G34 are cemented.

  In Example 5, the third lens unit L3 includes, in order from the object side to the image side, a cemented lens in which the positive lens G31, the negative lens G32, and the negative lens G33 are cemented, and a cemented lens in which the negative lens G34 and the positive lens G35 are cemented. ing.

  The third lens unit L3 is a lens unit that mainly performs zooming, and aberration variation associated with zooming is likely to occur. Therefore, the aberration variation during zooming is reduced by using a relatively symmetric lens configuration.

  Further, the positive lens G31 arranged closest to the object side in the third lens unit L3 has a convex surface on the object side so that many off-axis aberrations do not occur even when off-axis rays are largely refracted. .

  Furthermore, since the surface closest to the object side of the third lens unit L3 is the surface on which the axial ray is highest, spherical aberration and coma aberration are corrected well by making this surface an aspherical shape.

  In Examples 1 to 4, the image side surface of the negative lens G22 is concave, and in Example 5, the image side surface of the negative lens G23 is concave. Thus, coma generated on the object-side lens surface of the positive lens G21 is corrected on the image-side lens surface of the negative lens G22 or the negative lens G23.

  With the lens configuration as described above, the occurrence of aberration from the third lens unit L3 due to the high zoom ratio is reduced in the entire zoom range.

  In each embodiment, the fourth lens unit L4 includes one positive lens.

  The fourth lens unit L4 shares the combined refractive power of the first lens unit L1 to the third lens unit L3, and serves as a field lens. This achieves telecentric imaging on the image side necessary for an imaging apparatus using a solid-state imaging device.

  The fourth lens unit L4 is moved along the locus convex toward the object side or the image side during zooming from the wide-angle end to the telephoto end, but for zooming as a zoom lens in each embodiment, It may be fixed. If it does not move, mechanical members and actuators necessary for driving become unnecessary.

  In the zoom lens of each embodiment, focusing is performed by the fourth lens unit L4 having a small number of constituent lenses. This is preferable because the focus lens unit can be downsized.

  As described above, in each embodiment, in the zoom lens that precedes the lens unit having a negative refractive power, by configuring the lens unit as described above, a high zoom ratio and a reduction in thickness in the thickness direction of the imaging device can be achieved. We have a high performance zoom lens.

  In each embodiment, distortion among the various aberrations may be corrected using a known electrical aberration correction method.

Next, numerical examples of the respective embodiments will be shown.
In each numerical example, i indicates the order of the surfaces from the object side, and Ri is the radius of curvature of the lens surface. Di is the distance between the i-th surface and the (i + 1) -th surface, and Ndi and νdi are the refractive index and Abbe number with respect to the d-line, respectively.

In the aspherical shape, the light traveling direction is positive, and x is the amount of displacement from the surface vertex in the optical axis direction. h is the height from the optical axis in the direction perpendicular to the optical axis, and R is the paraxial radius of curvature. When k is a conic constant and B, D, C, and E are aspheric coefficients,
x = (h ² / R) / [1+ {1− (1 + k) * (h / R) ² } ^1/2 ]
+ B * h ⁴ + C * h ⁶ + D * h ⁸ + E * h ¹⁰
It is expressed by the following formula.

Note that “E ± XX” in each aspheric coefficient means “× 10 ^{± XX} ”.
The two surfaces closest to the image side are glass blocks such as face plates.
Table 4 shows the relationship between the above conditional expressions and numerical examples.

(Numerical example 1)

f = 4.81 ~ 14.46 ~ 33.68 Fno = 2.8 ~ 4.0 ~ 5.8 2ω = 73.1 ° 〜27.7 ° 〜12.1 °
R1 = 182.722 D1 = 1.45 Nd1 = 1.86400 νd1 = 40.6
* R2 = 13.061 D2 = 4.07
R3 = ∞ D3 = 18.00 Nd2 = 1.80610 νd2 = 40.9
R4 = ∞ D4 = 0.50
R5 = 56.583 D5 = 2.01 Nd3 = 1.80518 νd3 = 25.4
R6 = -147.160 D6 = (variable)
* R7 = -53.325 D7 = 0.68 Nd4 = 1.74320 νd4 = 49.3
R8 = 32.922 D8 = 0.34
R9 = 25.311 D9 = 2.10 Nd5 = 1.84666 νd5 = 23.8
R10 = 56.849 D10 = (variable)
R11 = ∞ (aperture stop) D11 = 0.50
* R12 = 11.753 D12 = 5.77 Nd6 = 1.77250 νd6 = 49.6
R13 = -25.073 D13 = 0.50 Nd7 = 1.58144 νd7 = 40.8
R14 = 10.539 D14 = 2.50
R15 = 32.424 D15 = 0.50 Nd8 = 1.92286 νd8 = 18.9
R16 = 10.086 D16 = 1.50 Nd9 = 1.63555 νd9 = 22.7
R17 = 30.802 D17 = 2.60 Nd10 = 1.74320 νd10 = 49.3
R18 = -62.505 D18 = (variable)
R19 = 16.208 D19 = 2.40 Nd11 = 1.48749 νd11 = 70.2
R20 = 62.974 D20 = (variable)
R21 = ∞ D21 = 1.28 Nd12 = 1.51633 νd12 = 64.1
R22 = ∞

Aspheric coefficient
k BCDE
R2 0.00000E + 00 -6.70249E-05 7.63001E-08 -3.41037E-09 6.65075E-12
R7 0.00000E + 00 -1.07616E-05 2.53956E-08 -2.60415E-09 2.52178E-11
R12 0.00000E + 00 -5.04203E-05 -2.70636E-07 -1.63903E-10 -2.25869E-11

(Numerical example 2)

f = 4.71-12.75-25.9 Fno = 2.8-4.0-5.6 2ω = 74.3 ° -31.3 ° -15.7 °
R1 = 179.323 D1 = 1.45 Nd1 = 1.77250 νd1 = 49.6
* R2 = 11.634 D2 = 3.78
R3 = ∞ D3 = 18.00 Nd2 = 1.80610 νd2 = 40.9
R4 = ∞ D4 = 0.46
R5 = 38.419 D5 = 2.01 Nd3 = 1.80518 νd3 = 25.4
R6 = 137.337 D6 = (variable)
* R7 = -30.313 D7 = 0.68 Nd4 = 1.74320 νd4 = 49.3
R8 = 64.766 D8 = 0.34
R9 = 43.847 D9 = 2.10 Nd5 = 1.84666 νd5 = 23.8
R10 = -670.518 D10 = (variable)
R11 = ∞ (aperture stop) D11 = 0.50
* R12 = 9.048 D12 = 4.35 Nd6 = 1.77250 νd6 = 49.6
R13 = -13.139 D13 = 0.50 Nd7 = 1.58144 νd7 = 40.8
R14 = 8.606 D14 = 0.94
R15 = 25.434 D15 = 0.50 Nd8 = 1.92286 νd8 = 18.9
R16 = 5.768 D16 = 1.34 Nd9 = 1.69560 νd9 = 17.7
R17 = 16.615 D17 = 2.60 Nd10 = 1.80139 νd10 = 45.5
* R18 = 240.596 D18 = (variable)
R19 = 13.499 D19 = 2.40 Nd11 = 1.48749 νd11 = 70.2
R20 = -216.397 D20 = (variable)
R21 = ∞ D21 = 1.28 Nd12 = 1.51633 νd12 = 64.1
R22 = ∞

Aspheric coefficient
k BCDE
R2 0.00000E + 00 -8.88164E-05 -3.24354E-07 -4.54027E-10 -2.38609E-11
R7 0.00000E + 00 1.55656E-06 -6.02482E-07 9.01560E-09 -4.10627E-11
R12 0.00000E + 00 -1.15877E-04 -7.21885E-07 -2.20159E-08 -1.44216E-10
R18 0.00000E + 00 2.26071E-05 4.11188E-08 -3.91237E-08 -2.44569E-09

(Numerical Example 3)

f = 6.00〜18.39〜35.50 Fno = 3.2〜4.5〜5.6 2ω = 61.5 ° 〜22.0 ° 〜11.5 °
R1 = 61.558 D1 = 1.45 Nd1 = 1.77250 νd1 = 49.6
* R2 = 13.821 D2 = 3.78
R3 = ∞ D3 = 16.00 Nd2 = 1.83481 νd2 = 42.7
R4 = ∞ D4 = 0.23
R5 = 34.704 D5 = 2.01 Nd3 = 1.78590 νd3 = 44.2
R6 = 273.557 D6 = (variable)
* R7 = -23.362 D7 = 0.68 Nd4 = 1.74320 νd4 = 49.3
R8 = 28.439 D8 = 0.50
R9 = 27.270 D9 = 2.10 Nd5 = 1.84666 νd5 = 23.8
R10 = 869.335 D10 = (variable)
R11 = ∞ (aperture stop) D11 = 0.50
* R12 = 10.396 D12 = 4.61 Nd6 = 1.77250 νd6 = 49.6
R13 = -14.483 D13 = 0.50 Nd7 = 1.60342 νd7 = 38.0
R14 = 13.443 D14 = 0.39
R15 = 11.873 D15 = 0.50 Nd8 = 1.84666 νd8 = 23.8
R16 = 6.520 D16 = 1.28 Nd9 = 1.54250 νd9 = 36.3
R17 = 9.905 D17 = 2.60 Nd10 = 1.77250 νd10 = 49.6
* R18 = 12.977 D18 = (variable)
R19 = 31.234 D19 = 2.40 Nd11 = 1.51633 νd11 = 64.1
R20 = -34.575 D20 = (variable)
R21 = ∞ D21 = 1.28 Nd12 = 1.51633 νd12 = 64.1
R22 = ∞

Aspheric coefficient
k BCDE
R2 0.00000E + 00 -3.94672E-05 -2.06988E-07 8.39884E-10 -1.07967E-11
R7 0.00000E + 00 -6.64533E-06 -1.62418E-07 2.20307E-09 -1.31529E-11
R12 0.00000E + 00 -4.46938E-05 -4.59396E-07 -5.59902E-09 -7.28390E-11
R18 0.00000E + 00 2.63788E-04 3.20366E-06 3.59807E-08 -8.56655E-10

(Numerical example 4)

f = 4.78〜12.8〜25.0 Fno = 2.8〜4.0〜5.6 2ω = 73.5 ° 〜31.1 ° 〜16.3 °
R1 = 260.272 D1 = 1.45 Nd1 = 1.77250 νd1 = 49.6
* R2 = 11.556 D2 = 3.78
R3 = ∞ D3 = 16.00 Nd2 = 1.83400 νd2 = 37.2
R4 = ∞ D4 = 0.49
R5 = 46.111 D5 = 2.01 Nd3 = 1.80518 νd3 = 25.4
R6 = 581.827 D6 = (variable)
* R7 = -158.493 D7 = 0.68 Nd4 = 1.69350 νd4 = 53.2
R8 = 22.275 D8 = 0.34
R9 = 15.046 D9 = 2.10 Nd5 = 1.84666 νd5 = 23.8
R10 = 21.437 D10 = (variable)
* R11 = ∞ (aperture stop) D11 = 0.50
R12 = 9.414 D12 = 4.23 Nd6 = 1.77250 νd6 = 49.6
R13 = -13.742 D13 = 0.50 Nd7 = 1.61293 νd7 = 37.0
R14 = 9.775 D14 = 1.19
R15 = 16.759 D15 = 0.50 Nd8 = 2.08200 νd8 = 30.4
R16 = 7.739 D16 = 2.07 Nd9 = 1.80400 νd9 = 46.6
* R17 = 45.372 D17 = (variable)
* R18 = 20.945 D18 = 2.40 Nd10 = 1.58313 νd10 = 59.4
R19 = -70.101 D19 = (variable)
R20 = ∞ D20 = 1.28 Nd11 = 1.51633 νd11 = 64.1
R21 = ∞

Aspheric coefficient
k BCDE
R2 0.00000E + 00 -7.02138E-05 -8.85766E-07 9.56564E-09 -8.41394E-11
R7 0.00000E + 00 -1.75663E-05 -5.22630E-07 5.79186E-09 -4.13642E-11
R12 0.00000E + 00 -7.86135E-05 -2.49900E-07 -1.41313E-08 -6.86383E-11
R17 0.00000E + 00 1.59304E-04 2.23715E-06 9.24042E-08 -1.32736E-09

(Numerical example 5)

f = 4.99〜18.28〜39.68 Fno = 2.8〜4.5〜5.8 2ω = 71.2 ° 〜22.1 ° 〜10.3 °
R1 = 549.708 D1 = 1.50 Nd1 = 1.77250 νd1 = 49.6
* R2 = 15.945 D2 = 3.78
R3 = ∞ D3 = 18.00 Nd2 = 1.80610 νd2 = 40.9
R4 = ∞ D4 = 0.46
R5 = 44.223 D5 = 2.00 Nd3 = 1.80518 νd3 = 25.4
R6 = 180.150 D6 = (variable)
R7 = -42.854 D7 = 0.68 Nd4 = 1.74320 νd4 = 49.3
R8 = 33.330 D8 = 2.10 Nd5 = 1.84666 νd5 = 23.8
R9 = 2538.594 D9 = (variable)
R10 = ∞ (aperture stop) D10 = 0.50
* R11 = 12.149 D11 = 6.41 Nd6 = 1.77250 νd6 = 49.6
R12 = -19.954 D12 = 0.50 Nd7 = 1.58144 νd7 = 40.8
R13 = 11.659 D13 = 0.40 Nd8 = 1.92286 νd8 = 18.9
* R14 = 9.327 D14 = 1.68
R15 = 24.039 D15 = 0.50 Nd9 = 1.69560 νd9 = 17.7
R16 = 11.414 D16 = 3.22 Nd10 = 1.80139 νd10 = 45.5
R17 = 263.343 D17 = (variable)
* R18 = 188.394 D18 = 2.40 Nd11 = 1.48749 νd11 = 70.2
R19 = -18.073 D19 = (variable)
R20 = ∞ D20 = 1.28 Nd12 = 1.51633 νd12 = 64.1
R21 = ∞

Aspheric coefficient
k BCDE
R2 0.00000E + 00 -2.34521E-05 -1.86967E-07 6.79397E-10 -2.70882E-12
R11 0.00000E + 00 -3.68661E-05 -2.92404E-07 -2.49403E-09 -7.49039E-12
R14 0.00000E + 00 5.12165E-05 -2.09782E-08 -9.18939E-09 -1.67895E-10
R18 0.00000E + 00 -2.07511E-04 7.76355E-06 -3.89543E-07 7.33657E-09

  FIG. 22 is a schematic diagram of a main part of a digital camera using the zoom lens of the present invention.

  In FIG. 22, 10 is a digital camera body, and 11 is a zoom lens for forming an image according to the present invention. Reference numeral 12 denotes a flash built in the camera body, 13 an external viewfinder, and 14 a shutter button. Reference numeral 15 denotes a schematic optical system arrangement relationship in the camera body of the zoom lens according to the present invention.

  Thus, by applying the zoom lens of the present invention to a digital camera or the like using a solid-state image sensor that receives an image, an imaging apparatus having a small size and high optical performance, in particular, the camera body can be made thin. Is realized.

  Further, in this example, the zoom lens is arranged so that the optical axis deflected by the reflecting member at the time of horizontal position photographing is in the vertical (vertical) direction. However, the deflected optical axis is in the horizontal (horizontal) direction. You may arrange so that it may become.

  As described above, when the zoom lens of the present invention is used in a photographing optical system of a digital still camera, a small and high-performance imaging device can be realized.

Sectional view of the lens when the optical path of Example 1 is bent 90 degrees Lens cross-sectional view at the wide-angle end of Example 1 Aberration diagram at the wide-angle end of Example 1 Aberration diagram at the intermediate zoom position in Example 1 Aberration diagram at telephoto end of Example 1 Lens sectional view at the wide-angle end in Example 2 Aberration diagrams at the wide-angle end of Example 2 Aberration diagram at the intermediate zoom position in Example 2 Aberration diagrams at the telephoto end of Example 2 Lens sectional view at the wide-angle end of Example 3 Aberration diagrams at the wide-angle end of Example 3 Aberration diagram at the intermediate zoom position in Example 3 Aberration diagrams at the telephoto end of Example 3 Lens sectional view at the wide-angle end in Example 4 Aberration diagrams at the wide-angle end of Example 4 Aberration diagrams at the intermediate zoom position of Example 4 Aberration diagrams at the telephoto end of Example 4 Lens cross-sectional view at the wide-angle end in Example 5 Aberration diagrams at the wide-angle end of Example 5 Aberration diagrams at the intermediate zoom position of Example 5 Aberration diagrams at the telephoto end of Example 5 Schematic diagram of main parts of an imaging apparatus of the present invention

Explanation of symbols

L1 First lens unit L2 Second lens unit L3 Third lens unit L4 Fourth lens unit SP Aperture stop G Glass block IP Image surface d d line g g line C C line ΔS Sagittal image surface ΔM Meridional image surface 10 Camera body 11 , 15 Zoom lens 12 Strobe 13 External viewfinder 14 Shutter button

Claims (13)

In order from the object side to the image side, the lens unit includes a first lens group having a negative refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a fourth lens group having a positive refractive power. ,
In zoom lenses in which the distance between lens groups changes during zooming from the wide-angle end to the telephoto end,
The first lens group does not move during zooming,
The first lens group includes an optical element for bending an optical path, a positive lens, and a negative lens.
When the imaging lateral magnification of the third lens group at the wide-angle end when focusing on an object at infinity is β3W,
0.3 <| β3W | <0.5
A zoom lens satisfying the following conditional expression: When the Abbe number of the material of the positive lens constituting the first lens group is ν1p and the Abbe number of the material of the negative lens is ν1n,
5 <| ν1p−ν1n | <30
The zoom lens according to claim 1, wherein the following condition is satisfied. The combined focal length of the first lens group and the second lens group at the wide angle end is f12W,
When the focal length of the entire system at the wide angle end is fW,
2.6 <| f12W | / fW <4.0
The zoom lens according to claim 1, wherein the following condition is satisfied. The fourth lens group moves on the optical axis during focusing, and when the radius of curvature of the object side surface of the positive lens included in the fourth lens group is ra and the radius of curvature of the image side surface is rb,
−5.0 <(r4a + r4b) / (r4a−r4b) <1.0
The zoom lens according to claim 1, wherein the following condition is satisfied. When the Abbe number of the material of at least one positive lens among the positive lenses included in the third lens group is νd3p and the partial dispersion ratio is θgF3p,
−0.00168 * νd3p + 0.644 <θgF3p
The zoom lens according to claim 1, wherein the following condition is satisfied. The third lens group includes a negative lens, and when the Abbe number of the material of at least one of the negative lenses is νd3n and the partial dispersion ratio is θgF3n,
θgF3n <−0.00168 * νd3n + 0.644
The zoom lens according to claim 1, wherein the following condition is satisfied.   2. The first lens group includes, in order from the object side to the image side, a negative meniscus lens having a convex object side, an optical element for bending an optical path, and a positive lens having a convex surface on the object side. 6. The zoom lens according to any one of 6 above.   8. The second lens group according to claim 1, wherein the second lens group includes two independent lenses of a negative lens and a positive lens or a cemented lens of a negative lens and a positive lens in order from the object side to the image side. Any one of the zoom lenses.   9. The third lens group includes, in order from the object side to the image side, a cemented lens of a positive lens and a negative lens, and a cemented lens of a negative lens, a positive lens, and a positive lens. The zoom lens according to any one of the above.   9. The third lens group according to claim 1, further comprising: a cemented lens composed of a positive lens and a negative lens and a cemented lens composed of a negative lens and a positive lens in order from the object side to the image side. The zoom lens of item 1.   9. The third lens group includes, in order from the object side to the image side, a cemented lens of a positive lens, a negative lens, and a negative lens, and a cemented lens of a negative lens and a positive lens. The zoom lens according to any one of the above.   The zoom lens according to claim 1, wherein an image is formed on a solid-state imaging device.   An image pickup apparatus comprising: the zoom lens according to claim 1; and a solid-state image pickup device that receives an image formed by the zoom lens.