JP2014126766A - Zoom lens and image capturing device having the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a zoom lens which has a large aperture ratio and a compact total system, is well corrected for various aberrations such as spherical aberration, coma aberration, and field curvature, and easily provides high optical performance.SOLUTION: A zoom lens comprises, in order from the object side to the image side, a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power, and a fourth lens group having positive refractive power and, when zooming from the wide-angle end to the telephoto end, the first lens group and the fourth lens group are stationary while the second lens group and the third lens group move and distance between the first lens group and the second lens group increases. The zoom lens includes an aperture stop, and a focal length fl of the first lens group, a focal length f3 of the third lens group, a total length TL of the lens, and an air-equivalent distance DSP from the aperture stop at the telephoto end to an image plane are each set appropriately.

Description

  The present invention relates to a zoom lens and an image pickup apparatus having the same, and is particularly suitable as an image pickup optical system used in image pickup apparatuses such as a still camera, a video camera, a digital still camera, a TV camera, and a surveillance camera.

  In recent years, an imaging optical system used in an imaging apparatus such as a video camera or a digital still camera using an imaging element has a short overall lens length (distance from the first lens surface to the image plane), the entire system is small, and has a large aperture. It is required to be a zoom lens with a ratio. As a zoom lens that satisfies these requirements, there is known a positive lead type four-group zoom lens composed of first to fourth lens units having positive, negative, positive, and positive refractive powers in order from the object side to the image side. It has been.

  In the above-described four-group zoom lens, zooming is performed by moving the second lens group, and the so-called inner focus type four-group zoom is performed in which the third lens group corrects image plane variation accompanying zooming and performs focusing. Lenses are known (Patent Documents 1 to 3).

  In general, an inner focus type zoom lens has a smaller effective diameter of the first lens group than a zoom lens that focuses by moving the first lens group, and the entire lens system can be easily downsized. Further, close-up photography, particularly close-up photography is facilitated. Further, since the small and lightweight lens group is moved during focusing, the driving force of the lens group is small, and quick focusing is easy.

JP 2006-201524 A JP 2009-86537 A JP 59-52215 A

  In recent years, with the increase in functionality and miniaturization of imaging devices, the lens system used therein has a large aperture with a high zoom ratio, the entire imaging lens system is small, and zoom with high optical performance with little chromatic aberration. There is a strong demand for lenses.

  In general, in a zoom lens, in order to reduce the size of the entire system while ensuring a high zoom ratio, the number of lenses may be reduced while increasing the refractive power of each lens group constituting the zoom lens. However, the zoom lens constructed in this manner increases the lens thickness as the refractive power of each lens surface increases, resulting in an insufficient overall shortening effect, making it difficult to miniaturize and simultaneously generating various aberrations. These corrections become difficult.

  In a positive lead type zoom lens, it is important to appropriately set each element constituting the zoom lens in order to obtain a high optical performance while ensuring a small size of the entire system and a large aperture ratio. For example, it is important to appropriately set the zoom type (the number of lens groups and the refractive power of each lens group), the movement trajectory associated with zooming of each lens group, and the variable magnification burden of each lens group. .

  If these configurations are not appropriate, the entire system becomes large when attempting to increase the diameter, and fluctuations in various aberrations associated with zooming increase, making it difficult to obtain high optical performance over the entire zoom range and the entire screen. It becomes difficult. For example, in the zoom lens disclosed in Patent Document 1, since the elements such as the lens group configuration and the refractive power sharing of each lens group are not necessarily appropriate when increasing the diameter, while maintaining the downsizing of the entire system, for example, It is difficult to make the aperture larger than F number 2.8.

  In Patent Document 1, if the magnification of the third lens group for focusing is appropriately set and the focus movement amount is optimized, the third lens group can be reduced in size. However, when the aperture is increased, the positive Petzval sum increases, and it is difficult to sufficiently improve this, and the field curvature tends to increase. In Patent Documents 2 and 3, the ratio of the refractive powers of the first lens group and the third lens group is not always appropriate, and the total lens length tends to increase.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a zoom lens that has a large aperture, has a small overall system, and has good optical performance over the entire zoom range from the wide-angle end to the telephoto end, and an image pickup apparatus having the zoom lens.

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 positive 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. A fourth lens group, and during zooming from the wide-angle end to the telephoto end, the first lens group and the fourth lens group are stationary; the second lens group and the third lens group move; In a zoom lens in which the distance between the first lens group and the second lens group is increased, the zoom lens has an aperture stop, the focal length of the first lens group is f1, the focal length of the third lens group is f3, and the total lens length. Is TL, and the air calculation distance from the aperture stop to the image plane at the telephoto end is DSP,
0.1 <f1 / f3 <2.4
0.10 <DSP / TL <0.32
It is characterized by satisfying the following conditional expression.

  According to the present invention, it is possible to realize a zoom lens that has a large aperture and a small entire system, and that can easily obtain high optical performance in which various aberrations such as spherical aberration, coma and curvature of field are well corrected.

(A), (B), (C) Lens cross-sectional views at the wide-angle end, the intermediate zoom position, and the telephoto end of Example 1. (A), (B), (C) Aberration diagrams at the wide-angle end, the intermediate zoom position, and the telephoto end of Example 1. (A), (B), (C) Lens cross-sectional views at the wide-angle end, the intermediate zoom position, and the telephoto end of Example 2. (A), (B), (C) Aberration diagrams at the wide-angle end, intermediate zoom position, and telephoto end of Example 2. (A), (B), (C) Lens cross-sectional views at the wide-angle end, the intermediate zoom position, and the telephoto end of Example 3 (A), (B), (C) Aberration diagrams at the wide-angle end, intermediate zoom position, and telephoto end of Example 3. Schematic diagram of main parts of an imaging apparatus of the present invention Schematic diagram of main parts of an imaging apparatus of the present invention

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. 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 positive refractive power (optical power = reciprocal of focal length), a second lens group having a negative refractive power, and a positive refractive power. The third lens group includes a fourth lens group having a positive refractive power. For zooming, the first lens group and the fourth lens group do not move, and the second lens group and the third lens group move.

  During zooming from the wide-angle end to the telephoto end, the second lens group moves monotonically to the image side. The third lens group moves non-linearly. In addition, the distance between the first lens group and the second lens group at the telephoto end is increased (wider) and the distance between the second lens group and the third lens group is reduced (narrowed) compared to the wide-angle end. .

  1A, 1B, and 1C are lens cross-sectional views at the wide-angle end (short focal length end), the intermediate zoom position, and the telephoto end (long focal length end) of the zoom lens according to Embodiment 1 of the present invention. is there. 2A, 2B, and 2C are aberration diagrams at the wide-angle end, the intermediate zoom position, and the telephoto end, respectively, of the zoom lens according to the first exemplary embodiment. The first embodiment is a zoom lens having a zoom ratio of 2.85, an aperture ratio of 1.85 to 2.40, and a shooting half angle of view of about 6.09 degrees to 2.14 degrees.

  3A, 3B, and 3C are lens cross-sectional views at the wide-angle end, the intermediate zoom position, and the telephoto end of the zoom lens according to Embodiment 2 of the present invention. 4A, 4B, and 4C are aberration diagrams of the zoom lens of Embodiment 2 at the wide-angle end, the intermediate zoom position, and the telephoto end, respectively. The second embodiment is a zoom lens having a zoom ratio of 2.85, an aperture ratio of 1.85 to 1.85, and a shooting half angle of view of about 8.02 degrees to 2.83 degrees.

  5A, 5B, and 5C are lens cross-sectional views at the wide-angle end, the intermediate zoom position, and the telephoto end of the zoom lens according to Embodiment 3 of the present invention. 6A, 6B, and 6C are aberration diagrams at the wide-angle end, the intermediate zoom position, and the telephoto end, respectively, of the zoom lens according to the third exemplary embodiment. Example 3 is a zoom lens having a zoom ratio of 1.9, an aperture ratio of 1.34 to 2.60, and a shooting half angle of view of about 3.55 to 1.87 degrees. FIG. 7 is a schematic view of a main part of a digital video camera using the zoom lens of the present invention. FIG. 8 is a schematic view of a main part of a network camera using the zoom lens of the present invention.

  The zoom lens of each embodiment is a photographing lens system used in an imaging apparatus such as a video camera, a digital camera, a silver salt film camera, or a TV camera. The zoom lens of each embodiment can also be used as a projection optical system for an image projection apparatus (projector). In the lens cross-sectional view, the left side is the object side (front), and the right side is the image side (rear). In the lens cross-sectional view, if i is the order of the lens group from the object side, Bi indicates the i-th lens group. In the lens cross-sectional view, B1 is a first lens group having a positive refractive power, B2 is a second lens group having a negative refractive power, B3 is a third lens group having a positive refractive power, and B4 is a fourth lens having a positive refractive power. It is a lens group.

  SP is an aperture stop that determines (limits) a light beam having an open F number (Fno). G is an optical block corresponding to an optical filter, a face plate, a low-pass filter, an infrared cut filter, or the like. IP is the image plane. The image plane IP corresponds to an imaging plane of a solid-state imaging device (photoelectric conversion device) such as a CCD sensor or a CMOS sensor when a zoom lens is used as an imaging optical system of a video camera or a network camera. When a zoom lens is used as a photographing optical system of a silver salt film camera, it corresponds to a film surface. Arrows indicate the movement trajectory of each lens unit during zooming (variation) from the wide-angle end to the telephoto end.

  In the zoom lens of each embodiment, the distance between the first lens unit B1 and the second lens unit B2 increases during zooming from the wide-angle end to the telephoto end zoom position, and the second lens unit B2 and the third lens unit. The interval with B3 is reduced. Specifically, when zooming from the wide-angle end to the telephoto end as indicated by the arrow, the second lens unit B2 is moved to the image side to perform zooming, and the image plane variation caused by zooming is changed to the third lens unit B3. It is corrected by moving it in a non-linear manner.

  Further, focusing is performed by moving the third lens unit B3 on the optical axis. A solid curve 3a and a dotted curve 3b relating to the third lens unit B3 show image plane fluctuations accompanying zooming from the wide-angle end to the telephoto end when focusing on an object at infinity and an object at close distance, respectively. This is a movement locus for correction. Further, when focusing from an infinitely distant object to a close object at the zoom position at the telephoto end, the third lens unit B3 is retracted to the image side as indicated by an arrow 3c. In the first to third embodiments, the aperture stop SP does not move for zooming, but may be moved independently or together with other lens groups as necessary.

  In the aberration diagrams, Fno is the F number, ω is the half field angle (degrees), and the field angle based on the ray tracing value. In the spherical aberration diagram, the solid line d is the d line (wavelength 587.6 nm), and the two-dot chain line g is the g line (wavelength 435.8 nm). In the astigmatism diagram, the solid line ΔS and the dotted line ΔM are the sagittal image surface and the meridional image surface at the d line, respectively. Distortion is shown for the d-line. In the chromatic aberration diagram of magnification, g of the two-dot chain line is the g line. In the following embodiments, the wide-angle end and the telephoto end are zoom positions when the lens unit for zooming (second lens unit B2) is positioned at both ends of a range in which the lens unit can move on the optical axis. .

  In each embodiment, in order to secure a predetermined zoom ratio and correct various aberrations, the first lens unit B1 having a positive refractive power and the second lens unit having a negative refractive power are sequentially arranged from the object side to the image side. B2, a third lens unit B3 having a positive refractive power, and a fourth lens unit B4 having a positive refractive power. During zooming from the wide-angle end to the telephoto end, the first lens unit B1 is fixed with respect to the imaging surface, and the second lens unit is moved to the image side for zooming.

  By fixing the first lens unit B1 with respect to the image plane during zooming, high positional accuracy is maintained and the change in the total lens length (distance from the first lens surface to the image plane) during zooming is eliminated. ing. In addition, the number of movable lens groups is reduced, and the mechanical parts are simplified. By simplifying the mechanical parts, the generation of dust and the like can be reduced, and a zoom lens maintaining high optical performance and an imaging device using the same are configured. Further, the strength of the lens barrel when attaching an accessory such as a converter lens is increased.

  During zooming, the second lens unit B2 and the third lens unit B3 are moved to minimize the number of movable lens units, thereby reducing the size of the entire lens system and simplifying the configuration. Further, focusing is performed by moving the third lens unit B3. This suppresses aberration fluctuations during focusing from an infinitely distant object to a close object. In particular, by providing a substantially afocal refractive power arrangement between the third lens unit B3 and the fourth lens unit B4, fluctuations in various aberrations during focusing, particularly coma, are suppressed.

In zooming, the fourth lens unit B4 is fixed with respect to the imaging surface, thereby improving the robustness while simplifying the lens barrel structure. In each embodiment, the focal length of the first lens unit B1 is f1, the focal length of the third lens unit B3 is f3, the total length of the lens is TL, and the air calculation distance (filter, etc.) from the aperture stop SP to the image plane position at the telephoto end. DSP) is the distance when the plane parallel plate is removed.
At this time,
0.1 <f1 / f3 <2.4 (1)
0.10 <DSP / TL <0.32 (2)
The following conditional expression is satisfied.

  Conditional expression (1) defines the ratio of the focal length f1 of the first lens unit B1 and the focal length f3 of the third lens unit B3. If the refractive power of the first lens unit B1 decreases beyond the upper limit of conditional expression (1), the total lens length becomes longer at the telephoto end, and the entire system becomes larger. Further, the object point with respect to the second lens unit B2 that performs zooming becomes far, and the imaging magnification of the second lens unit B2 decreases. As a result, in order to increase the zoom ratio, the amount of movement of the second lens unit B2 during zooming increases, and the entire system increases in size.

  If the refractive power of the first lens unit B1 increases beyond the lower limit of conditional expression (1), the total lens length at the telephoto end is shortened, but chromatic aberration remains on the telephoto side when the F-number is reduced. It is not preferable.

  Conditional expression (2) normalizes the position of the aperture stop SP in the zoom lens. When the aperture is increased, the radial direction of the aperture stop SP increases. In each embodiment, by satisfying conditional expression (2), the aperture stop SP is small in the radial direction so that the center of the light flux at the peripheral angle of view does not pass through the vicinity of the center of the aperture stop SP. And large diameter have been realized.

  If the upper limit of conditional expression (2) is exceeded, the entrance pupil position becomes close, and when the aperture is increased, the aperture diameter of the aperture stop SP increases in the radial direction on the wide angle side, which is not good. If the lower limit of conditional expression (2) is exceeded, especially on the telephoto side, the off-axis light beam incident on the first lens unit B1 moves away from the optical axis, and the first lens unit B1 increases in the radial direction.

  In each embodiment, the numerical ranges of conditional expressions (1) and (2) are more preferably set as follows.

0.9 <f1 / f3 <2.0 (1a)
0.15 <DSP / TL <0.30 (2a)
By satisfying the conditional expression (1a), it is easy to shorten the entire lens length while suppressing the occurrence of spherical aberration due to the large aperture. Also, by satisfying conditional expression (2a), it is easy to ensure a high zoom ratio while suppressing an increase in the total lens length. More preferably, the numerical ranges of conditional expressions (1a) and (2a) are set as follows.

1.1 <f1 / f3 <1.8 (1b)
0.20 <DSP / TL <0.26 (2b)
As described above, by satisfying the conditional expressions (1) and (2) at the same time, it is possible to realize a small zoom lens with a large aperture that achieves high imaging performance over the entire zoom range.

  In each embodiment, it is more preferable to satisfy one or more of the following conditional expressions. The focal length of the second lens unit B3 is f2, the focal length of the third lens unit B3 is f3, and the focal length of the fourth lens unit B4 is f4. Let the focal lengths of the entire system at the wide-angle end and the telephoto end be fW and fT, respectively.

  Of the positive lenses in the first lens unit B1, the focal length of the most object-side positive lens G1Fp is f1p, the refractive index at the d-line of the material of the positive lens G1Fp is nd1p, and the Abbe number is νd1p. Further, the curvature radii of the object-side lens surface and the image-side lens surface of the positive lens G1Fp are R11 and R12, respectively.

  The focal length of the negative lens G2Rn closest to the image among the negative lenses of the second lens unit B2 is defined as f2n. Of the positive lenses in the second lens unit B2, the refractive index of the material of the most image-side positive lens G2Rp at the d-line is nd2p, and the Abbe number is νd2p. The lateral magnifications at the wide-angle end and the telephoto end of the second lens group B2 are β2W and β2T, respectively. The third lens unit B3 is composed of one positive lens, and the Abbe number of the material of the positive lens is νd3. At this time, one or more of the following conditional expressions should be satisfied.

1.0 <f1p / f1 <3.0 (3)
1.0 <f2n / f2 <3.0 (4)
-2.0 <(R11 + R12) / (R11-R12) <2.0 (5)
1.49 <nd1p <2.00 (6)
45 <νd1p <75 (7)
1.8 <nd2p <2.2 (8)
15 <νd2p <30 (9)
0.2 <f3 / fT <1.0 (10)
0.8 <f1 / fW <3.0 (11)
0.6 <f1 / f4 <2.2 (12)
1.5 <β2T / β2W <4.0 (13)
35 <νd3 <65 (14)

  In the first lens unit B1, it is desirable to dispose a positive lens closest to the object side. In order to correct the spherical aberration associated with the increase in aperture and reduce the total lens length associated with telephoto, a positive lens is disposed closest to the object side, and the principal point position of the first lens unit B1 is brought closer to the object side. Is good.

  Conditional expression (3) is obtained by normalizing the focal length f1p of the positive lens G1Fp closest to the object among the positive lenses of the first lens unit B1 with the focal length f1 of the first lens unit B1. The refractive power distribution of the positive lens G1Fp in B1 is shown. If the upper limit of conditional expression (3) is exceeded and the refractive power of the positive lens G1Fp becomes relatively weak, the degree of convergence of the light beam becomes weak, and the radial direction of the entire first lens group B1 increases. Moreover, it becomes difficult to correct spherical aberration satisfactorily on the telephoto side.

  If the lower limit of conditional expression (3) is exceeded and the refractive power of the positive lens G1Fp becomes relatively strong, many higher-order spherical aberrations and magnification aberrations occur. In the second lens group B2, it is desirable for aberration correction to dispose the negative lens closest to the image side. In order to reduce the total lens length associated with telephoto while suppressing fluctuations in field curvature and astigmatism associated with zooming, a negative lens is disposed closest to the image side of the second lens unit B2, and the second lens unit It is preferable to bring the principal point position of B2 closer to the image side.

  Conditional expression (4) is obtained by normalizing the focal length f2n of the negative lens G2Rn closest to the image among the negative lenses of the second lens group B2 at this time, using the focal length f2 of the second lens group B2. The refractive power distribution of the negative lens G2Rn in the two-lens group B2 is shown.

  When the upper limit of conditional expression (4) is exceeded and the refractive power of the negative lens G2Rn becomes relatively weak, the amount of movement of the second lens unit B2 accompanying zooming when securing the focal length at the telephoto end to be longer. Will increase and the entire system will become larger. If the lower limit of conditional expression (4) is exceeded and the refractive power of the positive lens G2Rn becomes relatively strong, astigmatism will increase on the wide-angle side, making it difficult to correct this. In addition, the dispersion of the curvature of field for each wavelength increases on the wide-angle side.

  Conditional expression (5) defines the lens shape (shape factor) of the positive lens G1Fp closest to the object among the positive lenses of the first lens unit B1. Conditional expression (5) is a condition for mainly suppressing the occurrence of spherical aberration and the occurrence of coma aberration. If the upper limit of conditional expression (5) is exceeded and the radius of curvature of the lens surface on the object side of the positive lens G1Fp becomes too large, it will be difficult to satisfactorily correct spherical aberration on the wide angle side.

  If the curvature radius of the lens surface on the image side of the positive lens G1Fp becomes too large beyond the lower limit of conditional expression (5), the remaining spherical aberration that cannot be corrected by the positive lens G1Fp must be corrected by another lens. Instead, the number of lenses in the first lens unit B1 increases, and the entire system becomes larger.

Conditional expressions (6) and (7) define the refractive index and Abbe number of the material of the positive lens G1Fp closest to the object among the positive lenses in the first lens unit B1. The Abbe number νd of the material is Nd, NF, NC when the refractive index of the Fraunhofer line d-line, F-line, C-line is Nd, NF, NC.
νd = (Nd−1) / (NF−NC)
Defined by

  If the material of the positive lens G1Fp is outside the range of conditional expressions (6) and (7), it is difficult to correct monochromatic aberrations such as spherical aberration and coma aberration and axial chromatic aberration in a balanced manner.

  Conditional expressions (8) and (9) define the refractive index and Abbe number of the material of the positive lens G2Rp closest to the image side among the positive lenses of the second lens unit B2 at the d-line. Conditional expressions (8) and (9) are mainly for the purpose of reducing the thickness of the second lens group B2 and the achromaticity of the second lens group B2.

  When the upper limit of conditional expression (8) is exceeded and the refractive index of the material of the positive lens G2Rp becomes too high, the correction of field curvature becomes excessive. If the lower limit of conditional expression (8) is exceeded and the refractive index of the material of the positive lens G2Rp becomes low, it becomes difficult to suppress the occurrence of astigmatism on the wide angle side. Further, when a predetermined refractive power is secured in the second lens group B2, the number of lenses in the second lens group B2 increases for aberration correction.

  When out of the range of conditional expression (9), the radius of curvature of the object-side lens surface and the image-side lens surface of the positive lens G2Rp becomes small in order to perform achromaticity in the second lens unit B2, and the edge thickness is reduced. In order to ensure, the lens thickness increases, and the second lens unit B2 becomes larger. In each embodiment, the third lens unit B3 and the fourth lens unit B4 are configured to be approximately afocal. Then, by performing a focusing operation (focusing) in the third lens unit B3, fluctuations in spherical aberration accompanying the focusing operation are suppressed.

  Conditional expression (10) defines the ratio between the focal length f3 of the third lens unit B3 and the focal length fT of the entire system at the telephoto end. If the refractive power of the third lens unit B3 becomes weaker than the upper limit of conditional expression (10), the total lens length increases. Further, during focusing, the amount of movement of the third lens unit B3 becomes large, and quick focusing becomes difficult. If the lower limit of conditional expression (10) is exceeded and the refractive power of the third lens unit B3 becomes too strong, spherical aberration and coma aberration will be overcorrected over the entire zoom range, which is not preferable.

  Conditional expression (11) defines the ratio between the focal length f1 of the first lens unit B1 and the focal length fW of the entire system at the wide-angle end. If the upper limit of conditional expression (11) is exceeded and the refractive power of the first lens unit B1 becomes small, it is necessary to increase the total lens length in order to achieve a high zoom ratio, which is not preferable. Increasing the refractive power of the first lens unit B1 beyond the lower limit of the conditional expression (11) is advantageous for achieving a high zoom ratio and shortening the overall lens length. However, both spherical aberration and coma correction and chromatic aberration correction are compatible. Is difficult and undesirable.

  Conditional expression (12) defines the ratio of the focal length f1 of the first lens unit B1 and the focal length f4 of the fourth lens unit B4. By satisfying the conditional expression (12), the total length of the lens is shortened while a predetermined amount of back focus is secured. When the refractive power of the first lens unit is reduced beyond the upper limit of conditional expression (12), off-axis aberration can be reduced, but it is difficult to correct spherical aberration on the telephoto side when increasing the diameter. become.

  When the refractive power of the fourth lens unit B4 decreases beyond the lower limit of conditional expression (12), it becomes difficult to secure a predetermined amount of back focus, and an optical member such as a filter is disposed between the zoom lens and the image sensor. It becomes difficult.

  Furthermore, it is more preferable to satisfy the conditional expression (1) and the conditional expression (12) at the same time because it is easy to realize a refractive power arrangement that is substantially afocal between the third lens group B3 and the fourth lens group B4.

  Conditional expression (13) defines the variable magnification sharing of the second lens unit B2. This is for easily realizing a zoom ratio of about three. If the ratio of the lateral magnification of the second lens unit B2 at the telephoto end and the lateral magnification of the second lens unit B2 at the wide-angle end increases beyond the upper limit of the conditional expression (13), the variation in aberration due to zooming increases. It becomes difficult to correct various aberrations in a well-balanced manner over the entire zoom range. If the lower limit of conditional expression (13) is exceeded and the ratio of the lateral magnification of the second lens unit B2 at the telephoto end to the lateral magnification of the second group at the wide-angle end becomes small, it becomes difficult to obtain a predetermined zoom ratio. .

  Conditional expression (14) defines the Abbe number of the material of the positive lens of the third lens unit B3. When the third lens unit B3 is composed of one positive lens, a material outside the range of the conditional expression (14) has a large dispersion, and it is difficult to suppress fluctuations in chromatic aberration during zooming. It is preferable that conditional expressions (3) to (13) satisfy the following conditional expressions.

1.1 <f1p / f1 <2.0 (3a)
1.3 <f2n / f2 <2.5 (4a)
-1,5 <(R11 + R12) / (R11-R12) <1.0 (5a)
1.55 <nd1p <1.85 (6a)
50 <vd1p <70 (7a)
1.85 <nd2p <2.15 (8a)
16 <νd2p <25 (9a)
0.25 <f3 / fT <0.90 (10a)
1.0 <f1 / fW <2.8 (11a)
0.8 <f1 / f4 <2.0 (12a)
1.6 <β2T / β2W <3.5 (13a)
40 <νd3 <60 (14a)

  When the conditional expression (3a) is satisfied, the correction of spherical aberration of the most object-side positive lens G1Fp among the positive lenses in the first lens unit B1 becomes appropriate, and the first lens unit B1 can be easily thinned. By satisfying conditional expression (4a), it is possible to make the second lens unit B2 thinner while increasing the focal length at the telephoto end, and to reduce fluctuations in field curvature during zooming. Becomes easier. Satisfying conditional expression (5a) makes it easy to correct spherical aberration while increasing the diameter.

  By satisfying conditional expression (6a), it becomes easy to make the most object-side positive lens G1Fp out of the positive lenses in the first lens unit B1 thinner and to correct coma. Satisfying conditional expression (7a) facilitates correction of lateral chromatic aberration on the wide-angle side and axial chromatic aberration on the telephoto side. By satisfying conditional expression (8a), it becomes easy to correct curvature of field in the intermediate zoom range. By satisfying conditional expression (9a), it becomes easy to reduce the chromatic aberration of magnification accompanying the thinning and zooming of the second lens unit B2.

  By satisfying conditional expression (10a), it becomes easy to correct spherical aberration and coma on the telephoto side, and it is easy to reduce the number of lenses in the third lens unit B3. By satisfying conditional expression (11a), it is easy to increase the aperture while achieving a high zoom ratio. By satisfying the conditional expression (12a), a back focus having a predetermined length can be easily obtained, and it becomes easy to reduce a variation in lateral chromatic aberration due to zooming. By satisfying conditional expression (13a), it is easy to increase the zoom ratio and reduce the size of the entire system.

  By satisfying conditional expression (14a), it becomes easy to reduce fluctuations in chromatic aberration due to zooming. Preferably, the numerical ranges of conditional expressions (3a) to (14a) are set as follows.

1.2 <f1p / f1 <1.8 (3b)
1,6 <f2n / f2 <2.0 (4b)
-1.3 <(R11 + R12) / (R11-R12) <0.5 (5b)
1.6 <nd1p <1.7 (6b)
55 <vd1p <65 (7b)
1.90 <nd2p <2.11 (8b)
17 <νd2p <20 (9b)
0.30 <f3 / fT <0.75 (10b)
1.1 <f1 / fW <2.5 (11b)
1.0 <f1 / f4 <1.8 (12b)
1.7 <β2T / β2W <3.0 (13b)
45 <νd3 <55 (14b)

  In each embodiment, the above-described configuration achieves a high zoom ratio while shortening the total lens length at the wide-angle end and the telephoto end. In each embodiment, by configuring as described above, the curvature of field is favorably corrected at the wide-angle end without using an aspheric lens.

  Next, an embodiment of a digital video camera using the zoom lens of the present invention as a photographing optical system will be described with reference to FIG. In FIG. 7, reference numeral 10 denotes a camera body, and 11 denotes a photographing optical system constituted by any of the zoom lenses described in the first to third embodiments. Reference numeral 12 denotes a solid-state imaging device (photoelectric conversion device) such as a CCD sensor or a CMOS sensor that receives a subject image formed by the photographing optical system 11 and is built in the camera body. Reference numeral 13 denotes a viewfinder for observing a subject image formed on the solid-state image sensor 12, which includes a liquid crystal display or the like.

  An embodiment of a network camera using the zoom lens of the present invention as a photographing optical system will be described with reference to FIG. In FIG. 8, reference numeral 20 denotes a camera body, and reference numeral 21 denotes a photographing optical system constituted by any one of the zoom lenses described in the first to third embodiments. Reference numeral 22 denotes a solid-state imaging device (photoelectric conversion device) such as a CCD sensor or a CMOS sensor that receives a subject image formed by the photographing optical system 21 and is built in the camera body. In this way, by applying the zoom lens of the present invention to an imaging apparatus such as a digital video camera or a network camera, a small-sized imaging apparatus having high optical performance can be realized.

  In addition, the zoom lens of each embodiment can also be used as a projection optical system for a projection apparatus (projector).

  Hereinafter, specific numerical data of Numerical Examples 1 to 3 corresponding to Examples 1 to 3 will be shown. In each numerical example, i indicates the number of the surface counted from the object side. ri is the radius of curvature of the i-th optical surface (i-th surface). di is the axial distance between the i-th surface and the (i + 1) -th surface. ndi and νdi are the refractive index and Abbe number of the material of the i-th optical member with respect to the d-line, respectively. The two surfaces closest to the image correspond to the glass block G.

  BF is an air equivalent back focus. Table 1 shows the relationship between the above-described conditional expressions and numerical examples. Each numerical example shows values at the F-number, half angle of view (degree), image height, total lens length, BF, etc. at three focal lengths at the wide-angle end, the intermediate zoom position, and the telephoto end. The half field angle indicates a half field angle based on the ray tracing value. Table 1 shows the correspondence between the above-described conditional expressions and the respective examples with respect to the parameters.

[Numerical Example 1]
Unit mm

Surface data surface number rd nd νd
1 48.534 4.41 1.60311 60.6
2 -780.140 0.20
3 29.004 1.60 1.84666 23.8
4 19.803 6.79 1.49700 81.5
5 94.554 (variable)
6 89.689 0.80 1.83481 42.7
7 8.289 2.49 1.95906 17.5
8 13.872 2.28
9 -17.958 0.70 1.91082 35.3
10 593.130 (variable)
11 66.485 2.21 1.77250 49.6
12 -42.908 (variable)
13 24.843 2.13 1.77250 49.6
14 540.505 0.15
15 16.854 3.67 1.59522 67.7
16 -39.648 0.80 1.92286 18.9
17 30.560 4.00
18 (Aperture) ∞ 4.85
19 43.054 2.50 1.84666 23.8
20 -8.791 0.80 1.80 100 35.0
21 7.852 0.85
22 11.358 1.81 1.63636 35.4
23 -31.736 8.09
24 ∞ 2.30 1.51400 70.0
25 ∞ 1.00
Image plane ∞

Various data Zoom ratio 2.85
Wide angle Medium Telephoto focal length 28.14 58.46 80.32
F number 1.85 1.97 2.40
Half angle of view (degrees) 6.09 2.94 2.14
Image height 3.00 3.00 3.00
Total lens length 86.45 86.45 86.45
BF 10.61 10.61 10.61

d 5 11.42 18.92 20.79
d10 16.22 8.47 2.96
d12 5.16 5.42 9.06

Zoom lens group data group Start surface Focal length
1 1 48.46
2 6 -10.20
3 11 34.06
4 13 29.85
5 24 ∞

[Numerical Example 2]
Unit mm

Surface data surface number rd nd νd
1 121.088 3.55 1.62299 58.2
2 -96.851 0.20
3 26.184 1.60 1.84666 23.8
4 17.831 6.30 1.59522 67.7
5 46.571 (variable)
6 89.099 0.80 1.70154 41.2
7 10.169 2.61 1.95906 17.5
8 14.319 3.68
9 -19.663 0.70 1.83481 42.7
10 -137.956 (variable)
11 62.462 1.86 1.77250 49.6
12 -71.865 (variable)
13 25.796 2.35 1.77250 49.6
14 -252.749 0.15
15 14.752 3.64 1.59522 67.7
16 -57.273 0.80 1.95906 17.5
17 29.095 3.00
18 (Aperture) ∞ 4.65
19 21.739 2.15 1.84666 23.8
20 -11.045 0.80 1.77250 49.6
21 5.752 3.64
22 8.302 2.42 1.48749 70.2
23 -41.192 3.52
24 ∞ 2.30 1.51400 70.0
25 ∞ 1.00
Image plane ∞

Various data Zoom ratio 2.85
Wide angle Medium Tele focal length 21.30 44.06 60.63
F number 1.85 1.85 1.85
Half angle of view (degrees) 8.02 3.90 2.83
Image height 3.00 3.00 3.00
Total lens length 80.04 80.04 80.04
BF 6.04 6.04 6.04

d 5 2.66 13.56 16.29
d10 20.60 10.03 2.53
d12 5.86 5.53 10.30

Zoom lens group data group Start surface Focal length
1 1 51.52
2 6 -14.44
3 11 43.52
4 13 28.94
5 24 ∞

[Numerical Example 3]
Unit mm

Surface data surface number rd nd νd
1 38.475 5.29 1.60311 60.6
2 316.905 0.20
3 29.758 1.60 1.85478 24.8
4 19.117 7.53 1.49700 81.5
5 65.781 (variable)
6 53.697 1.00 1.77250 49.6
7 11.008 3.30 1.95906 17.5
8 15.008 5.01
9 -19.009 0.90 1.83481 42.7
10 -1071.173 (variable)
11 59.276 5.31 1.80 400 46.6
12 -43.689 (variable)
13 42.239 6.29 1.59522 67.7
14 -27.325 1.10 2.00069 25.5
15 4691.232 0.20
16 23.613 5.00 1.60311 60.6
17 -86.256 0.90 2.00069 25.5
18 266.706 7.00
19 (Aperture) ∞ 7.81
20 13.476 1.69 1.85478 24.8
21 54.125 0.80 1.80610 40.9
22 6.714 1.06
23 7.379 1.88 1.64769 33.8
24 16.618 5.78
25 ∞ 2.30 1.51400 70.0
26 ∞ 1.00
Image plane ∞

Various data Zoom ratio 1.90
Wide angle Medium Telephoto focal length 48.38 77.46 91.88
F number 1.34 2.34 2.60
Half angle of view (degrees) 3.55 2.22 1.87
Image height 3.00 3.00 3.00
Total lens length 104.17 104.17 104.17
BF 8.30 8.30 8.30

d 5 12.67 16.56 17.53
d10 14.81 6.33 2.58
d12 4.53 9.12 11.90

Zoom lens group data group Start surface Focal length
1 1 55.46
2 6 -13.24
3 11 32.02
4 13 52.60
5 25 ∞

B1 ... 1st lens group B2 ... 2nd lens group B3 ... 3rd lens group B4 ... 4th lens group

Claims (11)

In order from the object side to the image side, the lens unit includes a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a positive refractive power, and a fourth lens group having a positive refractive power. During zooming from the wide-angle end to the telephoto end, the first lens group and the fourth lens group are stationary, the second lens group and the third lens group are moved, and the first lens group and the first lens group are moved. In the zoom lens in which the distance between the two lens groups is increased, the zoom lens has an aperture stop, the focal length of the first lens group is f1, the focal length of the third lens group is f3, the total lens length is TL, and the telephoto end is When the air calculation distance from the aperture stop to the image plane is a DSP,
0.1 <f1 / f3 <2.4
0.10 <DSP / TL <0.32
A zoom lens characterized by satisfying the following conditional expression: When the focal length of the positive lens closest to the object among the positive lenses of the first lens group is f1p,
1.0 <f1p / f1 <3.0
The zoom lens according to claim 1, wherein the following conditional expression is satisfied. When the focal length of the negative lens closest to the image side among the negative lenses of the second lens group is f2n, and the focal length of the second lens group is f2.
1.0 <f2n / f2 <3.0
The zoom lens according to claim 1, wherein the following conditional expression is satisfied. When the curvature radii of the object-side lens surface and the image-side lens surface of the positive lens closest to the object side among the positive lenses of the first lens group are R11 and R12, respectively.
−2.0 <(R11 + R12) / (R11−R12) <2.0
The zoom lens according to claim 1, wherein the following conditional expression is satisfied. When the refractive index and Abbe number at the d-line of the material of the positive lens closest to the object side among the positive lenses in the first lens group are nd1p and νd1p,
1.49 <nd1p <2.00
45 <νd1p <75
The zoom lens according to claim 1, wherein the following conditional expression is satisfied. When the refractive index and Abbe number at the d-line of the material of the positive lens closest to the image side among the positive lenses in the second lens group are nd2p and νd2p, respectively.
1.8 <nd2p <2.2
15 <νd2p <30
The zoom lens according to claim 1, wherein the following conditional expression is satisfied. When the third lens unit moves during focusing, the focal length of the third lens unit is f3, and the focal length of the entire system at the telephoto end is fT.
0.2 <f3 / fT <1.0
The zoom lens according to claim 1, wherein the following conditional expression is satisfied. When the focal length of the first lens group is f1, and the focal length of the entire system at the wide angle end is fW,
0.8 <f1 / fW <3.0
The zoom lens according to claim 1, wherein the following conditional expression is satisfied. When the focal length of the fourth lens group is f4,
0.6 <f1 / f4 <2.2
The zoom lens according to claim 1, wherein the following conditional expression is satisfied. When the third lens group is composed of one positive lens and the Abbe number of the material of the positive lens of the third lens group is νd3,
35 <νd3 <65
The zoom lens according to claim 1, wherein the following conditional expression is satisfied.   An image pickup apparatus comprising: the zoom lens according to claim 1; and an image pickup element that receives an image formed by the zoom lens.