JP6099983B2 - Zoom lens and imaging apparatus having the same - Google Patents

Description

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

  Recently, imaging devices (cameras) such as a video camera and a digital still camera using a solid-state imaging element have been reduced in size and functionality. With the downsizing and higher functionality of the imaging device, the imaging optical system used for the imaging device includes a wide angle of view (shooting angle of view), and is a small zoom lens having high optical performance with a high zoom ratio. It has been demanded.

  As a zoom lens having a small overall system, a wide angle of view, and a high zoom ratio, a negative lead type zoom lens is known which is preceded by a lens unit having a negative refractive power (positioned closest to the object side). As a negative lead type zoom lens, in order from the object side to the image side, a three-group zoom including a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a positive refractive power Lenses are known (Patent Documents 1 and 2).

JP 2008-152189 A JP 2011-33770 A

  In recent years, there is a strong demand for zoom lenses used in imaging apparatuses to have a high zoom ratio and high optical performance over the entire zoom range.

  In general, in a zoom lens, in order to reduce the size of the entire system while ensuring a predetermined zoom ratio, the number of lenses may be reduced while increasing the refractive power of each lens group constituting the zoom lens. However, in such a zoom lens, as the refractive power of each lens surface increases, the lens thickness increases, the effect of shortening the lens system becomes insufficient, and the occurrence of various aberrations increases, resulting in high optical performance. Getting difficult. In order to obtain high optical performance over the entire zoom range, it is important to reduce the curvature of field, among other aberrations.

  In order to obtain a flat image plane characteristic over the entire zoom range, it is preferable to reduce the Petzval sum and reduce the curvature of field. For this purpose, it is effective to increase the number of lenses having a positive refractive power and share the positive refractive power among a plurality of positive lenses, or to use a high refractive index material for the positive lens material. However, if the refractive power of the positive lens is increased without increasing the number of positive lenses to reduce the size of the entire system, the Petzval sum increases and the occurrence of curvature of field increases. In particular, it is very difficult to realize a flat image plane characteristic when attempting to achieve a high zoom ratio and downsizing of the entire system.

  On the other hand, the negative lead type zoom lens described above is advantageous in widening the angle of view and downsizing the entire system. However, since the entire lens system is asymmetric with respect to the aperture stop, fluctuations in various aberrations accompanying zooming are large. It is difficult to obtain high optical performance over the entire zoom range.

  In a negative lead type zoom lens, in order to obtain high optical performance over the entire screen in the entire zoom range, unnecessary light that becomes flare light out of the off-axis light beam is blocked by an aperture stop or a light beam restricting member (flare cut stop). Is good. However, when the off-axis light beam is shielded by the light beam restricting member, if the off-axis light beam is shielded too much, the amount of light at the periphery of the screen increases, which is not preferable. For this reason, when unnecessary light is cut by the light beam limiting member, it is important to appropriately set the optical arrangement of the light beam limiting member and the movement conditions when moving the light beam along with zooming.

  In Patent Document 1, the second lens group is composed of four lenses, a flare-cut stop is disposed on the image side of the third lens group, and the refractive power of the second lens group is strengthened while suppressing the aberration satisfactorily. The system is miniaturized. In Patent Document 2, an aperture stop is disposed on the image side of the second lens group, and unnecessary light is effectively shielded to achieve a wide angle of view and a high zoom ratio. In order to effectively block flare light using the light flux limiting member and to obtain high optical performance over the entire zoom range, it is important to move the light flux limiting member appropriately especially during zooming, and this configuration is inappropriate. It becomes difficult to obtain high optical performance over the entire zoom range.

  The present invention provides a zoom lens capable of obtaining a high optical performance in the entire zoom range with a compact lens system, a wide angle of view, a high zoom ratio, and an imaging apparatus having the same by appropriately configuring a light flux limiting member. With the goal.

The zoom lens according to the present invention includes a first lens group having a negative refractive power, a second lens group having a positive refractive power, a light beam limiting member for limiting a passing light beam, and positive refraction, which are arranged in order from the object side to the image side. A third lens group of a force, and the distance between the first lens group and the second lens group is narrower at the telephoto end than at the wide-angle end, and the distance between the second lens group and the third lens group In zoom lenses in which each lens group moves so that
The first lens group includes a negative lens G11 and a positive lens G12 arranged in order from the object side to the image side.
The distance on the optical axis between the second lens group and the light flux limiting member at the wide angle end is δ2aw, and the maximum value on the optical axis between the second lens group and the light flux limiting member in the entire zoom range is δ2ai , When the amount of movement of the second lens group during zooming from the wide-angle end to the telephoto end is m2, and the amount of movement of the light beam limiting member during zooming from the wide-angle end to the telephoto end is ma ,
0.01 <| δ2ai−δ2aw | / δ2ai <0.99
0.60 <ma / m2 <0.95
It is characterized by satisfying the following conditional expression.

  According to the present invention, it is possible to obtain a zoom lens in which the entire lens system is compact, has a wide angle of view, a high zoom ratio, and high optical performance in the entire zoom range.

(A), (B), (C) Lens cross-sectional views at the wide-angle end, the intermediate zoom position, and the telephoto end of Embodiment 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 Embodiment 2. (A), (B), (C) Aberration diagrams at the wide-angle end, the intermediate zoom position, and the 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 Embodiment 3 (A), (B), (C) Aberration diagrams at the wide-angle end, the intermediate zoom position, and the telephoto end of Embodiment 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 Explanatory drawing when restricting light flux with a light flux restricting member according to the zoom lens 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 unit having a negative refractive power, a second lens group having a positive refractive power, a light beam limiting member for limiting a passing light beam, and a first lens unit having a positive refractive power. It consists of three lens groups. The distance between the first lens group and the second lens group is narrower and the distance between the second lens group and the third lens group is wider at the telephoto end (long focal length end) than at the wide angle end (short focal length end). Each lens group moves so that. The light beam limiting member moves in a different movement locus from the other lens groups during zooming.

  FIGS. 1A, 1 </ b> B, and 1 </ b> C are cross-sectional views of the zoom lens of Embodiment 1 at the wide-angle end, the intermediate zoom position, and the telephoto end, respectively. 2A, 2B, and 2C are aberration diagrams at the wide-angle end, the intermediate focal length, and the telephoto end, respectively, of the zoom lens according to the first exemplary embodiment. Example 1 is a zoom lens having a zoom ratio of 4.74, an aperture ratio of 2.37 to 5.80, and a shooting half angle of view of about 48.6 degrees at the wide angle end.

  FIGS. 3A, 3 </ b> B, and 3 </ b> C are lens cross-sectional views at the wide-angle end, the intermediate zoom position, and the telephoto end, respectively, of the zoom lens of Embodiment 2. FIGS. 4A, 4B, and 4C are aberration diagrams of the zoom lens of Example 2 at the wide-angle end, the intermediate focal length, and the telephoto end, respectively. Example 2 is a zoom lens having a zoom ratio of 4.79, an aperture ratio of 2.48 to 5.80, and a wide angle end half field angle of about 48.5 degrees.

  FIGS. 5A, 5 </ b> B, and 5 </ b> C are lens cross-sectional views at the wide-angle end, the intermediate zoom position, and the telephoto end, respectively, of the zoom lens according to the third exemplary embodiment. 6A, 6B, and 6C are aberration diagrams at the wide-angle end, the intermediate focal length, and the telephoto end of the zoom lens according to Embodiment 3, respectively. The third exemplary embodiment is a zoom lens having a zoom ratio of 4.56, an aperture ratio of 3.00 to 7.00, and a wide angle end half field angle of about 48.0 degrees.

7 and 8 are schematic views of the main part of the image pickup apparatus of the present invention. The zoom lens of each embodiment is a photographic lens system used in an imaging apparatus such as a video camera or a digital camera. In the lens cross-sectional view, the left side is the subject side (object side) (front), and the right side is the image side (rear). In the lens cross-sectional view, i indicates the order of the lens groups from the object side, and Bi is the i-th lens group. SP is an aperture stop that limits the F-number light beam. P is a light beam limiting member for limiting the passing light beam. In the first embodiment, the light flux limiting member P functions as an aperture stop SP.

  G is an optical 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 a photographing optical system of a video camera or a digital still camera, an imaging plane of a solid-state imaging device (photoelectric conversion device) such as a CCD sensor or a CMOS sensor is placed.

  In the aberration diagrams, d and g are d-line and g-line, respectively. ΔM and ΔS are a meridional image plane and a sagittal image plane, respectively. Lateral chromatic aberration is represented by the g-line. ω is a half angle of view (degree), and Fno is an F number. In the following embodiments, the wide-angle end and the telephoto end refer to zoom positions when the zoom lens unit is positioned at both ends of a range in which the mechanism can move on the optical axis.

The zoom lens of each embodiment includes, in order from the object side to the image side, a first lens unit B1 having a negative refractive power, a second lens unit B2 having a positive refractive power, and a third lens unit B3 having a positive refractive power. It consists of two lens groups. During zooming from the wide-angle end to the telephoto end, as indicated by an arrow in the lens cross-sectional view, the first lens unit B1 moves along a locus convex toward the image side, the second lens unit B2 moves toward the object side, and the third lens Group B3 has moved to the image side. The light flux limiting member P moves to the object side along a different path from the other lens groups. In Examples 2 and 3, the aperture stop SP is further provided in addition to the light flux limiting member P, and the aperture stop SP moves integrally with the second lens group B2.

  The zoom lens of each embodiment performs main zooming by moving the second lens unit B2, and corrects the movement of the image plane due to zooming by moving a convex locus on the image side of the first lens unit B1. ing. In addition, telecentric imaging on the image side, which is particularly necessary for a photographing apparatus using a solid-state imaging device or the like, is achieved by providing the third lens unit B3 with the role of a field lens.

  Further, a light flux limiting member P is disposed on the image side of the second lens group B2. The light flux limiting member P cuts harmful light rays (flare light) that degrade optical performance. Generally, when the entire zoom area is enlarged, a large amount of on-axis light is incident, but at the same time off-axis light is incident to a height at which the on-axis light passes. As the amount of light enters, the upper line of off-axis rays becomes coma flare, which adversely affects optical performance. The light flux limiting member P cuts the upper line of the off-axis light beam.

In each embodiment, the distance on the optical axis between the second lens group B2 and the light flux limiting member P at the wide angle end is δ2aw, and the distance on the optical axis between the second lens group B2 and the light flux limiting member P in the entire zoom range. Let the maximum value be δ2ai. At this time,
0.01 <| δ2ai−δ2aw | / δ2ai <0.99 (1)
The following conditional expression is satisfied.

  Conditional expression (1) defines the positional relationship between the second lens unit B2 and the light flux limiting member P. By satisfying conditional expression (1), off-axis light flux is limited, aperture efficiency around the screen is reduced, and high imaging performance is achieved while avoiding an increase in the number of lenses. In addition, while achieving a shooting angle of view of 90 degrees or more at the wide-angle end, the lens configuration is simplified and the entire system is downsized.

  In the three-group zoom lens of each embodiment, when the light beam limiting member P is disposed on the image side of the second lens group B2, and the light beam limiting member P is zoomed along the same locus as that of the second lens group B2, from the zoom intermediate range to the telephoto end. The off-axis light flux passes through a position away from the optical axis of the second lens group B2. Then, if the coma aberration is corrected for the spherical aberration and the off-axis light beam in the second lens unit B2, it becomes difficult to correct the field curvature well. On the other hand, if the aperture ratio is increased (darkened), the occurrence of spherical aberration can be suppressed and the occurrence of various off-axis aberrations can be suppressed. However, it becomes difficult to secure an F number having a desired brightness.

  Therefore, in each embodiment, the light flux limiting member P that restricts the light flux is moved during zooming along a different locus from the second lens unit B2, thereby securing spherical F, coma, and The field curvature is corrected well.

If the distance on the optical axis between the second lens unit B2 and the light flux limiting member P exceeds the upper limit of the conditional expression (1), the effective diameter of the light flux limiting member P increases, which is not preferable. In addition, when widening the angle of view, the distance from the lens closest to the object side to the light beam restricting member P is increased, the effective diameter of the front lens is increased, and the wider angle of view and the entire system are reduced. It becomes difficult.

When the lower limit of the conditional expression (1) is exceeded and the distance between the second lens unit B2 and the light beam restricting member P on the optical axis becomes small, the effect of cutting off the flare component of the off-axis light beam by the light beam restricting member P becomes small. If so, the effect of reducing the flare component of the off-axis light beam and the effect of reducing chromatic aberration due to fluctuations in coma aberration (chromatic coma aberration) occurring at each wavelength are insufficient. In addition, since the distance on the optical axis between the second lens unit B2 and the light beam limiting member P does not change much in the intermediate zoom range, coma increases when the zoom ratio is increased. In order to correct this, the total optical length (the length from the first lens surface to the final lens surface) at the telephoto end increases, and it is difficult to reduce the size of the entire system.

  In the zoom lens according to the present invention, in order to reduce the size of the entire system while ensuring a predetermined zoom ratio, a three-group zoom lens including lens groups having negative, positive, and positive refractive powers in order from the object side to the image side. It is constituted by. In addition, the power arrangement (refractive power arrangement) of each lens group is optimized to obtain high optical performance over the entire zoom range. In order to satisfactorily correct various aberrations while ensuring a predetermined zoom ratio, a light flux limiting member P for limiting the light flux is disposed on the image side of the second lens group B2.

  Here, the light beam limiting member P includes a light blocking member or an aperture stop that limits the incident light beam, a shutter device that can be driven to block the light beam and to allow the light beam to pass through, and the like. It has different characteristics from the flare cut diaphragm for cutting flare. Specifically, when the light beam restricting member P restricts the light beam (reducing the aperture), the deviation of the amount of passage of off-axis rays in the vertical line (so-called single diaphragm) does not occur, and the amount of light around the screen does not become extremely short. Has characteristics.

  By making the first lens unit B1 have a negative refractive power and a negative leading-type refractive power arrangement, the effective diameter of the front lens, which increases when the angle of view is increased, is reduced. Further, the second lens unit B2 having a positive refractive power is used as a main variable power lens unit, and a predetermined zoom ratio is secured. Further, the third lens unit B3 is set to have a positive refractive power so that the exit pupil is sufficiently distant from the image plane, and a back focus having a necessary length is ensured while the incident angle of the light beam incident on the solid-state image sensor is relaxed. This reduces the occurrence of shading on the solid-state image sensor.

  In the zoom lens of each embodiment, during zooming from the wide-angle end to the telephoto end, the first lens unit B1 moves to the image side from the zoom position at the wide-angle end to the intermediate zoom position, and from the intermediate zoom position to the telephoto end. Move to the object side until the zoom position. That is, it moves so as to have a part of a convex locus on the image side. The second lens unit B2 moves to the object side and performs zooming, and the third lens unit B3 moves to the image side. During zooming, the light flux limiting member P moves along a different locus from the second lens group B2.

  Further, focusing is performed by the third lens unit B3. As a result, the number of movable lens groups is reduced, the mechanical structure associated with driving is simplified, and the size of the lens barrel is reduced. Further, by making the third lens unit B3 have a positive refractive power, the third lens unit B3 has a role of a field lens, and in particular, the image side telecentricity necessary for an imaging apparatus using a solid-state imaging device or the like is provided. Good.

  In the first lens unit B1, the negative lens G11 having the curvature of the lens surface on the image side larger than that on the object side (having a small radius of curvature) is disposed closest to the object side. The first lens unit B1 has a role to form an off-axis chief ray at the center of the light flux limiting member P, and since the amount of refraction of the off-axis chief ray is large particularly on the wide angle side, various off-axis aberrations, In particular, astigmatism and distortion are likely to occur.

  Therefore, in each embodiment, the negative lens G11 is disposed in order to suppress the increase in the effective lens diameter closest to the object side, as in a normal wide-angle lens. Furthermore, the negative lens G11 has an aspherical surface in which the negative refractive power is weaker at the periphery of the lens than the center of the lens, thereby correcting astigmatism and distortion in a well-balanced manner, and making the entire system compact. Yes.

  In each embodiment, the first lens unit B1 is negatively coupled to the positive lens G11 in order to correct the variation in field curvature during zooming while achieving good correction of chromatic aberration and to achieve compactness of the entire system. It consists of two lenses G12. In the second lens group B2, the positive lens G21 having a convex object surface having a large refractive power of the object side lens surface compared to the image side is disposed on the most object side. Thereby, the refraction angle of the off-axis chief ray emitted from the first lens unit B1 is reduced, and the occurrence of off-axis aberration is suppressed.

  The positive lens G21 is a lens having the highest incident height through which an axial ray passes, and is a lens mainly involved in correction of spherical aberration and coma aberration. Therefore, in each embodiment, the positive lens G21 has an aspheric surface in which the positive refractive power is weaker at the periphery of the lens than at the center of the lens, so that spherical aberration and coma are corrected well.

  The third lens unit B3 is constituted by a meniscus or biconvex positive lens G31, and has a role as a field lens for improving the image side telecentricity. The exit pupil is sufficiently distant from the image plane, the incident angle of the light beam incident on the solid-state image sensor is relaxed, and shading that occurs on the solid-state image sensor is reduced.

In each embodiment, it is more preferable to satisfy one or more of the following conditional expressions. The total lens length at the wide-angle end (the air equivalent distance from the first lens surface to the image plane (the distance when an optical member such as a filter is removed)) is TDw, and the total lens length at the telephoto end is TDt. The air equivalent distance on the optical axis from the light beam limiting member P to the image plane at the wide-angle end is defined as Law. The amount of movement of the second lens unit B2 during zooming from the wide-angle end to the telephoto end is m2, and the amount of movement of the light beam limiting member P during zooming from the wide-angle end to the telephoto end is ma. The sign of the amount of movement is positive when moving to the image side and negative when moving to the object side.

The focal length of the first lens unit B1 is f1, the focal length of the second lens unit B2 is f2, and the focal length of the entire system at the wide angle end is fw. The third lens unit B3 includes a single positive lens G31 , and the curvature radii of the object-side and image-side lens surfaces of the positive lens G31 are R3a and R3b, respectively. The first lens unit B1 includes a negative lens G11 and a positive lens G12 arranged in order from the object side to the image side. The focal length of the negative lens G11 is f11, and the focal length of the positive lens G12 is f12.

The air-converted distance on the optical axis from the object-side lens surface of the second lens unit B2 located closest to the object side to the image plane at the telephoto end is L2t, and the light flux limiting member P at the telephoto end to the image plane is L2t. Let the air equivalent distance on the optical axis be Lat. At this time, it is preferable to satisfy one or more of the following conditional expressions.

0.1 <Law / TDw <0.3 (2)
0.60 <ma / m2 <0.95 (3)
0.4 <√ (| f1 | × fw) / f2 <0.8 (4)
0.7 <| f1 | / f2 <1.1 (5)
-0.5 <(R3a + R3b) / (R3a-R3b) <1.0 (6)
0.2 <| f11 | / f12 <0.5 (7)
0.01 <(L2t−Lat) / TDt <0.50 (8)

Conditional expression (2) defines the air-converted distance on the optical axis from the light beam limiting member P at the wide-angle end to the image plane position by the total lens length at the wide-angle end. When the upper limit of conditional expression (2) is exceeded, the change in the distance from the optical axis of the screen peripheral light beam incident on the screen periphery of the lens group behind (image side) the light beam limiting member P increases. As a result, in order to satisfactorily correct the aberration of the beam around the screen, the number of lenses must be increased, and the entire system becomes large. If the lower limit is exceeded, the off-axis light beam incident on the first lens unit B1 at the wide-angle end side moves away from the optical axis, the radial direction of the first lens unit B1 increases, and the entire system becomes larger.

  Conditional expression (3) defines the amount of movement of the light beam limiting member P accompanying zooming by the amount of movement of the second lens unit B2. Conditional expression (3) is intended to effectively cut flare light in the entire zoom range from the wide-angle end to the telephoto end, thereby achieving high performance and downsizing of the entire system.

  FIG. 9 is a schematic explanatory diagram for effectively cutting flare light in each embodiment. In FIG. 9, P is a light beam limiting member that suppresses the upper line of the off-axis light beam Lb without limiting the axial light beam La. When the refractive power of the second lens unit B2 is increased in order to reduce the size of the entire system, coma and curvature of field frequently occur in the zoom range from the zoom intermediate range to the telephoto side.

  In each embodiment, the off-axis light beam is effectively cut by the light beam restricting member P to reduce the occurrence of coma and field curvature, thereby achieving a wide angle of view and a high zoom ratio.

  If the amount of movement of the second lens unit B2 becomes smaller than the upper limit of the conditional expression (3), the total lens length can be easily shortened, but the refractive power of the second lens unit B2 can be realized in order to realize a predetermined zoom ratio. Need to be larger. Then, spherical aberration and coma increase on the telephoto side, and it becomes difficult to correct these various aberrations. When the lower limit of conditional expression (3) is exceeded and the amount of movement of the light beam restricting member P becomes small, it becomes difficult to effectively cut off-axis light beam from the zoom intermediate range on the telephoto side.

  Conditional expression (4) defines the product of the focal length of the first lens unit B1 and the focal length of the entire system at the wide angle end as the focal length of the second lens unit B2. Conditional expression (4) is for reducing the size of the entire system and increasing the angle of view. If the upper limit of conditional expression (4) is exceeded, the amount of movement of the second lens unit B2 during zooming increases and the total lens length increases.

  When the lower limit of conditional expression (4) is exceeded, the negative refractive power of the first lens unit B1 increases, and the light beam from the first lens unit B1 diverges greatly. In order for the divergent light beam to converge at the second lens unit B2 and the third lens unit B3, the refractive power of the second lens unit B2 must be increased, and as a result, the spherical aberration is larger than that of the second lens unit B2. It is not good because it occurs.

  Conditional expression (5) defines the focal length of the first lens unit B1 by the focal length of the second lens unit B2. This is to increase the angle of view by increasing the refractive power of the first lens unit B1 to some extent. Further, the second lens unit B2 has a refractive power increased to some extent, the amount of movement of the second lens unit B2 is reduced during zooming, the entire lens length is shortened at the telephoto end, and the entire system is reduced in size.

  If the upper limit of conditional expression (5) is exceeded and the refractive power of the second lens unit B2 increases, a large amount of spherical aberration occurs on the telephoto side, and in particular due to variations in spherical aberration (chromatic spherical aberration of color) occurring at each wavelength. Chromatic aberration increases. If the negative refractive power of the first lens unit B1 increases beyond the lower limit of conditional expression (5), astigmatism increases at the wide-angle end, making it difficult to correct this.

  Conditional expression (6) defines the lens shape (shape factor) of the positive lens G31 of the third lens unit B3. Conditional expression (6) is mainly for increasing the zoom ratio, reducing the size of the entire system, and improving the performance.

  When the upper limit of conditional expression (6) is exceeded, coma increases on the telephoto side, and it becomes difficult to correct this coma. In addition, it becomes difficult to suppress zoom fluctuation of distortion aberration caused by zooming. Further, when focusing is performed with the third lens unit B3, it is difficult to obtain high optical performance over the entire object distance from an infinitely distant object to a close object. If the lower limit of conditional expression (6) is exceeded, curvature of field will increase on the wide-angle side and distortion will increase on the telephoto side, making it difficult to correct these aberrations.

  The first lens unit B1 is composed of one negative lens and one positive lens in order to satisfactorily correct chromatic aberration and correct fluctuations in field curvature during zooming and to make the entire system compact. It is desirable to do.

  Conditional expression (7) defines the ratio between the focal length of the negative lens G11 and the focal length of the positive lens G12 in the first lens unit B1. Conditional expression (7) is mainly for the purpose of widening the angle of view while favorably suppressing the curvature of field. If the upper limit of conditional expression (7) is exceeded and the refractive power of the positive lens G12 increases, it becomes difficult to shorten the total lens length. If the lower limit of conditional expression (7) is exceeded and the refractive power of the negative lens G11 is increased, it is easy to increase the field angle, but the field curvature increases on the wide angle side, and this correction becomes difficult.

Conditional expression (8) defines the distance between the second lens unit B2 and the light flux limiting member P on the optical axis by the total lens length at the telephoto end. If the distance between the light beam limiting member P and the second lens group B2 increases beyond the upper limit of the conditional expression (8) at the telephoto end, the lens outer diameter of the second lens group B2 becomes undesirably large. If the lower limit of the conditional expression (8) is exceeded and the distance between the light beam limiting member P and the second lens unit B2 is narrowed at the telephoto end, the action of moving the exit pupil away from the image plane becomes stronger, but the flare light is cut insufficiently. It becomes difficult to correct aberrations.

  The image pickup apparatus using the zoom lens according to the present invention preferably includes a circuit that electrically corrects at least one of distortion and lateral chromatic aberration.

  If the zoom lens has such a configuration that can tolerate distortion, it is easy to reduce the number of lenses of the zoom lens and to reduce the size of the entire system. In addition, by electrically correcting the chromatic aberration of magnification, it is possible to reduce the color blur of the captured image and to improve the resolution. The third lens unit B3 preferably has at least one aspheric surface.

  In order to reduce the curvature of field at the wide-angle end and suppress the variation of distortion due to zooming, it is desirable to have an aspherical surface. In Examples 1 to 3, the aberration of the positive lens G31 is further reduced by making the lens surface of at least one of the positive lenses G31 of the third lens unit B3 aspherical. That is, the aberration caused by the reference spherical surface of the positive lens G31 is balanced with the aberration caused by the reference spherical surface and the aberration caused by the aspherical surface.

  In each embodiment, it is more preferable to set the numerical ranges of the conditional expressions (1) to (8) as follows.

0.20 <| δ2ai−δ2aw | / δ2ai <0.95 (1a)
0.2 <Law / TDw <0.3 (2a)
0.7 <ma / m2 <0.9 (3a)
0.5 <√ (| f1 | × fw) / f2 <0.7 (4a)
0.8 <| f1 | / f2 <1.1 (5a)
−0.4 <(R3a + R3b) / (R3a−R3b) <0.8 (6a)
0.25 <| f11 | / f12 <0.40 (7a)
0.05 <(L2t−Lat) / TDt <0.30 (8a)

  By satisfying conditional expression (1a), it is more preferable to achieve a wide angle of view and high performance while achieving downsizing of the entire lens system. It is preferable to satisfy the conditional expression (2a) because the luminous flux around the screen can be more effectively limited at the wide angle end. By satisfying conditional expression (3a), more effective flare cutting is facilitated in the zoom range from the intermediate zoom range to the telephoto end, which is preferable. By satisfying conditional expression (4a), it is easy to satisfactorily correct all higher-order field curvature, spherical aberration, and coma aberration on the wide-angle side while reducing the size of the entire system, which is more preferable.

  By satisfying conditional expression (5a), it becomes easier to reduce the size and increase the performance of the entire system while increasing the zoom ratio. By satisfying conditional expression (6a), it becomes easier to suppress positive distortion from the zoom intermediate range to the telephoto end. By satisfying conditional expression (7a), it becomes easier to suppress variation in field curvature during zooming and downsizing. By satisfying conditional expression (8a), higher performance and smaller lens outer diameter of the second lens unit B2 become easier. Furthermore, it is preferable to set the numerical ranges of the conditional expressions (1a) to (8a) as follows.

0.45 <| δ2ai−δ2aw | / δ2ai <0.93 (1b)
0.23 <Law / TDw <0.27 (2b)
0.75 <ma / m2 <0.90 (3b)
0.55 <√ (| f1 | × fw) / f2 <0.65 (4b)
0.9 <| f1 | / f2 <1.1 (5b)
−0.35 <(R3a + R3b) / (R3a−R3b) <0.70 (6b)
0.30 <| f11 | / f12 <0.35 (7b)
0.07 <(L2t−Lat) / TDt <0.15 (8b)

  As described above, according to the respective embodiments, zooms having a wide field angle, a small lens system as a whole, and high optical performance with a zoom ratio of 4 or more, in which various aberrations such as spherical aberration, coma, and curvature of field are satisfactorily corrected. A lens is obtained.

  In Examples 1 to 3, the use of an aspheric lens for the first lens unit B1 corrects the curvature of field at the wide-angle end. In addition, by adopting an aspheric lens for the second lens unit B2, spherical aberration and coma are favorably corrected on the wide angle side while ensuring a predetermined brightness. In the first to third embodiments, camera shake correction may be performed by moving an arbitrary lens group in a direction having a component perpendicular to the optical axis and moving the imaging position in a direction perpendicular to the optical axis.

  Next, an embodiment of a digital video camera as an image pickup apparatus 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 photographic 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 digital still camera as an image pickup apparatus 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 21 denotes a photographing optical system constituted by any 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 still camera or a video camera, an imaging apparatus having a small size and 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).

Next, numerical examples 1 to 3 corresponding to the first to third embodiments of the present invention will be described. In each numerical example, i indicates the order of surfaces from the object. ri represents the radius of curvature of the lens surface, and di represents the surface between the i-th surface and the i + 1-th surface. ndi and νdi are the refractive index and the Abbe number of the i-th optical member based on the d-line, respectively. When the aspherical shape is x with the displacement in the optical axis direction at the position of the height h from the optical axis as x based on the surface vertex,
x = (h ² / R) / [1+ {1− (1 + K) (h / R) ² } ^1/2 ] + A4h ⁴ + A6h ⁶ + A8h ⁸ + A10h ¹⁰
It is represented by

Where K is a conic constant, A4, A6, A8, and A10 are fourth-order, sixth-order, eighth-order, and tenth-order aspheric coefficients, and R is a paraxial radius of curvature. “E-X” means “× 10 ^−X ”. Table 1 shows the relationship between the above-described conditional expressions and numerical examples. In the numerical examples 2 and 3, the distance d5 is negative because the aperture stop SP and the second lens group B2 are counted in this order.

[Numerical Example 1]
Unit mm

Surface data surface number rd nd νd
1 * 5192.584 0.70 1.85135 40.1
2 * 4.738 2.47
3 10.564 1.31 2.14352 17.8
4 19.933 (variable)
5 * 6.215 1.52 1.82080 42.7
6 * -131.152 0.20
7 8.541 0.80 1.48749 70.2
8 18.514 0.50 1.92286 20.9
9 4.834 1.65
10 -19.738 0.87 1.49700 81.5
11 -6.451 (variable)
12 (P) ∞ (variable)
13 42.991 1.52 1.55332 71.7
14 * -17.850 (variable)
15 ∞ 0.80 1.51633 64.1
16 ∞ 0.50
Image plane ∞

Aspheric data 1st surface
K = -2.52890e + 008 A 4 = -1.44681e-004 A 6 = 2.56273e-006
A 8 = -2.85100e-008 A10 = 8.30706e-011

Second side
K = -1.59789e + 000 A 4 = 7.56802e-004 A 6 = -1.44796e-005
A 8 = 4.11309e-007 A10 = -6.67356e-009

5th page
K = -3.35594e-001 A 4 = -6.21244e-005 A 6 = 5.15397e-006
A 8 = -7.76989e-007 A10 = 6.06531e-008

6th page
K = 8.77898e + 001 A 4 = 5.44453e-004 A 6 = -1.02429e-006

14th page
K = -1.15903e + 000 A 4 = 3.34298e-004 A 6 = -1.20220e-005
A 8 = 3.51212e-007

Various data Zoom ratio 4.74
Wide angle Medium Telephoto focal length 3.67 10.45 17.43
F number 2.37 4.05 5.80
Half angle of view (degrees) 48.6 20.4 12.3
Image height 3.30 3.88 3.88
Total lens length 36.74 33.06 39.63
BF 4.72 4.47 4.22

d 4 16.72 3.62 0.78
d11 0.35 2.44 4.52
d12 3.40 10.98 18.56
d14 3.69 3.44 3.19

Zoom lens group data group Start surface Focal length
1 1 -9.36
2 5 10.21
3 12 ∞
4 13 23.00
5 15 ∞

[Numerical Example 2]
Unit mm

Surface data surface number rd nd νd
1 * ∞ 0.70 1.85 135 40.1
2 * 4.981 2.47
3 10.950 1.54 2.14352 17.8
4 20.578 (variable)
5 ∞ -0.30
6 * 6.122 1.56 1.82080 42.7
7 * -120.006 0.20
8 8.053 0.83 1.48749 70.2
9 17.521 0.50 1.92286 20.9
10 4.712 0.77
11 -12.164 1.21 1.49700 81.5
12 -5.907 (variable)
13 (P) ∞ (variable)
14 18.358 1.65 1.55332 71.7
15 * -34.972 (variable)
16 ∞ 0.80 1.51633 64.1
17 ∞ 0.50
Image plane ∞

Aspheric data 1st surface
K = -2.52890e + 008 A 4 = -7.30527e-005 A 6 = 1.87758e-006
A 8 = -2.85100e-008 A10 = 8.30706e-011

Second side
K = -1.63387e + 000 A 4 = 7.25040e-004 A 6 = -7.03149e-006
A 8 = 2.04085e-007 A10 = -5.21639e-009

6th page
K = -3.06226e-001 A 4 = -9.32252e-005 A 6 = -1.35185e-005
A 8 = -2.58326e-007 A10 = -1.91906e-008

7th page
K = -1.44358e + 002 A 4 = 5.77218e-004 A 6 = -2.65546e-005

15th page
K = -5.56094e + 001 A 4 = 2.53698e-004 A 6 = -1.92214e-005
A 8 = 4.89317e-007

Various data Zoom ratio 4.79
Wide angle Medium Telephoto focal length 3.65 10.46 17.48
F number 2.48 4.11 5.80
Half angle of view (degrees) 48.5 20.4 12.3
Image height 3.30 3.88 3.88
Total lens length 36.92 32.69 38.99
BF 4.45 4.20 3.95

d 4 17.45 4.04 1.15
d12 0.48 1.65 2.82
d13 3.40 11.66 19.92
d15 3.42 3.17 2.92

Zoom lens group data group Start surface Focal length
1 1 -9.77
2 5 10.12
3 13 ∞
4 14 22.00
5 16 ∞

[Numerical Example 3]
Unit mm

Surface data surface number rd nd νd
1 * ∞ 0.70 1.85 135 40.1
2 * 5.412 2.47
3 10.066 1.71 2.14352 17.8
4 16.190 (variable)
5 ∞ -0.20
6 * 5.867 1.64 1.49710 81.6
7 * -8.607 0.15
8 25.542 1.77 1.91082 35.3
9 -3.450 0.45 1.68893 31.2
10 * 4.205 (variable)
11 (P) ∞ (variable)
12 59.545 1.33 1.55332 71.7
13 * -10.936 (variable)
14 ∞ 0.80 1.51633 64.1
15 ∞ 0.36
Image plane ∞

Aspheric data 1st surface
K = -2.52890e + 008 A 4 = -1.20236e-004 A 6 = 2.58922e-006
A 8 = -2.85100e-008 A10 = 8.30706e-011

Second side
K = -1.68754e + 000 A 4 = 6.88547e-004 A 6 = -8.26037e-006
A 8 = 3.27341e-007 A10 = -5.19812e-009

6th page
K = -1.03851e + 000 A 4 = -2.18454e-003 A 6 = -1.10264e-004
A 8 = -1.92871e-005

7th page
K = 4.36807e + 000 A 4 = 1.20860e-003 A 6 = -3.27060e-005

10th page
K = 5.48955e-001 A 4 = -2.01862e-004

Side 13
K = 2.28003e + 000 A 4 = 8.63629e-004 A 6 = -1.34888e-005
A 8 = 5.10084e-007

Various data Zoom ratio 4.56
Wide angle Medium telephoto focal length 3.66 10.04 16.68
F number 3.00 4.97 7.00
Half angle of view (degrees) 48.0 21.1 12.9
Image height 3.15 3.88 3.88
Total lens length 35.74 30.64 35.38
BF 3.82 3.57 3.32

d 4 17.00 4.23 1.32
d10 1.50 1.57 3.14
d11 3.40 11.24 17.58
d13 2.93 2.68 2.43

Zoom lens group data group Start surface Focal length
1 1 -10.25
2 5 9.48
3 11 ∞
4 12 16.81
5 14 ∞

B1 ... 1st lens group B2 ... 2nd lens group B3 ... 3rd lens group P ... Light flux limiting member

Claims (11)

From a first lens group having a negative refractive power, a second lens group having a positive refractive power, a light beam limiting member for limiting a passing light beam, and a third lens group having a positive refractive power, which are arranged in order from the object side to the image side. Each lens is configured such that the distance between the first lens group and the second lens group is narrower and the distance between the second lens group and the third lens group is wider at the telephoto end than at the wide-angle end. In the zoom lens where the group moves,
The first lens group includes a negative lens G11 and a positive lens G12 arranged in order from the object side to the image side.
The distance on the optical axis between the second lens group and the light flux limiting member at the wide angle end is δ2aw, and the maximum value on the optical axis between the second lens group and the light flux limiting member in the entire zoom range is δ2ai , When the amount of movement of the second lens group during zooming from the wide-angle end to the telephoto end is m2, and the amount of movement of the light beam limiting member during zooming from the wide-angle end to the telephoto end is ma ,
0.01 <| δ2ai−δ2aw | / δ2ai <0.99
0.60 <ma / m2 <0.95
A zoom lens that satisfies the following conditional expression: When the total lens length at the wide-angle end is TDw, and the air equivalent distance on the optical axis from the light flux limiting member to the image plane at the wide-angle end is Law,
0.1 <Law / TDw <0.3
The zoom lens according to claim 1, wherein the following conditional expression is satisfied. And when When the focal length of the first lens group is f1, the focal length of the second lens group is f2, and the focal length of the entire system at the wide angle end is fw,
0.4 <√ (| f1 | × fw) / f2 <0.8
The zoom lens according to claim 1 or 2, characterized by satisfying the following conditional expression. When the focal length of the first lens group is f1, and the focal length of the second lens group is f2, 0.7 <| f1 | / f2 <1.1.
The zoom lens according to any one of claims 1 to 3 and satisfies the following conditional expression. The third lens group is composed of a single positive lens G31, and when the curvature radii of the object-side and image-side lens surfaces of the positive lens G31 are R3a and R3b, respectively.
−0.5 <(R3a + R3b) / (R3a−R3b) <1.0
The zoom lens according to any one of claims 1 to 4, characterized by satisfying the following conditional expression. When the previous SL focal length of the negative lens G11 f11, and the focal length of a positive lens G12 f12,
0.2 <| f11 | / f12 <0.5
The zoom lens according to any one of claims 1 to 5, characterized by satisfying the following conditional expression. The air-converted distance on the optical axis from the lens surface on the object side of the second lens group at the telephoto end closest to the object side to the image plane is L2t, and the light flux limiting member at the telephoto end to the image plane is L2t. When the air equivalent distance on the optical axis is Lat and the total lens length at the telephoto end is TDt,
0.01 <(L2t−Lat) / TDt <0.50
The zoom lens according to any one of claims 1 to 6 and satisfies the following conditional expression. During zooming from the wide-angle end to the telephoto end, the first lens group moves along a convex locus toward the image side, and the second lens group and the light beam restricting member move toward the object side along different loci, 3 lens group zoom lens according to any one of claims 1 to 7, characterized in that moves toward the image side. The light beam limiting member zoom lens according to any one of claims 1 to 8, characterized in that it has a function as an aperture stop. The zoom lens according to any one of claims 1 to 8, further comprising an aperture stop that moves integrally with the second lens group during zooming. Imaging apparatus characterized by having an image pickup device which receives an image formed by the zoom lens and the zoom lens according to any one of claims 1 to 10.