JP2015028530A - Zoom lens and imaging apparatus including the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a zoom lens having a wide angle of view and high optical performance over the whole object distance.SOLUTION: The zoom lens includes, in order from the object side to the image side, a first lens group L1 having negative refractive power, and a rear group having one or more lens groups and having positive refractive power as a whole, and the distance between the first lens group and the rear group is decreased when zooming from the wide angle end to the telephoto end. The rear group includes, in order from the object side to the image side, a second-a lens group having positive refractive power, a second-b lens group having positive refractive power, and a second-c lens group having positive or negative refractive power. When focusing from infinity to the closest distance, the second-a lens group is moved to the image side, and the second-b lens group is moved to the object side. The focal distance f2a of the second-a lens group and the focal distance f2b of the second-b lens group are set appropriately.

Description

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

  In recent years, an imaging optical system used in an imaging apparatus using a solid-state imaging device is required to be a zoom lens having a wide angle of view, small distortion, and high performance (high resolution) over the entire object distance. In the case of an interchangeable lens of a single-lens reflex camera in which a quick return mirror is disposed on the image plane side, it is required to have a sufficiently long back focus. As a wide-angle zoom lens, a negative lead type zoom lens in which a lens unit having a negative refractive power precedes (most positioned on the object side) is known. Among these, zoom lenses having a wide angle of view capable of zooming from a wide angle range with a total field angle of 100 degrees or more are known (Patent Documents 1 and 2).

  In Patent Document 1, a wide-angle lens includes a first lens group having a negative refractive power, a second lens group having a positive refractive power, a third lens group having a positive refractive power, and a fourth lens group having a positive or negative refractive power. A zoom lens having a wide angle of view with a zooming ratio of about 2 and a total angle of view of 120 degrees at the end is disclosed. In Patent Document 2, a wide-angle image having a total angle of view of 114.7 degrees at the wide-angle end and a zoom ratio of about 1.65, which includes a first lens unit having a negative refractive power and a second lens group having a positive refractive power. An angular zoom lens is disclosed.

  In addition, Patent Document 2 includes 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, and has a total field of view of 114.7 at the wide-angle end. A zoom lens having a wide angle of view with a zoom ratio of about 1.65 is disclosed.

JP 2005-106878 A JP 2007-94174 A

  It is easy to obtain a wide angle of view and a long back focus with a negative lead type zoom lens.

  However, since the negative lead type zoom lens has an asymmetrical arrangement with respect to the aperture stop, many aberrations such as field curvature and distortion occur, making it difficult to correct these aberrations. In particular, a zoom lens including an extremely wide angle of view where the shooting angle of view exceeds 120 degrees causes many of the above-mentioned various aberrations. In addition, the negative lead type zoom lens also has large aberration fluctuations during focusing, and it is difficult to obtain high optical performance over the entire object distance from infinity to close range.

  In Patent Document 1, the first lens group is divided into a negative refractive power first A lens group composed of two negative lenses and a negative refractive power first B lens group including two negative lenses. And focusing. In Patent Document 1, the lens group is divided into two partial lens groups at the portion where the off-axis light rays are largely refracted in the first lens group, and focusing is performed with one of the first B lens groups. The optical path variation of off-axis rays accompanying the movement of the 1B lens group is large.

  For this reason, off-axis aberrations due to focusing, particularly the field curvature, vary greatly, and it tends to be difficult to obtain good optical performance in all regions from infinity to close range.

  In Patent Document 2, focusing is performed using a cemented lens having a positive refractive power in the second lens group as a focus lens group. However, the angle of off-axis rays incident on the focus lens group is large in an ultra-wide field angle range of about 110 degrees. Therefore, the fluctuation of the optical path of off-axis rays due to the movement of the focus lens group is large, the off-axis aberration due to focusing, especially the fluctuation of the field curvature, is large, and good optical performance is obtained in all regions from infinity to close range. There was a tendency to get difficult.

  In general, a zoom lens including a wide angle of view region has a remarkable change in the path of a light beam passing through the optical system due to focusing, and thus tends to have a large variation in off-axis aberration due to focusing. In order to obtain high optical performance over the entire object distance while achieving a wide angle of view in a negative lead type zoom lens, it is important to appropriately set a focus lens group that is moved during focusing. Furthermore, it is important to appropriately set the refractive power of the focus lens group and the amount of movement of the focus lens group during focusing from infinity to a close distance.

  If these configurations are inappropriate, it becomes very difficult to obtain high optical performance over the entire object distance from infinity to the closest distance while widening the angle of view.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a zoom lens capable of obtaining high optical performance over a wide object angle and a wide object angle, 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 unit L1 having a negative refractive power and one or more lens units, and is configured by a rear group having a positive refractive power as a whole. A zoom lens in which a distance between the first lens group and the rear group is shortened during zooming from the first lens unit to the telephoto end, and the second group is a second lens unit having a positive refractive power in order from the object side to the image side. 2b lens group having a positive refractive power and a second c lens group having a positive or negative refractive power. When focusing from infinity to the closest distance, the second a lens group moves to the image side, and the second b When the lens group moves to the object side, the focal length of the second a lens group is f2a, and the focal length of the second b lens group is f2b.
1.1 <f2b / f2a <3.0
It satisfies the following conditional expression.

  According to the present invention, it is possible to obtain a zoom lens that can provide high optical performance over a wide object angle and a wide object distance.

Lens cross-sectional view at the wide-angle end of Example 1 (A), (b) Longitudinal aberration diagrams at infinity and closest distance at the wide angle end of Example 1 (A), (b) Longitudinal aberration diagrams at infinity and closest distance at the telephoto end in Example 1 Lens sectional view at the wide-angle end in Example 2 (A), (b) Longitudinal aberration diagrams at infinity and closest distance at the wide-angle end in Example 2 (A), (b) Longitudinal aberration diagrams at infinity and closest distance at the telephoto end in Example 2 Lens sectional view at the wide-angle end of Example 3 (A), (b) Longitudinal aberration diagrams at infinity and closest distance at the wide angle end in Example 3 (A), (b) Longitudinal aberration diagrams at infinity and closest distance at the telephoto end in Example 3 Schematic diagram of the main part of an imaging apparatus using a zoom lens according to 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 L1 having a negative refractive power and one or more lens units, and is configured by a rear group having a positive refractive power as a whole. During zooming from the wide-angle end to the telephoto end, the distance between the first lens unit L1 and the rear unit LR is shortened. The rear group LR includes, in order from the object side to the image side, a 2a lens group having a positive refractive power, a 2b lens group having a positive refractive power, and a second c lens group having a positive or negative refractive power.

  When focusing from infinity to the closest distance, the 2a lens group moves to the image side, and the 2b lens group moves to the object side at different speeds.

  FIG. 1 is a lens cross-sectional view at the wide-angle end (short focal length end) of Embodiment 1 of the present invention. FIGS. 2A and 2B are longitudinal aberration diagrams at the infinity and the closest distance at the wide angle end according to the first embodiment. 3A and 3B are longitudinal aberration diagrams at the telephoto end (long focal length end) of Example 1 at infinity and the closest distance. FIG. 4 is a lens cross-sectional view at the wide angle end according to Embodiment 2 of the present invention. 5A and 5B are longitudinal aberration diagrams at the infinity and the closest distance at the wide-angle end in Example 2. FIG. FIGS. 6A and 6B are longitudinal aberration diagrams at infinity and the closest distance at the telephoto end according to the first embodiment.

  FIG. 7 is a lens cross-sectional view at the wide angle end according to Embodiment 3 of the present invention. 8A and 8B are longitudinal aberration diagrams of Example 3 at the infinity and the closest distance at the wide angle end. FIGS. 9A and 9B are longitudinal aberration diagrams at the infinite distance and the closest distance at the telephoto end according to the third embodiment. FIG. 10 is a schematic diagram of a main part of a single-lens reflex camera (imaging device) including the zoom lens of the present invention. The zoom lens of each embodiment is an imaging optical system used in an imaging apparatus such as a digital still camera or a video camera. 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, L1 is a first lens unit having a negative refractive power (optical power = reciprocal of focal length). LR is a rear group having a positive refractive power as a whole including one or more lens groups. In Examples 1 to 3, the rear lens group LR is sequentially arranged from the object side to the image side, the second lens unit L2a having a positive refractive power, the second b lens unit L2b having a positive refractive power, and the second c lens having a positive or negative refractive power. It is composed of a group L2c.

  SP is a photographic beam diameter determining member (hereinafter referred to as “aperture stop”) having a variable aperture diameter that controls the photographic beam diameter according to the aperture value at the time of shooting. SSP1 and SSP2 are open F number apertures (open F apertures) whose aperture diameter changes in accordance with zooming, and determine the open F number at each zoom position. FC1 and FC2 are flare cutters that cut off (shield) flare light outside the open F-number light beam.

  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. Further, when used as a photographing optical system for a silver salt film camera, a photosensitive surface corresponding to the film surface is provided. 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 dotted line M represents the d-line meridional image plane, and the solid line S represents the d-line sagittal image plane. Further, the chromatic aberration of magnification represents the difference of the g-line when the d-line is used as a reference.

  Fno is an F number. ω is a shooting half angle of view (degrees). In each of the following embodiments, the wide-angle end and the telephoto end are zoom positions when the zoom lens unit is positioned at both ends movable on the optical axis due to the mechanism. In the lens cross-sectional view, arrows indicate the movement trajectory of each lens unit during zooming from the wide-angle end to the telephoto end.

  In each embodiment, when zooming from the wide-angle end to the telephoto end, as shown by an arrow, the air distance between the first lens unit L1 having a negative refractive power and the rear group LR having a positive refractive power is shortened (decreased). To do. Specifically, the first lens unit L1 moves on the optical axis along a locus that is convex on the image side. The movement of the rear group LR is as follows.

  In Example 1 of FIG. 1 and Example 2 of FIG. 4, the 2a lens group L2a, the 2b lens group L2b, and the 2c lens group L2c move to the object side along different paths. In Example 3 of FIG. 7, the 2a lens group moves to the object side, and the 2b lens group L2b and the 2c lens group L2c move to the object side along a different locus from the 2a lens group L2a. The second b lens unit L2b and the second c lens unit L2c move along the same locus.

  By performing such movement during zooming, a zoom lens having an ultra-wide field angle exceeding 120 ° is obtained. In particular, zooming from the wide-angle end to the telephoto end is efficiently performed, and the correction of the image plane position by zooming is reliably performed by the movement of the first lens unit L1.

  In the first lens unit L1, at least three meniscus negative lenses having a convex surface facing the object side are arranged in order from the object side to the image side. At least two of these three negative lenses are aspherical. One of the at least two aspheric surfaces at this time has an aspheric shape in which positive refractive power increases from the optical axis (lens center) toward the periphery, and the other one is negative from the optical axis toward the periphery. This is an aspherical shape with a strong refractive power. The aspherical shape in which the positive refractive power increases from the optical axis toward the periphery plays a role of correcting strong negative distortion generated by the negative lens arranged in the first lens unit L1.

  In the zoom lens having an ultra-wide angle of view as in the present invention, a large amount of lenses having a strong negative refractive power are arranged in the first lens unit L1 on the object side, so that a large amount of negative distortion occurs. In order to satisfactorily correct the negative distortion, it is preferable to effectively dispose an aspheric surface having a positive refractive power that increases from the optical axis toward the periphery.

  On the other hand, an aspheric surface having a negative refractive power that increases from the optical axis toward the periphery plays a role of correcting field curvature, which is a problem in a wide-angle zoom lens. In general, in an asymmetrical ultra-wide-angle zoom lens of the retrofocus type as in the present invention, a curvature of field occurs in which the image plane suddenly falls in the over direction at the periphery of the screen.

  In particular, this tendency becomes stronger when the angle of view is increased. For this reason, in each embodiment, in addition to the two aspheric surfaces described above, the curvature of field is corrected by an aspheric surface having a negative refractive power that increases from the optical axis toward the periphery. In a zoom lens including an ultra-wide field angle region, it is important to correct distortion and field curvature in a balanced manner, particularly at the wide-angle end. Therefore, in each embodiment, the lens configuration of the first lens unit L1 is the lens configuration as described above.

  In the zoom lenses of the embodiments, the rear lens group LR having a positive refractive power is sequentially arranged from the object side to the image side, the second lens unit L2a having a positive refractive power, the second lens unit L2b having a positive refractive power, and a positive or negative lens unit. The second c lens unit L2c having a refractive power of 1 mm is provided.

  When focusing from infinity to the closest distance, the 2a lens unit L2a moves on the optical axis to the image side, and the 2b lens unit L2b moves on the optical axis on the object side. At this time, the 2a lens unit L2a mainly performs the function of focusing, and the absolute value of the amount of movement on the optical axis during focusing is set so that the 2a lens unit L2a is larger than the 2b lens unit L2b. ing. The second b lens unit L2a is a lens unit having a weak positive refractive power, and has a small focusing effect even when moved on the optical axis, and corrects a variation in curvature of field that occurs during focusing by the second a lens unit L2a. Playing a role.

  The lens group refers to a portion divided by the lens interval along the optical axis that changes during zooming and focusing. In a negative lens group leading zoom lens including an ultra-wide field angle range, when focusing is performed with a partial lens unit having a positive refractive power closest to the object side in the rear lens group LR having a positive refractive power, the distance from infinity to the closest distance In this focusing, the sagittal image plane largely fluctuates in the under direction. Here, the partial lens unit having a positive refractive power is, for example, the second-a lens unit L2a.

  Therefore, in each embodiment, the fluctuation during focusing of the sagittal image plane at that time is corrected by moving the second-b lens unit L2b and the second-a lens unit L2a having weak refractive power in opposite directions on the optical axis at different speeds. Yes.

  That is, in each embodiment, the so-called floating focus is performed by moving the second-b lens unit L2b having a positive refractive power at a different speed from the second-a lens unit L2a having a positive refractive power in the opposite direction on the optical axis. When the 2b lens unit L2b is moved in the direction opposite to the 2a lens unit L2a on the optical axis, the sagittal image plane changes in the opposite direction to that when the 2a lens unit L2a is moved, and the image focal position is It changes in the same direction as when the 2a lens unit L2b is moved.

  That is, by moving the 2b lens unit L2b in the direction opposite to the 2a lens unit L2a on the optical axis, the focus drive amount is kept small and the sagittal image plane fluctuates in focusing from infinity to the closest distance. Obtained few good shot images.

  The second-b lens unit L2b includes at least one lens surface having a convex lens surface on the object side and a lens surface having a convex surface on the image side. Then, the aberration generated in the second b lens unit L2b is canceled out, and the entire second b lens unit L2b is maintained in a state having a moderately weak refractive power. Thereby, the second-b lens unit L2b does not significantly affect the focusing action, and corrects the variation in field curvature.

  Further, the most image side lens surface of the second b lens unit L2b has a lens shape with a gentle convex surface facing the image side. Thereby, positive refraction is given to the light beam emitted from the second lens group L2b, and a field curvature that varies depending on the focus of the second lens group L2a having a positive refractive power is generated in the reverse direction and corrected. Further, the zoom lens of each embodiment is configured to satisfy the following conditional expression when the focal length f2a of the 2a lens unit L2a and the focal length of the 2b lens unit L2b are f2b.

1.1 <f2b / f2a <3.0 (1)
Conditional expression (1) defines the ratio of the focal length of the second lens group L2b to the focal length of the second lens group L2a. Conditional expression (1) is for appropriately supplementing the focusing by the second-a lens unit L2a by the floating of the second-b lens unit L2b and favorably correcting the fluctuation of the field curvature due to the focusing. If the lower limit of conditional expression (1) is exceeded and the refractive power of the second b lens unit L2b becomes too strong, fluctuations in various aberrations including spherical aberration become large, and correction of various aberrations becomes difficult.

  On the other hand, if the refractive power of the second b lens unit L2b becomes too weak beyond the upper limit of the conditional expression (1), the correction of the curvature of field curvature is insufficient during focusing. At the same time, the amount of movement of the second b lens unit L2b when floating is too large, which is not desirable.

  As described above, according to the present invention, a zoom lens capable of obtaining high optical performance over the entire object distance can be obtained. In each embodiment, it is more preferable to satisfy one or more of the following conditional expressions. The amount of movement of the second a lens unit L2a in focusing from infinity to the closest distance is DF1, and the amount of movement of the second b lens unit L2b in focusing from infinity to the closest distance is DF2.

  Here, the amount of movement of the lens unit in focusing from infinity to the closest distance refers to a difference in the position of the lens unit at infinity and the closest distance. The sign of the amount of movement is positive when the lens group moves to the image side during focusing from infinity to the closest distance, and negative when it moves to the object side. Let fR be the focal length of the rear lens group LR at the wide-angle end. The focal length of the second c lens unit L2c is set to f2c. Let fw be the focal length of the entire system at the wide-angle end. The focal length of the first lens unit L1 is f1, and the total lens length at the telephoto end (the distance on the optical axis from the lens surface closest to the object side to the image plane) is TDLt. At this time, it is preferable to satisfy one or more of the following conditional expressions.

−0.50 <DF2 / DF1 <−0.05 (2)
0.7 <f2a / fR <3.0 (3)
-0.5 <fR / f2c <0.5 (4)
2.5 <f2a / fw <6.0 (5)
0.06 <| f1 | / TDLt <0.25 (6)
1.2 <fR / | f1 | <3.0 (7)
Next, the technical meaning of each conditional expression described above will be described.

  Conditional expression (2) defines the ratio of the moving amount of the second b lens unit L2b to the moving amount of the second a lens unit L2a during focusing, and mainly corrects fluctuations in field curvature during focusing well. Is.

  If the absolute value of the amount of movement of the 2b lens unit relative to the amount of movement of the 2a lens unit L2a exceeds the lower limit of the conditional expression (2), it is desirable that the correction of the curvature of field becomes excessive during focusing. Absent. At the same time, the air space for focusing of the second b lens unit L2b is increased, and the entire system is enlarged, which is not desirable. Further, if the absolute value of the moving amount of the second b lens unit L2b with respect to the moving amount of the second a lens unit L2a exceeding the upper limit of the conditional expression (2) is small, the fluctuation of the curvature of field is corrected during focusing. Becomes difficult.

  Conditional expression (3) appropriately defines the focal length of the 2a lens unit L2a in the rear lens group LR, and mainly performs focusing and aberration correction with a good balance between the 2a lens unit L2a. If the refractive power of the second-a lens unit L2a becomes too strong beyond the lower limit of conditional expression (3), variations in various aberrations including spherical aberration will increase during focusing, making it difficult to correct the variations in various aberrations. become. Also, if the refractive power of the second lens unit L2a becomes too weak beyond the upper limit of conditional expression (3), the amount of focus movement required for focusing from infinity to the closest distance increases, and the entire system becomes large. Not desirable.

  Conditional expression (4) appropriately defines the ratio of the focal length of the rear group LR to the focal length of the second c lens unit L2c, and mainly reduces the size of the entire system while ensuring a sufficiently long back focal length. This is for correcting various aberrations in a balanced manner. If the lower limit of conditional expression (4) is exceeded and the refractive power of the second c lens unit L2c increases in the negative direction, the back focus becomes too long and the entire system becomes large, which is not desirable.

  At the same time, the positive refractive power of the second lens unit L2a and the second lens unit L2b becomes too strong in order to maintain the balance of refractive power in the rear lens group LR with positive refractive power, and various aberrations are generated. These corrections are difficult. If the refractive power of the second c lens unit L2c is increased in the positive direction beyond the upper limit of the conditional expression (4), it is difficult to secure a sufficiently long back focus, which is not desirable. At the same time, the positive refractive power of the entire rear group LR becomes too strong, and various aberrations are greatly generated in the positive direction, making it difficult to correct them.

  Conditional expression (5) defines the ratio of the focal length of the second-a lens unit L2a to the focal length of the entire system at the wide-angle end, and is mainly for achieving a good balance between focusing and aberration correction by the second-a lens unit L2a. is there. If the refractive power of the second-a lens unit L2a becomes too strong beyond the lower limit of conditional expression (5), various aberrations such as spherical aberration will increase during focusing, and it will be difficult to correct variations in the various aberrations. . If the refractive power of the 2a lens unit L2a becomes too weak beyond the upper limit of the conditional expression (5), the amount of focus movement required for focusing from infinity to the closest distance increases, and the entire system increases in size. Not desirable.

  Conditional expression (6) defines the ratio of the focal length of the first lens unit L1 to the total lens length of the entire system at the telephoto end, and mainly reduces the size of the entire system while ensuring a sufficiently long back focal length. This is for correcting various aberrations in a balanced manner.

  If the lower limit of the conditional expression (6) is exceeded and the absolute value of the negative refractive power of the first lens unit L1 becomes too large, the incident height of light incident on the rear group LR increases and the rear group LR increases in size. Further, the negative aberration generated in the first lens unit L1 becomes large, and it is difficult to correct this by the rear unit LR. If the absolute value of the negative refractive power of the first lens unit L1 is too small beyond the upper limit of conditional expression (6), it is difficult to widen the angle of view and a sufficiently long back focus is secured. Difficult to do.

  Conditional expression (7) defines the ratio of the focal length of the rear lens group LR at the wide-angle end to the focal length of the first lens unit L1, mainly reducing the size of the entire system while ensuring a sufficiently long back focus. This is for correcting various aberrations in a balanced manner. If the absolute value of the negative refractive power of the first lens unit L1 is smaller than the refractive power of the rear group LR beyond the lower limit of the conditional expression (7), it is difficult to ensure a sufficiently long back focus. At the same time, a large on-axis aberration occurs, making this correction difficult.

  Further, when the refractive power of the rear group LR becomes smaller than the absolute value of the negative refractive power of the first lens group L1 exceeding the upper limit of the conditional expression (7), the rear group LR becomes larger and the first lens is increased. Negative aberration generated from the group L1 becomes large, and it becomes difficult to correct this by the rear group LR. In order to make the zoom lens of the present invention more preferable, it is preferable to set the ranges of the conditional expressions as follows.

1.2 <f2b / f2a <2.8 (1a)
−0.40 <DF2 / DF1 <−0.06 (2a)
1.0 <f2a / fR <2.5 (3a)
−0.3 <fR / f2c <0.3 (4a)
3.0 <f2a / fw <5.5 (5a)
0.07 <| f1 | / TDLt <0.23 (6a)
1.4 <fR / | f1 | <2.8 (7a)

  As described above, according to each embodiment, it is possible to obtain a high-quality image that maintains an excellent image plane characteristic in the entire focus range with an ultra-wide angle of view exceeding 120 degrees at the wide angle end. In each embodiment, in order to obtain good optical performance over the entire zoom range and over the entire object distance, the first lens unit L1 and the rear lens unit LR are configured as follows.

  The 2a lens group includes a cemented lens and a positive lens in which a negative lens and a positive lens are cemented in order from the object side to the image side. The 2b lens group includes a positive lens, a negative lens, and a positive lens in order from the object side to the image side. The second c lens group includes a cemented lens in which a negative lens and a positive lens are cemented in order from the object side to the image side, a positive lens, and a cemented lens in which a negative lens and a positive lens are cemented. In addition, the first lens unit is composed of four meniscus negative lenses having a convex object side surface, a biconcave negative lens, and a positive lens in order from the object side to the image side.

  Next, the lens configuration of the zoom lens of each embodiment will be described. The first exemplary embodiment is a negative lead type zoom lens, which includes, in order from the object side to the image side, a first lens unit L1 having a negative refractive power and a rear group LR having a positive refractive power. The rear group LR includes a second-a lens unit L2a having a positive refractive power, a second-b lens unit L2b having a positive refractive power, and a second-c lens unit L2c having a negative refractive power. The second c lens unit L2c may have a positive refractive power.

  During zooming from the wide-angle end to the telephoto end, the first lens unit L1 moves along a locus that is convex on the image side so that the distance between the first lens unit L1 and the rear unit LR is narrowed (shortened). . The second a lens unit L2a, the second b lens unit L2b, and the second c lens unit L2c all move toward the object side along different paths.

  Example 1 is a four-group zoom lens. The first lens unit L1 includes, in order from the object side to the image side, a lens with negative refractive power (hereinafter simply referred to as “negative lens”) G11, a negative lens G12, and a negative lens G13. Furthermore, a negative lens G14, a negative lens G15, and a positive lens G16 having a concave surface facing the image side are provided. During focusing from infinity to the closest distance, the second-a lens unit L2a moves to the image side, and the second-b lens unit L2b moves to the object side.

  In addition, a flare cutter aperture FC1 that moves independently during zooming is disposed on the object side of the second-a lens unit L2a. An open F-number stop SSP1 is disposed between the second b lens unit L2b and the second c lens unit L2c. The open F number stop SSP1 determines the center light flux at the open F number. Furthermore, a flare cutter diaphragm FC2 that is stationary during zooming is also arranged on the image side of the second lens unit L2c. The aperture stop SP is disposed on the object side of the second b lens unit L2b, and moves integrally with the second b lens unit L2b (same locus) during zooming.

  As is apparent from the respective aberration diagrams, this embodiment has high optical performance in which various aberrations are well corrected over the entire zoom range. In addition, there is little variation in field curvature during focusing to the nearest distance, and high optical performance is obtained in the entire focus range.

  The second exemplary embodiment is a negative lead type zoom lens, which includes, in order from the object side to the image side, a first lens unit L1 having a negative refractive power and a rear group LR having a positive refractive power. The rear group LR includes a second-a lens unit L2a having a positive refractive power, a second-b lens unit L2b having a positive refractive power, and a second-c lens unit L2c having a negative refractive power. The second c lens unit L2c may have a positive refractive power. During zooming from the wide-angle end to the telephoto end, the distance between the first lens unit L1 and the rear unit LR is reduced. Specifically, the first lens unit L1 moves along a locus convex toward the image side.

  The second a lens unit L2a, the second b lens unit L2b, and the second c lens unit L2c all move toward the object side along different paths. Example 2 is a four-group zoom lens. The lens configurations of the first lens group L1 and the rear group LR are the same as those in the first embodiment. Focusing from infinity to the closest distance is the same as in the first embodiment. In addition, a flare cutter aperture FC1 that moves independently during zooming is disposed on the object side of the second-a lens unit L2a.

  An open F-number stop SSP1 is disposed between the second b lens unit L2b and the second c lens unit L2c. The open F number stop SSP1 plays a role as a flare cutter that cuts off the flare component outside the center light flux as well as determining the center light flux at the open F number. Furthermore, a flare cutter aperture FC2 that is stationary during zooming is also arranged on the image side of the second c lens unit L2c. The aperture stop SP is disposed on the object side of the second b lens unit L2b and moves integrally with the second b lens unit L2b during zooming.

  As is apparent from the respective aberration diagrams, this embodiment has high optical performance in which various aberrations are well corrected over the entire zoom range. In addition, there is little variation in field curvature during focusing to the nearest distance, and high optical performance is obtained in the entire focus range.

  The third exemplary embodiment is a negative lead type zoom lens, which includes, in order from the object side to the image side, a first lens unit L1 having a negative refractive power and a rear group LR having a positive refractive power. The rear group LR includes a second-a lens unit L2a having a positive refractive power, a second-b lens unit L2b having a positive refractive power, and a second-c lens unit L2c having a negative refractive power. The second c lens unit L2c may have a positive refractive power. The focusing from infinity to the closest distance is the same as in the first embodiment.

  During zooming from the wide-angle end to the telephoto end, the first lens unit moves along a locus that is convex toward the image side. The second-a lens unit L2a moves to the object side. The second b lens unit L2b and the second c lens unit L2c move to the object side along a different locus from the second a lens unit L2a. The second b lens unit L2b and the second c lens unit L2c move along the same locus.

  Further, an open F-number aperture stop SSP1 and an aperture stop SP are arranged in order from the object side on the object side of the second a lens unit L2a, and move together with the second a lens unit L2a during zooming. An open F-number aperture stop SSP2 is disposed between the second b lens unit L2b and the second c lens unit L2c. The open F-number stop SSP1 and the open F-number stop SSP2 play a role as a flare cutter that cuts off the flare component outside the center light flux as well as determining the center light flux at the open F-number. Furthermore, a flare cutter stop FC1 that is stationary during zooming is also arranged on the image side of the second c lens unit L2c.

  As is apparent from the respective aberration diagrams, this embodiment has high optical performance in which various aberrations are well corrected over the entire zoom range. In addition, there is little variation in field curvature during focusing to the closest distance, and high optical performance is achieved in the entire focus range.

  As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to these embodiment, A various deformation | transformation and change are possible within the range of the summary.

  Next, an embodiment of a single-lens reflex camera system (imaging device) using the zoom lens of the present invention will be described with reference to FIG. In FIG. 10, 10 is a single-lens reflex camera body, and 11 is an interchangeable lens equipped with the zoom lens of the present invention. Reference numeral 12 denotes a recording unit such as a film or an image sensor for recording a subject image obtained through the interchangeable lens 11. Reference numeral 13 denotes a finder optical system for observing the subject image from the interchangeable lens 11, and reference numeral 14 denotes a quick return mirror that rotates to switch the subject image formed by the interchangeable lens 11 to the recording means 12 and the finder optical system 13 for transmission. is there.

  When observing the subject image with the finder, the subject image formed on the focusing plate 15 via the quick return mirror 14 is made into an erect image with the pentaprism 16 and then magnified and observed with the eyepiece optical system 17. At the time of shooting, the quick return mirror 14 rotates in the direction of the arrow, and the subject image is formed and recorded on the recording means 12. Reference numeral 18 denotes a submirror, and 19 denotes a focus detection device.

  Thus, by applying the zoom lens of the present invention to an imaging device such as an interchangeable lens such as a single-lens reflex camera, an imaging device having high optical performance can be realized. The zoom lens of the present invention can be similarly applied to a single-lens reflex camera without a quick return mirror. Further, the present invention can be similarly applied to a projection lens for a projector.

  Next, numerical examples of the respective embodiments of the present invention will be shown. In each numerical example, i indicates the order of the surfaces from the object side, ri is the radius of curvature of the lens surface, di is the lens thickness and air spacing between the i-th surface and the i + 1-th surface, and ndi and νdi are respectively The refractive index with respect to d line of the material of the i-th lens and the Abbe number are shown. BF is the back focus, and is indicated by the distance from the final lens surface to the image plane. The total lens length is the distance from the first lens surface to the image plane. The aspherical shape is the X axis in the optical axis direction, the H axis in the direction perpendicular to the optical axis, the light traveling direction is positive, R is the paraxial radius of curvature, K is the conic constant, A4, A6, A8, A10, A12, A14. Are respectively aspherical coefficients,

It is expressed by the following formula. [E-X] means [× 10 ^−X ]. An aspherical surface is indicated by adding * after the surface number. Further, the portion where the distance d between the optical surfaces is (variable) changes during zooming. Table 1 shows the relationship between the above-described conditional expressions and numerical examples.

(Numerical example 1)
Unit mm
Surface data surface number rd nd νd
1 44.642 3.50 1.77250 49.6
2 30.575 9.02
3 * 39.834 3.50 1.59522 67.7
4 26.292 6.00
5 32.116 2.80 1.56907 71.3
6 * 14.569 9.50
7 39.825 2.00 1.83481 42.7
8 20.395 10.80
9 -49.294 1.80 1.49700 81.5
10 41.949 2.83
11 39.739 6.53 1.59551 39.2
12 -74.048 (variable)
13 (FC1) ∞ (variable)
14 34.156 1.00 1.83481 42.7
15 16.677 3.67 1.49700 81.5
16 69.429 0.15
17 28.518 3.06 1.68893 31.1
18 786.593 (variable)
19 (Aperture SP) ∞ 1.38
20 103.013 3.85 1.51633 64.1
21 -23.139 0.52
22 -22.534 0.80 1.83481 42.7
23 86.583 0.61
24 32.307 3.80 1.62588 35.7
25 -51.738 0.56
26 (SSP1) ∞ (variable)
27 87.697 0.80 1.83481 42.7
28 13.146 3.82 1.49700 81.5
29 46.364 0.28
30 21.023 4.80 1.49700 81.5
31 -24.714 0.10
32 -54.812 1.00 1.80 400 46.6
33 14.730 5.56 1.58313 59.4
34 * -52.555 (variable)
35 (FC2) ∞

Aspheric data 3rd surface
K = 0.000 A 4 = 4.70510e-006 A 6 = -1.28063e-008 A 8 = 2.85216e-011
A10 = -2.80741e-014 A12 = 1.21207e-017

6th page
K = -1.14600 A 4 = 3.01502e-005 A 6 = -1.31934e-007 A 8 = 7.95882e-010
A10 = -2.46864e-012 A12 = 3.61458e-015 A14 = -2.36308e-018

34th page
K = 1.43692 A 4 = 1.31360e-005 A 6 = -3.73780e-008 A 8 = 4.19002e-010
A10 = -3.63062e-012

Various data
Wide angle Medium telephoto focal length 12.30 17.96 23.64
F number 4.10 4.10 4.10
Half angle of view (degrees) 60.38 50.30 42.46
Image height 21.64 21.64 21.64
Optical total length 167.40 160.44 162.15
BF 38.80 38.80 38.80

d12 18.90 5.61 1.00
d13 9.98 5.14 0.30
d18 4.60 4.42 4.24
d26 1.07 1.37 1.68
d34 0.00 11.04 22.09

Zoom lens group data group Focal length
L1 -18.76
2a 49.43
2b 79.06
2c -2933.36
LR 37.65

Focus movement amount (object distance infinity → closest distance (300mm))
Group travel
2a 3.045
2b -0.300

(Numerical example 2)
Surface data surface number rd nd νd
1 45.887 3.50 1.77250 49.6
2 30.720 8.06
3 * 38.003 3.50 1.59522 67.7
4 26.162 6.00
5 31.599 2.80 1.56907 71.3
6 * 14.150 9.50
7 37.908 2.00 1.83481 42.7
8 20.303 11.07
9 -48.934 1.80 1.49700 81.5
10 41.161 2.86
11 39.443 6.64 1.59551 39.2
12 -74.091 (variable)
13 (FC1) ∞ (variable)
14 34.330 1.00 1.85026 32.3
15 16.113 3.67 1.54814 45.8
16 58.966 0.18
17 28.385 3.08 1.68893 31.1
18 1324.046 (variable)
19 (Aperture SP) ∞ 1.42
20 91.644 3.86 1.49700 81.5
21 -23.242 0.55
22 -22.946 0.80 1.88300 40.8
23 93.124 0.70
24 35.278 3.65 1.68893 31.1
25 -52.709 0.59
26 (SSP1) ∞ (variable)
27 87.305 0.80 1.83481 42.7
28 13.178 3.81 1.49700 81.5
29 46.385 0.26
30 20.826 4.82 1.49700 81.5
31 -24.729 0.10
32 -54.747 1.00 1.80 400 46.6
33 14.647 5.62 1.58313 59.4
34 * -52.077 (variable)
35 (FC2) ∞

Aspheric data 3rd surface
K = 0.000 A 4 = 4.03292e-006 A 6 = -1.28699e-008 A 8 = 2.82932e-011
A10 = -2.78839e-014 A12 = 1.19245e-017

6th page
K = -1.13252 A 4 = 2.96520e-005 A 6 = -1.34434e-007 A 8 = 7.93257e-010
A10 = -2.45844e-012 A12 = 3.60709e-015 A14 = -2.34289e-018

34th page
K = 2.05983 A 4 = 1.33558e-005 A 6 = -3.47592e-008 A 8 = 3.64581e-010
A10 = -3.31340e-012

Various data
Wide angle Medium telephoto focal length 12.30 17.95 23.60
F number 4.10 4.10 4.10
Half angle of view (degrees) 60.38 50.32 42.51
Image height 21.64 21.64 21.64
Optical total length 167.40 160.21 161.82
BF 38.80 38.80 38.80

d12 19.28 5.74 1.00
d13 9.99 5.15 0.30
d18 4.63 4.55 4.47
d26 1.07 1.30 1.54
d34 0.00 11.04 22.09

Zoom lens group data group Focal length
L1 -18.94
2a 49.15
2b 82.15
2c -32674.69
LR 37.92

Focus movement (object distance infinity → closest distance (300mm))
Group travel
2a 3.098
2b -0.379

(Numerical Example 3)
Surface data surface number rd nd νd
1 47.728 3.50 1.77250 49.6
2 31.157 7.74
3 * 41.094 3.50 1.59522 67.7
4 25.707 6.00
5 30.632 2.80 1.56907 71.3
6 * 14.238 9.50
7 35.822 2.00 1.83481 42.7
8 20.125 11.13
9 -51.475 1.80 1.49700 81.5
10 40.426 2.26
11 36.576 6.95 1.59551 39.2
12 -76.990 (variable)
13 (SSP1) ∞ 0.50
14 (Aperture SP) ∞ 0.50
15 31.195 1.00 1.83400 37.2
16 15.838 3.79 1.51742 52.4
17 61.117 0.15
18 28.366 3.00 1.67270 32.1
19 366.598 (variable)
20 85.928 4.01 1.49700 81.5
21 -22.195 0.35
22 -22.104 0.80 1.83481 42.7
23 88.064 0.81
24 38.049 3.69 1.67270 32.1
25 -46.614 0.50
26 (SSP2) ∞ 1.15
27 110.524 0.80 1.83481 42.7
28 13.389 3.94 1.49700 81.5
29 56.474 0.15
30 21.374 5.03 1.49700 81.5
31 -24.002 0.10
32 -49.555 1.00 1.80 400 46.6
33 14.867 6.06 1.58313 59.4
34 * -54.784 (variable)
35 (FC2) ∞

Aspheric data 3rd surface
K = 0.000 A 4 = 5.82898e-006 A 6 = -1.43491e-008 A 8 = 2.99848e-011
A10 = -2.87674e-014 A12 = 1.21227e-017

6th page
K = -1.07646 A 4 = 3.04718e-005 A 6 = -1.30498e-007 A 8 = 7.85119e-010
A10 = -2.43141e-012 A12 = 3.59143e-015 A14 = -2.44438e-018

34th page
K = 2.62355 A 4 = 1.32159e-005 A 6 = -3.88594e-008 A 8 = 3.62573e-010
A10 = -3.24894e-012

Various data
Wide angle Medium telephoto focal length 12.30 17.96 23.60
F number 4.10 4.10 4.10
Half angle of view (degrees) 60.38 50.30 42.51
Image height 21.64 21.64 21.64
Optical total length 167.40 160.30 162.09
BF 38.80 38.80 38.80

d12 29.16 10.63 1.00
d19 4.95 5.24 5.54
d34 0.00 11.13 22.25

Zoom lens group data group Focal length
L1 -19.14
2a 49.76
2b 73.18
2c -642.52
LR 37.87

Focus movement (object distance infinity → closest distance (300mm))
Group travel
2a 3.206
2b -0.317

L1 1st lens group LR Rear group L2a 2a lens group L2b 2b lens group L2c 2c lens group

Claims (12)

In order from the object side to the image side, the first lens unit L1, which has a negative refractive power, has one or more lens units, and is composed of a rear group having a positive refractive power as a whole. During zooming from the wide-angle end to the telephoto end A zoom lens in which an interval between the first lens group and the rear group is shortened,
The rear group includes, in order from the object side to the image side, a second a lens group having a positive refractive power, a second b lens group having a positive refractive power, and a second c lens group having a positive or negative refractive power,
When focusing from infinity to the closest distance, the 2a lens group moves to the image side, the 2b lens group moves to the object side, the focal length of the 2a lens group is f2a, and the 2b lens group When the focal length is f2b,
1.1 <f2b / f2a <3.0
A zoom lens satisfying the following conditional expression: When the amount of movement of the second lens group in focusing from infinity to the closest distance is DF1, and the amount of movement of the second lens group in focusing from infinity to the closest distance is DF2.
−0.50 <DF2 / DF1 <−0.05
The zoom lens according to claim 1, wherein the following conditional expression is satisfied. When the focal length of the rear group at the wide angle end is fR,
0.7 <f2a / fR <3.0
The zoom lens according to claim 1, wherein the following conditional expression is satisfied. When the focal length of the second c lens group is f2c and the focal length of the rear group at the wide angle end is fR,
−0.5 <fR / f2c <0.5
The zoom lens according to claim 1, wherein the following conditional expression is satisfied. When the focal length of the entire system at the wide angle end is fw
2.5 <f2a / fw <6.0
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 total lens length at the telephoto end is TDLt,
0.06 <| f1 | / TDLt <0.25
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 rear group at the wide angle end is fR,
1.2 <fR / | f1 | <3.0
The zoom lens according to claim 1, wherein the following conditional expression is satisfied.   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 a lens group, the second b lens group, and the second c lens group move along different paths. The zoom lens according to claim 1, wherein the zoom lens moves to a side.   During zooming from the wide-angle end to the telephoto end, the first lens group moves along a convex locus toward the image side, the second a lens group moves toward the object side, and the second b lens group and the second c lens group. 8 moves toward the object side along a different locus from the second a lens group, and the second b lens group and the second c lens group move along the same locus. Zoom lens described in 1. The 2a lens group includes, in order from the object side to the image side, a cemented lens in which a negative lens and a positive lens are cemented, and a positive lens.
The second b lens group includes, in order from the object side to the image side, a positive lens, a negative lens, and a positive lens.
The second c lens group includes, in order from the object side to the image side, a cemented lens in which a negative lens and a positive lens are cemented, a positive lens, and a cemented lens in which a negative lens and a positive lens are cemented. The zoom lens according to any one of 1 to 9.   The first lens group includes four meniscus negative lenses having a convex object-side surface, a biconcave negative lens, and a positive lens in order from the object side to the image side. The zoom lens according to any one of 1 to 10.   An image pickup apparatus comprising the zoom lens according to claim 1.