JP6226610B2 - 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 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

Negative-lead Zumuren's is easy to obtain a wide angle of view and a long back focus. 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 lens group and the amount of movement during focusing from the infinity to the closest distance.

  If these configurations are inappropriate, it becomes very difficult to obtain high optical performance over the entire object distance from infinity to short 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 of the present invention, in order from the object side to the image side, a front group having a negative refractive power and a rear group having positive refractive power, at the telephoto end than at the wide-angle end, of the rear group and the front group The zoom lens has a short interval, and the front group is composed of one lens group that moves integrally during zooming, and the rear group is arranged in order from the object side to the image side and has a positive refractive power. The second a lens group, the second b lens group having a positive or negative refractive power, and the second c lens group having a positive refractive power, and when focusing from infinity to the closest distance, the second a lens group and the second b lens group Move to the image side along different trajectories, the focal length of the 2a lens group is f2a, the focal length of the 2b lens group is f2b, and the amount of movement of the 2a lens group during focusing from infinity to the closest distance DF1, When the amount of movement of the 2b lens group in the focusing to limit near future closest distance and DF2,
0.01 <f2a / | f2b | <0.30
0.05 <DF2 / DF1 <0.50
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 of the present invention, in order from the object side to the image side, a front group having a negative refractive power, and is from the group after the positive refractive power. The distance between the front group and the rear group becomes shorter at the telephoto end than at the wide angle end. Front group Ru negative first lens group refractive power Tona to move integrally during zooming. The rear group includes a second refractive power 2a lens group, a positive or negative refractive power second b lens group, and a positive refractive power second c lens group, which are arranged in order from the object side to the image side. . When focusing ( focusing ) from infinity to the closest distance, both the second a lens group and the second b lens group move along different tracks toward the image side.

  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. Here, the object distance is a distance from the image plane when a numerical example described later is expressed in mm.

  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, LF is a front group of 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 front lens group LF includes a first lens unit L1 having a negative refractive power. The rear group LR includes, in order from the object side to the image side, a second-a lens unit L2a having a positive refractive power, a second-b lens unit L2b having a positive or negative refractive power, and a second-c lens unit L2c having a positive refractive power. Yes.

  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 (flare cut apertures) whose aperture diameter changes in accordance with zooming, and determine the open F number at each zoom position. At the same time, flare light outside the open F number light beam is cut (shielded).

  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, during zooming from the wide-angle end to the telephoto end, as shown by an arrow, the air moves between the front group LF having a negative refractive power and the rear group LR having a positive refractive power so as to be short (small). Specifically, the front group LF moves on the optical axis along a locus that has a convex shape on the image side. The movement of the rear group LR is as follows.

In Example 1 of FIG. 1, the rear group LR moves monotonically as a whole toward the object side. In Example 2 in FIG. 4 and Example 3 in FIG. 7, the 2a lens unit L2a moves monotonously to the object side. Further, the second b lens unit L2b and the second c lens unit L2c move monotonously toward 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. 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 performed efficiently, and the correction of the image plane position by zooming is reliably performed by moving the front lens group LF .

In the front group LF , 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 aspheric 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 disposed in the front group LF .

In a zoom lens having an ultra-wide angle of view as in the present invention, a large amount of negative distortion is generated because a large number of lenses having a strong negative refractive power are disposed in the front lens group LF on the object side. 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. Therefore, in each embodiment, in addition to the two aspheric surfaces described above, the curvature of field is corrected by a third 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 front group LF is the lens configuration as described above.

In the zoom lens of each embodiment, the rear lens group LR having a positive refractive power, in order 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 or negative refractive power, The second c lens unit L2c having a refractive power of 1 mm is used .

  At the time of focusing from infinity to the closest distance, the 2a lens unit L2a and the 2b lens unit L2b move on the optical axis along different paths. At this time, the 2a lens unit L2a mainly performs the function of focusing, and the amount of movement on the optical axis during focusing is such that the 2a lens unit L2a is larger than the 2b lens unit L2b. The second b lens unit L2a is a lens unit having a weak positive or negative refractive power. Even if it is moved on the optical axis, there is little focusing action, and the variation in field curvature that occurs during the focusing by the second a lens unit L2a. Plays the role of correcting.

  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 at the time of focusing of the sagittal image plane is corrected by moving the second b lens unit L2b having a weak refractive power in the same direction as the second a lens unit L2a and in a different locus. As a result, a good photographed image is obtained with less fluctuation of the image plane during focusing from infinity to the closest distance.

  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 loose concave surface facing the image side. Thereby, negative refraction is given to the light beam emitted from the second lens group L2b, and the curvature of field that fluctuates due to the focus of the second lens group L2a having a positive refractive power is generated in the reverse direction for correction.

In each embodiment, the focal length of the second lens group L2a is f2a, and the focal length of the second lens group L2b is f2b. The amount of movement of the 2a lens unit L2a at the time of focusing from infinity to the shortest distance is DF1, and the amount of movement of the 2b lens unit L2b at the time of focusing from infinity to the shortest distance is DF2. At this time,
0.01 <f2a / | f2b | <0.30 (1)
0.05 <DF2 / DF1 <0.50 (2)
The following conditional expression is satisfied. Here, the moving amount refers to a difference in the position of the lens group 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.

  Next, the technical meaning of each conditional expression described above will be described. Conditional expression (1) defines the ratio of the focal length of the 2a lens unit L2a to the focal length of the 2b lens unit L2b, and mainly corrects the variation in field curvature during focusing by the floating of the 2b lens unit L2b. Is to do.

  If the lower limit of conditional expression (1) is exceeded and the absolute value of the refractive power of the second-b lens unit L2b becomes too small, correction of field curvature variation during focusing will be insufficient. If the absolute value of the refractive power of the second lens group L2b exceeds the upper limit of the conditional expression (1), the variation of various aberrations including spherical aberration increases, and the variation of various aberrations is corrected. Becomes difficult.

  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 amount of movement of the 2b lens unit is small relative to the amount of movement of the 2a lens unit L2a during focusing beyond the lower limit of the conditional expression (2), it is insufficient to correct the variation in field curvature during focusing.

  Further, if the amount of movement of the second b lens unit L2b is larger than the amount of movement of the second a lens unit L2a exceeding the upper limit of the conditional expression (2), correction of fluctuations in field curvature during focusing becomes excessive. Not desirable. 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.

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. 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 front lens group LF 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.

0.8 <f2a / fR <3.0 (3)
1.0 <f2c / fR <2.8 (4)
3.0 <f2a / fw <7.0 (5)
0.07 <| 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 (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) defines the ratio of the focal length of the second c lens unit L2c to the focal length of the rear unit LR at the wide-angle 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 conditional expression (4) is exceeded and the refractive power of the second c lens unit L2c becomes too strong, it is difficult to secure a sufficiently long back focus and a large on-axis aberration occurs, which is desirable. Absent. On the other hand, if the refractive power of the second c lens unit L2c becomes too weak beyond the upper limit of conditional expression (4), the total length of the lens becomes longer and the entire system becomes larger, which is not desirable.

  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 front lens unit LF to the total lens length of the entire system at the telephoto end, and while maintaining a sufficiently long back furcus, the entire system is downsized. This is for correcting various aberrations in a well-balanced manner.

If the absolute value of the negative refractive power of the front group LF becomes too large beyond the lower limit of the conditional expression (6), the incident height of light incident on the rear group LR becomes high and the rear group LR is enlarged. Further, the negative aberration generated in the front group LF becomes large, and it becomes difficult to correct this by the rear group LR. If the absolute value of the negative refractive power of the front lens unit LF 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. It becomes difficult.

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 front lens group LF , and mainly reduces the size of the entire system while ensuring a sufficiently long back focus. However, it is for correcting various aberrations in a well-balanced manner. If the absolute value of the negative refractive power of the front group LF is smaller than the refractive power of the rear group LR at the wide angle end 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, if the refractive power of the rear group LR at the wide angle end exceeds the upper limit of the conditional expression (7) and becomes smaller than the absolute value of the negative refractive power of the front group LF , the rear group LR becomes larger. At the same time, the negative aberration generated from the front group LF becomes large and it is difficult to correct this by the rear group LR. In each embodiment, more preferably, the numerical ranges of conditional expressions (1) to (7) are set as follows.

0.012 <f2a / | f2b | <0.250 (1a)
0.10 <DF2 / DF1 <0.40 (2a)
1.0 <f2a / fR <2.5 (3a)
1.2 <f2c / fR <2.5 (4a)
3.5 <f2a / fw <6.5 (5a)
0.08 <| f1 | / TDLt <0.22 (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, the lens units of the front group LF and the rear group LR are configured as follows in order to obtain good optical performance over the entire zoom range and the entire object distance. The 2a lens group is composed of a cemented 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 arranged 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, a positive lens, and a cemented lens in which a negative lens and a positive lens are cemented , which are arranged in order from the object side to the image side.

Also disposed a front unit LF in order from the object side to the image side, four negative meniscus lens having a convex surface on the object side, a biconcave negative lens, and constitutes a positive lens.

Next, the lens configuration of the zoom lens of each embodiment will be described. Example 1 is a negative lead type zoom lens, which is composed of a front group LF having a negative refractive power and a rear group LR having a positive refractive power in order from the object side to the image side. The rear group LR includes a 2a lens unit L2a having a positive refractive power, a second b lens unit L2b having a negative refractive power, and a second c lens unit L2c having a positive refractive power. During zooming from the wide-angle end to the telephoto end, so that the distance of the front unit LF and the rear lens group LR is narrowed (shorter), the front unit LF moves along a locus convex to the image side, of the rear group LR each The lens group moves monotonously on the object side along the same locus.

Example 1 is a two-group zoom lens. The front group LF includes, in order from the object side to the image side, a negative refractive power lens (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 2a lens unit L2a and the 2b lens unit L2b are moved to the image side along different paths on the optical axis. Further, on the object side of the second-a lens unit L2a, an open F-number aperture stop SSP1 and an aperture stop SP are sequentially provided from the object side to the image side. An open F-number aperture stop SSP2 is provided between the second b lens unit L2b and the second c lens unit L2c. The open F-number aperture SSP1 and the open F-number aperture SSP2 have a constant or variable aperture diameter, and play a role as a flare cutter that cuts off the flare components outside of the center F-number at the open F-number. I'm in charge.

  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 front group LF 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 positive refractive power. During zooming from the wide-angle end to the telephoto end, the distance between the front group LF and the rear group LR is reduced.

Specifically, the front group LF 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. At this time, the second a lens unit L2a, the second b lens unit L2b, and the second c lens unit L2c move so that the distance between the second a lens unit L2a and the second b lens unit L2b is larger at the telephoto end than at the wide angle end. .

Example 2 is a three-group zoom lens. The lens configurations of the front group LF 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. Similarly to the first embodiment, an open F number aperture SSP1, an aperture aperture SP, and an open F number aperture SSP2 are sequentially provided from the object side to the image side.

  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 front group LF 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 positive refractive power. Zooming from the wide-angle end to the telephoto end is the same as in the second embodiment. Focusing from infinity to the closest distance is the same as in the first embodiment. Similarly to the first embodiment, an open F number aperture SSP1, an aperture stop SP, and an open F number aperture SSP2 are sequentially provided from the object side to the image side.

  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 * 53.188 3.50 1.77250 49.6
2 32.000 6.73
3 35.627 3.50 1.58313 59.4
4 * 16.207 11.80
5 54.779 2.80 1.85400 40.4
6 * 33.140 7.93
7 118.830 2.00 1.72916 54.7
8 22.931 8.97
9 -71.979 1.70 1.49700 81.5
10 49.831 0.60
11 39.761 7.11 1.83400 37.2
12 -127.521 (variable)
13 (open aperture) ∞ 0.50
14 (aperture stop) ∞ 0.50
15 24.932 1.00 1.91082 35.3
16 13.464 5.51 1.64769 33.8
17 -1170.148 3.28
18 100.975 3.55 1.57099 50.8
19 -28.793 0.71
20 -30.086 0.80 1.91082 35.3
21 45.447 0.20
22 23.544 3.26 1.62588 35.7
23 229.974 2.23
24 (open F stop) ∞ 0.20
25 33.843 0.90 1.83481 42.7
26 12.362 4.41 1.49700 81.5
27 45.544 0.15
28 19.249 6.72 1.49700 81.5
29 -20.840 0.15
30 -42.098 0.90 1.77250 49.6
31 14.095 5.49 1.58313 59.4
32 * -60.703 (variable)
Image plane ∞

Aspheric data 1st surface
K = 0.00000 A 4 = -4.41878e-7 A 6 = -8.28369e-10 A 8 = 2.05804e-12 A10 = -1.25151e-15 A12 = 3.09628e-19

4th page
K = -8.58227e-1 A 4 = -1.61397e-6 A 6 = -2.86033e-8 A 8 = 5.89916e-11 A10 = -8.41661e-14 A12 = 4.28229e-17

6th page
K = -2.39611 A 4 = 1.63159e-5 A 6 = 4.89317e-9 A 8 = 7.75804e-11 A10 = -2.35802e-13 A12 = 3.44658e-16 A14 = 5.34466e-21

32nd page
K = -1.01681e + 2 A 4 = -3.10081e-5 A 6 = 6.01757e-7 A 8 = -4.39086e-9 A10 = 1.78706e-11

Various data Zoom ratio 2.06
Wide angle Medium Telephoto focal length 11.30 19.24 23.30
F number 4.10 4.10 4.10
Half angle of view (degrees) 62.42 48.36 42.88
Image height 21.64 21.64 21.64
Total lens length 169.16 160.12 162.18
BF 38.80 55.14 63.51

d12 33.29 7.90 1.59
d32 38.80 55.14 63.51

Zoom lens group data group Focal length
LF -18.37
L2a 55.95
L2b -3611.18
L2c 70.95
LR 37.84

Focus movement amount (object distance infinity → closest distance (300mm))
Group travel
L2a 3.222
L2b 0.743

(Numerical example 2)
Surface data surface number rd nd νd
1 * 50.378 3.50 1.77250 49.6
2 32.000 7.45
3 35.459 3.50 1.58313 59.4
4 * 17.773 11.80
5 45.510 2.80 1.85400 40.4
6 * 25.722 8.95
7 103.253 2.00 1.72916 54.7
8 25.065 8.55
9 -73.840 1.70 1.49700 81.5
10 45.797 2.26
11 44.800 5.82 1.83400 37.2
12 -129.427 (variable)
13 (open aperture) ∞ 0.50
14 (aperture stop) ∞ 0.50
15 24.481 1.00 1.91082 35.3
16 13.420 5.29 1.66680 33.0
17 233.768 (variable)
18 63.688 3.89 1.51742 52.4
19 -26.894 0.61
20 -28.711 0.80 1.91082 35.3
21 46.145 0.20
22 25.166 3.21 1.62004 36.3
23 653.051 1.98
24 (open F stop) ∞ 0.20
25 34.667 0.90 1.83481 42.7
26 12.581 4.35 1.49700 81.5
27 48.982 0.15
28 19.162 6.57 1.49700 81.5
29 -21.724 0.15
30 -46.236 0.90 1.77250 49.6
31 13.650 5.49 1.58313 59.4
32 * -64.911

Aspheric data 1st surface
K = 0.00000 A 4 = 3.96934e-7 A 6 = -1.36187e-9 A 8 = 1.88321e-12 A10 = -9.56942e-16 A12 = 1.99181e-19

4th page
K = -7.48168e-1 A 4 = 3.44582e-6 A 6 = -2.52605e-8 A 8 = 5.78821e-11 A10 = -8.67650e-14 A12 = 3.85344e-17

6th page
K = -2.04770 A 4 = 1.73955e-5 A 6 = -4.05101e-9 A 8 = 9.81574e-11 A10 = -2.46621e-13 A12 = 2.74939e-16 A14 = 1.87959e-20

32nd page
K = -1.02336e + 2 A 4 = -2.22454e-5 A 6 = 4.78613e-7 A 8 = -3.42086e-9 A10 = 1.42442e-11

Various data Zoom ratio 2.06
Wide angle Medium Telephoto focal length 11.30 17.33 23.30
F number 4.10 4.10 4.10
Half angle of view (degrees) 62.42 51.31 42.88
Image height 21.64 21.64 21.64
Total lens length 170.80 161.34 163.26
BF 38.80 50.91 63.01

d12 33.76 11.68 1.00
d17 3.24 3.74 4.25
d32 38.80 50.91 63.01

Zoom lens group data group Focal length
LF -18.88
L2a 59.69
L2b 2943.94
L2c 69.08
LR 38.06

Focus movement amount (object distance infinity → closest distance (300mm))
Group travel
L2a 3.055
L2b 0.617

(Numerical Example 3)
Surface data surface number rd nd νd
1 * 69.605 3.50 1.77250 49.6
2 32.200 6.34
3 35.597 3.50 1.59201 67.0
4 * 19.479 11.80
5 45.881 2.80 1.85400 40.4
6 * 25.307 9.05
7 109.841 2.00 1.72916 54.7
8 28.484 7.45
9 -70.833 1.70 1.49700 81.5
10 44.224 1.55
11 41.405 5.96 1.83400 37.2
12 -131.030 (variable)
13 (open aperture) ∞ 0.50
14 (aperture stop) ∞ 0.50
15 26.726 1.00 1.91082 35.3
16 13.704 5.17 1.68893 31.1
17 452.034 (variable)
18 70.017 3.14 1.51823 58.9
19 -44.538 0.80 1.91082 35.3
20 48.791 0.20
21 22.189 3.44 1.53172 48.8
22 267.298 2.24
23 (open aperture F) ∞ 0.20
24 35.860 0.90 1.83481 42.7
25 12.903 4.18 1.49700 81.5
26 44.919 0.15
27 18.849 6.18 1.49700 81.5
28 -24.651 0.15
29 -69.813 0.90 1.77250 49.6
30 13.695 4.82 1.58313 59.4
31 * -116.576

Aspheric data 1st surface
K = 0.00000 A 4 = 4.04664e-6 A 6 = -4.01540e-9 A 8 = 3.70230e-12 A10 = -1.71717e-15 A12 = 3.70705e-19

4th page
K = -6.43598e-1 A 4 = 1.10372e-5 A 6 = -2.28093e-8 A 8 = 4.47676e-11 A10 = -1.03206e-13 A12 = 6.29144e-17

6th page
K = -1.69321 A 4 = 1.66924e-5 A 6 = -1.81587e-9 A 8 = 1.66703e-10 A10 = -3.32336e-13 A12 = 1.41157e-16 A14 = 8.30917e-19

No. 31
K = -2.50544e + 2 A 4 = 8.63344e-6 A 6 = 2.12370e-7 A 8 = -1.12171e-9 A10 = 7.78530e-12

Various data Zoom ratio 2.06
Wide angle Medium Telephoto focal length 11.30 17.33 23.30
F number 4.10 4.10 4.10
Half angle of view (degrees) 62.42 51.31 42.88
Image height 21.64 21.64 21.64
Total lens length 164.14 155.40 157.52
BF 38.80 50.59 62.39

d12 32.26 11.20 1.00
d17 2.96 3.49 4.02
d31 38.80 50.59 62.39

Zoom lens group data group Focal length
LF -18.69
L2a 59.65
L2b 480.10
L2c 76.88
LR 36.67

Focus movement amount (object distance infinity → closest distance (300mm))
Group travel
L2a 2.938
L2b 0.773

LF Front group L1 First lens group LR Rear group L2a 2a lens group L2b 2b lens group L2c 2c lens group

Claims (11)

In order from the object side to the image side, a front group having a negative refractive power and a rear group having positive refractive power, at the telephoto end than at the wide-angle end, the zoom lens spacing of the rear group and the front group becomes shorter There,
The front group consists of one lens group that moves integrally during zooming,
Said rear group arranged in this order from the object side to the image side, the 2a lens group having a positive refractive power, the 2b lens group of positive or negative refractive power and a third 2c lens unit having a positive refractive power,
During focusing from infinity to the closest distance, the 2a lens group and the 2b lens group move to the image side along different paths,
The focal length of the 2a lens group is f2a, the focal length of the 2b lens group is f2b, the amount of movement of the 2a lens group in focusing from infinity to the closest distance is DF1, and focusing from infinity to the closest distance is performed. When the movement amount of the second b lens group at DF2 is DF2,
0.01 <f2a / | f2b | <0.30
0.05 <DF2 / DF1 <0.50
A zoom lens satisfying the following conditional expression: When the focal length of the rear group at the wide angle end is fR,
0.8 <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,
1.0 <f2c / fR <2.8
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,
3.0 <f2a / fw <7.0
The zoom lens according to claim 1, wherein the following conditional expression is satisfied. When the focal length of the front group is f1, and the total lens length at the telephoto end is TDLt,
0.07 <| f1 | / TDLt <0.25
The zoom lens according to claim 1, wherein the following conditional expression is satisfied. When the focal length of the front 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 front 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 toward the object side along the same locus. The zoom lens according to claim 1, wherein the zoom lens moves.   During zooming from the wide-angle end to the telephoto end, the front 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 move toward the object side. 7. The apparatus according to claim 1, wherein the second b lens group and the second c lens group move along the same locus, and move toward the object side along a different locus from the second a lens group. Zoom lens. The 2a lens group, disposed in order from the object side to the image side, a cemented lens obtained by cementing a negative lens and a positive lens,
The 2b lens group, disposed in order from the object side to the image side and a positive lens, a negative lens, a positive lens,
Wherein said 2c lens group, disposed in order from the object side to the image side, a cemented lens obtained by cementing a negative lens and a positive lens, wherein the positive lens, characterized in that a cemented lens obtained by cementing a negative lens and a positive lens Item 9. The zoom lens according to any one of Items 1 to 8. The front group, claims, characterized arranged in order from the object side to the image side, a negative lens of four meniscus shape with a convex surface on the object side, a double concave negative lens, that is a positive lens The zoom lens according to any one of 1 to 9.   An image pickup apparatus comprising: the zoom lens according to claim 1; and an image pickup element that receives an image formed by the zoom lens.