JP4928248B2 - Zoom lens and imaging apparatus having the same - Google Patents

Description

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

  In recent years, a photographing lens used in an imaging apparatus such as a digital still camera or a video camera is required to be a zoom lens that has high optical performance over the entire screen, is small, and is lightweight.

  As a zoom lens that satisfies these requirements, in order from the object side to the image side, the zoom lens includes a first lens unit L1 having a negative refractive power and a second lens unit having a positive refractive power, and each lens unit is moved for zooming. A negative lead type two-group zoom lens is known (Patent Documents 1 to 3).

  In addition, in order from the object side to the image side, the 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, each lens group is moved. A negative lead type three-group zoom lens that performs zooming is known (Patent Documents 4 and 5).

In such a negative lead type three-group zoom lens, a three-group zoom lens using an aspherical surface to improve optical performance is known (Patent Document 6).
Japanese Patent Laid-Open No. 11-052235 JP 2003-131128 A JP 2004-102111 A JP 2000-147381 A JP 2000-284177 A JP 2001-100098 A

  Since the negative lead type two-group zoom lens can be configured with a relatively small number of lenses, the entire lens system can be easily downsized. Further, the negative lead type three-group zoom lens has a feature that it is easy to achieve a high zoom ratio while achieving miniaturization.

  However, in these negative lead type zoom lenses, the curvature of field around the screen increases at the wide-angle end, and the image quality around the screen tends to deteriorate.

  For this reason, in a negative lead type two-group zoom lens or three-group zoom lens, it is important to appropriately set the refractive power of each lens group and the lens configuration of each lens group. If these are not satisfied, aberration fluctuations around the screen accompanying zooming increase, and it becomes difficult to obtain high optical performance over the entire screen.

  On the other hand, in these zoom lenses, if an aspherical surface is used as a part of the lens system, aberration fluctuations associated with zooming can be reduced, and high optical performance can be easily obtained in the entire zoom range.

  However, it is difficult to manufacture an aspherical surface. For this reason, when using an aspherical surface, it is important to provide the aspherical surface at an appropriate position in the lens system so that the effect of the aspherical surface can be increased with a small number of aspherical surfaces.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a zoom lens that maintains a good optical performance over the entire screen with little variation in curvature of field around the screen in all zoom regions.

The zoom lens of the present invention includes, in order from the object side to the image side, a first lens group having a negative refractive power and a second lens group having a positive refractive power, and the first lens group and the second lens group during zooming. In the zoom lens in which the lens group moves independently, the first lens group includes two or more negative lenses, two or more air lenses, and two or more aspheric surfaces, and the second lens group includes four or more positive lenses. A lens, an aperture stop that moves integrally during zooming, and one or more aspheric surfaces, where the focal length of the first lens group is f1, and the focal length of the second lens group is f2.
1.39 ≦ | f1 / f2 | <2.00
It is characterized by satisfying the following conditions.

  According to the present invention, it is possible to obtain a zoom lens in which, in all zoom regions, there is little variation in curvature of field around the screen, and good optical performance is maintained over the entire screen.

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

  FIG. 1 is a lens cross-sectional view at the wide-angle end (short focal length end) of the zoom lens according to the first exemplary embodiment of the present invention. FIGS. 2A and 2B are aberration diagrams when focusing on an object at infinity at the wide-angle end and the telephoto end (long focal length end) of the zoom lens of Example 1, respectively.

  Example 1 is a zoom lens having a zoom ratio of 2.0 and an aperture ratio of 4.0.

  FIG. 3 is a lens cross-sectional view at the wide-angle end of the zoom lens according to the second embodiment of the present invention. FIGS. 4A and 4B are aberration diagrams when focusing on an object at infinity at the wide-angle end and the telephoto end of the zoom lens of Example 2, respectively. The second embodiment is a zoom lens having a zoom ratio of 1.98 and an aperture ratio of 4.0.

  FIG. 5 is a lens cross-sectional view at the wide-angle end of the zoom lens according to Embodiment 3 of the present invention. 6A and 6B are aberration diagrams when the zoom lens of Example 3 is focused on an object at infinity at the wide-angle end and the telephoto end, respectively. Example 3 is a zoom lens having a zoom ratio of 1.98 and an aperture ratio of 4.0.

  FIG. 7 is a lens cross-sectional view at the wide-angle end of the zoom lens according to the fourth exemplary embodiment of the present invention. FIGS. 8A and 8B are aberration diagrams when the zoom lens of Example 4 is focused on an object at infinity at the wide-angle end and the telephoto end, respectively. Example 4 is a zoom lens with a zoom ratio of 1.97 and an aperture ratio of 4.0.

  FIG. 9 is a schematic diagram of a main part of a digital still camera (imaging device) including the zoom lens of the present invention.

  The zoom lens of each embodiment is a photographic lens system used in the imaging apparatus, and in the lens cross-sectional view, the left side is the object side and the right side is the image side.

  1, 3, 5, and 7, L1 is a first lens unit having negative refractive power (optical power = reciprocal of focal length), and L2 is positive refraction. This is the second lens group of force. 3 and 5, L3 is a third lens group having a positive refractive power.

  SP is an F number determining member (hereinafter also referred to as “aperture stop”) that functions as an aperture stop that determines (limits) an open F number (Fno) light beam. The aperture stop SP is located in the lens system of the second lens unit L2, and moves integrally with the second lens unit L2 during zooming.

FC is a flare-cut stop whose aperture diameter does not change, and is located on the image side of the second lens unit L2. i indicates the order of the lenses from the object side, and Gi is the i-th lens.

IP is an image plane, and when used as a photographing optical system for a video camera or a digital still camera, a photosensitive surface corresponding to an imaging surface of a solid-state imaging device (photoelectric conversion device) such as a CCD sensor or a CMOS sensor is placed. Yes.

  The arrows indicate the movement trajectory of each lens unit and the flare cut stop FC during zooming from the wide-angle end to the telephoto end.

  In the aberration diagrams, d, g, F, and C are d line, g line, F line, and C line in this order. ΔM and ΔS are represented by meridional image surface, sagittal image surface, and lateral chromatic aberration by g-line, F-line, and C-line.

  Fno is an F number. Y is the image height.

  In the zoom lens of Example 1 in FIG. 1, during zooming from the wide-angle end to the telephoto end zoom position, the first lens unit L1 moves so as to draw a part of a convex locus on the image side. The second lens unit L2 moves to the object side integrally with the aperture stop SP. The flare cut stop FC moves so as to draw a part of a convex locus on the image side.

  In the zoom lens of Example 2 in FIG. 3, during zooming from the wide-angle end to the telephoto end zoom position, the first lens unit L1 moves to draw a part of a convex locus on the image side. The second lens unit L2 moves integrally with the aperture stop SP toward the object side. The third lens unit L3 does not move.

  The flare cut stop FC moves so as to draw a part of a convex locus on the image side.

  In the zoom lens of Example 3 in FIG. 5, during zooming from the wide-angle end to the telephoto end zoom position, the first lens unit L1 moves so as to draw a part of a convex locus on the image side.

  The second lens unit L2 is moved to the object side so as to be integrated with the aperture stop SP so that the distance from the first lens unit L1 is small. The third lens unit L3 moves so as to draw a part of a convex locus on the image side.

  The flare cut stop FC moves while drawing a part of a convex locus on the image side.

  In the zoom lens of Example 4 in FIG. 7, during zooming from the wide-angle end to the telephoto end zoom position, the first lens unit L1 moves so as to draw a part of a convex locus on the image side. The second lens unit L2 moves to the object side integrally with the aperture stop SP.

The flare cut stop FC moves so as to draw a part of a convex locus on the object side.

  In each embodiment, the zoom positions at the wide-angle end and the telephoto end refer to zoom positions when the zoom lens unit (second lens unit) is positioned at both ends of a range that moves on the optical axis due to the mechanism.

  In the zoom lens of each embodiment, main zooming is performed by moving the second lens unit L2, and movement of the image point accompanying zooming is corrected by moving the first lens unit L1.

  In Examples 1 and 4, focusing is performed by the first lens unit L1. In Examples 2 and 3, focusing is performed by the first lens unit L1 or the third lens unit L3.

In the zoom lens of each embodiment, the first lens unit having negative refractive power has two or more negative lenses (lens having negative refractive power) , two or more air lenses, and two or more aspheric surfaces. Yes. Here, the air lens means a lens action by an air space sandwiched between two lens surfaces.

  In each embodiment, since the first lens unit L1 is composed of three independent first to third lenses G1 to G3, the number of air lenses is two.

  The air lens formed by the first lens G1 and the second lens G2 has a negative refractive power. The air lens formed by the second lens G2 and the third lens G3 has a positive refractive power.

  Specifically, the first lens unit L1 includes a meniscus negative first lens G1, a biconcave negative second lens G2, and a meniscus positive third lens G3 in order from the object side to the image side. The aspherical surface is an image side surface of the first lens G1 and an image side surface of the third lens G3. By making the surfaces through which light beams of different image heights pass aspherical in this way, the curvature of field and astigmatism at the intermediate image height and the peripheral image height, which are particularly large at the wide-angle end, are corrected. . In addition, the optical performance is corrected without greatly affecting the optical performance in other zoom ranges, and good optical performance is obtained in which there is little variation in field curvature in the entire zoom range.

  The second lens unit L2 having a positive refractive power, in which the aperture stop SP is integrated, has one or more aspheric surfaces.

  In each embodiment, the object side surface of the positive fourth lens G4 closest to the object side in the second lens unit L2 has an aspherical shape. As a result, spherical aberration that increases particularly at the telephoto end is corrected, fluctuations in spherical aberration during zooming are reduced, and good optical performance is obtained over the entire screen.

  Furthermore, the material of the positive fourth lens G4 is made of a material having a high ultraviolet transmittance, so that the aspherical shape is molded with a replica resin. Desired optical performance is obtained by this aspherical surface.

Further, the second lens unit L2 has a positive lens on the 4 or more, thereby to share the correction of the spherical aberration caused in the first lens group L1, has excellent optical performance in the entire screen.

  The aperture stop SP is arranged after the positive fourth lens, the positive fifth lens, and the negative sixth lens are arranged in order from the object side to the image side of the second lens unit L2.

  This facilitates correction of various aberrations.

  In Examples 2 and 3, the third lens unit L3 having a positive refractive power is constituted by a single positive eleventh lens G11. As a result, high optical performance is obtained over the entire zoom range.

In each embodiment, the focal length of the first lens unit L1 is f1, and the focal length of the second lens unit L2 is f2. At this time,
1.39 ≦ | f1 / f2 | <2.00 (1)
Is satisfied.

  Conditional expression (1) relates to the ratio of the refractive powers of the first lens unit L1 and the second lens unit L2, and reduces aberration fluctuations during zooming and obtains high optical performance over the entire zoom range. .

  If the upper limit of conditional expression (1) is exceeded and the refractive power of the first lens unit L1 is weak, the amount of movement of the first lens unit L1 during zooming increases, and the variation in field curvature increases, resulting in a desired change. It becomes difficult to satisfy optical performance.

  If the refractive power of the first lens unit L1 exceeds the lower limit, the amount of variation in spherical aberration during zooming increases, and the optical performance deteriorates.

More preferably, conditional expression (1) is
1.39 ≦ | f1 / f2 | <1.50 (1a)
It is desirable to satisfy the following conditions.

Let the focal length of the second lens unit L2 be f2. Let fw be the focal length of the entire system at the wide-angle end. At this time,
0.90 <f2 / fw <1.60 (2)
Is satisfied.

  Conditional expression (2) shows the range of the focal length of the second lens unit L2, that is, the range of the appropriate refractive power of the second lens unit L2.

  If the upper limit of conditional expression (2) is exceeded and the refractive power of the second lens unit L2 is weak, the amount of movement of the second lens unit L2 during zooming increases, and the entire system increases in size.

  If the lower limit of conditional expression (2) is exceeded and the refractive power of the second lens unit L2 is strong, aberration fluctuations due to zooming are large, and it becomes difficult to maintain good optical performance.

More preferably, conditional expression (2) is
1.10 <f2 / fw <1.40 (2a)
It is desirable to satisfy the following conditions.

The most image side lens of the first lens unit L1 is a positive lens. The Abbe number of the material of this positive lens is ν13. At this time,
30.0 <ν13 (3)
Is satisfied.

  Conditional expression (3) relates to the Abbe number of the material of the positive lens closest to the image side in the first lens unit L1, and is for molding a positive lens having an aspherical shape with a replica resin.

  A material having a small Abbe number of the material of the positive lens beyond the lower limit of conditional expression (3) has a low transmittance in the ultraviolet region, and is difficult to form with a replica resin.

More preferably, conditional expression (3) is 33.0 <ν13 (3a)
It is good to satisfy the conditions.

Let the focal length of the first lens unit L1 be f1. At this time,
1.00 <| f1 / fw | <2.00 (4)
Is satisfied.

  Conditional expression (4) relates to the ratio between the focal length f1 of the first lens unit L1 and the focal length fw at the wide-angle end of the entire system in order to appropriately maintain the refractive power of the first lens unit L1.

  If the upper limit of conditional expression (4) is exceeded and the refractive power of the first lens unit L1 is weak, the imaging magnification at the wide-angle end of the second lens unit L2 becomes small, and the amount of movement in zooming of the first lens unit L1 is small. growing.

  As a result, the variation in field curvature during zooming increases, making it difficult to obtain desired optical performance.

  When the lower limit of conditional expression (4) is exceeded and the refractive power of the first lens unit L1 is strong, the variation in spherical aberration during zooming becomes large, and it becomes difficult to maintain good optical performance.

More preferably, conditional expression (4) is
1.50 <| f1 / fw | <1.90 (4a)
It is desirable to satisfy the following conditions.

  If each conditional expression is satisfied as described above, in the negative lead type two or more zoom lenses, there is little fluctuation of the field curvature during zooming, and good optical performance can be obtained over the entire screen.

  In each of the embodiments described above, a converter lens or a field lens may be added to the object side of the first lens unit L1 and / or the image side of the final lens unit.

  Next, numerical examples 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 i-th surface (i-th surface), di is the distance between the i-th surface and the (i + 1) -th surface, ni, ν i represents a refractive index and an Abbe number based on the d-line of the i-th member, respectively.

In the aspherical shape, when the displacement in the optical axis direction at the position of the height h from the optical axis is x with respect to the surface vertex, x = (h ² / R) / [1+ {1- (h / R ² } ^1/2 ]
+ Ah ² + Bh ⁴ + Ch ⁶ + Dh ⁸
It is represented by However, k is a conic constant, A, B, C, and D are aspherical coefficients, and R is a paraxial radius of curvature.

“E-0x” means “× 10 ^−x ”. f indicates a focal length, and Fno indicates an F number.

  Table 1 shows the relationship between the above-described conditional expressions and the respective examples.

  Next, an embodiment of a digital still camera (image pickup apparatus) using the zoom lens of the present invention as a photographing optical system will be described with reference to FIG.

  In FIG. 9, reference numeral 20 denotes a camera body. Reference numeral 21 denotes a photographing optical system constituted by the zoom lens of the present invention. Reference numeral 22 denotes a solid-state imaging device (photoelectric conversion device) such as a CCD sensor or a CMOS sensor that receives a subject image by the photographing optical system 21. Reference numeral 23 denotes a memory for recording a subject image received by the image sensor 22, and reference numeral 24 denotes a finder for observing the subject image displayed on a display element (not shown).

  The display element is constituted by a liquid crystal panel or the like, and a subject image formed on the image sensor 22 is displayed.

  Thus, by applying the zoom lens of the present invention to an image pickup apparatus such as a digital still camera, a small image pickup apparatus having high optical performance is realized.

Optical cross-sectional view of the zoom lens of Example 1 Aberration diagram when focusing on an object at infinity at the wide-angle end and the telephoto end of the zoom lens of Example 1 Optical sectional view of the zoom lens of Example 2 Aberration diagram when focusing on an object at infinity at the wide-angle end and the telephoto end of the zoom lens of Example 2 Optical sectional view of the zoom lens of Example 3 Aberration diagram when focusing on an object at infinity at the wide-angle end and the telephoto end of the zoom lens of Example 3 Optical sectional view of the zoom lens of Example 4 Aberration diagram when focusing on an object at infinity at the wide-angle end and the telephoto end of the zoom lens of Example 4 Schematic diagram of main parts of an imaging apparatus of the present invention

Explanation of symbols

L1 First lens unit L2 Second lens unit L3 Third lens unit SP Aperture FC Flare cutter aperture IP Image plane Fno F number Y Image height solid line Two-dot chain line in d-line magnification chromatic aberration diagram One-dot chain line in g-line magnification chromatic aberration diagram C Chain line in line magnification chromatic aberration diagram F line ΔM Meridional image plane ΔS Sagittal image plane

Claims (7)

A first lens unit having a negative refractive power and a second lens group having a positive refractive power are provided in order from the object side to the image side, and the first lens group and the second lens group move independently during zooming. In the zoom lens, the first lens group includes two or more negative lenses, two or more air lenses, and two or more aspheric surfaces, and the second lens group is integrated with four or more positive lenses during zooming. When the focal length of the first lens group is f1, and the focal length of the second lens group is f2,
1.39 ≦ | f1 / f2 | <2.00
A zoom lens characterized by satisfying the following conditions: When the focal length of the entire system at the wide angle end is fw,
0.90 <f2 / fw <1.60
The zoom lens according to claim 1, wherein the following condition is satisfied. When the most image side lens of the first lens group is a positive lens, and the Abbe number of the material of the positive lens is ν13,
30.0 <ν13
The zoom lens according to claim 1 or 2, wherein the following condition is satisfied. When the focal length of the entire system at the wide angle end is fw,
1.00 <| f1 / fw | <2.00
The zoom lens according to claim 1, wherein the following condition is satisfied. The first lens group includes, in order from the object side to the image side, a first lens having a negative refractive power, a second lens having a negative refractive power, and a third lens having a positive refractive power. air lens formed by the second lens is a negative refractive power, wherein the second lens air lens formed by the third lens is a positive of claims 1 to 4, characterized in that a refractive power Any one of the zoom lenses. Any one of the zoom lens according to claim 1, wherein the forming an image on a solid-state image device. And any one of the zoom lens according to claim 1 to 6, the imaging apparatus characterized by having a solid-state imaging device for receiving an image formed by the zoom lens.

Images