JP2016062053A - Zoom lens and imaging device having the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a zoom lens small in the whole lens system and having a wide angle of view and a high zoom ratio, in which high optical performance can be easily obtained over the whole zoom range.SOLUTION: A zoom lens comprises, sequentially from an object side to an image side, first to third lens groups having negative, positive and negative refractive power, respectively, in which each lens group moves upon zooming to vary a distance between adjoining lens groups. A lateral magnification β2w of the second lens group at the wide angle end, a lateral magnification β2t of the second lens group at the telephoto end, a lateral magnification β3w of the third lens group at the wide angle end, and a lateral magnification β3t of the third lens group at the telephoto end, are each suitably set.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a zoom lens, and is particularly suitable as an imaging optical system used in an imaging apparatus such as a surveillance camera, a digital camera, a video camera, and a broadcast camera.

  An imaging optical system used in an imaging apparatus using a solid-state imaging device is required to be a zoom lens having high optical performance that can cope with higher definition of the solid-state imaging device, and having a wide angle of view and a high zoom ratio. Has been.

  In addition, the entire system is required to be a small zoom lens from the viewpoint of portability in the case of a camera and installation in the case of a surveillance camera or the like. As a zoom lens satisfying these demands, a negative lead type zoom lens in which a lens group having a negative refractive power is disposed closest to the object side is known. As a negative lead type zoom lens, it is composed of first to third lens groups having negative, positive, and negative refractive powers in order from the object side to the image side, and a three-group zoom in which all the lens groups move during zooming. Lenses are known (Patent Documents 1 and 2).

JP 2004-333572 A Japanese Patent Laid-Open No. 2007-233045

  The negative lead type three-group zoom lens described above is relatively easy to achieve a wide angle of view and a high zoom ratio while reducing the size of the entire system. However, in order to obtain a zoom lens having such characteristics, it is important to appropriately set the refractive power of each lens group constituting the zoom lens, the lens configuration of each lens group, and the like.

  For example, the imaging magnification of the second lens group at the wide-angle end and the telephoto end, the imaging magnification of the third lens group at the wide-angle end and the telephoto end, the refractive power of the first, second and third lens groups, and the first lens group It is important to appropriately set the lens configuration of the second lens group. If these configurations are inappropriate, it becomes very difficult to obtain a zoom lens having a wide angle of view and a high zoom ratio and high optical performance while reducing the size of the entire system. For example, Patent Document 1 has a zoom ratio of about 4 times and is not necessarily a zoom lens with a high zoom ratio. Also, Patent Document 2 has a zoom ratio of about 3 times, and is not necessarily a zoom lens with a high zoom ratio.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a zoom lens and an image pickup apparatus having the zoom lens in which the entire lens system has a small size, a wide angle of view, a high zoom ratio, and high optical performance can be easily obtained in the entire zoom range.

The zoom lens according to the present invention includes, in order from the object side to the image side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a negative refractive power. A zoom lens in which each lens group moves so that the interval between adjacent lens groups changes,
The lateral magnification of the second lens group at the wide-angle end is β2w, the lateral magnification of the second lens group at the telephoto end is β2t, the lateral magnification of the third lens group at the wide-angle end is β3w, and the third lens group at the telephoto end When the horizontal magnification of β3t,
2.7 <β2t / β2w <5.0
0.52 <(β3t / β3w) / (β2t / β2w) <0.90
It satisfies the following conditional expression.

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

(A), (B) Diagram of the lens cross section and movement trajectory at the wide-angle end and the telephoto end of Example 1 (A), (B), (C) Various aberration diagrams in Example 1 at the wide-angle end, the intermediate zoom position, and the telephoto end FIG. 10 is a diagram of a lens cross section and a movement locus at the wide angle end according to the second embodiment. (A), (B), (C) Various aberration diagrams in Example 2 at the wide-angle end, the intermediate zoom position, and the telephoto end FIG. 12 is a diagram of a lens cross section and a movement locus at the wide angle end according to the third embodiment. (A), (B), (C) Various aberration diagrams at the wide-angle end, the intermediate zoom position, and the telephoto end of Example 3. FIG. 12 is a diagram of a lens cross section and a movement locus at the wide angle end according to the fourth embodiment. (A), (B), (C) Various aberration diagrams of Example 4 at the wide-angle end, the intermediate zoom position, and the telephoto end Embodiment of the digital camera of the present invention Example of surveillance camera of the present invention

  Hereinafter, a zoom lens of the present invention and an image pickup apparatus having the same will be described with reference to the drawings. The zoom lens according to the present invention includes, in order from the object side to the image side, a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a negative refractive power. Each lens unit moves so that the interval between adjacent lens units changes during zooming.

  FIGS. 1A and 1B are lens cross-sectional views at the wide-angle end (short focal length end) and the telephoto end (long focal length end) of the zoom lens according to Embodiment 1 of the present invention. 2A, 2B, and 2C are aberration diagrams at the wide-angle end, the intermediate zoom position, and the telephoto end of the zoom lens according to Embodiment 1 of the present invention. The first embodiment is a zoom lens having a zoom ratio of 6.2 and an aperture ratio of 2.05 to 6.54.

  FIG. 3 is a lens cross-sectional view at the wide-angle end of the zoom lens according to Embodiment 2 of the present invention. FIGS. 4A, 4B, and 4C are aberration diagrams at the wide-angle end, the intermediate zoom position, and the telephoto end of the zoom lens according to the second embodiment of the present invention. Example 2 is a zoom lens having a zoom ratio of 6.8 and an aperture ratio of 2.03 to 5.96. 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. FIGS. 6A, 6B, and 6C are aberration diagrams at the wide-angle end, the intermediate zoom position, and the telephoto end of the zoom lens according to the third exemplary embodiment of the present invention. Example 3 is a zoom lens having a zoom ratio of 9.4 and an aperture ratio of 1.99 to 7.08.

  FIG. 7 is a lens cross-sectional view at the wide-angle end of the zoom lens according to a fourth exemplary embodiment of the present invention. FIGS. 8A, 8B, and 8C are aberration diagrams at the wide-angle end, the intermediate zoom position, and the telephoto end of the zoom lens according to the fourth exemplary embodiment of the present invention. Example 4 is a zoom lens having a zoom ratio of 11.5 and an aperture ratio of 2.02 to 7.69. FIG. 9 is a schematic view of a main part of a digital camera (imaging device) having the zoom lens of the present invention. FIG. 10 is a schematic view of a main part of a surveillance camera (imaging device) having a zoom lens according to the present invention.

  The zoom lens of each embodiment is a photographic lens system used in an imaging apparatus. In the lens cross-sectional view, the left side is the object side (front) and the right side is the image side (rear). The zoom lens of each embodiment may be used in an optical device such as a projector. In this case, the left side is a screen and the right side is a projected image. In the lens cross-sectional view, L1 is a first lens group having negative refractive power (optical power = reciprocal of focal length), L2 is a second lens group having positive refractive power, and L3 is a third lens group having negative refractive power. It is. 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.

  G is an optical block corresponding to an optical filter, a face plate, a quartz low-pass filter, an infrared cut filter, or the like. IP is an image plane, and when used as a photographing optical system of a video camera or a digital still camera, an imaging plane of a solid-state imaging device (photoelectric conversion device) such as a CCD sensor or a CMOS sensor is placed.

  The arrows indicate the movement trajectory of each lens unit during zooming from the wide-angle end to the telephoto end. An arrow 3a related to the third lens unit L3 indicates a movement locus during zooming from the wide-angle end to the telephoto end when focusing at infinity. An arrow 3b indicates a movement locus during zooming from the wide-angle end to the telephoto end when focusing on a short distance. An arrow F related to the third lens unit L3 indicates a moving direction during focusing from infinity to a short distance. Note that focusing may be performed by all or part of the third lens unit L3.

  Among the aberration diagrams, in the spherical aberration diagram, d indicates the d line and g indicates the g line. Fno is an F number. In the astigmatism diagram, ΔM is a meridional image plane, and ΔS is a sagittal image plane. Lateral chromatic aberration is represented by the g-line. ω is a half angle of view (degree). 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 of the range in which the zoom lens unit can move on the optical axis.

  In each example, the first lens unit L1 having a negative refractive power, the second lens unit L2 having a positive refractive power, and the third lens unit L3 having a negative refractive power are sequentially arranged from the object side to the image side. This is a zoom lens having a configuration. When zooming from the wide-angle end to the telephoto end, each lens unit moves as indicated by an arrow. Specifically, during zooming from the wide-angle end to the telephoto end, the first lens unit L1 moves along a locus convex to the image side, the second lens unit L2 monotonously moves to the object side, and the third lens unit L3 Moves to the object side.

  The aperture stop SP is installed in front of the second lens unit L2 or in the second lens unit L2, and is moved integrally with the second lens unit during zooming. The aperture stop SP may be moved independently during zooming. This makes it easy to cut flare rays. Further, regarding the movement locus for zooming of the second lens unit L2 and the third lens unit L3, preferably, in zooming from the wide angle end to the telephoto end, both are monotonously moved in the same direction from the image plane side to the object side. Good trajectory. As a result, it is easy to share the movement trajectory range, and it is easy to downsize the entire system while reducing the total lens length.

  The zoom type of the zoom lens of each embodiment has a lens configuration suitable for zooming by changing the interval between adjacent lens groups, while being a negative lead type that is advantageous for miniaturization with a small lens group configuration. During zooming from the wide-angle end to the telephoto end, zooming is performed by moving the second lens unit L2 and the third lens unit L3 (both a variator and a variable power lens unit). Then, the image plane variation due to zooming is corrected by the first lens unit L1 (compensator, correction lens unit).

  Further, regarding the movement of each lens group, in addition to the zooming action (the lateral magnification ratio between the wide-angle end and the telephoto end) of the second lens group L2, the zooming effect is also positively given to the third lens group L3. Yes. This reduces the increase in the amount of movement of the lens unit during zooming and achieves a high zoom ratio while maintaining the miniaturization of the entire system.

  During focusing, the third lens unit L3 moves. Specifically, during focusing from infinity to a short distance, the third lens unit L3 moves to the object side. This is performed by the third lens unit L3 that easily reduces the lens diameter, thereby reducing the configuration of the lens barrel for focus driving, and is suitable for downsizing the imaging apparatus.

In each embodiment, the lateral magnifications of the second lens unit L2 at the wide-angle end and the telephoto end are β2w and β2t, respectively. The lateral magnifications of the third lens unit L3 at the wide-angle end and the telephoto end are β3w and β3t, respectively. At this time,
2.7 <β2t / β2w <5.0 (1)
0.52 <(β3t / β3w) / (β2t / β2w) <0.90 (2)
The following conditional expression is satisfied.

  Conditional expression (1) appropriately sets the lateral magnification ratio of the second lens unit L2 at the wide-angle end and the telephoto end. Conditional expression (2) appropriately sets a preferable lateral magnification ratio at the wide-angle end and the telephoto end of the second lens unit L2 and the third lens unit L3, that is, a condition for variable magnification sharing. In the zoom lens of each embodiment, in order to achieve a high zoom ratio, the variable power distribution is distributed to the second lens unit L2 and the third lens unit L3, and the amount of movement during zooming is suppressed (the total lens length is suppressed), The entire system is downsized. For this purpose, the zoom ratio of the third lens unit L3 is effectively obtained while a certain amount of zoom ratio is secured by moving the second lens unit L2 during zooming.

  If the upper limit of the conditional expression (1) is exceeded and the variable magnification sharing by the second lens unit L2 is too large, the amount of movement during zooming of the second lens unit L2 increases, the total lens length increases, and the entire system increases. Miniaturization becomes difficult. If the lower limit of the conditional expression (1) is exceeded and the variable power sharing by the second lens unit L2 becomes too small, the third lens unit L3 must obtain the variable power effect instead, and the third lens is used for zooming. The amount of movement of the group L3 increases, making it difficult to downsize the entire system.

  If the variable magnification sharing of the third lens unit L3 becomes too large beyond the upper limit of conditional expression (2), the amount of movement of the third lens unit L3 increases during zooming. In addition, various aberrations occur, and in order to correct this, it is necessary to increase the number of lenses, and it is difficult to reduce the size of the entire system. When the lower limit of conditional expression (2) is exceeded and the variable magnification share of the second lens unit L2 becomes too large, the amount of movement of the second lens unit L2 during zooming increases, the overall lens length increases, and the entire system increases. Miniaturization becomes difficult.

More preferably, the numerical ranges of conditional expressions (1) and (2) should be limited as follows.
2.8 <β2t / β2w <4.8 (1a)
0.53 <(β3t / β3w) / (β2t / β2w) <0.85 (2a)
More preferably, the numerical ranges of the conditional expressions (1a) and (1b) are set as follows.
2.9 <β2t / β2w <4.6 (1b)
0.54 <(β3t / β3w) / (β2t / β2w) <0.75 (2b)

  By adopting the configuration as described above, it is possible to easily obtain a zoom lens having a compact optical system with a high zoom ratio and high optical performance over the entire zoom range. In each embodiment, it is more preferable that at least one of the following conditional expressions is satisfied.

  Let the focal length of the first lens unit L1 be f1. Let the focal length of the second lens unit L2 be f2. Let the focal length of the third lens unit L3 be f3. The focal length of the entire system at the wide-angle end is fw, and the focal length of the entire system at the telephoto end is ft. The first lens unit L1 includes a cemented lens obtained by cementing a positive lens and a negative lens, and the Abbe number of the material of the positive lens of the cemented lens is νd1p, and the Abbe number of the material of the negative lens of the cemented lens is νd1n. The second lens unit L2 includes a plurality of positive lenses, and an average value of Abbe numbers of the materials of the plurality of positive lenses is νd2p.

At this time, it is preferable to satisfy one or more of the following conditional expressions.
−1.6 <(f2 · f3) / (fw · ft) <− 0.3 (3)
−1.08 <f1 / √ (fw · ft) <− 0.60 (4)
−1.30 <f2 / f3 <−0.50 (5)
27.0 <νd1p−νd1n <50.0 (6)
62.0 <νd2p (7)
−0.85 <f3 / ft <−0.10 (8)

  Next, the technical meaning of each conditional expression described above will be described. Conditional expression (3) appropriately sets the refractive powers of the second lens unit L2 and the third lens unit L3. The second lens group L2 and the third lens group L3 are both lens groups responsible for the multiplication effect. For this reason, the refractive powers of the two lens groups are appropriately set to achieve a high zoom ratio while maintaining the miniaturization of the entire system.

  If the total refractive power of the second lens unit L2 and the third lens unit L3 becomes too strong beyond the upper limit value of the conditional expression (3), various aberrations such as spherical aberration and coma increase. If the total refractive power of the second lens unit L2 and the third lens unit L3 becomes too weak beyond the lower limit value of the conditional expression (3), the second lens unit L2 and the third lens unit L3 move during zooming. The amount increases and the total lens length increases.

Preferably, the numerical range of conditional expression (3) is set as follows.
-1.55 <(f2 · f3) / (fw · ft) <− 0.35 (3a)
More preferably, the numerical range of the conditional expression (3a) is set as follows.
-1.55 <(f2 · f3) / (fw · ft) <− 0.40 (3b)
Conditional expression (4) relates to the focal length of the first lens unit L1. Conditional expression (4) appropriately sets the refractive power for correcting the image plane fluctuation (compensator) accompanying zooming while reducing the amount of movement of the first lens unit L1 during zooming.

If the upper limit of conditional expression (4) is exceeded and the negative refractive power of the first lens unit L1 becomes too strong, distortion and field curvature will increase. If the lower limit of conditional expression (4) is exceeded and the negative refractive power of the first lens unit L1 becomes too weak, the amount of movement during zooming increases and the effective diameter of the front lens also increases. It becomes difficult. Preferably, the numerical range of conditional expression (4) is set as follows.
−1.07 <f1 / √ (fw · ft) <− 0.65 (4a)
More preferably, the numerical range of the conditional expression (4a) is set as follows.
−1.06 <f1 / √ (fw · ft) <− 0.70 (4b)

  Conditional expression (5) sets the ratio of the refractive powers of the second lens unit L2 and the third lens unit L3 appropriately. When the upper limit of conditional expression (5) is exceeded and the focal length of the third lens unit L3 becomes longer (when the negative refractive power becomes weaker), zooming is performed to give the third lens unit L3 a predetermined zooming effect. At this time, it is necessary to increase the movement amount. This is not preferable because the total lens length increases. If the lower limit of conditional expression (5) is exceeded and the negative focal length of the third lens unit L3 becomes shorter (when the negative refractive power becomes stronger), various aberrations such as astigmatism and field curvature increase. It becomes difficult to correct various aberrations.

Preferably, the numerical range of conditional expression (5) is set as follows.
−1.20 <f2 / f3 <−0.55 (5a)
More preferably, the numerical range of conditional expression (5a) is set as follows.
−1.00 <f2 / f3 <−0.60 (5b)

  Conditional expression (6) defines the positive lens material and the negative lens material of the cemented lens in which the positive lens and the negative lens constituting the first lens unit L1 are cemented. Conditional expression (6) appropriately sets the material of the cemented lens included in the first lens unit L1 in order to satisfactorily correct chromatic aberration while reducing the size of the entire system. By adopting a cemented lens, lateral chromatic aberration is corrected well at the wide-angle end, and axial chromatic aberration is corrected well at the telephoto end. The Abbe number νd of the material is defined as follows.

The refractive index for the d-line (587.6 nm) is nd, the refractive index for the F-line (486.1 nm) is nF, and the refractive index for the C-line (656.3 nm) is nC. At this time, the Abbe number νd is νd = (nd−1) / (nF−nC).
It is.

If the upper limit of conditional expression (6) is exceeded and the Abbe number difference becomes too large, chromatic aberration is overcorrected. If the lower limit of conditional expression (6) is exceeded and the difference in Abbe number becomes smaller, the chromatic aberration will be undercorrected. Preferably, the numerical range of conditional expression (6) is set as follows.
30.0 <νd1p−νd1n <47.0 (6a)
More preferably, the numerical range of conditional expression (6a) is set as follows.
32.0 <νd1p−νd1n <45.0 (6b)

  Conditional expression (7) is defined for the materials of a plurality of positive lenses included in the second lens unit L2 for zooming in order to correct chromatic aberration that occurs when a high zoom ratio is achieved. Conditional expression (7) is for reducing the fluctuation of longitudinal chromatic aberration during zooming. If the lower limit of conditional expression (7) is exceeded, chromatic aberration will be undercorrected. In particular, axial chromatic aberration increases at the telephoto end. Preferably, the numerical range of conditional expression (7) is set as follows.

64.0 <νd2p (7a)
More preferably, the numerical range of conditional expression (7a) is set as follows.
66.0 <νd2p (7b)

  Conditional expression (8) is mainly for obtaining a zooming effect of a certain level or more with respect to the negative refractive power of the third lens unit L3. When the upper limit of conditional expression (8) is exceeded and the negative refractive power of the third lens unit L3 becomes too strong, various aberrations such as astigmatism and coma increase. If the lower limit of conditional expression (8) is exceeded and the negative refractive power of the third lens unit L3 becomes too weak, the amount of movement of the third lens unit L3 during zooming increases and the entire system becomes larger. . Preferably, the numerical range of conditional expression (8) is set as follows.

−0.75 <f3 / ft <−0.15 (8a)
More preferably, the numerical range of conditional expression (8a) is set as follows.
−0.65 <f3 / ft <−0.18 (8b)
As described above, according to each embodiment, it is possible to easily obtain a zoom lens having a zoom ratio of about 6 to 12 and having a small overall system and high optical performance.

  The lens configuration of each lens group according to the zoom lens of the present invention is as follows. The first lens unit L1, in order from the object side to the image side, joins a negative lens with a concave surface on the image side, a negative lens with a concave surface on the image side, and a positive lens with a convex surface on the object side It consists of a cemented lens. Alternatively, the first lens unit L1 includes, in order from the object side to the image side, a negative lens having a concave surface on the image side, a positive lens having a convex shape on the object side, a negative lens having a concave surface on the image side, and a surface on the object side. Is composed of a cemented lens in which a positive positive lens is cemented.

  The second lens unit L2 includes a positive lens, a negative lens, a positive lens, and a positive lens in order from the object side to the image side. Alternatively, the second lens unit L2 includes a positive lens, a positive lens, a negative lens, a positive lens, and a positive lens in order from the object side to the image side. Alternatively, the second lens unit L2 includes a positive lens, a negative lens, a positive lens, a positive lens, and a positive lens in order from the object side to the image side. The third lens unit L3 includes one negative lens.

  Alternatively, the third lens unit L3 includes a negative lens, a positive lens, a negative lens, and a positive lens in order from the object side to the image side. Alternatively, the third lens unit L3 includes a negative lens, a negative lens, and a positive lens in order from the object side to the image side.

  Next, the lens configuration of each example will be described. Hereinafter, the lens configurations will be described in the order in which they are arranged in order from the object side to the image side unless otherwise specified.

Example 1
The first lens unit L1 includes a negative meniscus lens G11 convex on the object side, a negative lens G12 concave on the image side, and a positive meniscus lens G13 convex on the object side. The negative lens G12 and the positive lens G13 are composed of cemented cemented lenses, and chromatic aberration is favorably corrected by taking the difference in Abbe number of both materials.

  The second lens unit L2 includes a biconvex positive lens G21, a negative meniscus lens G22 that is convex on the object side, a positive meniscus lens G23 that is convex on the object side, and a biconvex G24. The negative lens G22 and the positive lens G23 correct chromatic aberration better by taking a difference in Abbe number of both materials than a cemented cemented lens.

  At this time, both lens surfaces of the positive lens G21 and the image-side lens surface of the positive lens G23 are aspherical. An aspherical surface is appropriately disposed in the second lens unit L2 in which the on-axis light beam that determines the F-number spreads, and the spherical aberration that increases with an increase in the diameter is satisfactorily corrected. The positive lens of the second lens unit L2 uses low-dispersion glass (such that the Abbe number exceeds 70) and corrects chromatic aberration well. The third lens unit L3 includes a meniscus negative lens G31 having a convex image side.

(Example 2)
The first lens unit L1 is the same as that in the first embodiment. The second lens unit L2 includes a biconvex positive lens G21, a positive meniscus lens G22 that is convex on the object side, a negative meniscus lens G23 that is convex on the object side, a positive lens G24 that is biconvex, and a meniscus shape that is convex on the object side. It consists of a positive lens G25. The positive lens G22, the negative lens G23, and the positive lens G24 are made of cemented cemented lenses and correct chromatic aberration well.

  At this time, both surfaces of the positive lens G21 are aspherical, and the positive lens G24 has an aspherical surface on the image side. The positive lens G25 uses ultra-low dispersion glass (such that the Abbe number exceeds 80), and corrects axial chromatic aberration more satisfactorily.

  The third lens unit L3 includes a negative meniscus lens G31 convex on the object side, a positive biconvex lens G32, a negative meniscus lens G33 convex on the image side, and a positive meniscus lens G34 convex on the object side. Yes. At this time, the positive lens G32 and the negative lens G33 are cemented cemented lenses. The third lens unit L3 includes at least one positive lens and at least one negative lens, and has a variable magnification share while correcting aberrations well.

(Example 3)
The first lens unit L1 is the same as that in the first embodiment. The second lens unit L2 includes a biconvex positive lens G21, a negative meniscus lens G22 convex on the object side, a biconvex positive lens G23, and a biconvex positive lens G24. The negative lens G22 and the positive lens G23 are cemented lenses that are cemented. The positive lens G21 has two aspheric surfaces, and the positive lens G23 has an aspheric surface on the image side. The third lens unit L3 includes a negative meniscus lens G31 having a convex object side surface, a negative meniscus lens G32 having a convex image side surface, and a biconvex positive lens G33.

Example 4
The first lens unit L1 includes a negative meniscus lens G11 having a convex object side, a positive meniscus lens G12 having a convex object side, a negative biconcave lens G13, and a positive meniscus lens G14 having a convex object side. Yes. The negative lens G13 and the positive lens G14 are cemented lenses that are cemented.

  The second lens unit L2 includes a biconvex positive lens G21, a negative meniscus lens G22 convex on the object side, a biconvex positive lens G23, a positive meniscus lens G24 convex on the object side, and a meniscus convex on the image side. It is formed by a positive lens G25 having a shape. At this time, both sides of the positive lens G21 are aspherical, the positive lens G23 is aspherical on the image side, and the positive lens G25 is aspherical on both sides. The negative lens G22 and the positive lens G23 are cemented lenses that are cemented.

Ultra-low dispersion glass is used for the positive lens G24. The positive lens G25 has both aspheric surfaces and is made of plastic, and is lighter than glass. Further, when the focal length of the positive lens G25 made of a plastic material is fp, it is preferable that the following condition is satisfied.
3.5 <fp / f2 (A)
According to this, it becomes easy to reduce the focus fluctuation | variation by an environment (temperature change). More preferably, the numerical range of the conditional expression (A) is set as follows.
4.0 <fp / f2 (Aa)

  Since the refractive index change depending on temperature is larger than that of glass, the refractive power of the lens is weakened to give priority to the effect of the aspherical surface. The third lens unit L3 includes a negative meniscus lens G31 convex on the object side, a negative meniscus lens G32 convex on the image side, and a positive meniscus lens G33 convex on the object side. At this time, the negative lens G32 has aspherical surfaces on both sides, thereby favorably correcting off-axis aberrations such as astigmatism. In the first to fourth embodiments, an aspherical surface may be used in a lens made of another glass as appropriate. Moreover, it is good also as a structure which consists of a plastic material suitably and uses an aspherical surface.

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

  In FIG. 9, reference numeral 20 denotes a camera body, and reference numeral 21 denotes a photographing optical system constituted by any of the zoom lenses described in the first to fourth embodiments. Reference numeral 22 denotes a solid-state image sensor such as a CCD sensor or a CMOS sensor that is built in the camera body and receives a subject image formed by the photographing optical system 21. A memory 23 records information corresponding to a subject image photoelectrically converted by the solid-state imaging device 22. Reference numeral 24 is a finder for observing a subject image formed on the solid-state image sensor 22, which is constituted by a display panel such as a liquid crystal display.

  Next, an embodiment of a surveillance camera (imaging device) using the zoom lens of the present invention as an imaging optical system will be described with reference to FIG.

  In FIG. 10, 30 is a surveillance camera body, and 31 is a photographing optical system constituted by any of the zoom lenses described in the first to fourth embodiments. Reference numeral 32 denotes a solid-state imaging device such as a CCD sensor or a CMOS sensor that is built in the camera body and receives a subject image formed by the photographing optical system 31. Reference numeral 33 denotes a memory for recording information corresponding to the subject image photoelectrically converted by the solid-state image sensor 32. Reference numeral 34 denotes a network cable for transferring a subject image photoelectrically converted by the photographed 32.

  As described above, according to each embodiment, it is possible to obtain a zoom lens having a wide field angle and a bright zoom lens that has a small size and a high magnification and has high optical performance over the entire zoom range, and an imaging apparatus having the same.

In each embodiment, the following means configuration may be adopted.
-It is not limited to the shape and the number of glasses shown in the examples, but should be changed as appropriate.
A configuration in which the aperture stop SP is moved independently.
-Move some lenses and lens groups so that they have a component in a direction perpendicular to the optical axis, thereby correcting image blur due to vibration such as camera shake.
-Correct distortion and chromatic aberration with electrical correction means.

  The preferred embodiments of the present invention have been described above, but the present invention is not limited to these embodiments and optical specifications (view angle and Fno), and various modifications and changes can be made within the scope of the gist.

  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, and ri is the radius of curvature of the lens surface. di is a lens thickness and an air space between the i-th surface and the (i + 1) -th surface. ndi and νdi denote the refractive index and Abbe number for the d-line, respectively. * Indicates an aspherical surface. The two surfaces closest to the image side are glass materials such as face plates.

  The reason why the value of d8 is negative in Numerical Example 2 is because the aperture stop SP and the 22nd lens G22 are described in this order. In the numerical value example 4, the value of d8 is negative because the aperture stop SP and the 21st lens G21 are described in this order. K, A4, A6, A8, and A10 are aspherical coefficients.

When the aspherical shape is x with the displacement in the optical axis direction at the position of the height h from the optical axis as x based on the surface vertex,
x = (h ² / R) / [1+ {1− (1 + k) (h / R) ² } ^1/2 ] + A4 · h ⁴ + A6 · h ⁶ + A8 · h ⁸ + A10 · h ¹⁰
It is represented by Where R is the paraxial radius of curvature.

“ ^Ez ” means “10 ^−z ”. Note that the back focus BF is indicated by an air-converted distance from the most image side lens surface to the image surface. The total lens length is a value obtained by adding back focus to the distance from the first lens surface to the final lens surface. The angle of view is a numerical value of a half angle of view (ω) related to a shootable angle of view in consideration of the amount of distortion. Table 1 shows the relationship between the above-described conditional expressions and numerical examples.

[Numerical Example 1]

Surface number rd nd νd
1 * 13.471 0.9 1.85 135 40.1
2 * 8.009 3.72
3 ∞ 0.65 1.69680 55.5
4 9.203 2.12 1.95906 17.5
5 13.086 (variable)
6 * 50.198 1.96 1.55332 71.7
7 * -10.739 3.3
8 (Aperture) ∞ 0.43
9 11.603 0.45 1.91082 35.3
10 4.587 2.64 1.55332 71.7
11 * 19.112 3.5
12 14.375 2 1.60311 60.6
13 -11.117 (variable)
14 -5.59 0.5 1.59522 67.7
15 -17.567 (variable)
16 ∞ 1 1.51633 64.1
17 ∞ 1.26

Aspheric data
First side
K = -1.57310e-001 A 4 = -7.10544e-004 A 6 = 1.18537e-005
A 8 = -9.11729e-008 A10 = 3.27074e-010
Second side
K = 0.00000e + 000 A 4 = -8.88744e-004 A 6 = 1.10941e-005
A 8 = -7.13643e-008
6th page
K = 9.06874e + 001 A 4 = -7.55455e-004 A 6 = -3.97438e-006
A 8 = -4.64585e-007
7th page
K = 0.00000e + 000 A 4 = -2.45568e-004 A 6 = -7.35782e-007
A 8 = -3.70781e-007 A10 = 2.11130e-009
11th page
K = 0.00000e + 000 A 4 = -6.19524e-004 A 6 = -1.22533e-005
A 8 = 5.36529e-007 A10 = -5.74455e-008

Various data
Zoom ratio 6.2
Wide angle Medium telephoto
Focal length 4.2 14.59 26.06
F number 2.05 4.12 6.54
Half angle of view (degrees) 41.9 15.2 8.5
Image height 3.1 3.88 3.88
Total lens length 58.17 46.19 52.00
BF 3.58 12.92 22.17

Distance Wide angle Medium telephoto
d 5 27.62 5.54 1.24
d13 4.8 5.56 6.41
d15 1.66 11 20.25


Each group focal length
1 group -11.0
2 groups 11.6
3 groups -14.0

[Numerical Example 2]

Surface number rd nd νd
1 * 96.381 0.9 1.85 135 40.1
2 * 14.507 2.21
3 ∞ 0.65 1.69680 55.5
4 11.067 1.98 1.95906 17.5
5 17.063 (variable)
6 * 84.063 1.99 1.55332 71.7
7 * -16.512 4.28
8 (Aperture) ∞ -0.67
9 17.324 1.35 1.60 300 65.4
10 43.644 0.45 1.91082 35.3
11 12.634 2.88 1.55332 71.7
12 * -18.604 0.15
13 8.503 1.88 1.49700 81.5
14 36.559 (variable)
15 10.019 0.64 1.91082 35.3
16 4.983 4.34
17 464.201 1.92 1.69895 30.1
18 -5.824 0.5 1.88300 40.8
19 -59.792 1.06
20 8.605 2 1.49700 81.5
21 13.039 (variable)
22 ∞ 1 1.51633 64.1
23 ∞ 1.43

Aspheric data
First side
K = 0.00000e + 000 A 4 = -5.23100e-005 A 6 = 3.49740e-007
A 8 = 5.94687e-009 A10 = -4.66633e-011
Second side
K = 0.00000e + 000 A 4 = -6.24971e-005 A 6 = 3.37915e-007
A 8 = 7.70778e-009
6th page
K = 9.41499e + 001 A 4 = -3.64570e-004 A 6 = 5.93647e-007
A 8 = -4.98713e-008 A10 = 3.47042e-009
7th page
K = 0.00000e + 000 A 4 = -1.11236e-004 A 6 = 1.62728e-006
A 8 = -6.23806e-008 A10 = 3.49706e-009
12th page
K = 0.00000e + 000 A 4 = -1.44714e-004 A 6 = 1.48629e-007
A 8 = -8.47978e-010 A10 = 8.00274e-011


Various data
Zoom ratio 6.8
Wide angle Medium telephoto
Focal length 5.4 19.86 36.69
F number 2.03 3.92 5.96
Half angle of view (degrees) 42.4 13.5 7.3
Image height 4.00 4.65 4.65
Total lens length 61.65 51.56 60.11
BF 3.65 15.13 26.79

Distance Wide angle Medium telephoto
d 5 28.68 5.72 1.39
d14 0.82 2.21 3.42
d21 1.56 13.04 24.7


Each group focal length
1 group -11.4
2 groups 9.6
3 groups -12.9

[Numerical Example 3]

Surface number rd nd νd
1 * 46.57 0.9 1.85 135 40.1
2 * 11.503 3.15
3 1000 0.65 1.69 680 55.5
4 11.399 2.05 1.95906 17.5
5 19.75 (variable)
6 * 58.855 2.59 1.55332 71.7
7 * -10.647 0.15
8 (Aperture) ∞ 4.08
9 90.954 0.45 1.91082 35.3
10 9.777 3.4 1.55332 71.7
11 * -25.474 1.06
12 11.496 2.31 1.49700 81.5
13 -19.314 (variable)
14 6.295 0.44 1.91082 35.3
15 4.75 4.2
16 -6.158 0.5 1.69680 55.5
17 -19.424 0.15
18 24.912 0.76 1.80809 22.8
19 -88.944 (variable)
20 ∞ 1 1.51633 64.1
21 ∞ 1.77

Aspheric data
First side
K = 0.00000e + 000 A 4 = -4.02648e-004 A 6 = 1.12348e-005
A 8 = -9.66643e-008 A10 = 3.03386e-010
Second side
K = 0.00000e + 000 A 4 = -4.26523e-004 A 6 = 9.96940e-006
A 8 = 9.13538e-009
6th page
K = 9.77946e + 001 A 4 = -4.22650e-004 A 6 = -2.34107e-006
A 8 = 4.39550e-008 A10 = -1.20674e-009
7th page
K = 0.00000e + 000 A 4 = 5.03980e-005 A 6 = -9.59450e-007
A 8 = 3.55531e-008
11th page
K = 0.00000e + 000 A 4 = -3.16099e-004 A 6 = 1.37523e-006
A 8 = -3.32856e-008 A10 = 2.07776e-010


Various data
Zoom ratio 9.4
Wide angle Medium telephoto
Focal length 4.2 20.7 39.53
F number 1.99 4.4 7.08
Half angle of view (degrees) 42.6 10.7 5.6
Image height 3.15 3.88 3.88
Total lens length 66.18 62.26 64.07
BF 3.58 18.43 33.36

Distance Wide angle Medium telephoto
d 5 34.87 5.03 0.91
d13 0.89 1.96 2.95
d19 1.15 16 30.93


Each group focal length
1 group -11.6
2 groups 11.0
3 groups -13.1

[Numerical Example 4]
Surface number rd nd νd
1 * 22.136 1.15 1.69350 53.2
2 * 9.914 3.45
3 23.287 1.65 1.91082 35.3
4 47.669 2.36
5 -28.123 0.65 1.69680 55.5
6 15.173 1.66 1.95906 17.5
7 20.577 (variable)
8 (Aperture) ∞ -0.2
9 * 30.833 2.32 1.55332 71.7
10 * -15.179 1.78
11 18.225 0.45 1.83481 42.7
12 6.666 3.09 1.55332 71.7
13 * -59.927 0.15
14 10.213 1.88 1.49700 81.5
15 282.508 0.57
16 * -35.319 1.3 1.52996 55.8
17 * -13.645 (variable)
18 9.673 0.44 1.91082 35.3
19 4.677 4.83
20 * -7.801 0.55 1.69350 53.2
21 * -13.017 0.15
22 11.137 0.74 1.80809 22.8
23 21.084 (variable)
24 ∞ 1 1.51633 64.1
25 ∞ 1.65

Aspheric data
First side
K = 0.00000e + 000 A 4 = -4.51256e-004 A 6 = 6.04592e-006
A 8 = -2.65084e-008 A10 = 4.35018e-011
Second side
K = 0.00000e + 000 A 4 = -5.78199e-004 A 6 = 5.62383e-006
A 8 = -2.04618e-008 A10 = 2.79823e-010
9th page
K = 2.48691e + 001 A 4 = -3.71902e-004 A 6 = -1.05364e-006
A 8 = 1.04323e-007 A10 = -2.80408e-009
10th page
K = 0.00000e + 000 A 4 = 8.65726e-005 A 6 = 6.74462e-007
A 8 = 6.20196e-008
Side 13
K = 0.00000e + 000 A 4 = -2.85427e-004 A 6 = 1.82032e-006
A 8 = 4.56771e-008
A10 = -1.14495e-009
16th page
K = 0.00000e + 000 A 4 = 1.85001e-005 A 6 = 9.63450e-007
A 8 = -6.99446e-009
17th page
K = 0.00000e + 000 A 4 = -7.21698e-006 A 6 = -2.61393e-006
A 8 = 3.07166e-008
20th page
K = 0.00000e + 000 A 4 = -4.19959e-004 A 6 = 6.93449e-006
A 8 = 1.17496e-007
21st page
K = 0.00000e + 000 A 4 = -3.65551e-004 A 6 = 1.01530e-005

Various data Zoom ratio 11.5
Wide angle Medium telephoto
Focal length 4.3 25.13 49.49
F number 2.02 4.7 7.69
Half angle of view (degrees) 41.0 8.8 4.5
Image height 3.1 3.88 3.88
Total lens length 74.16 55.84 69.05
BF 3.56 19.84 36.32

Distance Wide angle Medium telephoto
d 7 40.92 5.2 1.02
d17 0.7 1.82 2.73
d23 1.25 17.53 34.01

Each group focal length
1 group -12.9
2 groups 9.2
3 groups -10.9

L1 First lens group L2 Second lens group L3 Third lens group

Claims (17)

In order from the object side to the image side, 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 negative refractive power are provided. A zoom lens in which each lens group moves to change,
The lateral magnification of the second lens group at the wide-angle end is β2w, the lateral magnification of the second lens group at the telephoto end is β2t, the lateral magnification of the third lens group at the wide-angle end is β3w, and the third lens group at the telephoto end When the horizontal magnification of β3t,
2.7 <β2t / β2w <5.0
0.52 <(β3t / β3w) / (β2t / β2w) <0.90
A zoom lens satisfying the following conditional expression: When the focal length of the second lens group is f2, the focal length of the third lens group is f3, the focal length of the entire system at the wide angle end is fw, and the focal length of the entire system at the telephoto end is ft,
−1.6 <(f2 · f3) / (fw · ft) <− 0.3
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, the focal length of the entire system at the wide angle end is fw, and the focal length of the entire system at the telephoto end is ft,
−1.08 <f1 / √ (fw · ft) <− 0.60
The zoom lens according to claim 1, wherein the following conditional expression is satisfied. When the focal length of the second lens group is f2, and the focal length of the third lens group is f3,
−1.30 <f2 / f3 <−0.50
The zoom lens according to claim 1, wherein the following conditional expression is satisfied. The first lens group includes a cemented lens in which a positive lens and a negative lens are cemented, and the Abbe number of the material of the positive lens of the cemented lens is νd1p, and the Abbe number of the material of the negative lens of the cemented lens is νd1n. ,
27.0 <νd1p−νd1n <50.0
The zoom lens according to claim 1, wherein the following conditional expression is satisfied. When the second lens group has a plurality of positive lenses and the average value of the Abbe numbers of the materials of the plurality of positive lenses is νd2p,
62.0 <νd2p
The zoom lens according to claim 1, wherein the following conditional expression is satisfied. When the focal length of the third lens group is f3 and the focal length of the entire system at the telephoto end is ft,
-0.85 <f3 / ft <-0.10
The zoom lens according to claim 1, wherein the following conditional expression is satisfied.   The first lens group includes, in order from the object side to the image side, a negative lens having a concave surface on the image side, a negative lens having a concave surface on the image side, and a positive lens having a convex surface on the object side. The zoom lens according to any one of claims 1 to 7, wherein the zoom lens includes a cemented lens.   The first lens group includes, in order from the object side to the image side, a negative lens having a concave surface on the image side, a positive lens having a convex shape on the object side, a negative lens having a concave surface on the image side, and a surface on the object side. The zoom lens according to claim 1, wherein the zoom lens includes a cemented lens in which a convex positive lens is cemented.   The zoom lens according to any one of claims 1 to 9, wherein the second lens group includes a positive lens, a negative lens, a positive lens, and a positive lens in order from the object side to the image side. .   The second lens group includes a positive lens, a positive lens, a negative lens, a positive lens, and a positive lens in order from the object side to the image side. Zoom lens.   10. The first lens group according to claim 1, wherein the second lens group includes a positive lens, a negative lens, a positive lens, a positive lens, and a positive lens in order from the object side to the image side. Zoom lens.   The zoom lens according to any one of claims 1 to 12, wherein the third lens group moves toward the object side during focusing from infinity to a short distance.   The zoom lens according to claim 1, wherein the third lens group includes one negative lens.   The zoom lens according to any one of claims 1 to 13, wherein the third lens group includes a negative lens, a positive lens, a negative lens, and a positive lens in order from the object side to the image side. .   The zoom lens according to any one of claims 1 to 13, wherein the third lens group includes a negative lens, a negative lens, and a positive lens in order from the object side to the image side.   An image pickup apparatus comprising: the zoom lens according to claim 1; and a solid-state image pickup device that receives an image formed by the zoom lens.