JP2006195064A - Photographing optical system and imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compact photographing optical system capable of securing telecentric property with respect to a comparatively large imaging device, even though the system is a zoom optical system. <P>SOLUTION: The photographing optical system includes, in order from the side of an object to be photographed, a 1st lens group (G1) having negative power, a 2nd lens group (G2) having positive power, and a 3rd lens group (G3) having positive power, zooming is performed by shifting the 1st lens group (G1), the 2nd lens group (G2) and the 3rd lens group (G3), and focusing is performed by shifting the 3rd lens group (G3). The 3rd lens group (G3) is constituted of a meniscus lens (L7) having negative power and a lens (L8) having positive power. Provided that the focal distance of the 1st lens group (G1) is expressed by f1 and the focal distance of the 3rd lens group (G3) is expressed by f3, the relation of 0.7≤¾f1/f3¾≤2.0 is satisfied. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a photographing optical system and an imaging apparatus, and more particularly to a photographing optical system having a variable focal length.

  In recent years, digital cameras equipped with an image sensor such as a CCD (Charge Coupled Device) or a CMOS (Complementary Metal-Oxide Semiconductor) that convert an optical image into an electric signal instead of a silver salt film have been widely used. The number of pixels of the image sensor tends to increase year by year, and accordingly, a photographic optical system that forms an image of light from the imaging target on the image sensor is required to be compact but have higher performance. It has become. In general, since the photographing optical system of a digital camera is a zoom optical system that can change the focal length, a compact zoom optical system that does not cause deterioration in image quality during zooming is particularly desired.

  Furthermore, the ability of semiconductor elements to generate image data representing captured images by processing the output signals of the image sensor has advanced, and personal computers, mobile computers, mobile phones, personal digital assistants (PDAs), etc. It is also common to have a zoom optical system built in or externally attached to information processing equipment. For this reason, the demand for a high-performance and compact zoom optical system is increasing.

  As such a zoom optical system, the first lens group having negative optical power, the second lens group having positive optical power, and the third lens group having positive optical power in order from the object side. Many so-called negative-positive-positive three-component systems have been proposed. The negative positive / positive three-component zoom optical system has a feature that the number of constituent lenses is small, the mechanism for moving the lenses is simple, and it is suitable for downsizing.

  A large number of microlenses corresponding to each pixel of the image sensor are provided on the front surface of the image sensor, and the exit pupil of the photographing optical system must be aligned with the pupil of the microlens. For this reason, the exit pupil of the photographing optical system needs to be separated from the image plane to some extent, and the principal rays of the light beams incident on each microlens need to be parallel (that is, telecentric) or close to each other.

In the negative-positive-positive three-component zoom optical system, the third lens group has a positive power so as to maintain telecentricity, but the image surface tends to fall to the under side. For the correction, it has been proposed to include a negative power lens in the third lens group (see, for example, Patent Documents 1 to 3).
Japanese Patent No. 3433734 US Pat. No. 6,532,114 US Pat. No. 6,308,011

  However, in the zoom optical systems of Patent Document 1 and Patent Document 2, since the negative lens of the third lens group has a concave surface on the image side, the position of off-axis light at the positive lens of the third lens group is the optical axis. When the image sensor is large, it becomes difficult to ensure telecentricity. In addition, the zoom optical system of Patent Document 3 has a problem that it becomes large because the power of the first lens group is weak.

  The present invention has been made in view of such a problem, and provides a compact photographing optical system that can ensure telecentricity even with a relatively large image pickup device while being a zoom optical system. The purpose is to do. It is another object of the present invention to provide a small and high-performance imaging device provided with such a photographing optical system.

In order to achieve the above object, according to the present invention, a photographing optical system that forms an image of light from a photographing target on an image sensor includes a first lens group having negative power and a positive power in order from the photographing target side. A meniscus lens having a negative power convex toward the imaging element side in order from the imaging target side, and at least a third lens group having a positive power and a third lens group having a positive power It includes a lens having a positive power convex toward the object side, moves the first lens group, the second lens group, and the third lens group to change the focal length, and satisfies the relationship of the following expression (1). Shall.
0.7 ≦ | f1 / f3 | ≦ 2.0 (1)
Here, f1 is the focal length of the first lens group, and f3 is the focal length of the third lens group.

  Formula 1 defines an appropriate range of the balance of optical powers of the first lens group and the third lens group. If the value of | f1 / f3 | exceeds the upper limit of Expression 1, it is difficult to make the front lens diameter small by largely bending off-axis light in the first lens group. Conversely, if the value of | f1 / f3 | does not reach the lower limit of Equation 1, it becomes difficult to correct negative distortion that occurs at the wide-angle end.

  By including a negative lens and a positive lens in the third lens group, it is possible to correct the tilt of the image plane that occurs in the positive lens of the third lens group toward the object to be imaged, and further, off-axis light with the negative lens. As a result, the telecentricity can be easily ensured even when the image sensor is large. In addition, the negative lens is a meniscus lens that is convex toward the imaging element side, and the positive lens is convex toward the object to be imaged, thereby increasing the distance between the negative lens and the positive lens at a position away from the optical axis. And off-axis light can be further increased.

If the relationship of the following formula 1 ′ is satisfied instead of the formula 1, a higher-performance photographing optical system is obtained.
0.7 ≦ | f1 / f3 | ≦ 1.0 (1)

Furthermore, it is preferable to satisfy the relationship of the following formula 2.
0.2 ≦ | (C3o−C3s) / (C3o + C3s) | ≦ 1 Equation 2
Here, C3o and C3s are the radii of curvature of the imaging target side surface and imaging device side surface of the meniscus lens having negative power included in the third lens group, respectively.

  Expression 2 defines an appropriate range of the surface shape of the negative lens of the third lens group. If the value of | (C3o−C3s) / (C3o + C3s) | does not reach the lower limit of Equation 2, the off-axis light jumping up by the negative lens becomes small, and it is difficult to ensure telecentricity when the imaging device is large. Become. Conversely, if the upper limit of Equation 2 is exceeded, the angle of off-axis light incident on the positive lens will increase, and it will be necessary to increase the power of the positive lens in order to bend the light beam, and the image plane will fall to the subject side. It becomes easy.

If the relationship of the following equation 2 ′ is satisfied instead of the equation 2, a higher-performance photographing optical system is obtained.
0.3 ≦≦ | (C3o−C3s) / (C3o + C3s) | ≦ 0.6 Equation 2 ′

  It is preferable that at least one of the surface on the imaging target side and the surface on the imaging element side of the lens having positive power convex toward the imaging target side included in the third lens group is an aspherical surface. By providing the positive lens with an aspherical surface, it is possible to more favorably correct image plane distortion generated in the positive lens.

In that case, it is preferable to further satisfy the relationship of the following Expression 3.
−5 × 10 ⁻³ ≦ φ · (Ns−No) · [d {X (y) −X0 (y)} / dy] ≦ 0
... Formula 3
Where φ is the power of the surface on the image sensor side of the lens having positive power included in the third lens group (unit: 1 / mm), and No and Ns have positive power included in the third lens group, respectively. The refractive index of the medium located on the imaging target side and the medium located on the imaging element side across the aspherical surface of the lens, y is the distance from the optical axis of the lens having positive power included in the third lens group, and X ( y) is a sag at a distance y of the aspherical surface of the lens having positive power included in the third lens group, and X0 (y) is a reference spherical surface of the aspherical surface of the lens having positive power included in the third lens group. Sag Y ′ at the distance y is the maximum image height. Note that y ≦ Y ′. The surface power is the reciprocal of the focal length, and here the unit is 1 / mm.

  Expression 3 defines an appropriate range of the aspheric surface shape of the positive lens of the third lens group. That the value of the central equation is less than the upper limit of Equation 3, that is, 0 or less, indicates that the power of the aspheric surface becomes weaker as the distance from the optical axis increases. As a result, it is possible to correct an image plane that has fallen to the photographing target side. Further, if the value of the central expression does not reach the lower limit of Expression 3, the power of the peripheral part of the aspheric surface becomes too weak, and it becomes difficult to ensure telecentricity.

If the relationship of the following expression 3 ′ is satisfied instead of expression 3, a higher-performance photographing optical system can be obtained.
−2 × 10 ⁻³ ≦ φ · (Ns−No) · [d {X (y) −X0 (y)} / dy] ≦ 0
... Formula 3 '

  It is preferable that the third lens group includes only the two lenses. In order to reduce the size of the zoom optical system, it is preferable to use a rear focus that performs focus adjustment with a lens group closest to the image sensor. In that case, by configuring the third lens group for focus adjustment with only two lenses, the driving force required for focus adjustment can be reduced and focus adjustment can be performed quickly. become.

Moreover, it is preferable to satisfy the relationship of the following formula 4.
2.3 ≦ (ft / fw) · (Lt / Lw) ≦ 4 (4)
Here, ft and fw are the focal lengths of the entire photographing optical system at the telephoto end and the wide-angle end, respectively, and Lt and Lw are the lengths of the entire photographing optical system at the telephoto end and the wide-angle end, respectively.

  Expression 4 defines a preferable range of the relationship between the zoom ratio and the total length of the optical system. If the value of (ft / fw) · (Lt / Lw) does not reach the lower limit of Expression 4, the zoom ratio becomes too small or the total length at the wide-angle end becomes long. When the zoom ratio is too small, the significance as a zoom optical system is lowered. If the total length at the wide-angle end becomes long, the interval between the lens groups is reduced when not in use, and the lens groups at the time of activation are set to the position at the wide-angle end at the time of activation. As a result, the amount of movement increases and time is required for activation. If the value of (ft / fw) · (Lt / Lw) exceeds the upper limit of Expression 4, the total length at the telephoto end becomes long and the size is increased.

If a relationship of the following expression 4 ′ is satisfied instead of expression 4, a more compact photographing optical system is obtained.
2.3 ≦ (ft / fw) · (Lt / Lw) ≦ 3 Equation 4 ′

  In order to achieve the above object, in the present invention, an imaging apparatus also includes an imaging element and any one of the above-described imaging optical systems.

  In the photographing optical system of the present invention, since the balance of the optical powers of the first lens group and the third lens group is appropriate, it is possible to suppress the negative distortion that tends to occur at the wide-angle end without increasing the front lens. it can. In addition, since the third lens group includes a meniscus lens having a negative power convex toward the imaging element side and a lens having a positive power convex toward the imaging target side, the image surface is directed toward the imaging target side. The fall can be prevented, and it becomes easy to ensure telecentricity even when the image pickup device is large. The image pickup apparatus of the present invention including the photographing optical system having such a feature is a small and high-performance apparatus.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. An appearance of the digital camera 1 according to the first embodiment is schematically shown in FIG. In FIG. 1, (a) is a perspective view showing a front surface and an upper surface, and (b) is a rear view. The digital camera 1 has a main body 10 and a lens barrel 11 attached to the main body 10. The lens barrel 11 is composed of a plurality of stages, and is configured to be movable in the front-rear direction so that it projects forward of the main body 10 when photographing and can be accommodated in the main body 10 when not photographing. The lens barrel 11 houses and holds the photographing optical system 12.

  The imaging optical system 12 guides light from the imaging target to the imaging device 21 (see FIG. 2) accommodated in the main body 10 and forms an image on the imaging device 21. The focal length of the photographing optical system 12 is variable, that is, the photographing optical system 12 is a zoom optical system.

  The digital camera 1 has an optical finder objective window 13a and a flash light emitting unit 14 on the front, a power button 15 and a shutter release button 16 on the upper surface, an eyepiece window 13b, a display unit 17, a zoom button 18 and other operations on the back. A button 19 is provided. The optical viewfinder provides an optical image of the subject to be photographed, and the flash light emitting unit 14 emits flash light that illuminates the subject to be photographed. The power button 15 is operated for instructing the supply and stop of power to each unit operating with power, including the image sensor 21, and the shutter release button 16 is operated for instructing to capture a recording image.

  The display unit 17 is composed of a liquid crystal display, and displays various information such as a photographed image, the setting status of the digital camera 1 and operation guidance. The zoom button 18 is operated to set the focal length of the photographing optical system 12. When one end of the zoom button 18 is pressed, the focal length of the photographic optical system 12 changes in the increasing direction, the photographic angle of view is narrowed, and the photographic magnification is increased. When the other end portion of the zoom button 18 is pressed, the focal length of the photographic optical system 12 is changed in a decreasing direction, the photographic field angle is wide, and the photographic magnification is small. Of the range in which the focal length of the photographing optical system 12 can be set, the longest end is called the telephoto end, and the shortest end is called the wide-angle end. The operation buttons 19 are operated for various settings of the digital camera 1.

  FIG. 2 schematically shows the configuration of the digital camera 1. In addition to the photographing optical system 12 and the display unit 17, the digital camera 1 includes an imaging element 21, a signal processing unit 22, a recording unit 23, an operation unit 24, a photographing optical system driving unit 25, and a control unit 26. The image sensor 21 is a CCD area sensor and outputs a signal indicating the amount of received light for each pixel. The signal processing unit 22 processes the output signal of the image sensor 21 and generates image data representing the captured image. The recording unit 23 records the image data generated by the signal processing unit 22 on a detachable recording medium 23a, and reads the image data from the recording medium 23a for reproducing and displaying the image. The operation unit 24 is a general term for the above-described buttons 16 to 19, and transmits user operations to the control unit 26.

  The photographic optical system drive unit 25 has a transmission mechanism (not shown) that transmits several motors and driving force thereof to the lens group of the photographic optical system 12, and determines the focal length and focal position of the photographic optical system 12. Set. The control unit 26 controls each unit according to an instruction given via the operation unit 24.

  The configuration of the photographing optical system 12 is shown in FIG. The photographing optical system 12 includes a first lens group G1, a second lens group G2, and a third lens group G3 in order from the photographing target side.

  The first lens group G1 includes two lenses L1 and L2, and has a negative optical power as a whole. The second lens group G2 includes four lenses L3, L4, L5, and L6, and has a positive optical power as a whole. The third lens group G3 includes two lenses L7 and L8, and has a positive optical power as a whole.

  Of the two lenses L7 and L8 of the third lens group G3, the lens L7 located closer to the photographing target is a meniscus lens having negative optical power and convex toward the image sensor 21 side. The lens L8 located closer to the imaging element 21 is a biconvex lens having positive optical power. In addition, the lens L8 should just have the positive power convex toward the imaging | photography object side at least.

  A diaphragm S having a variable aperture diameter is provided between the first lens group G1 and the second lens group G2. The diaphragm S moves together with the second lens group G2. In addition, a low-pass filter F and a cover glass C are disposed immediately before the image sensor 21. The low-pass filter F and the cover glass C are in close contact.

  Reference numerals r1 to r20 illustrated in FIG. 3 are surfaces of the lenses L1 to L11, the diaphragm S, the filter F, and the cover glass C. Of the two surfaces of the same lens (filter), the one with the smaller numerical value of the sign is the surface closer to the object to be photographed. For example, the lens L2 has a surface r3 and a surface r4, but the surface r3 is located on the imaging target side, and the surface r4 is located on the imaging element 21 side. Note that the surface of the cover glass C on the imaging target side is the same as the surface 19 of the filter F on the imaging element 21 side. The diaphragm S has only one surface r5. The medium before and after the surface r5 of the stop S is air, and naturally the refractive index does not change before and after the surface r5.

  The surface r2 of the lens L1, the surfaces r12 and r13 of the lens L6, and the surfaces r16 and r17 of the lens L8 are all aspherical surfaces. Further, the lens L4 and the lens L5 are bonded, and an adhesive is present between the surface r9 and the surface r10.

  The arrows shown in FIG. 3 represent the positions of the lens groups G1 to G3 during zooming. The base end of the arrow corresponds to the wide-angle end, and the tip corresponds to the telephoto end. Zooming is performed by moving the first lens group G1, the second lens group G2, and the third lens group G3 and changing their intervals. The third lens group G3 is also responsible for prevention of focus position fluctuations accompanying zooming, that is, focusing. The filter F and the cover glass C are fixed.

  The focal lengths at the wide-angle end and the telephoto end are 7.20 mm and 20.44 mm, respectively, and thus the zoom ratio is 2.84. The F numbers at the wide-angle end and the telephoto end are 2.71 and 5.07, respectively. Further, the F number when the focal length is an intermediate 12.13 mm is 3.63.

  The construction data of the photographing optical system 12 is shown in Table 1. In Table 1, the axial top surface spacing of each row is the spacing between the surface of the row and the surface of the next row, and the refractive index and Abbe number of each row are also the refraction of the medium between the surface of the row and the surface of the next row. Rate and Abbe number (omitted for air). The refractive index and Abbe number are for the d-line. The unit of distance is mm. In addition, with respect to the axial top surface distance that changes due to zooming, values at the wide-angle end, the intermediate focal length, and the telephoto end are shown in order from the left. For aspheric surfaces, an asterisk (* mark) is added to the end of the reference numeral.

[Table 1]
Surface Curvature Radius Axis Top Surface Refractive Index Abbe Number
r1 164.676 1.000 1.80610 40.74
r2 * 6.811 3.050
r3 13.196 1.731 1.92286 20.88
r4 30.263 14.900〜 7.110〜 2.000
r5 ∞ 0.758
r6 14.348 1.282 1.88300 40.79
r7 69.358 0.100
r8 8.800 3.054 1.80420 46.50
r9 -22.882 0.010 1.51400 42.83
r10 -22.882 1.500 1.84666 23.78
r11 7.559 1.000
r12 * -22.769 1.300 1.52510 56.38
r13 * -12.897 3.250-10.320-19.436
r14 -13.000 1.000 1.51742 52.15
r15 -43.263 0.100
r16 * 18.662 2.924 1.52510 56.38
r17 * -12.452 4.928 ~ 3.332 ~ 1.642
r18 ∞ 0.700 1.54426 69.60
r19 ∞ 0.500 1.51633 64.14
r20 ∞

The aspherical surface is defined by the following formula 5.
X (H) = C · H ² / {1+ (1−ε · C ² · H ² ) ^1/2 } + ΣAk · H ^k Formula 5
Here, H is the height in the direction perpendicular to the optical axis, X (H) is the sag at the position of height H, that is, the amount of displacement in the optical axis direction (reference to the surface vertex), C is the paraxial curvature, ε Is a quadratic surface parameter, k is the order of an aspheric surface, and Ak is a k-th order aspheric coefficient. Table 2 shows data relating to the aspheric surface.

[Table 2]
Surface r2
ε = 1.0000
A4 = -0.25603448 × 10 ^-3 A6 = -0.62583992 × 10 ^-5 A8 = 0.91116042 × 10 ^-7
A10 = -0.47316015 × 10 ^-8
Surface r12
ε = 1.0000
A4 = -0.12550298 × 10 ^-3 A6 = 0.10364119 × 10 ^-3 A8 = -0.30296689 × 10 ^-5
A10 = 0.56671291 × 10 ^-7
Surface r13
ε = 1.0000
A4 = 0.54295054 × 10 ^-3 A6 = 0.10630235 × 10 ^-3 A8 = -0.23401219 × 10 ^-5
A10 = 0.86519545 × 10 ^-7
Surface r16
ε = 1.0000
A4 = -0.93410702 × 10 ^-4 A6 = -0.32590549 × 10 ^-5 A8 = 0.53595403 × 10 ^-6
A10 = -0.15864702 × 10 ^-7
Surface r17
ε = 1.0000
A4 = 0.21635682 × 10 ^-3 A6 = -0.17554883 × 10 ^-4 A8 = 0.11656038 × 10 ^-5
A10 = -0.25039133 × 10 ^-7

  When the focal length of the first lens group G1 is represented by f1 and the focal length of the third lens group G3 is represented by f3, | f1 / f3 | = 0.636. Therefore, the relationship of the above-described formula 1 is satisfied, and the relationship of the formula 1 'is also satisfied.

  When the curvature radii of the surface r14 on the imaging target side and the surface r15 on the imaging element 21 side of the meniscus lens L7 having negative power included in the third lens group G3 are represented by C3o and C3s, respectively, | (C3o-C3s ) / (C3o + C3s) | = 0.54. Therefore, the relationship of Expression 2 is satisfied, and the relationship of Expression 2 'is also satisfied.

  Further, the power of the surface r17 on the imaging element 21 side of the lens L8 having positive power included in the third lens group G3 is φ (unit: 1 / mm), and the aspherical surface r16 of the lens L8 is sandwiched on the imaging target side. The refractive indexes of the medium (air) and the medium (lens L8) located on the imaging element 21 side are respectively No and Ns, the distance from the optical axis of the lens L8 is y, and the sag at the distance y of the aspherical surface r16 is X ( y) When the sag at the distance y of the reference spherical surface of the aspherical surface r16 is represented by X0 (y) and the maximum image height is represented by Y ′, the relationship of the above-described Expression 3 is satisfied within the range of y ≦ Y ′. The relationship of equation 3 ′ is also satisfied. The maximum image height Y ′ is 4.5 mm.

  The power of the surface r17 on the imaging element 21 side of the lens L8 having positive power included in the third lens group G3 is φ, the medium (lens L8) located on the imaging target side with the aspheric surface r17 of the lens L8 interposed therebetween, and the imaging The refractive index of the medium (air) located on the element 21 side is No and Ns, the distance from the optical axis of the lens L8 is y, the sag at the distance y of the aspheric surface r17 is X (y), and the reference spherical surface of the aspheric surface r17. Even if the sag at the distance y is expressed as X0 (y), the relationship of Expression 3 is satisfied within the range of y ≦ Y ′, and the relationship of Expression 3 ′ is also satisfied.

  Table 3 shows some values of φ · (Ns−No) · [d {X (y) −X0 (y)} / dy] corresponding to the distance y for the aspheric surface r16. Similar values are shown in Table 4.

[Table 3]
Surface r16
y φ · (Ns−No) · [d {X (y) −X0 (y)} / dy]
0.54 -4.8 × 10 ^-7
1.08 -4.6 × 10 ^-6
1.62 −1.8 × 10 ⁻⁵
2.16 -4.9 × 10 ^-5
2.70-9.6 × 10 ⁻⁵
3.24 -1.5 × 10 ^-4
3.78 −2.2 × 10 ⁻⁴
4.32 −4.3 × 10 ⁻⁴

[Table 4]
Surface r17
y φ · (Ns−No) · [d {X (y) −X0 (y)} / dy]
0.56 -3.2 × 10 ^-6
1.12 -2.3 × 10 ^-5
1.68−6.7 × 10 ⁻⁵
2.24-1.3 × 10 ⁻⁴
2.80 -2.4 × 10 ^-4
3.36 -4.2 × 10 ^-4
3.92-7.2 × 10 ⁻⁴
4.48-9.6 × 10 ⁻⁴

  Further, the focal lengths of the entire photographic optical system 12 at the telephoto end and the wide-angle end are ft and fw, respectively, and the entire lengths of the photographic optical system 12 at the telephoto end and the wide-angle end (including the low-pass filter F and the cover glass C). When expressed by Lt and Lw, respectively, (ft / fw) · (Lt / Lw) = 2.84. Therefore, the relationship of the above-described formula 4 is satisfied, and the relationship of the formula 4 'is also satisfied.

  Aberrations of the photographing optical system 12 are shown in FIG. In FIG. 4, (a) is at the wide-angle end, (b) is at the above intermediate focal length, and (c) is at the telephoto end. The spherical aberration line d is the d-line aberration, and the line g is the g-line aberration. Line SC represents the unsatisfactory amount of the sine condition. Astigmatism lines DM and DS are aberrations on the meridional surface and the sagittal surface, respectively. The unit is percentage only for the horizontal axis of the distortion, and mm for all other axes.

  In the photographic optical system 12 of the digital camera 1 of the present embodiment, the maximum image height is set to be as large as 4.5 mm so as to be compatible with the large image sensor 21, but as shown in FIG. It is suppressed well and has high imaging characteristics. Moreover, even if the total length includes the cover glass C, it is about 40 mm, and is small.

  Hereinafter, a digital camera according to another embodiment will be described. However, since the configuration other than the photographing optical system is the same as that of the first embodiment, a duplicate description will be omitted, and only the photographing optical system will be described. In FIGS. 5 to 10 shown below, the same notation method as in FIGS. 3 and 4 is adopted. The definition of the aspherical surface is in accordance with the above-mentioned formula 5. In Table 5, Table 6, Table 8, Table 9, Table 11, and Table 12, the same notation method as in Table 1 and Table 2 is adopted.

  FIG. 5 shows a configuration of the photographing optical system 12 of the digital camera 2 according to the second embodiment. The photographing optical system 12 of the digital camera 2 includes a first lens group G1, a second lens group G2, and a third lens group G3 in order from the photographing target side.

  The first lens group G1 includes two lenses L1 and L2, and has a negative optical power as a whole. The second lens group G2 includes four lenses L3, L4, L5, and L6, and has a positive optical power as a whole. The third lens group G3 includes two lenses L7 and L8, and has a positive optical power as a whole.

  Of the two lenses L7 and L8 of the third lens group G3, the lens L7 located closer to the photographing target is a meniscus lens having negative optical power and convex toward the image sensor 21 side. The lens L8 located closer to the imaging element 21 is a biconvex lens having positive optical power. In addition, the lens L8 should just have the positive power convex toward the imaging | photography object side at least.

  A diaphragm S is provided between the second lens group G2 and the third lens group G3. The diaphragm S moves together with the second lens group G2. In addition, a low-pass filter F and a cover glass C are disposed immediately before the image sensor 21.

  The surface r2 of the lens L1, the surfaces r12 and r13 of the lens L6, and the surfaces r16 and r17 of the lens L8 are all aspherical surfaces. Further, the lens L4 and the lens L5 are bonded, and an adhesive is present between the surface r9 and the surface r10.

  Zooming is performed by moving the first lens group G1, the second lens group G2, and the third lens group G3. The third lens group G3 also controls focusing. The filter F and the cover glass C are fixed.

  The focal lengths at the wide-angle end and the telephoto end are 7.20 mm and 20.45 mm, respectively, and thus the zoom ratio is 2.84. The F numbers at the wide-angle end and the telephoto end are 2.70 and 5.07, respectively. Further, the F number when the focal length is an intermediate 12.14 mm is 3.62.

  Table 5 shows construction data of the photographing optical system 12 and Table 6 shows data related to the aspherical surface.

[Table 5]
Surface Curvature Radius Axis Top Surface Refractive Index Abbe Number
r1 -116.371 1.000 1.80610 40.74
r2 * 6.526 2.410
r3 13.335 2.063 1.84666 23.78
r4 86.272 14.900〜 7.139〜 2.000
r5 ∞ 0.752
r6 14.317 1.322 1.80420 46.50
r7 132.387 0.100
r8 8.800 3.790 1.71300 53.94
r9 -14.729 0.010 1.51400 42.83
r10 -14.729 1.158 1.76182 26.61
r11 7.747 1.000
r12 * -21.030 1.300 1.52510 56.38
r13 * -12.856 2.975〜10.163〜19.309
r14 -13.000 1.000 1.58913 61.25
r15 -27.473 0.100
r16 * 22.408 2.806 1.52510 56.38
r17 * -12.394 5.047 ~ 3.361 ~ 1.612
r18 ∞ 0.700 1.54426 69.60
r19 ∞ 0.500 1.51633 64.14
r20 ∞

[Table 6]
Surface r2
ε = 1.0000
A4 = -0.37039953 × 10 ^-3 A6 = -0.97602247 × 10 ^-5 A8 = 0.20554819 × 10 ^-6
A10 = -0.85065389 × 10 ^-8
Surface r12
ε = 1.0000
A4 = -0.15450877 × 10 ^-3 A6 = 0.12056378 × 10 ^-3 A8 = -0.57126916 × 10 ^-5
A10 = 0.18520003 × 10 ^-6
Surface r13
ε = 1.0000
A4 = 0.49392921 × 10 ^-3 A6 = 0.12651561 × 10 ^-3 A8 = -0.55058164 × 10 ^-5
A10 = 0.24724400 × 10 ^-6
Surface r16
ε = 1.0000
A4 = -0.56639147 × 10 ^-4 A6 = -0.11227892 × 10 ^-4 A8 = 0.99272284 × 10 ^-6
A10 = -0.26348660 × 10 ^-7
Surface r17
ε = 1.0000
A4 = 0.26833965 × 10 ^-3 A6 = -0.28028 360 × 10 ^-4 A8 = 0.16872221 × 10 ^-5
A10 = -0.35364982 × 10 ^-7

  When the focal length of the first lens group G1 is represented by f1, and the focal length of the third lens group G3 is represented by f3, | f1 / f3 | = 0.734. Therefore, the relationship of the above-described formula 1 is satisfied, and the relationship of the formula 1 'is also satisfied.

  When the curvature radii of the surface r14 on the imaging target side and the surface r15 on the imaging element 21 side of the meniscus lens L7 having negative power included in the third lens group G3 are represented by C3o and C3s, respectively, | (C3o-C3s ) / (C3o + C3s) | = 0.36. Therefore, the relationship of Expression 2 is satisfied, and the relationship of Expression 2 'is also satisfied.

  Further, the power of the surface r17 on the imaging element 21 side of the lens L8 having positive power included in the third lens group G3 is φ (unit: 1 / mm), and the aspherical surface r17 of the lens L8 is sandwiched between the imaging target side. The refractive indexes of the medium (lens L8) and the medium (air) located on the imaging element 21 side are respectively No and Ns, the distance from the optical axis of the lens L8 is y, and the sag at the distance y of the aspheric surface r17 is X ( y) When the sag at the distance y of the reference spherical surface of the aspherical surface r17 is represented by X0 (y) and the maximum image height is represented by Y ′, the relationship of the above-described Expression 3 is satisfied within the range of y ≦ Y ′. The relationship of equation 3 ′ is also satisfied. The maximum image height Y ′ is 4.5 mm.

  Table 7 shows some values of φ · (Ns−No) · [d {X (y) −X0 (y)} / dy] corresponding to the distance y for the aspheric surface r17.

[Table 7]
Surface r17
y φ · (Ns−No) · [d {X (y) −X0 (y)} / dy]
0.56 -4.0 × 10 ^-6
1.12 -2.8 × 10 ^-5
1.68-7.4 × 10 ⁻⁵
2.24-1.3 × 10 ⁻⁴
2.80 −2.0 × 10 ⁻⁴
3.36 -3.3 × 10 ^-4
3.92-5.3 × 10 ⁻⁴
4.48 −5.5 × 10 ⁻⁴

  Further, the focal lengths of the entire photographic optical system 12 at the telephoto end and the wide-angle end are ft and fw, respectively, and the entire lengths of the photographic optical system 12 at the telephoto end and the wide-angle end (including the low-pass filter F and the cover glass C). When expressed by Lt and Lw, respectively, (ft / fw) · (Lt / Lw) = 2.84. Therefore, the relationship of the above-described formula 4 is satisfied, and the relationship of the formula 4 'is also satisfied.

  The aberrations of the photographing optical system 12 are shown in FIG. In the photographic optical system 12 of the digital camera 2 of the present embodiment, the maximum image height is set to be as large as 4.5 mm so as to be compatible with the large image sensor 21, but as shown in FIG. It is suppressed well and has high imaging characteristics. Moreover, even if the total length includes the cover glass C, it is about 43 mm, and is small.

  FIG. 7 shows a configuration of the photographing optical system 12 of the digital camera 2 according to the third embodiment. The photographing optical system 12 of the digital camera 2 includes a first lens group G1, a second lens group G2, and a third lens group G3 in order from the photographing target side.

  The first lens group G1 includes two lenses L1 and L2, and has a negative optical power as a whole. The second lens group G2 includes four lenses L3, L4, L5, and L6, and has a positive optical power as a whole. The third lens group G3 includes two lenses L7 and L8, and has a positive optical power as a whole.

  Of the two lenses L7 and L8 of the third lens group G3, the lens L7 located closer to the photographing target is a meniscus lens having negative optical power and convex toward the image sensor 21 side. The lens L8 located closer to the imaging element 21 is a biconvex lens having positive optical power. In addition, the lens L8 should just have the positive power convex toward the imaging | photography object side at least.

  A diaphragm S is provided between the second lens group G2 and the third lens group G3. The diaphragm S moves together with the second lens group G2. In addition, a low-pass filter F and a cover glass C are disposed immediately before the image sensor 21.

  The surface r2 of the lens L1, the surfaces r12 and r13 of the lens L6, and the surface r17 of the lens L8 are all aspheric. Further, the lens L4 and the lens L5 are bonded, and an adhesive is present between the surface r9 and the surface r10.

  Zooming is performed by moving the first lens group G1, the second lens group G2, and the third lens group G3. The third lens group G3 also controls focusing. The filter F and the cover glass C are fixed.

  The focal lengths at the wide-angle end and the telephoto end are 7.20 mm and 20.44 mm, respectively, and thus the zoom ratio is 2.84. The F numbers at the wide-angle end and the telephoto end are 2.71 and 5.07, respectively. The F number when the focal length is an intermediate 12.13 mm is 3.62.

  Table 8 shows construction data of the photographing optical system 12 and Table 9 shows data related to the aspheric surface.

[Table 8]
Surface Curvature Radius Axis Top Surface Refractive Index Abbe Number
r1 169.842 1.000 1.80610 40.74
r2 * 6.816 3.080
r3 13.297 1.730 1.92286 20.88
r4 30.774 14.900〜 7.067〜 2.000
r5 ∞ 0.757
r6 14.416 1.285 1.88300 40.79
r7 72.808 0.100
r8 8.800 3.015 1.80420 46.50
r9 -23.170 0.010 1.51400 42.83
r10 -23.170 1.500 1.84666 23.78
r11 7.554 1.000
r12 * -23.363 1.300 1.52510 56.38
r13 * -13.217 3.293 to 10.344 to 19.526
r14 -13.000 1.000 1.51742 52.15
r15 -47.681 0.100
r16 17.703 2.933 1.52510 56.38
r17 * -12.589 4.927〜 3.367〜 1.594
r18 ∞ 0.700 1.54426 69.60
r19 ∞ 0.500 1.51633 64.14
r20 ∞

[Table 9]
Surface r2
ε = 1.0000
A4 = -0.26148557 × 10 ^-3 A6 = -0.58401159 × 10 ^-5 A8 = 0.72058082 × 10 ^-7
A10 = -0.43433267 × 10 ^-8
Surface r12
ε = 1.0000
A4 = -0.11292224 × 10 ^-4 A6 = 0.67571853 × 10 ^-4 A8 = 0.36094608 × 10 ^-5
A10 = -0.41515219 × 10 ^-6
Surface r13
ε = 1.0000
A4 = 0.65316790 × 10 ^-3 A6 = 0.67395081 × 10 ^-4 A8 = 0.48211735 × 10 ^-5
A10 = -0.42115797 × 10 ^-6
Surface r17
ε = 1.0000
A4 = 0.30217167 × 10 ^-3 A6 = -0.86670357 × 10 ^-5 A8 = 0.31088404 × 10 ^-6
A10 = -0.44180523 × 10 ^-8

  When the focal length of the first lens group G1 is represented by f1 and the focal length of the third lens group G3 is represented by f3, | f1 / f3 | = 0.636. Therefore, the relationship of the above-described formula 1 is satisfied, and the relationship of the formula 1 'is also satisfied.

  When the curvature radii of the surface r14 on the imaging target side and the surface r15 on the imaging element 21 side of the meniscus lens L7 having negative power included in the third lens group G3 are represented by C3o and C3s, respectively, | (C3o-C3s ) / (C3o + C3s) | = 0.57. Therefore, the relationship of Expression 2 is satisfied, and the relationship of Expression 2 'is also satisfied.

  Further, the power of the surface r17 on the imaging element 21 side of the lens L8 having positive power included in the third lens group G3 is φ (unit: 1 / mm), and the aspherical surface r17 of the lens L8 is sandwiched between the imaging target side. The refractive indexes of the medium (lens L8) and the medium (air) located on the imaging element 21 side are respectively No and Ns, the distance from the optical axis of the lens L8 is y, and the sag at the distance y of the aspheric surface r17 is X ( y) When the sag at the distance y of the reference spherical surface of the aspherical surface r17 is represented by X0 (y) and the maximum image height is represented by Y ′, the relationship of the above-described Expression 3 is satisfied within the range of y ≦ Y ′. The relationship of equation 3 ′ is also satisfied. The maximum image height Y ′ is 4.5 mm.

  Table 10 shows some values of φ · (Ns−No) · [d {X (y) −X0 (y)} / dy] corresponding to the distance y for the aspheric surface r17.

[Table 10]
Surface r17
y φ · (Ns−No) · [d {X (y) −X0 (y)} / dy]
0.56 -4.6 × 10 ^-6
1.12 −3.5 × 10 ⁻⁵
1.68 -1.1 × 10 ^-4
2.24 -2.5 × 10 ^-4
2.80 −4.5 × 10 ⁻⁴
3.36-7.3 × 10 ⁻⁴
3.92 −1.1 × 10 ⁻³
4.48 −1.6 × 10 ⁻³

  Further, the focal lengths of the entire photographic optical system 12 at the telephoto end and the wide-angle end are ft and fw, respectively, and the entire lengths of the photographic optical system 12 at the telephoto end and the wide-angle end (including the low-pass filter F and the cover glass C). When expressed by Lt and Lw, respectively, (ft / fw) · (Lt / Lw) = 2.84. Therefore, the relationship of the above-described formula 4 is satisfied, and the relationship of the formula 4 'is also satisfied.

  The aberration of the photographing optical system 12 is shown in FIG. In the photographic optical system 12 of the digital camera 3 of the present embodiment, the maximum image height is set to be as large as 4.5 mm so as to be compatible with the large image sensor 21, but as shown in FIG. It is suppressed well and has high imaging characteristics. Moreover, even if the total length includes the cover glass C, it is about 43 mm, and is small.

  FIG. 9 shows the configuration of the photographing optical system 12 of the digital camera 2 according to the fourth embodiment. The photographing optical system 12 of the digital camera 2 includes a first lens group G1, a second lens group G2, and a third lens group G3 in order from the photographing target side.

  The first lens group G1 includes two lenses L1 and L2, and has a negative optical power as a whole. The second lens group G2 includes four lenses L3, L4, L5, and L6, and has a positive optical power as a whole. The third lens group G3 includes two lenses L7 and L8, and has a positive optical power as a whole.

  Of the two lenses L7 and L8 of the third lens group G3, the lens L7 located closer to the photographing target is a meniscus lens having negative optical power and convex toward the image sensor 21 side. The lens L8 located closer to the imaging element 21 is a biconvex lens having positive optical power. In addition, the lens L8 should just have the positive power convex toward the imaging | photography object side at least.

  A diaphragm S is provided between the second lens group G2 and the third lens group G3. The diaphragm S moves together with the second lens group G2. In addition, a low-pass filter F and a cover glass C are disposed immediately before the image sensor 21.

  The surface r2 of the lens L1, the surfaces r12 and r13 of the lens L6, the surface r15 of the lens L7, and r17 of the lens L8 are all aspherical surfaces. Further, the lens L4 and the lens L5 are bonded, and an adhesive is present between the surface r9 and the surface r10.

  Zooming is performed by moving the first lens group G1, the second lens group G2, and the third lens group G3. The third lens group G3 also controls focusing. The filter F and the cover glass C are fixed.

  The focal lengths at the wide-angle end and the telephoto end are 7.09 mm and 20.14 mm, respectively, and thus the zoom ratio is 2.84. The F numbers at the wide-angle end and the telephoto end are 2.72 and 5.07, respectively. Further, the F number when the focal length is an intermediate 11.95 mm is 3.64.

  Table 11 shows construction data of the photographing optical system 12 and Table 12 shows data related to the aspherical surface.

[Table 11]
Surface Curvature Radius Axis Top Surface Refractive Index Abbe Number
r1 213.609 1.000 1.80610 40.74
r2 * 6.780 3.010
r3 13.181 1.743 1.92286 20.88
r4 30.905 14.900〜 7.160〜 2.000
r5 ∞ 0.757
r6 14.061 1.304 1.88300 40.79
r7 100.743 0.100
r8 8.800 3.110 1.72916 54.67
r9 -19.482 0.010 1.51400 42.83
r10 -19.482 1.500 1.80518 25.46
r11 7.611 1.000
r12 * -20.638 1.300 1.52510 56.38
r13 * -11.941 3.084〜10.154〜19.175
r14 -13.000 1.000 1.52510 56.38
r15 * -31.131 0.100
r16 22.260 2.876 1.52510 56.38
r17 * -12.349 4.932 to 3.311 to 1.741
r18 ∞ 0.700 1.54426 69.60
r19 ∞ 0.500 1.51633 64.14
r20 ∞

[Table 12]
Surface r2
ε = 1.0000
A4 = -0.26129900 × 10 ^-3 A6 = -0.67551779 × 10 ^-5 A8 = 0.10193191 × 10 ^-6
A10 = -0.50052335 × 10 ^-8
Surface r12
ε = 1.0000
A4 = -0.89028905 × 10 ^-4 A6 = 0.82433478 × 10 ^-4 A8 = 0.25211291 × 10 ^-5
A10 = -0.36482300 × 10 ^-6
Surface r13
ε = 1.0000
A4 = 0.53420575 × 10 ^-3 A6 = 0.86404099 × 10 ^-4 A8 = 0.21598133 × 10 ^-5
A10 = -0.23926368 × 10 ^-6
Surface r15
ε = 1.0000
A4 = 0.22771042 × 10 ^-3 A6 = -0.10827801 × 10 ^-4 A8 = 0.10265186 × 10 ^-6
A10 = 0.50600610 × 10 ^-8
Surface r17
ε = 1.0000
A4 = 0.78911207 × 10 ^-4 A6 = -0.46349782 × 10 ^-5 A8 = 0.56293440 × 10 ^-6
A10 = -0.13168875 × 10 ^-7

  When the focal length of the first lens group G1 is represented by f1, and the focal length of the third lens group G3 is represented by f3, | f1 / f3 | = 0.729. Therefore, the relationship of the above-described formula 1 is satisfied, and the relationship of the formula 1 'is also satisfied.

  When the curvature radii of the surface r14 on the imaging target side and the surface r15 on the imaging element 21 side of the meniscus lens L7 having negative power included in the third lens group G3 are represented by C3o and C3s, respectively, | (C3o-C3s ) / (C3o + C3s) | = 0.41. Therefore, the relationship of Expression 2 is satisfied, and the relationship of Expression 2 'is also satisfied.

  Further, the power of the surface r17 on the imaging element 21 side of the lens L8 having positive power included in the third lens group G3 is φ (unit: 1 / mm), and the aspherical surface r17 of the lens L8 is sandwiched between the imaging target side. The refractive indexes of the medium (lens L8) and the medium (air) located on the imaging element 21 side are respectively No and Ns, the distance from the optical axis of the lens L8 is y, and the sag at the distance y of the aspheric surface r17 is X ( y) When the sag at the distance y of the reference spherical surface of the aspherical surface r17 is represented by X0 (y) and the maximum image height is represented by Y ′, the relationship of the above-described Expression 3 is satisfied within the range of y ≦ Y ′. The relationship of equation 3 ′ is also satisfied. The maximum image height Y ′ is 4.5 mm.

  Table 13 shows some values of φ · (Ns−No) · [d {X (y) −X0 (y)} / dy] corresponding to the distance y for the aspheric surface r17.

[Table 13]
Surface r17
y φ · (Ns−No) · [d {X (y) −X0 (y)} / dy]
0.56 -1.2 × 10 ^-6
1.12 −9.0 × 10 ⁻⁶
1.68 -2.9 × 10 ^-5
2.24-6.8 × 10 ⁻⁵
2.80 −1.5 × 10 ⁻⁴
3.36 -3.3 × 10 ^-4
3.92-6.4 × 10 ⁻⁴
4.48 −1.0 × 10 ⁻³

  Further, the focal lengths of the entire photographic optical system 12 at the telephoto end and the wide-angle end are ft and fw, respectively, and the entire lengths of the photographic optical system 12 at the telephoto end and the wide-angle end (including the low-pass filter F and the cover glass C). When expressed by Lt and Lw, respectively, (ft / fw) · (Lt / Lw) = 2.84. Therefore, the relationship of the above-described formula 4 is satisfied, and the relationship of the formula 4 'is also satisfied.

  The aberrations of the photographing optical system 12 are shown in FIG. In the photographic optical system 12 of the digital camera 4 of the present embodiment, the maximum image height is set to be as large as 4.5 mm so as to correspond to the large image sensor 21, but as shown in FIG. It is suppressed well and has high imaging characteristics. Moreover, even if the total length includes the cover glass C, it is about 43 mm, and is small.

  In each of the above embodiments, an example of a digital camera that captures a still image has been described. However, the imaging optical system of the present invention is applicable to a digital video camera that captures a moving image, a mobile computer, a cellular phone, an information portable terminal, and the like. It can also be employed in cameras incorporated into information processing equipment.

The perspective view (a) and back view (b) which show typically the appearance of the digital camera of each embodiment. The figure which shows typically the structure of the digital camera of each embodiment. 1 is a diagram illustrating a configuration of a photographing optical system of a digital camera according to a first embodiment. The figure which shows the aberration in the wide angle end (a), intermediate | middle focal distance (b), and telephoto end (c) of the imaging optical system of the digital camera of 1st Embodiment. The figure which shows the structure of the imaging | photography optical system of the digital camera of 2nd Embodiment. The figure which shows the aberration in the wide-angle end (a), intermediate | middle focal distance (b), and telephoto end (c) of the imaging optical system of the digital camera of 2nd Embodiment. The figure which shows the structure of the imaging optical system of the digital camera of 3rd Embodiment. The figure which shows the aberration at the wide angle end (a), intermediate | middle focal distance (b), and telephoto end (c) of the imaging optical system of the digital camera of 3rd Embodiment. The figure which shows the structure of the imaging optical system of the digital camera of 4th Embodiment. The figure which shows the aberration at the wide-angle end (a), intermediate | middle focal distance (b), and telephoto end (c) of the imaging optical system of the digital camera of 4th Embodiment.

Explanation of symbols

1 to 4 Digital camera 10 Camera body 11 Lens barrel 12 Shooting optical system 13a, 13b Optical viewfinder window 14 Flash light emitting unit 15 Power button 16 Shutter release button 17 Display unit 18 Zoom button 19 Operation button 21 Image sensor 22 Signal processing unit 23 Recording unit 23a Recording medium 24 Operation unit 25 Shooting optical system driving unit 26 Control unit G1 to G3 Lens group L1 to L8 Lens S Aperture F Low pass filter C Cover glass r1 to r20 surface

Claims (7)

In a photographic optical system that forms an image of light from a subject on an image sensor,
A first lens group having a negative power, a second lens group having a positive power, and a third lens group having a positive power are provided in order from the imaging target side, and the third lens group is arranged from the imaging target side. In order, the first lens group, the second lens group, and the third lens include a meniscus lens having a negative power convex toward the image sensor side and a lens having a positive power convex toward the imaging target side. When the focal length is changed by moving the group, the focal length of the first lens group is represented by f1, and the focal length of the third lens group is represented by f3.
0.7 ≦ | f1 / f3 | ≦ 2.0
An imaging optical system characterized by satisfying the above relationship. When the curvature radii of the imaging target side surface and the imaging element side surface of the meniscus lens having negative power included in the third lens group are respectively represented by C3o and C3s,
0.2 ≦ | (C3o−C3s) / (C3o + C3s) | ≦ 1
The imaging optical system according to claim 1, wherein the relationship is satisfied.   The at least one of a surface on the imaging target side and a surface on the imaging element side of at least a lens having positive power convex toward the imaging target side included in the third lens group is an aspherical surface. The photographing optical system according to 1. The power on the imaging element side surface of the lens having positive power included in the third lens group is φ (unit: 1 / mm), and the aspherical surface of the lens having positive power included in the third lens group is sandwiched between them. The refractive indexes of the medium located on the imaging object side and the medium located on the imaging element side are No and Ns, respectively, the distance from the optical axis of the lens having positive power included in the third lens group is y, and the third lens group X (y) is the sag at the aspherical distance y of the aspherical lens of the positive lens included in X3, and the sag at the distance y of the aspherical reference sphere of the positive lens included in the third lens group is X0 ( y) When the maximum image height is represented by Y ′, in the range of y ≦ Y ′,
−5 × 10 ⁻³ ≦ φ · (Ns−No) · [d {X (y) −X0 (y)} / dy] ≦ 0
The imaging optical system according to claim 3, wherein the relationship is satisfied.   The photographic optical system according to claim 1, wherein the third lens group includes only the two lenses. When the focal length of the entire photographing optical system at the telephoto end and the wide angle end is represented by ft and fw, respectively, and the length of the entire photographing optical system at the telephoto end and the wide angle end is represented by Lt and Lw, respectively.
2.3 ≦ (ft / fw) · (Lt / Lw) ≦ 4
The imaging optical system according to claim 1, wherein the relationship is satisfied.   An image pickup apparatus comprising: an image pickup element; and the photographing optical system according to claim 1.

Images