JP2012168456A - Imaging optical system and imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an imaging optical system which is suitable for moving image photographing regardless of a large diameter and further, and has excellent optical performance even when a subject distance is changed, and to provide an imaging apparatus.SOLUTION: An imaging optical system 1 comprises a first lens group 11, a second lens group 12, a third lens group 13, and a fourth lens group 14 in order from an object side to an image side. These lens groups 11 to 14 satisfy a conditional expression of Fno≤2.0, the second lens group 12 and the fourth lens group 14 are configured so as to be moved in an optical axis direction, when focusing on a subject, and the second lens group 12 comprises two lenses.

Description

  The present invention relates to an image pickup optical system and an image pickup apparatus including the image pickup optical system.

  In recent years, for example, in digital single-lens reflex camera systems, not only still images but also moving images have been requested. When shooting a movie, it is necessary to perform autofocus continuously at high speed. In order to perform autofocus continuously at high speed, so-called wobbling is performed in which the focus lens group reciprocates (vibrates) at high speed in the optical axis direction. Then, a focus lens that creates a focused state from the out-of-focus state, a non-focused state from the focused state, detects a signal component in a frequency band with a partial image region from the output signal of the image sensor, and becomes a focused state The optimum position of the group is obtained, and the focus lens group is moved to the optimum position. By repeating this series of operations, the focus lens group can be moved to the optimum position. Further, in order to prevent a sense of incongruity such as flicker from occurring, it is necessary to display a moving image at a high speed of, for example, 30 frames / second, and it is basically necessary to perform shooting at the same 30 frames / second. Therefore, in order to perform autofocus on a moving image, it is necessary to continuously wobble the focus lens group at a high speed of 30 Hz.

  2. Description of the Related Art Conventionally, large-aperture imaging optical systems are widely known in which the number of lenses in the focus lens group is three or more. However, when the number of lenses in the focus lens group is three or more, the weight is too heavy for wobbling and is not suitable for moving image shooting.

  For example, in Patent Document 1, a focus lens group that moves in the optical axis direction when focusing on a subject is used as one lens group, and the number of lenses in the focus lens group that includes the one lens group is two. What is comprised is disclosed. In such a focus lens group, since the number of lenses is two, it can be made suitable for wobbling.

JP 2009-186609 A

  However, in the one disclosed in Patent Document 1, since there is one focus lens group that moves in the optical axis direction when focusing on the subject, optical performance is good in shooting when the subject distance changes. There is a tendency to deteriorate significantly. This tendency becomes more prominent as the aperture becomes larger.

  An object of the present invention is to provide an image pickup optical system and an image pickup apparatus that are suitable for moving image shooting with a large aperture and that have good optical performance even when the subject distance changes.

In order to solve the above technical problem, the present invention provides an imaging optical system and an imaging apparatus having the following configurations. Note that the terms used in the following description are defined as follows in this specification.
(A) A refractive index is a refractive index with respect to the wavelength (587.56 nm) of d line | wire.
(B) Abbe number is nd, nF, nC, and Abbe number is νd for d-line, F-line (wavelength 486.13 nm), C-line (wavelength 656.28 nm), respectively.
νd = (nd−1) / (nF−nC)
The Abbe number νd obtained by the definition formula
(C) When the notation “concave”, “convex” or “meniscus” is used for the lens, these represent the lens shape near the optical axis (near the center of the lens).
(D) The notation of optical power (reciprocal of focal length, refractive power) in each single lens constituting the cemented lens is power when both sides of the lens surface of the single lens are air.

  The imaging optical system according to an aspect of the present invention includes a plurality of lens groups in order from the object side to the image side, and the plurality of lens groups satisfy the following conditional expression (1) and match the subject. It includes two lens groups configured to move in the optical axis direction when performing focusing, and one of the two lens groups is configured so that the number of lenses is two or less. This is a characteristic imaging optical system.

Fno ≦ 2.0 (1)
However, Fno is an F number.

  Since the imaging optical system having such a configuration adopts a floating configuration in which the two lens groups move in the optical axis direction when focusing on the subject, the imaging has good optical performance even when the subject distance changes. Can be an optical system. In addition, since one of the two lens groups is configured to have two or less lenses, the one lens group can be made suitable for wobbling for moving image shooting.

  In the imaging optical system according to another aspect of the present invention, the lens group in which the number of lenses is two or less in the imaging optical system described above satisfies the conditional expression (2) below, It is preferable that any one of the two lens groups includes at least a positive lens and a negative lens, and an aperture stop is provided between the two lens groups.

0.9 <| fa / f | <1.7 (2)
Here, fa is the focal length of the lens group configured with the number of lenses being two or less, and f is the focal length of the entire system.

  The conditional expression (2) is an expression that serves as an index of a change in photographing magnification during wobbling. That is, when the focus lens group moves in the optical axis direction, the focal length of the entire lens system changes, and when the change in photographing magnification due to wobbling is large, a sense of incongruity occurs. Therefore, it is necessary to pay attention to the fact that the size of the image corresponding to the subject changes during wobbling, and if it is below the lower limit value, the change in photographing magnification during wobbling becomes large, and there is a high possibility that a sense of incongruity will occur. . On the other hand, if the value exceeds the upper limit value, the amount of movement when focusing on the subject increases and the total length of the imaging optical system becomes longer, which is not preferable.

  In addition, since either one of the two lens groups includes at least a positive lens and a negative lens, various aberrations such as field curvature and lateral chromatic aberration can be favorably corrected.

  In addition, since an aperture stop is provided between the two lens groups, coma can be corrected well.

  An imaging optical system according to another aspect of the present invention is the imaging optical system described above, wherein the surface power is negative in the vicinity of the aperture stop and the center of curvature of the surface is on the aperture stop side. At least one lens configured as described above is provided.

  According to this configuration, an optical system having good optical performance with reduced curvature of field can be obtained without generating coma and the like.

  An imaging apparatus according to an aspect of the present invention includes any one of the above-described imaging optical systems and an imaging element that converts an optical image into an electrical signal, and the imaging optical system is on a light receiving surface of the imaging element. It is possible to form an optical image of an object.

  According to this configuration, it is possible to provide an image pickup apparatus that is suitable for moving image shooting with a large aperture and that has good optical performance even when the subject distance changes.

  According to the present invention, it is possible to provide an imaging optical system and an imaging apparatus that are suitable for moving image shooting with a large aperture and that have good optical performance even when the subject distance changes.

It is a lens sectional view showing the composition typically for explanation of an image pick-up optical system in an embodiment. It is a schematic diagram of one embodiment of an imaging device provided with an imaging optical system. 3 is a cross-sectional view illustrating an arrangement of lens groups in the imaging optical system in Embodiment 1. FIG. FIG. 6 is a diagram illustrating a state of movement of each lens group from the time of shooting an object at infinity to the time of shooting an object at a short distance by the imaging optical system of Example 1. 7 is a cross-sectional view illustrating an arrangement of lens groups in an imaging optical system in Embodiment 2. FIG. FIG. 10 is a diagram illustrating a state of movement of each lens group from the time of photographing an object at infinity to the time of photographing a short distance object in the imaging optical system of Example 2. 6 is a cross-sectional view illustrating an arrangement of lens groups in an imaging optical system in Embodiment 3. FIG. It is a figure which shows the mode of a movement of each lens group at the time of near-distance object imaging | photography from the time of infinite distance object imaging | photography of the imaging optical system of Example 3. FIG. 6 is an aberration diagram when the imaging optical system according to the first embodiment is used for photographing an object at infinity. FIG. 6 is an aberration diagram when the imaging optical system according to the first embodiment is used for photographing a short distance object. FIG. 6 is an aberration diagram when the imaging optical system in Example 2 is used for shooting an object at infinity. FIG. 10 is an aberration diagram when the short-distance object shooting is performed by the imaging optical system according to the second embodiment. FIG. 10 is an aberration diagram when the imaging optical system in Example 3 is used for shooting an object at infinity. FIG. 10 is an aberration diagram when the imaging optical system according to Example 3 is used for photographing a short distance object.

  Hereinafter, an embodiment according to the present invention will be described with reference to the drawings. In addition, the structure which attached | subjected the same code | symbol in each figure shows that it is the same structure, The description is abbreviate | omitted suitably. Further, the number of lenses in the cemented lens is not expressed as one for the entire cemented lens, but is represented by the number of single lenses constituting the cemented lens.

  FIG. 1 is a lens cross-sectional view schematically illustrating the configuration of an imaging optical system in the embodiment.

  The imaging optical system 1 forms an optical image of an object (subject) on the light receiving surface (image surface) of an image sensor Y1 that converts an optical image into an electrical signal. A plurality of lens groups are included in order. As shown in FIG. 1, the imaging optical system 1 of this embodiment includes a first lens group 11 having a positive optical power and a second lens group having a negative optical power in order from the object side to the image side. 12, a third lens group 13 having a positive optical power, and a fourth lens group 14 having a positive optical power. The imaging optical system 1 illustrated in FIG. 1 has the same configuration as an imaging optical system 1A (FIG. 3) of Example 1 described later.

  In FIG. 1, the first lens group 11 is fixed from when shooting an object at infinity to when shooting a short distance object. In order from the object side to the image side, a biconvex positive lens 111 and a positive meniscus lens convex toward the object side. 112 and a biconcave negative lens 113.

  The second lens group 12 moves from when shooting an object at infinity to when shooting a short distance object, and is composed of a positive meniscus lens 121 convex toward the image side and a biconcave negative lens 122 in order from the object side to the image side. Has been. The positive meniscus lens 121 and the negative lens 122 are cemented lenses.

  The third lens group 13 is fixed from the time of object shooting at infinity to the time of shooting an object at a close distance, and in order from the object side to the image side, a positive meniscus lens 131 convex toward the image side, a biconcave negative lens 132, and both sides And a convex positive lens 133.

  The fourth lens group 14 moves from when shooting an object at infinity to when shooting a short distance object, and sequentially from the object side to the image side, a biconvex positive lens 141, a biconcave negative lens 142, and a biconvex positive lens. And a lens 143.

  In the imaging optical system 1, the aperture stop ST moves in the optical axis direction between the positive lens 131 and the negative lens 132 in the third lens group 13, in other words, when focusing on the subject. It is arranged between the second lens group 12 and the fourth lens group 14 configured as described above. The aperture stop ST may be a mechanical shutter.

  In the imaging optical system 1 according to this embodiment, the first lens group 11 to the fourth lens group 14 have a large diameter t that satisfies the following conditional expression (1). When the imaging optical system 1 performs focusing on the subject as described above, the two lens groups of the second lens group 142 and the fourth lens group 142 move in the direction of the optical axis AX. It is configured.

  In addition, in this embodiment, the second lens group 14 is configured so that the number of lenses is two or less, whichever one of the two lens groups moves in the optical axis AX direction.

Fno ≦ 2.0 (1)
However, Fno is an F number.

  In the imaging optical system having such a configuration, the subject distance changes because the two lens groups of the second lens group 12 and the fourth lens group 14 move in the optical axis AX direction when focusing on the subject. Even in this case, an imaging optical system having good optical performance can be obtained.

  Further, the second lens group 12 as one of these two lens groups is configured to have two lenses, so that it can be made suitable for wobbling for moving image shooting.

  In the imaging optical system of this embodiment, the second lens group 12 satisfies the following conditional expression (2), and the fourth lens group 14 as the other of the two lens groups is at least positive. A lens (in this embodiment, two positive lenses 141 and 143) and a negative lens 142 are included, and an aperture stop ST is provided between the second lens group 12 and the fourth lens group 14.

0.9 <| fa / f | <1.7 (2)
Here, fa is the focal length of one of the above (in this embodiment, the second lens group 12), and f is the focal length of the entire system.

  The conditional expression (2) is an expression that serves as an index of a change in photographing magnification during wobbling. In other words, when the focus lens group moves in the optical axis direction, the focal length of the entire lens system changes, resulting in a sense of incongruity when the change in shooting magnification due to wobbling is large. It should be noted that the size of the corresponding image changes, and if it is less than the lower limit value, the change in photographing magnification during wobbling may become large, which may cause a sense of discomfort. On the other hand, if the value exceeds the upper limit value, the amount of movement when focusing on the subject increases and the total length of the imaging optical system becomes longer, which is not preferable.

  The fourth lens group 14 as the other of the two lens groups includes positive lenses 141 and 143 and a negative lens 142, so that various aberrations such as field curvature and lateral chromatic aberration are excellent. Can be corrected.

  In addition, since the aperture stop ST is provided between the second lens group 12 and the fourth lens group 14, coma can be corrected well.

  In this embodiment, the power of the surface 132a is negative near the aperture stop ST, and the center of curvature O of the surface 132a is on the aperture stop ST side (with respect to the aperture stop ST). At least one lens 132 configured so as to have a shape close to a lick is provided.

  According to this configuration, an optical system having good optical performance with reduced curvature of field can be obtained without generating coma and the like.

  In the imaging optical system 1 having such a configuration, when a plastic lens is used, it is a lens molded using a material in which particles having a maximum length of 30 nanometers or less are dispersed in plastic (resin material). Is preferred.

  In general, mixing fine particles with a transparent resin material scatters light and reduces the transmittance, making it difficult to use as an optical material. However, the size of the fine particles should be smaller than the wavelength of the transmitted light beam. The light is not substantially scattered. And although a resin material will have a refractive index falling with a temperature rise, an inorganic particle will raise a refractive index with a temperature rise conversely. For this reason, it is possible to make the refractive index change hardly occur with respect to the temperature change by acting so as to cancel each other by utilizing such temperature dependency. More specifically, by dispersing inorganic fine particles having a maximum length of 30 nanometers or less in a resin material as a base material, a resin material with reduced temperature dependency of the refractive index is obtained. For example, fine particles of niobium oxide (Nb2O5) are dispersed in acrylic. In the imaging optical system 1 having such a configuration, by using a lens made of a plastic material in which such inorganic fine particles are dispersed for at least one lens, a back focus shift due to an environmental temperature change of the imaging optical system 1 is achieved. Can be kept small.

  Such a lens made of a plastic material in which inorganic fine particles are dispersed is preferably molded as follows.

The temperature change n (T) of the refractive index is expressed by Equation 3 by differentiating the refractive index n with respect to the temperature T based on the Lorentz-Lorentz equation. n (T) = ((n2 + 2) × (n2-1)) / 6n × (−3α + (1 / [R]) × (∂ [R] / ∂T)) (3)
Where α is a linear expansion coefficient and [R] is molecular refraction.

  In the case of a resin material, in general, the contribution of the refractive index to the temperature dependence is smaller in the second term than in the first term in Equation 3, and can be almost ignored. For example, in the case of PMMA resin, the linear expansion coefficient α is 7 × 10 −5, and when it is substituted into Equation 3, it becomes n (T) = − 12 × 10 −5 (/ ° C.), which is almost the actual measurement value. Match.

  Specifically, the temperature change n (T) of the refractive index, which was conventionally about −12 × 10 −5 [/ ° C.], can be suppressed to an absolute value of less than 8 × 10 −5 [/ ° C.]. preferable. More preferably, the absolute value is less than 6 × 10 −5 [/ ° C.].

  Therefore, as such a resin material, a polyolefin resin material, a polycarbonate resin material, or a polyester resin material is preferable. In the polyolefin resin material, the refractive index temperature change n (T) is about −11 × 10 −5 (/ ° C.), and in the polycarbonate resin material, the refractive index temperature change n (T) is about −14 × 10 −5 (/ ° C.), and in a polyester resin material, the temperature change n (T) of the refractive index is about −13 × 10 −5 (/ ° C.).

<Description of imaging device incorporating imaging optical system>
Next, a mirrorless type imaging apparatus combined with the imaging optical system 1 described above will be described. FIG. 2 is a block diagram illustrating a configuration of the imaging apparatus according to the embodiment. In FIG. 2, the imaging device Z includes an interchangeable lens device X and an imaging device body Y.

  The interchangeable lens device X is an optical system that can be attached to and detached from the imaging device main body Y. The interchangeable lens device X includes an imaging optical system 1 as shown in FIG. 1 that functions as an imaging lens, and a lens driving device (not shown) that drives a focus lens in the optical axis direction to perform focusing. Composed.

  The imaging device main body Y includes an imaging element Y1, a first display device Y2, a second display device Y3 for a finder, a processing control unit Y4, and an eyepiece Y5. The light beam from the subject is imaged on the light receiving surface of the image sensor Y1 by the imaging optical system 1 and becomes an optical image of the subject.

  The imaging element Y1 converts the optical image of the subject formed by the imaging optical system 1 into an electrical signal (image signal) of R, G, and B color components, and controls processing as an image signal of each color of R, G, and B This is output to the part Y4. The imaging element Y1 is, for example, a two-dimensional image sensor such as a charge-coupled device (CCD) image sensor or a complementary metal-oxide semiconductor (CMOS) image sensor. The image pickup device Y1 is controlled by the processing control unit Y4 to pick up either a still image or a moving image, or to read out an output signal of each pixel in the image pickup device Y1 (horizontal synchronization, vertical synchronization, transfer) and the like. The

  The processing control unit Y4 generates image data of the subject image based on the R, G, and B color image signals output from the image sensor Y1. More specifically, the processing control unit Y4 performs amplification processing, digital conversion processing, and the like on the analog output signal from the image sensor Y1, and determines an appropriate black level, γ correction, and white for the entire image. Image data is generated from the image signal by performing known image processing such as balance adjustment (WB adjustment), contour correction, and color unevenness correction. Then, the processing control unit Y4 performs predetermined image processing such as resolution conversion on the image data. The process control unit Y4 outputs the image data to the first display device and the second display device, respectively. Further, the process control unit Y4 controls the entire imaging apparatus main body Y. By this control, the imaging apparatus body Y is controlled to execute at least one of the still image shooting and the moving image shooting of the subject. The processing control unit Y4 includes, for example, a microprocessor, a storage element, a peripheral circuit, and the like.

  Further, if necessary, the processing control unit Y4 could not be corrected by the imaging optical system 1 such as a known distortion correction process for correcting distortion in the optical image of the subject formed on the light receiving surface of the imaging element Y1. It may be configured to correct aberrations. In the distortion correction, an image distorted by aberration is corrected to a natural image having a similar shape similar to a sight seen with the naked eye and having substantially no distortion. With this configuration, even if the optical image of the subject guided to the image sensor Y1 by the imaging optical system 1 is distorted, it is possible to generate a natural image with substantially no distortion. Further, in the configuration in which such distortion is corrected by image processing by information processing, in particular, only other aberrations other than distortion aberration need to be considered, so that the degree of freedom in designing the imaging optical system 1 is increased and the design is improved. It becomes easier.

  Further, the processing control unit Y4 may include a known peripheral illuminance decrease correction process for correcting the peripheral illuminance decrease in the optical image of the subject formed on the light receiving surface of the image sensor Y1, as necessary. The peripheral illuminance drop correction (shading correction) is executed by storing correction data for performing the peripheral illuminance drop correction in advance and multiplying the image (pixel) after photographing by the correction data. Since the decrease in ambient illuminance mainly occurs due to the incident angle dependency of the sensitivity in the image sensor Y1, the vignetting of the lens, the cosine fourth law, and the like, the correction data has a predetermined value that corrects the decrease in illuminance caused by these factors. Is set. With such a configuration, even if the peripheral illuminance drops in the optical image of the subject guided to the image sensor Y1 by the imaging optical system 1, it is possible to generate an image having sufficient illuminance to the periphery. It becomes.

  The first display device Y2 is disposed on the back surface of the imaging device main body Y, and displays an image of a subject by image data from the processing control unit Y4. The first display device Y2 is, for example, an LCD (liquid crystal display), an organic EL display, or the like. A so-called live view is displayed by the first display device Y2.

  The second display device Y3 is arranged in the imaging device main body Y, and displays an image of a subject by image data from the processing control unit Y4 as an electronic viewfinder. The second display device Y3 is, for example, an LCD (liquid crystal display), an organic EL display, or the like. The image displayed on the second display device Y3 is observed through the eyepiece lens Y5.

  In the above description, the imaging device Z is an interchangeable lens type, but may be an integrated type in which the imaging device body and the imaging optical system of the imaging optical system 1 are combined together. Further, the second display device Y3 and the eyepiece lens Y5 may be omitted.

  In the image pickup apparatus Z having such a configuration, first, when shooting a still image, the processing control unit Y4 controls the image pickup apparatus Z to take a still image, and the lens driving device (not shown) is also illustrated. The focusing is performed by moving the second lens group 12 and the fourth lens group 14 (see FIG. 1), which are focus lenses. As a result, the focused optical image is periodically and repeatedly formed on the light receiving surface of the image sensor Y1, converted into R, G, and B color component image signals, and then output to the processing control unit Y4. . The image signal is subjected to image processing by the processing control unit Y4, and then an image based on the image signal is displayed on each of the first and second display devices Y2 and Y3. Then, the photographer can adjust the main subject to be in a desired position in the screen by referring to the second display device Y3 via the first display device Y2 or the eyepiece Y5. Become. When a so-called shutter button (not shown) is pressed in this state, image data is stored in a storage element as a still image memory in the processing control unit Y4, and a still image is obtained.

  In addition, when performing moving image shooting, the processing control unit Y4 causes the second lens group 12 (see FIG. 1) to reciprocate at high speed in the optical axis direction to perform wobbling, and a partial image is output from the output signal of the image sensor. A signal component in a certain frequency band with a region is detected, the optimum position of the second lens group 12 in a focused state is obtained, and the second lens group 12 is moved to the optimum position to capture a moving image. Control to perform. After that, as in the case of still image shooting, the photographer refers to the second display device Y3 via the first display device Y2 or the eyepiece lens Y5, so that the image of the subject is displayed on the screen. Adjustments can be made to fit in the desired position. When a shutter button (not shown) is pressed, moving image shooting is started. At the time of moving image shooting, the processing control unit Y4 controls the imaging device Z to take a moving image and operates the lens driving device (not shown) to perform focusing. As a result, a focused optical image is periodically and repeatedly formed on the light receiving surface of the image sensor Y1, converted into R, G, and B color component image signals, and then output to the processing control unit Y4. . The image signal is subjected to image processing by the processing control unit Y4, and then an image based on the image signal is displayed on each of the first and second display devices Y2 and Y3. Then, when the shutter button (not shown) is pressed again, the moving image shooting is completed. The photographed moving image is stored in a storage element as a moving image memory in the processing control unit Y4 to obtain a moving image.

<Description of More Specific Embodiment of Imaging Optical System>
Hereinafter, the specific configuration of the imaging optical system 1 as shown in FIG. 1, that is, the imaging optical system 1 provided in the imaging apparatus Z as shown in FIG. 3 will be described with reference to the drawings.

  FIG. 3 is a cross-sectional view illustrating the arrangement of lens groups in the imaging optical system 1A of the first embodiment. FIG. 3 shows the case of shooting an object at infinity. Note that FIGS. 5 and 7, which are cross-sectional views showing the arrangement of lens groups of the imaging optical systems 1 </ b> B and 1 </ b> C in Example 2 and Example 3 described later, also show the case of photographing an object at infinity. FIG. 4 is a diagram illustrating a state of movement of each lens group from the time of shooting an object at infinity to the time of shooting an object at a close distance in the imaging optical system 1 of the first embodiment.

  FIGS. 9 and 10 are aberration diagrams of the imaging optical system in Example 1. FIG. 9 shows a case of photographing an object at infinity, and FIG. 10 shows a case of photographing a short distance object.

  As shown in FIG. 3, the imaging optical system 1A of Embodiment 1 includes a first lens in which each lens group (Gr1, Gr2, Gr3, Gr4) has a positive optical power as a whole in order from the object side to the image side. A group (Gr1), a second lens group (Gr2) having a negative optical power as a whole, a third lens group (Gr3) having a positive optical power as a whole, including the aperture stop ST, and a positive as a whole 4 component lens group consisting of a fourth lens group (Gr4) having the following optical power, and from the time of infinite distance object shooting to the near distance object shooting, as shown in FIG. The first lens group (Gr1) is fixed, the second lens group (Gr2) is moved, the third lens group (Gr3) is fixed, and the fourth lens group (Gr4) is moved.

  More specifically, in the imaging optical system 1A according to the first exemplary embodiment, each lens group (Gr1, Gr2, Gr3, Gr4) is configured as follows in order from the object side to the image side.

  The first lens group (Gr1) includes a biconvex positive lens (first lens L1), a positive meniscus lens (second lens L2) convex toward the object side, and a biconcave negative lens (third lens L3). It is composed of

  The second lens group (Gr2) moves from the time of shooting an object at infinity to the time of shooting an object at a close distance, and in order from the object side to the image side, a positive meniscus lens (fourth lens L4) convex toward the image side and a biconcave lens. Negative lens (fifth lens L5). The fourth lens L4 and the fifth lens L5 are cemented lenses.

  The third lens group (Gr3) is fixed from the time of shooting an object at infinity to the time of shooting an object at a close distance, and a positive meniscus lens (sixth lens L6) convex toward the image side in order from the object side to the image side, Negative lens (seventh lens L7) and positive lenses convex on both sides (eighth lens L8). An aperture stop ST is provided between the sixth lens L6 and the seventh lens L7.

  The fourth lens group (Gr4) moves from when shooting an object at infinity to when shooting a short distance object. In order from the object side to the image side, a biconvex positive lens (9th lens L9) and a biconcave negative lens are arranged. (Tenth lens L10) and a biconvex positive lens (eleventh lens L11).

  Then, on the image side of the fourth lens group (Gr4), the light receiving surface of the image sensor Y1 is disposed via a parallel plate FT as a filter. The parallel plate FT is a cover glass of various optical filters or an image sensor.

  In FIG. 3, the number ri (i = 1, 2, 3,...) Given to each lens surface is the i-th lens surface when counted from the object side (however, the cemented surface of the lens is 1). It shall be counted as one surface.) The aperture stop ST, both surfaces of the parallel plate FT, and the light receiving surface of the image sensor Y1 are also handled as one surface.

  Under such a configuration, light rays incident from the object side are sequentially arranged along the optical axis AX in the first lens group (Gr1), the second lens group (Gr2), and the third lens group (Gr3) (on the way, An optical image of the object is formed on the light receiving surface of the image sensor Y1 through the fourth lens group (Gr4) and the parallel plate FT. In the image sensor Y1, the optical image is converted into an electrical signal. This electrical signal is subjected to predetermined digital image processing as necessary, and recorded as a digital video signal, for example, in a memory of a digital device such as a digital camera or transmitted to another digital device by wired or wireless communication. Or

  In the optical system 1A of the first embodiment, as shown in FIG. 4, the first lens group (Gr1) is fixed and the second lens group (Gr2) Moved substantially linearly to the image side, the third lens group (Gr3) is fixed, and the fourth lens group (Gr4) is moved substantially linearly to the object side. In this way, from the time of infinite object shooting to the time of short-distance object shooting, the second lens group (Gr2) and the fourth lens group (Gr4) move so that the distance between them becomes narrow.

  The construction data of each lens in the imaging optical system 1A of Example 1 is shown below.

Numerical example 1
Unit mm
Surface data surface number r d nd νd
Object ∞ ∞
1 98.003 3.352 1.72916 546588.00
2 -157.466 0.800
3 28.585 4.819 1.72916 54.66
4 315.581 1.184
5 -311.615 1.300 1.69895 30.13
6 34.558 Variable 7 -85.730 1.620 1.83400 37.16
8 (8 ') -42.355 1.000 1.48749 70.41
9 29.896 Variable 10 954.874 2.466 1.83481 42.72
11 -48.885 0.100
12 stops ∞ 2.465
13 -33.693 1.000 1.71736 29.52
14 28.193 2.476
15 34.246 3.272 1.90265 35.70
16 -226.007 Variable 17 30.184 4.700 1.90265 35.70
18 -43.125 0.894
19 -34.687 1.000 1.76182 26.56
20 21.504 1.777
21 51.707 3.400 1.83481 42.72
22 -52.860 Bf
Various data
When shooting an object at infinity When shooting a close object Distance of the subject d0 ∞ 346.570
d6 3.379 9.985
d9 8.990 2.384
d16 3.634 0.800
Lens data fa / f = -1.31
Total system focal length f 42.65
F number 1.45
Half angle of view Y 11
Back focus Bf 21.47
Fa -55.74 of the second lens group
Lens group data group Start surface End surface Focal length 1 1 6 59.87
2 7 9 -55.74
3 10 16 231.10
4 17 22 37.66

  In the above surface data, the surface number corresponds to the number i of the symbol ri (i = 1, 2, 3,...) Given to each lens surface shown in FIG.

  Also, “r” is the radius of curvature of each surface (unit is mm), “d” is the distance between the lens surfaces on the optical axis in the infinite focus state (axis upper surface distance), and “nd” is The refractive index “νd” of each lens with respect to the d-line (wavelength 587.56 nm) indicates the Abbe number. Since the aperture stop ST, both surfaces of the plane parallel plate FT, and the light receiving surface of the image sensor Y1 are flat surfaces, their radii of curvature are ∞ (infinite).

  Each aberration in the imaging lens 1A of Example 1 under the lens arrangement and configuration as described above is shown in FIGS. 9 and 10, spherical aberration, astigmatism, and distortion are shown in order from the upper left, and coma is shown below. The abscissa of the spherical aberration represents the focal position shift in mm, and the ordinate represents the value normalized by the maximum incident height. The horizontal axis of astigmatism represents the focal position shift in mm, and the vertical axis represents the image height in mm. The horizontal axis of the distortion aberration represents the actual image height as a percentage (%) with respect to the ideal image height, and the vertical axis represents the image height in mm. Moreover, in the figure of astigmatism, the broken line represents the result on the tangential (meridional) surface, and the solid line represents the result on the sagittal (radial) surface.

  The above handling is the same in FIGS. 11 to 14 showing the aberrations according to Examples 2 and 3 described below.

  In Example 1 configured as described above, the two lens groups, the second lens group Gr2 and the fourth lens group Gr4, move in the optical axis direction when focusing on the subject, so the subject distance is Even if it changes, it can be set as the imaging optical system which has favorable optical performance. Further, since the number of lenses of the second lens group Gr2 is 2, it can be made suitable for wobbling for moving image shooting.

  Further, since the fourth lens group Gr4 includes a positive lens and a negative lens, various aberrations such as field curvature and lateral chromatic aberration can be favorably corrected as shown in FIGS.

  Further, since the aperture stop ST is provided between the second lens group Gr2 and the fourth lens group Gr4, coma aberration can be corrected well as shown in FIGS.

  Further, in the vicinity of the aperture stop ST, the power of the surface r13 is negative, and the center of curvature O of the surface r13 is on the aperture stop ST side (a shape close to concentric with the aperture stop ST). Since at least one constructed lens L7 is provided, an optical system having good optical performance with reduced curvature of field can be obtained without generating coma and the like.

  FIG. 5 is a cross-sectional view illustrating the arrangement of lens groups in the imaging optical system according to the second embodiment. 11 and 12 are aberration diagrams of the image pickup optical system in the second embodiment.

As shown in FIG. 5, the imaging optical system 1B of Embodiment 2 includes a first lens in which each lens group (Gr1, Gr2, Gr3, Gr4) has a positive optical power as a whole in order from the object side to the image side. A group (Gr1), a second lens group (Gr2) having a negative optical power as a whole, a third lens group (Gr3) having a positive optical power as a whole, including the aperture stop ST, and a positive as a whole A positive, negative, positive, and positive four-component lens group comprising a fourth lens group (Gr4) having the following optical power, and when shooting an object at infinity to shooting a short distance object, as shown in FIG. The first lens group (Gr1) is fixed, the second lens group (Gr2) is moved, the third lens group (Gr3) is fixed, and the fourth lens group (Gr4) is moved.

  More specifically, in the imaging optical system 1B of Example 2, each lens group (Gr1, Gr2, Gr3, Gr4) is configured as follows in order from the object side to the image side.

  The first lens group (Gr1) includes a biconvex positive lens (first lens L1), a positive meniscus lens convex to the object side (second lens L2), and a positive meniscus lens convex to the object side (third lens). L3) and a negative meniscus lens (fourth lens L4) convex toward the object side.

  The second lens group (Gr2) moves from the time of shooting an object at infinity to the time of shooting an object at a close distance, and in order from the object side to the image side, a positive meniscus lens (fifth lens L5) convex to the image side and a biconcave lens Negative lens (sixth lens L6). The fifth lens L5 and the sixth lens L6 are cemented lenses.

  The third lens group (Gr3) is composed of a positive meniscus lens (seventh lens L7) that is fixed from the time of infinite object shooting to the time of close-up object shooting and is convex on the image side. An aperture stop ST is provided on the image side of the seventh lens L7 (between the seventh lens L7 and the sixth lens L6 of the second lens group (Gr2)).

  The fourth lens group (Gr4) moves from when shooting an object at infinity to when shooting a short distance object, and in order from the object side to the image side, a biconcave negative lens (eighth lens L8) and a biconvex positive lens. (Ninth lens L9), a positive biconvex lens (tenth lens L10), and a negative meniscus lens (eleventh lens L11) convex to the image side.

  Then, on the image side of the fourth lens group (Gr4), the light receiving surface of the image sensor Y1 is disposed via a parallel plate FT as a filter. The parallel plate FT is a cover glass of various optical filters or an image sensor.

  In the imaging optical system 1B of the second embodiment, as shown in FIG. 6, the first lens group (Gr1) is fixed and the second lens group (Gr2) is fixed from the time of shooting an object at infinity to the time of shooting a short distance object. The third lens group (Gr3) is fixed and the fourth lens group (Gr4) is moved substantially linearly to the object side. In this way, from the time of infinite object shooting to the time of short-distance object shooting, the second lens group (Gr2) and the fourth lens group (Gr4) move so that the distance between them becomes narrow.

  The construction data of each lens in the imaging optical system 1B of Example 2 is shown below.

Numerical example 2
Unit mm
Surface data surface number r d nd νd
Object ∞ ∞
1 175.256 2.43 1.60311 60.69
2 -162.363 0.80
3 39.032 3.36 1.69680 55.46
4 186.518 0.80
5 34.573 4.24 1.43299 49.22
6 145.481 1.14
7 25469.321 1.55 1.78472 25.72
8 32.118 Variable 9 -161.601 1.40 1.75211 25.05
10 (10 ') -54.563 0.90 1.56883 56.04
11 29.554 Variable 12 aperture ∞ 1.46
13 -50.934 1.49 1.69680 55.46
14 -33.061 Variable 15 -15.307 1.00 1.71736 29.50
16 78.968 0.93
17 186.491 4.08 1.90265 35.70
18 -19.950 0.80
19 34.808 4.16 1.72916 54.67
20 -35.288 1.07
21 -32.573 2.27 1.73020 27.07
22 -394.817 Bf
Various data
When shooting an object at infinity When shooting a close object Distance of the subject d0 ∞ 346.570
d8 4.018 9.009
d11 6.869 1.878
d14 5.341 2.077
Lens data fa / f = -1.14
Total system focal length f 42.65
F number 1.45
Half angle of view Y 11
Back focus Bf 21.29
Fa -48.51 of the second lens group
Lens group data group Start surface End surface Focal length 1 1 8 53.60
2 9 11 -48.51
3 13 14 130.73
4 15 22 34.68

  FIG. 11 and FIG. 12 show spherical aberration, astigmatism, distortion and coma aberration in the imaging lens 1B of Example 2 under the lens arrangement and configuration as described above. FIG. 11 shows the case of shooting an object at infinity, and FIG. 12 shows the case of shooting a short distance object.

  Also in Example 2 configured in this way, the two lens groups, the second lens group Gr2 and the fourth lens group Gr4, move in the optical axis direction when focusing on the subject, so the subject distance is Even if it changes, it can be set as the imaging optical system which has favorable optical performance. Further, since the number of lenses of the second lens group Gr2 is 2, it can be made suitable for wobbling for moving image shooting.

  Since the fourth lens group Gr4 includes a positive lens and a negative lens, various aberrations such as field curvature and lateral chromatic aberration can be favorably corrected as shown in FIGS.

  In addition, since the aperture stop ST is provided between the second lens group Gr2 and the fourth lens group Gr4, coma aberration can be favorably corrected as shown in FIGS.

  Further, in the vicinity of the aperture stop ST, the power of the surface r13 is negative, and the center of curvature O of the surface r13 is on the aperture stop ST side (a shape close to concentric with the aperture stop ST). Since at least one constructed lens L7 is provided, an optical system having good optical performance with reduced curvature of field can be obtained without generating coma and the like.

  FIG. 7 is a cross-sectional view illustrating the arrangement of lens groups in the imaging optical system according to the third embodiment. FIG. 8 is a diagram illustrating a state of movement of each lens group from the time of shooting an object at infinity to the time of shooting an object at a close distance in the imaging optical system of the third embodiment. FIG. 12 is an aberration diagram of the image pickup optical system according to the third embodiment.

  As shown in FIG. 7, the imaging optical system 1C of Example 3 includes a first lens in which each lens group (Gr1, Gr2, Gr3, Gr4) has a positive optical power as a whole in order from the object side to the image side. A group (Gr1), a second lens group (Gr2) having negative optical power as a whole, a third lens group (Gr3) having negative optical power as a whole, including the aperture stop ST, and a positive overall The positive, negative, negative, and positive four-component lens unit structure including the fourth lens unit (Gr4) having the optical power as shown in FIG. The first lens group (Gr1) is fixed, the second lens group (Gr2) is moved, the third lens group (Gr3) is fixed, and the fourth lens group (Gr4) is moved.

  More specifically, in the imaging optical system 1C of Example 3, each lens group (Gr1, Gr2, Gr3, Gr4) is configured as follows in order from the object side to the image side.

  The first lens group (Gr1) includes a biconvex positive lens (first lens L1), a positive meniscus lens (second lens L2) convex toward the object side, and a negative meniscus lens (third lens) convex toward the object side. L3).

  The second lens group (Gr2) moves from the time of shooting an object at infinity to the time of shooting an object at a close distance, and in order from the object side to the image side, a positive meniscus lens (fourth lens L4) convex to the image side and a biconcave lens It consists of a negative lens (fifth lens L5). The fourth lens L4 and the fifth lens L5 are cemented lenses.

  The third lens group (Gr3) is fixed from the time of infinite object shooting to the time of close-up object shooting, and includes a biconcave negative lens (sixth lens L6) and a biconvex positive lens (seventh lens L7). It is configured. An aperture stop ST is provided on the image side of the sixth lens L6 (between the sixth lens L6 and the fifth lens L5 of the second lens group (Gr2)).

  The fourth lens group (Gr4) moves from when shooting an object at infinity to when shooting a short distance object. In order from the object side to the image side, a positive meniscus lens (eighth lens L8) convex toward the image side and a biconvex lens. Positive lens (9th lens L9), a biconcave negative lens (10th lens L10), and a positive meniscus lens (11th lens L11) convex on the object side.

  Then, on the image side of the fourth lens group (Gr4), the light receiving surface of the image sensor Y1 is disposed via a parallel plate FT as a filter. The parallel plate FT is a cover glass of various optical filters or an image sensor.

  In the imaging optical system 1C according to the third embodiment, the first lens group (Gr1) is fixed and the second lens group (Gr2) is fixed as shown in FIG. The third lens group (Gr3) is fixed and the fourth lens group (Gr4) is moved substantially linearly to the object side. In this way, from the time of infinite object shooting to the time of short-distance object shooting, the second lens group (Gr2) and the fourth lens group (Gr4) move so that the distance between them becomes narrow.

  The construction data of each lens in the imaging optical system 1C of Example 3 is shown below.

Numerical Example 3
Unit mm
Surface data surface number r d nd νd
Object ∞ ∞
1 154.678 2.747 1.72916 54.66
2 -154.922 0.800
3 32.225 4.180 1.72916 54.66
4 208.987 0.800
5 346.844 1.200 1.84666 23.78
6 74.641 Variable 7 -195.773 1.800 1.87085 27.96
8 (8 ') -63.643 1.000 1.48749 70.41
9 30.534 Variable 10 aperture ∞ 3.103
11 -23.302 1.000 1.71120 27.81
12 34.651 0.998
13 46.397 3.812 1.72916 54.66
14 -42.088 Variable 15 -39.461 1.964 1.90265 35.70
16 -27.934 0.800
17 30.873 4.500 1.90265 35.70
18 -46.331 0.800
19 -40.866 1.200 1.71537 27.64
20 21.892 1.298
21 31.956 4.000 1.90265 35.70
22 183.284 Bf
Various data
When shooting an object at infinity When shooting a close object Distance of the subject d0 ∞ 346.570
d6 4.045 10.460
d9 9.297 2.882
d14 4.160 2.303
Lens data
fa / f = -1.63
Total system focal length f 42.63
F number 1.45
Half angle of view Y 11
Back focus Bf 21.59
Fa -69.37 of the second lens group
Lens group data group Start surface End surface Focal length 1 1 6 47.97
2 7 9 -69.37
3 11 14 -67.73
4 15 22 28.93

  FIG. 13 and FIG. 14 show spherical aberration, astigmatism, distortion and coma aberration in the imaging lens 1C of Example 3 under the lens arrangement and configuration as described above. FIG. 13 shows the case of shooting an object at infinity, and FIG. 14 shows the case of shooting a short distance object.

  Also in Example 2 configured in this way, the two lens groups, the second lens group Gr2 and the fourth lens group Gr4, move in the optical axis direction when focusing on the subject, so the subject distance is Even if it changes, it can be set as the imaging optical system which has favorable optical performance. Further, since the number of lenses of the second lens group Gr2 is 2, it can be made suitable for wobbling for moving image shooting.

  Since the fourth lens group Gr4 includes a positive lens and a negative lens, various aberrations such as field curvature and lateral chromatic aberration can be favorably corrected as shown in FIGS.

  Further, since the aperture stop ST is provided between the second lens group Gr2 and the fourth lens group Gr4, coma aberration can be corrected well as shown in FIGS.

  Further, in the vicinity of the aperture stop ST, the power of the surface r11 is negative, and the center of curvature O of the surface r11 is on the aperture stop ST side (a shape close to the concentric shape with respect to the aperture stop ST). Since at least one constructed lens L6 is provided, an optical system having good optical performance with reduced curvature of field can be obtained without generating coma and the like.

  As described above, the imaging optical systems 1A to 1C in the first to third embodiments satisfy the requirements according to the present invention, so that they are suitable for moving image shooting with a large aperture, and the subject distance changes. Even so, it can have good optical performance.

  In the first to third embodiments, the number of lenses of the second lens group Gr2 configured to move in the optical axis direction when focusing on the subject is set to two so that wobbling is performed during moving image shooting. However, the number of lenses of the second lens group Gr2 may be one, and can be changed as appropriate.

  Further, for example, when focusing on a subject, the number of lenses of the fourth lens group Gr4 configured to move in the optical axis direction is set to two or less, and the fourth lens group Gr4 is wobbled at the time of moving image shooting. You may make it let.

  In the first to third embodiments, the lens group is composed of four groups of the first lens group Gr1 to the fourth lens group Gr4. However, the present invention is not limited to this configuration, and the lens group is composed of two or more groups. And can be changed as appropriate.

  In the first to third embodiments, one lens arranged concentrically is provided near the aperture stop, but two or more lenses may be provided. In the first to third embodiments, the lens surface is on the image side with respect to the aperture stop, and the center of curvature of the surface is on the object side with respect to the aperture stop. The center of curvature of the surface may be on the object side with respect to the aperture stop, and may be changed as appropriate on the object side with respect to the aperture stop.

  In the first to third embodiments, a lens group for correcting camera shake may be provided. In Examples 1 to 3, the lens is not limited to having a spherical surface, and may include an aspherical surface, and can be changed as appropriate.

  In the first to third embodiments, a lens group for correcting camera shake may be provided. In Examples 1 to 3, the lens is not limited to having a spherical surface, and may include an aspherical surface, and can be changed as appropriate.

  In order to express the present invention, the present invention has been properly and fully described through the embodiments with reference to the drawings. However, those skilled in the art can easily change and / or improve the above-described embodiments. It should be recognized that this is possible. Therefore, unless the modifications or improvements implemented by those skilled in the art are at a level that departs from the scope of the claims recited in the claims, the modifications or improvements are not covered by the claims. To be construed as inclusive.

AX Optical axis 1, 1A to 1C Imaging optical system 11, Gr1 first lens group 12, Gr2 second lens group 13, Gr3 third lens group 14, Gr4 fourth lens group
Y1 Image sensor Y Imaging device

Claims (4)

Including a plurality of lens groups in order from the object side to the image side,
The plurality of lens groups includes two lens groups that satisfy the conditional expression (1) below and are configured to move in the optical axis direction when focusing on a subject.
One of the two lens groups is configured so that the number of lenses is two or less.
Fno ≦ 2.0 (1)
However, Fno is F number The lens group in which the number of lenses is two or less satisfies the following conditional expression (2):
The other of the two lens groups includes at least a positive lens and a negative lens,
The imaging optical system according to claim 1, wherein an aperture stop is provided between the two lens groups.
0.9 <| fa / f | <1.7 (2)
However,
fa: focal length of one of the above f: focal length of the entire system   3. The lens according to claim 2, wherein at least one lens is provided in the vicinity of the aperture stop so that the power of the surface is negative and the center of curvature of the surface is on the aperture stop side. The imaging optical system described. The imaging optical system according to any one of claims 1 to 3,
An image sensor that converts an optical image into an electrical signal,
An image pickup apparatus, wherein the image pickup optical system is capable of forming an optical image of an object on a light receiving surface of the image pickup element.

Images