JP2005128065A - Zoom lens and imaging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rear focus type zoom lens capable of further downsizing a prism and reducing the entire lens system without impairing optical performance.
A first lens group GR1 that is arranged closest to the object side has a negative refractive power in order from the object side. A front lens group (for example, lens L1), an optical member (for example, prism P1) that bends the optical path, and a rear lens group (for example, lens L2) having a positive refractive power. Further, the front lens group and the rear lens group interfere with each other by forming at least one lens (for example, the lens L2) included in the rear lens group into a shape in which a part of the outer diameter is omitted. To prevent.
[Selection] Figure 5

Description

  The present invention relates to a zoom lens and an image pickup apparatus using the zoom lens as an image pickup lens, and in particular, a rear focus type zoom lens suitable for a small image pickup apparatus such as a digital still camera or a home video camera, and the zoom lens. The present invention relates to an imaging apparatus using the.

  In recent years, digital still cameras and digital video cameras have been widely used for home use, but further miniaturization is required for these small-sized imaging devices. For this reason, miniaturization by shortening the overall length and depth is also demanded for photographing lenses mounted on them, particularly zoom lenses. Further, for such a photographing lens, particularly for a digital still camera, there is a demand for an improvement in lens performance as well as a reduction in size in response to an increase in the number of pixels of an image sensor.

For example, a so-called rear focus type zoom lens that performs focusing by moving a lens group other than the first lens group arranged closest to the object side relatively easily reduces the size of the entire lens system and reduces the number of pixels. It is known that imaging performance suitable for many solid-state imaging devices can be obtained. Also, recently, the optical path from the first lens group to the image plane is bent halfway to shorten the front-rear length when it is incorporated in an imaging device, and the movable direction of the lens during zooming is set to the vertical direction. It has been considered to eliminate the protrusions of the lens during shooting. For example, in order from the object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a fourth lens group having a positive refractive power And a first lens unit having a negative refractive power in order from the object side, the first lens unit having a four-unit lens configuration in which zooming is performed by moving the second and fourth lens units, There has been a zoom lens having a prism that bends the optical path and a single second lens having positive refractive power (see, for example, Patent Document 1).
Japanese Unexamined Patent Publication No. 2000-131610 (paragraph numbers [0010] to [0027], FIG. 1)

  By the way, in a zoom lens having an optical system in which the optical path is bent using a prism, it is possible to further reduce the size and thickness by reducing the size of the prism. However, the zoom lens disclosed in Patent Document 1 has a problem that the optical performance deteriorates when the diameter and thickness of the lens included in the first lens group are further reduced.

  Further, when the prism is miniaturized without deteriorating the optical performance, the end portions of the two lenses arranged with the prism interposed therebetween interfere with each other, so that the distance between the lenses arranged in the first lens group is reduced. Cannot be shortened, resulting in difficulty in reducing the depth and width of the prism.

  The present invention has been made in view of such a problem, and provides a rear focus type zoom lens capable of reducing the size of the entire lens system by further downsizing the prism without impairing optical performance. With the goal.

  Another object of the present invention is to provide an imaging apparatus using a rear focus type zoom lens that can reduce the size of the prism system and the entire lens system without impairing optical performance. is there.

  In the present invention, in order to solve the above problem, in a zoom lens having a structure in which a plurality of lens groups are arranged in order from the object side, the first lens group arranged closest to the object side among the lens groups is More sequentially, a front lens group having a negative refractive power, an optical member that bends the optical path, and a rear lens group having a positive refractive power, and at least one lens included in the rear lens group, A zoom lens characterized by having a shape with a part of the diameter missing is provided.

  In such a zoom lens, the first lens group includes, in order from the object side, a front lens group having negative refractive power, an optical member that bends the optical path, and a rear lens group having positive refractive power. When zooming by moving the lens closer to the image plane side, the moving direction of the lens becomes the optical axis direction of the rear lens group, and the lens system is thinned. In addition, since at least one lens included in the rear lens group has a shape in which a part of its outer diameter is missing, an optical member that bends the optical path when the distance between the lenses in the first lens group is shortened. This prevents the front lens group and the rear lens group from interfering with each other.

  In the present invention, in an imaging apparatus using a zoom lens having a structure in which a plurality of lens groups are arranged in order from the object side as an imaging lens, the first lens group arranged closest to the object side among the lens groups is , In order from the object side, a front lens group having negative refractive power, an optical member that bends the optical path, and a rear lens group having positive refractive power, and at least one lens included in the rear lens group is There is provided an imaging apparatus characterized by having a shape in which a part of the outer diameter is missing.

  In the zoom lens provided in such an imaging apparatus, the first lens group includes, in order from the object side, a front lens group having negative refractive power, an optical member that bends the optical path, and a rear lens group having positive refractive power. With this arrangement, when zooming is performed by moving the lens on the image plane side, the moving direction of the lens becomes the optical axis direction of the rear lens group, and the lens system is thinned. In addition, since at least one lens included in the rear lens group has a shape in which a part of its outer diameter is missing, an optical member that bends the optical path when the distance between the lenses in the first lens group is shortened. This prevents the front lens group and the rear lens group from interfering with each other.

  According to the zoom lens of the present invention, since the first lens includes an optical member that bends the optical path, the lens system can be thinned, and at least one lens included in the rear lens group includes: Since a part of the outer diameter is missing, the front lens group and the rear lens group do not interfere with each other, the distance between the lenses in the first lens group is shortened, and the optical member is miniaturized. Can do. Therefore, a small zoom lens having good optical performance is realized.

  According to the imaging apparatus of the present invention, the first lens of the zoom lens used as the imaging lens includes an optical member that bends the optical path, so that the lens system can be thinned and the rear lens. Since at least one lens included in the group has a shape in which a part of its outer diameter is missing, the distance between the lenses in the first lens group is reduced without interference between the front lens group and the rear lens group. While shortening, an optical member can be reduced in size. Therefore, a small zoom lens having good optical performance is realized, and the imaging device is downsized.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a cross-sectional view showing a lens configuration example of a zoom lens according to an embodiment of the present invention.
In FIG. 1, as an example, a configuration example of a zoom lens used as an imaging lens of an imaging apparatus such as a digital still camera is shown. In this zoom lens, in order from the object side to the image plane IMG side, a first lens group GR1 having a positive refractive power, a second lens group GR2 having a negative refractive power, and a third lens group GR3 having a positive refractive power. A fourth lens group GR4 having a positive refractive power and a fifth lens group GR5 having a negative refractive power are disposed. Further, an iris IR for adjusting the amount of light is disposed on the image plane IMG side of the third lens group GR3, and a filter including a low-pass filter such as an infrared cut filter is further disposed on the image plane IMG side of the fifth lens group GR5. The FL and the cover glass CG of the image sensor are disposed. The image plane IMG is a light receiving surface of an image sensor such as a CCD (Charge Coupled Devices).

  This zoom lens is configured to perform zooming by moving the second lens group GR2 and the fourth lens group GR4. When zooming from the short focal length end to the long focal length end, the second lens group is moved from the object side to the image plane IMG side, and the fourth lens group is moved from the image plane IMG side to the object side. Further, this zoom lens employs a so-called rear focus system, and focusing can be performed by moving the fourth lens group GR4 or the fifth lens group GR5.

  Further, the first lens group GR1 includes, in order from the object side, a single lens L1 having a negative refractive power, a prism P1 for bending the optical path, and a single lens L2 having a positive refractive power. ing. With such a configuration, the moving direction of the lens that moves during zooming and focusing is different from the optical axis direction of the lens L1 closest to the object side, and is the optical axis direction of the lens L2, thereby reducing the depth of the lens system. The depth can be kept constant regardless of zooming, focusing, or power on / off.

  In the present embodiment, the lens L1 is configured by a meniscus lens having a negative refractive power and having a convex shape toward the object side. The lens L2 has a positive refractive power, and both lens surfaces thereof are convex aspheric surfaces.

  The second lens group GR2 includes three lenses L3, L4, and L5 in order from the object side, and a lens surface between the lens L4 and the lens L5 is cemented. The third lens group GR3 is composed of a single lens L6. The fourth lens group GR4 is composed of two lenses L7 and L8, and the lens surface between the lens L7 and the lens L8 is cemented. The fifth lens group GR5 includes two lenses L9 and L10, and a lens surface between the lens L9 and the lens L10 is cemented. Of these, both the lens surfaces of the lens L6 and the object-side surface of the lens L7 are aspherical.

Next, specific numerical examples of the zoom lens having the configuration shown in FIG. 1 will be described.
Table 1 shows numerical examples of the lens system in the zoom lens. Table 2 shows values of the focal length f, the F number (FNo.), And the half angle of view ω at each focal position in the present embodiment. Further, Table 3 shows the aspheric coefficients of the surfaces constituted by aspheric surfaces in this embodiment.

  In Table 1, surface numbers S1 to S24 indicate lenses L1 to L10, prism P1, iris IR, filter FL, and light incident surface and light exit surface in the central axis of the cover glass CG in order from the object side. . For example, the surface number S1 indicates the lens surface on the object side of the lens L1, and the surface number S2 indicates the lens surface on the image plane IMG side. The surface number S3 indicates the object side surface of the prism P1, and the surface number S4 indicates the image surface IMG side surface. For the cemented lens, the cemented surface of each lens is indicated by the same surface number. For example, the surface number S10 indicates the cemented surface between the lens L4 and the lens L5.

  R represents the curvature of each surface, d represents the distance between the surfaces, ne represents the refractive index with respect to the e-line, and νe represents the Abbe number based on the e-line. In the field of curvature R, the surface indicated by “ASP” after the numerical value indicates that the surface is constituted by an aspheric surface. A distance d indicates a distance between the surface and a surface adjacent to the image plane IMG side. For example, the value of the distance d described in the field of the surface number S1 indicates the thickness between the object side and the image surface IMG side of the lens L1. Further, the distance d between the surfaces that move during zooming and focusing is shown in the order of short focal length end, intermediate focal length, and long focal length end during zooming.

  In this embodiment, both surfaces (surface numbers S5 and S6) of the lens L2, the object side surface (surface number S12) of the lens L6, and the object side surface (surface number S15) of the lens L7 are aspherical surfaces. It is constituted by. The shape of the aspherical surface is represented by the following formula (1).

  Here, the distance in the optical axis direction from the vertex of each lens surface is x, the radius of curvature of the lens at the vertex is r, and the conic constant is κ. In addition, the fourth-order, sixth-order, eighth-order and tenth-order aspheric coefficients are C4, C6, C8 and C10, respectively, and Table 3 shows the values of these aspheric coefficients. Further, “E” in Table 3 means an exponential expression with a base of 10.

  As in this embodiment, at least one lens surface of the lenses included in the first lens group GR1 is aspherical, so that distortion is corrected and the effective diameter of the lens L1 is reduced, thereby reducing the prism. P1 can be downsized. In the fifth lens group GR5, the cemented surface of the lens L9 and the lens L10 has a convex shape on the object side, so that chromatic aberration is corrected and the fifth lens group GR5 has a lens performance deterioration. Sensitivity can be reduced. By using a cemented lens, it is possible to reduce the disturbance of the image plane due to the eccentricity in the lens group and to facilitate the manufacture.

2 to 4 are graphs showing various aberrations at the short focal length end, the intermediate focal length, and the long focal length end for the above-described embodiment.
Here, (A) of each figure shows spherical aberration, the vertical axis shows the ratio to the open F value, and the horizontal axis shows the focus amount. Further, the solid line indicates the spherical aberration at the d-line (wavelength 587.6 nm), the broken line indicates the g-line (wavelength 435.8 nm), and the alternate long and short dash line indicates the spherical aberration at the C-line (wavelength 656.3 nm). Also, (B) in each figure shows field curvature (astigmatism), the vertical axis shows the image height, the horizontal axis shows the focus amount, the solid line shows the value on the sagittal image plane, and the broken line shows the value on the meridional image plane. Show. Furthermore, (C) in each figure shows distortion, the vertical axis shows the image height, and the horizontal axis shows the ratio (%).

  In the above embodiment, the lens system depth is reduced by the structure in which the prism P1 that bends the optical path is arranged in the first lens group GR1, and the depth is reduced during zooming, focusing, or power on / off. Regardless of the situation, it is always constant. Further, since the imaging magnification of the first lens group GR1 is lower than the conventional one, both the effective diameter and focal length of the lenses in the first lens group GR1 are reduced, and the total length of the lens system is reduced. The prism P1 is reduced in size while being shortened. Furthermore, according to the various aberration diagrams of FIGS. 2 to 4, it is understood that various aberrations are corrected in a balanced manner at the short focal length end, the intermediate focal length, and the long focal length end in the above embodiment. Therefore, a zoom lens with a zoom ratio of about 4 times that is small and thin and has good optical performance is realized. This zoom lens is suitable as an imaging lens for an imaging apparatus, particularly an imaging lens for a thin digital still camera having a relatively large number of pixels.

Next, FIG. 5 is an enlarged view showing the first lens group GR1.
FIG. 5A shows an enlarged cross-sectional view of the first lens group GR1, and FIG. 5B shows a plan view of the lens L2 viewed from the optical axis direction. Moreover, in each figure, the continuous line has shown the external shape of the actual lens and prism, and the broken line has shown the missing part of the lens outer diameter.

  In the zoom lens described above, it is possible to reduce the size of the prism P1 by reducing the effective diameter and focal length of each of the lenses L1 and L2 in the first lens group GR1. However, as a result, the distance between the lenses L1 and L2 and the prism P1 is reduced, and the outer peripheral portions of the lenses L1 and L2 having different optical axes interfere with each other. In order to prevent such interference, if one of the lenses L1 and L2 is moved away from the prism P1, it is necessary to make the prism P1 larger, so that the depth of the lens system increases.

  In order to solve such a problem, in the zoom lens described above, as shown in FIG. 5, a part of the outer diameter of the lens L2 is lost, thereby preventing interference between the lenses. The lens L2 has a shape in which the side close to the object that interferes with the lens L1 and the side facing it are omitted. As a result, the lenses L1 and L2 can be brought closer to the prism P1, and the prism P1 can be miniaturized to reduce the depth of the lens system.

  Further, for example, a part of the outer diameter of the lens L1 can be omitted instead of the lens L2. In this case, the lens L1 is positioned on the outermost surface of the lens system. If the outer diameter of the lens is lost, the strength is weakened. Therefore, the lens L1 may be damaged when a force is applied from the outside. Further, if the center thickness of the lens L1 is increased in order to maintain the strength, the depth of the lens system increases, which is not appropriate. On the other hand, such a problem does not occur in the lens L2 disposed inside.

  By the way, the reflected light from the subject is collected by the zoom lens, and the image plane IMG that is the light receiving surface of the film or the image sensor is usually rectangular. For this reason, particularly in a lens located away from the iris IR, an area close to a rectangle corresponding to the shape of the image plane IMG is an effective area through which light passes. In such a lens, light passes to the vicinity of the lens outer diameter in the diagonal direction of the effective region, but the range through which light passes on the long side and the short side is narrower. Therefore, on the long side and the short side, a missing portion may be provided in the outer diameter of the lens in a region through which light does not pass.

FIG. 6 is a diagram for explaining the position of the outer diameter missing portion on the lens.
FIG. 6 schematically shows the positional relationship between the lens L2 and the image plane IMG when viewed along the optical axis from the prism P1 to the image plane IMG. For example, when the zoom lens of the present invention is used in a state where the optical axis from the prism P1 to the image plane IMG is in the vertical direction, the long side of the image plane IMG is positioned on the outermost surface as shown in FIG. The lens L1 is directed in the optical axis direction. In this case, the lens L2 also has a shape in which the long side of the effective area is omitted from the outer diameter of the lens L2, so that the depth of the prism P1 can be further reduced and the camera housing in which the lens is accommodated. The depth of the body 90 can be reduced.

  Further, in the zoom lens described above, not only the lens L2 but also a lens disposed on the image plane IMG side from the lens L2 may have a shape in which a part of the outer diameter is missing. In this case, the missing position is made to coincide with the same side as the lens L2, that is, the long side of the image plane IMG as shown in FIG. As a result, the depth of the lens system can be reduced. In particular, in the lens close to the prism P1 and the image plane IMG, the missing portion can be increased as compared with the lens close to the iris IR, which has the effect of downsizing. large.

  Each lens may be provided with a missing portion not only on the long side of the image plane IMG but also on the short side. As a result, the width of the lens system can be reduced. For example, a lens driving mechanism or the like can be disposed in the vacant space.

Next, an example of an imaging apparatus using the zoom lens will be described. FIG. 7 is a block diagram showing a configuration example of a digital still camera in which the zoom lens of the present invention can be mounted.
The digital still camera shown in FIG. 7 has a camera block 10 that performs an imaging function, a camera signal processing unit 20 that performs signal processing such as analog-digital conversion of a captured image signal, and an image that performs recording and reproduction processing of the image signal. A processing unit 30, an LCD (Liquid Crystal Display) 40 for displaying captured images, an R / W (reader / writer) 50 for writing / reading data to / from the memory card 51, and a CPU 60 for controlling the entire apparatus , An input unit 70 for operation input by the user, and a lens drive control unit 80 for controlling driving of the lenses in the camera block 10 are provided.

  The camera block 10 includes an optical system including a zoom lens 11 to which the present invention is applied, an image sensor 12 such as a CCD, and the like. The camera signal processing unit 20 performs signal processing such as conversion of an output signal from the image sensor 12 into a digital signal, noise removal, image quality correction, and conversion into a luminance / color difference signal. The image processing unit 30 performs compression encoding / decompression decoding processing of an image signal based on a predetermined image data format, conversion processing of data specifications such as resolution, and the like.

  The memory card 51 is composed of a detachable semiconductor memory. The R / W 50 writes the image data encoded by the image processing unit 30 to the memory card 51 and reads the image data recorded on the memory card 51. The CPU 60 is a control processing unit that controls each circuit block in the digital still camera, and controls each circuit block based on an instruction input signal or the like from the input unit 70.

  The input unit 70 includes, for example, a shutter release button for performing a shutter operation, a selection switch for selecting an operation mode, and the like, and outputs an instruction input signal corresponding to an operation by a user to the CPU 60. The lens drive control unit 80 controls a motor (not shown) that drives the lens in the zoom lens 11 based on a control signal from the CPU 60.

The operation of this digital still camera will be briefly described below.
In the shooting standby state, under the control of the CPU 60, the image signal captured by the camera block 10 is output to the LCD 40 via the camera signal processing unit 20 and displayed as a camera through image. When an instruction input signal for zooming is input from the input unit 70, the CPU 60 outputs a control signal to the lens drive control unit 80, and the zoom lens 11 in the zoom lens 11 is controlled based on the control of the lens drive control unit 80. A predetermined lens is moved.

  When a shutter (not shown) of the camera block 10 is released by an instruction input signal from the input unit 70, the captured image signal is output from the camera signal processing unit 20 to the image processing unit 30 and subjected to compression encoding processing. Is converted into digital data of the data format. The converted data is output to the R / W 50 and written to the memory card 51.

  The focusing is performed by the lens drive control unit 80 based on a control signal from the CPU 60 based on a control signal from the CPU 60, for example, when the shutter release button is half-pressed or when it is fully pressed for recording. This is done by moving the lens.

  When reproducing the image data recorded on the memory card 51, predetermined image data is read from the memory card 51 by the R / W 50 in response to an operation by the input unit 70, and decompressed and decoded by the image processing unit 30. After the conversion processing, the reproduced image signal is output to the LCD 40. As a result, a reproduced image is displayed.

FIG. 8 is a cross-sectional view showing a component mounting structure in the digital still camera.
FIG. 8 shows the inside of the digital still camera when a subject is present on the left side in the drawing. The zoom lens 11 is housed in the camera housing 90, and the image sensor 12 is provided below the zoom lens 11. The LCD 40 is provided on the surface of the camera housing 90 on the side facing the subject, and is used to adjust the angle of view at the time of shooting, to reproduce images, and to check various setting information.

  The zoom lens of the present invention can perform zooming and focusing by bending the optical axis of light from a subject with a prism and moving a predetermined lens along the bent direction (vertical direction in the figure). It has become. Therefore, it is possible to perform shooting without projecting the zoom lens 11 from the camera housing 90, and the depth of the camera body at the time of shooting is shortened. In addition, by designing the zoom lens 11 so as to satisfy the above-described conditions, the camera housing 90 can be further thinned and downsized in the vertical direction. It is possible to obtain a high-quality captured image with a small aberration at various focal lengths.

  In the above embodiment, the case where the zoom lens of the present invention is applied to a digital still camera has been described. However, the present invention can also be applied to other imaging devices such as a video camera.

It is sectional drawing which shows the lens structural example of the zoom lens which concerns on embodiment of this invention. It is an aberration diagram in the short focal distance end about the Example of this invention. FIG. 6 is a diagram illustrating various aberrations at an intermediate focal length according to an example of the present invention. FIG. 6 is a diagram showing various aberrations at the long focal length end for the example of the present invention. It is a figure which expands and shows a 1st lens group. It is a figure for demonstrating the position on the lens of an outer diameter missing part. It is a block diagram which shows the structural example of the digital still camera which can mount the zoom lens of this invention. It is sectional drawing which shows the attachment structure of the components in the digital still camera which concerns on embodiment of this invention.

Explanation of symbols

GR1: First lens group, GR2: Second lens group, GR3: Third lens group, GR4: Fourth lens group, GR5: Fifth lens group, L1 to L10: Lens, P1: Prism, IR ... Iris, FL ... Filter, CG ... Cover glass, IMG ... Image plane

Claims (9)

In a zoom lens having a structure in which a plurality of lens groups are arranged in order from the object side,
The first lens group arranged closest to the object side among the lens groups includes, in order from the object side, a front lens group having a negative refractive power, an optical member for bending an optical path, and a rear lens group having a positive refractive power. The zoom lens according to claim 1, wherein at least one lens included in the rear lens group has a shape in which a part of the outer diameter is missing.   2. The at least one lens included in the rear lens group has a shape in which an outer diameter of a side closest to the front lens group and a side opposite thereto are missing. Zoom lens.   In order from the object side, the first lens group having a positive refractive power as a whole, the second lens group having a negative refractive power, the third lens group having a positive refractive power, and the fourth lens having a positive refractive power 2. The zoom lens according to claim 1, wherein the zoom lens includes at least a group, and is configured to perform zooming by moving the second lens group and the fourth lens group.   The zoom lens according to claim 3, wherein at least a part of the lenses included in the second to fourth lens groups has a shape in which a part of an outer diameter thereof is omitted.   In order from the object side, the first lens group having a positive refractive power as a whole, the second lens group having a negative refractive power, the third lens group having a positive refractive power, and the fourth lens having a positive refractive power 2. The zoom lens system according to claim 1, further comprising a fifth lens group having a negative refractive power, and performing zooming by moving at least the second lens group and the fourth lens group. Zoom lens.   The zoom lens according to claim 5, wherein at least a part of the lenses included in the second to fifth lens groups has a shape in which a part of an outer diameter thereof is omitted. In an imaging apparatus using a zoom lens having a structure in which a plurality of lens groups are arranged in order from the object side as an imaging lens,
The first lens group arranged closest to the object side among the lens groups includes, in order from the object side, a front lens group having a negative refractive power, an optical member for bending an optical path, and a rear lens group having a positive refractive power. An imaging apparatus comprising: at least one lens included in the rear lens group having a shape in which a part of an outer diameter thereof is missing. An image sensor for receiving the light collected by the zoom lens;
The at least one lens included in the rear lens group has a shape in which at least one of a long side or a short side of the imaging element is omitted from an outer diameter thereof. Imaging device.   At least one of the lenses arranged on the image plane side from the first lens group has a shape in which at least one of the long side or the short side of the imaging element is omitted from the outer diameter. The imaging apparatus according to claim 8, characterized in that:

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