JP2005062318A - Variable-focal-length optical system and imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a variable-focal-length optical system capable of making angle variation of a main light beam incident on an imaging plane small with magnification used for photography, for example, between a wide-angle end and a telephoto end, and to provide imaging apparatus. <P>SOLUTION: In a comparison example, the angle of incidence is large at the wide-angle end and the angle of incidence of the main light beam is small at the telephoto end, but in this embodiment, using a variable-focus lens VL nearly equalizes the angle of incidence between the wide-angle end and telephoto end and an image of high picture quality can be obtained through the imaging of an image sensor CMOS. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a variable focal length optical system suitable for forming an optical image on a solid-state imaging device such as a CCD image sensor or a CMOS image sensor, and an imaging apparatus using the same.

  In recent years, imaging devices such as digital still cameras and digital video cameras using solid-state imaging devices such as CCD (Charge Coupled Devices) type image sensors or CMOS (Complementary Metal-Oxide Semiconductor) type image sensors have become widespread. In addition, along with the downsizing and increase in the number of pixels of solid-state image sensors, there is an increasing demand for further miniaturization and higher performance in optical systems mounted on these image pickup apparatuses.

  In particular, for example, an optical system used in an imaging apparatus including a high-pixel solid-state imaging element is required to be image-side telecentric and have good aberration characteristics in order to obtain good light receiving sensitivity over the entire screen. The Image-side telecentric means that the principal ray enters the imaging surface of the solid-state imaging device at an angle parallel to the optical axis at each image height. For example, in the case of an imaging apparatus that uses a single-focus imaging lens, a substantially image-side telecentric optical system that actually enters the imaging surface at an angle of about 5 ° to 30 ° with the downsizing of the imaging device. It has become common to use.

  However, in a general zoom optical system having a wide-angle end and a telephoto end, the optical axis position of each lens element is different at the wide-angle end and the telephoto end, so that the optical system is telecentric at any position. In order to design the system, it is necessary to increase the size of the zoom optical system, and it is extremely difficult to design the system with a small number of lenses. On the other hand, if the change in the angle of the principal ray incident on the imaging surface is reduced with the magnification used for photographing from the wide-angle end to the telephoto end, a solid-state image sensor corresponding to the incident angle will be increased even if the incident angle is somewhat increased. By using it, it is possible to suppress a drop in the amount of light around the imaging surface.

However, in a zoom optical system that moves the lens element in the optical axis direction, in order to reduce the change in the angle of the principal ray incident on the imaging surface between the wide-angle end and the telephoto end, the optical system from a completely different viewpoint Need to design. On the other hand, Patent Document 1 discloses a variable focus lens using an electrocapillary phenomenon.
WO99 / 18456

  However, Patent Document 1 does not specifically describe what kind of optical system is configured using such a variable focus lens, and in particular, how to solve the problems of the optical system in the imaging apparatus. It is not described how to solve this problem.

  The present invention has been made in view of such problems. For example, the angle change of the principal ray incident on the imaging surface can be reduced at a magnification used for imaging between the wide-angle end and the telephoto end. It is an object of the present invention to provide a variable focal length optical system and an image pickup apparatus using the same.

  The variable focal length optical system according to claim 1, further comprising a plurality of moving lens groups, wherein the variable focal length optical system performs zooming by moving the moving lens group in the optical axis direction. Since the incident angle change reducing means for reducing the change in the incident angle of the light beam to the (eg, imaging surface) is provided, if the incident angle reducing means suppresses the change in the incident angle to a small value, the image pickup device corresponding thereto By using, the amount of light around the imaging surface can be secured, and a high-quality image can be obtained.

  A variable focal length optical system according to a second aspect of the present invention is the variable focal length optical system according to the first aspect of the present invention, wherein the incident angle change reducing means mixes the conductive or polar first liquid and the first liquid with each other. The second liquid that is not to be sealed is contained in the container so that the interface has a predetermined shape, and a voltage is applied between the first liquid and the electrode provided in the container, Since it is configured by a liquid optical element in which the refractive power is adjusted by changing the shape of the interface, variable focus can be achieved by electrical control without moving in the optical axis direction, thereby It is possible to effectively reduce the change in the incident angle of the light beam on the focal plane due to zooming.

  The variable focal length optical system according to claim 3 is the invention according to claim 1 or 2, wherein the refractive power at the wide-angle end of the incident angle change reducing means is PW and the refractive power at the telephoto end is PT. Sometimes, PT <PW.

  A variable focal length optical system according to a fourth aspect of the present invention is the invention according to any one of the first to third aspects, wherein the incident angle changing means has a positive refractive power at the wide-angle end and a negative refractive power at the telephoto end. It is characterized by having.

  The imaging apparatus according to claim 5 includes a plurality of moving lens groups, a variable focal length optical system that performs zooming by moving the moving lens groups in an optical axis direction, and a subject image by the variable focal length optical system. An image pickup apparatus including an image pickup device that forms an image of an image is provided with an incident angle reducing unit that reduces a change in an incident angle of a light beam to the image pickup device due to zooming. The operational effects of the present invention are the same as those of the first aspect of the present invention.

  According to a sixth aspect of the present invention, in the invention according to the fifth aspect, the incident angle change reducing means may mix the first liquid having conductivity or polarity and the first liquid with each other. A second liquid that is not sealed in a container so that the interface has a predetermined shape, and a voltage is applied between the first liquid and an electrode provided in the container, thereby It is constituted by a liquid optical element whose shape is changed to adjust the refractive power.

  According to a seventh aspect of the present invention, there is provided the imaging device according to the fifth or sixth aspect, wherein the control means for controlling the voltage applied to the liquid optical element according to the focal length set by the variable focal length optical system. It is characterized by providing.

  According to the present invention, for example, a variable focal length optical system capable of reducing the angle change of the principal ray incident on the imaging surface at a magnification used for imaging between the wide-angle end and the telephoto end, and imaging using the same An apparatus can be provided.

  1A and 1B are cross-sectional views in the optical axis direction of an imaging apparatus including a variable focal length optical system according to an embodiment of the present invention. FIG. 1A is at the wide-angle end, and FIG. However, the drive unit and other electrical circuits of the variable focus lens VL are omitted. In FIG. 1, the variable focal length optical system includes, in order from the object side, a first lens L1, an aperture stop S, a second lens L2, a third lens L2, a fourth lens L4, and incident angle change reducing means. The variable focal length lens VL, the variable focal length optical system, the cover glass CG disposed on the image side of the variable focal length lens VL, and the image sensor CMOS which is a solid-state imaging device constitute an imaging device. . The first lens L1 constitutes the first group I, the aperture stop S, the second lens L2, and the third lens L2 constitute the second group II, the fourth lens L4 constitutes the third group III, The variable focus lens VL constitutes the fourth group IV, and here, the first group I and the second group II move in the optical axis direction to perform zooming.

  FIG. 2 is a schematic configuration diagram of the variable focus lens VL and its driving unit. Reference numeral VL denotes a variable focus lens according to the present embodiment. Reference numeral 40 denotes a lower container formed of a nonconductor. A first recess 41 is formed in the peripheral portion of the bottom surface (the right inner surface in the figure) of the lower container 40, and the first sealing plate 2 is disposed on the inner diameter side (center side) than this. The 2nd recessed part 42 to hold | maintain is formed. The first sealing plate 2 is made of transparent acrylic or glass.

  A second electrode ring 43 is provided on the entire inner periphery of the peripheral wall of the lower container 40, and the surface of the second electrode ring 43 is made of an acrylic resin or the like that also covers the electrode end face 43a. An insulating layer 44 is formed in close contact.

  Here, the peripheral wall portion of the lower container 40 is inclined with respect to the optical axis X so that the right end side is closer to the optical axis X than the left end side in the drawing. For this reason, the first electrode ring 43 and the insulating layer 44 are both inclined with respect to the optical axis X.

  Further, the thickness of the insulating layer 44 gradually increases toward the right in the figure. Further, the water repellent layer 11 is formed by applying a water repellent treatment agent below the entire inner circumference of the insulating layer 44. Further, a hydrophilic treatment agent is applied to the left side of the entire inner circumference of the insulating layer 44 to form the hydrophilic layer 12.

  Reference numeral 50 denotes an upper container formed of a non-conductor, and holds the second sealing plate 6 formed of transparent acrylic or glass on the inner diameter side thereof. A sheet-like first electrode ring 51 is formed in close contact with the right end surface of the peripheral portion of the upper container 50.

  An insulating layer 52 is formed in close contact with the surface of the first electrode ring 51. The insulating layer 52 is insulated so as to have an exposed portion 51a for contacting the first liquid 21 described later and applying a voltage thereto. The layer 52 is formed so as to cover only the outer edge side of the first electrode ring 51.

  Then, the peripheral wall portion of the lower container 40 and the upper container 50 are sealed in a liquid-tight manner, thereby being surrounded by the lower container 40, the upper container 50, the first sealing plate 2, and the second sealing plate 6. A container having a predetermined volume of liquid chamber is formed.

  This container has an axisymmetric shape with respect to the optical axis X. The liquid chamber is filled with two types of liquids as follows.

  First, in the state where the optical axis X of the lower container 40 to which the first sealing plate 2 is attached is oriented in the vertical direction, the upper surface of the first sealing plate 2 that is the bottom surface of the liquid chamber and the peripheral side of the lower container 40 The second liquid 22 is dripped onto the bottom surface of these layers (which correspond to the interface-facing surfaces) by an amount so that the height of the liquid column is intermediate between the water-repellent film 11 on the peripheral wall portion.

  The second liquid 22 is a colorless and transparent silicone oil having a specific gravity of 1.06 and a refractive index of 1.45 at room temperature. Subsequently, the remaining space in the liquid chamber is filled with the first liquid 21. The first liquid 21 is an electrolyte solution (conductive or polar) having a specific gravity of 1.06 and a refractive index of 1.35 at room temperature, in which water and ethyl alcohol are mixed at a predetermined ratio and a predetermined amount of salt is added. A liquid).

  That is, as the first and second liquids 21 and 22, liquids having the same specific gravity, different refractive indexes, and incompatible with each other (insoluble) are selected. And both the liquids 21 and 22 form the interface 24, and each exists independently, without mixing.

  The shape of the interface 24 is determined by the balance of the three interfacial tensions acting on the inner surface of the liquid chamber (container), the three substances of the first liquid 21 and the second liquid 22, that is, the outer edge of the interface 24. Then, two types of liquids are sealed by attaching the upper container 50 to which the second sealing plate 6 is attached to the lower container 40.

  Reference numeral 31 denotes a power supply circuit connected to the first electrode ring 25 and the second electrode ring 3.

  Two amplifiers (not shown) of the power feeding circuit 31 are respectively connected to the first electrode ring 51 and the second electrode ring 43 along the right end surface of the upper container 50 in the direction orthogonal to the optical axis 51b, 43b.

  In the above configuration, when a voltage is applied to the first liquid 21 via the first electrode ring 51 and the second electrode ring 43, the interface 24 is deformed by a so-called electrowetting effect.

  Next, the deformation of the interface 24 in the variable focus lens VL and the optical action caused by this deformation will be described.

  First, when no voltage is applied to the first liquid 21, as shown in FIG. 2, the shape of the interface 24 is such that the interface tension between the two liquids 21 and 22, the first liquid 21 and the insulating layer 44. It is determined by the interfacial tension between the water repellent film 11 or the hydrophilic film 12, the interfacial tension between the second liquid 22 and the water repellent film 11 or the hydrophilic film 12 on the insulating layer 44, and the volume of the second liquid 22.

  On the other hand, when a voltage is applied to the first liquid 21 from the power supply circuit 31, the interfacial tension between the first liquid 21 and the hydrophilic film 12 decreases due to the electrowetting effect, and the first liquid 21 becomes the hydrophilic film 12. Over the boundary between the water repellent film 11 and the water repellent film 11. As a result, the height of the second liquid 22 on the optical axis increases.

  In this way, the application of voltage to the first liquid 21 through the first and second electrode rings 51 and 43 changes the balance of the interface tension between the two liquids, and the interface 24 between the two liquids 21 and 22 changes. The shape changes. In this way, an optical element that can freely change the shape of the interface 24 by controlling the voltage of the power feeding circuit 31 can be realized.

  Further, since the first and second liquids 21 and 22 have different refractive indexes, optical power (1 / f: f is a focal length) as an optical lens is given, that is, variable focus. The focal length of the lens VL changes due to the shape change of the interface 24.

  Assuming that magnification has been changed in the imaging apparatus shown in FIG. 1, the power feeding circuit 31 obtains the set magnification (focal length) from, for example, information corresponding to the moved position of the second group II, and the like at each magnification. An applied voltage corresponding to a set magnification is obtained from a table that previously stores a voltage to be applied to the variable focus lens VL, and is applied to the variable focus lens VL. By controlling in this way, the variable focus lens VL changes the optical power as desired, and reduces the change in the incident angle to the image sensor CMOS due to the change in the magnification of the variable focal length optical system. .

  The optical image formed on the imaging surface by passing through the variable focal length optical system whose focal length is adjusted in this way is converted into an electrical signal by the image sensor CMOS and further subjected to predetermined processing. Is converted into an image signal.

  3A and 3B are cross-sectional views in the optical axis direction of the imaging apparatus including the optical system according to the comparative example, in which FIG. 3A is at the wide-angle end and FIG. 3B is at the telephoto end. Since the comparative example is different from the present embodiment of FIG. 1 only in that it does not have a variable focus lens, the same components are denoted by the same reference numerals, and description thereof is omitted.

  As is apparent from a comparison between FIGS. 1 and 3, in the case of the comparative example, the incident angle is large at the wide angle end and the incident angle of the chief ray is small at the telephoto end. By using the focus lens VL, the incident angles of chief rays can be made substantially equal at the wide-angle end and the telephoto end, and a high-quality image can be obtained by imaging with the image sensor CMOS.

  Examples of the variable focal length optical system suitable for the present embodiment (corresponding to FIG. 1) and comparative examples (corresponding to FIG. 3) are shown below, but the present invention is not limited to such examples. . In the present embodiment and the comparative example, the aspherical shape is an orthogonal coordinate system in which the vertex of the surface is the origin and the optical axis direction is the X axis, the vertex curvature is C, the conic constant is K, the aspheric coefficient is A4, A6. , A8, A10, and A12 are represented by the following “Equation 1”.

  Table 1 shows lens data of the variable focal length optical system according to the present example, and Table 2 shows the focal length f, inter-lens distances d1 to d4, and the radius of the interface of the variable focus lens. The refracting power PW at the wide-angle end of the variable focal length lens in the present embodiment is +0.0143, and the refracting power at the telephoto end is −0.0125.

  Table 3 shows lens data of the optical system according to the comparative example, and Table 4 shows the focal length f and the inter-lens distances d1 and d2.

  In the comparative example, by design, the incident angle of the principal ray on the imaging surface at the wide-angle end is 17.0 °, and the incident angle of the principal ray on the imaging surface at the telephoto end is 10.8 °. However, in this embodiment, the incident angle of the chief ray on the imaging surface at the wide-angle end is 13.9 °, and the chief ray is incident on the imaging surface at the telephoto end. Since the angle is 13.9 °, the difference is 0, and there is a feature that the amount of peripheral light on the imaging surface does not change even when the magnification is changed.

  The present invention has been described above with reference to the embodiments. However, the present invention should not be construed as being limited to the above-described embodiments, and can be modified or improved as appropriate. The image pickup apparatus of the present invention is preferably mounted on a small digital still camera, a portable terminal such as a mobile phone or a PDA, but can also be used for other applications such as a personal computer camera.

1 is a cross-sectional view in the optical axis direction of an imaging apparatus including a variable focal length optical system according to an embodiment of the present invention. It is a schematic block diagram of the variable focus lens VL and its drive part. It is an optical axis direction sectional view of an imaging device containing an optical system concerning a comparative example.

Explanation of symbols

L1 First lens S Aperture stop L2 Second lens L3 Third lens L4 Fourth lens VL Variable focus lens CMOS Image sensor

Claims (7)

In a variable focal length optical system that includes a plurality of moving lens groups and performs zooming by moving the moving lens groups in the optical axis direction,
A variable focal length optical system comprising an incident angle change reducing means for reducing an incident angle change of a light beam on a focal plane due to zooming.   The incident angle change reducing means includes a first liquid that is conductive or polar and a second liquid that does not mix with the first liquid in a container so that the interface has a predetermined shape. The liquid optical element is configured to be hermetically sealed and adjust the refractive power by changing the shape of the interface by applying a voltage between the first liquid and the electrode provided in the container. The variable focal length optical system according to claim 1.   The variable focal length optical system according to claim 1, wherein the incident angle change reducing unit is provided in the vicinity of the subject side of the focal plane.   4. The PT according to claim 1, wherein PT <PW when the refractive power at the wide-angle end of the incident angle change reducing means is PW and the refractive power at the telephoto end is PT. 5. Variable focal length optical system. A variable focal length optical system that includes a plurality of moving lens groups, and performs zooming by moving the moving lens groups in the optical axis direction, and an imaging element on which a subject image is formed by the variable focal length optical system In the imaging device
An image pickup apparatus comprising an incident angle reducing means for reducing a change in an incident angle of a light beam on an image pickup element due to zooming.   The incident angle change reducing means includes a first liquid that is conductive or polar and a second liquid that does not mix with the first liquid in a container so that the interface has a predetermined shape. The liquid optical element is configured to be hermetically sealed and adjust the refractive power by changing the shape of the interface by applying a voltage between the first liquid and the electrode provided in the container. The imaging apparatus according to claim 5, wherein: The imaging apparatus according to claim 5, further comprising a control unit that controls a voltage applied to the liquid optical element in accordance with a focal length set by the variable focal length optical system.

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