JP2010078801A - Imaging lens and image capturing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging lens having a compact five-element constitution, while having an optical performance compatible with a large solid-state image sensor, and to provide an image capturing apparatus. <P>SOLUTION: The compact imaging lens is acquired by forming a five-element constitution wherein a negative lens is used as a lens on the most object side. Further, an optical performance suitable for a large solid-state image sensor such as an APS format can be acquired by satisfying expression (1): 0.15<T24/T15<0.55, and expression (2): 0.03<T1/2Y<0.09. In the expression (1) and the expression (2), T24 is a length on the axis including an air interval from the second lens to the fourth lens, T15 is a length on the axis including an air interval from the first lens to the fifth lens, T1 is an axial thickness of the first lens, and 2Y is an imaging face orthogonal length of the solid-state image sensor, respectively. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an imaging lens and an imaging apparatus suitable for an imaging apparatus using a solid-state imaging device such as a CCD (Charge Coupled Devices) type image sensor or a CMOS (Complementary Metal-Oxide Semiconductor) type image sensor.

In recent years, video cameras and digital cameras equipped with an imaging device using a solid-state imaging device such as a CCD type image sensor or a CMOS type image sensor have become widespread, and a solid having a high number of pixels so that a higher quality image can be obtained. A device equipped with an image pickup device using an image pickup element has been supplied to the market. By the way, increasing the size of the solid-state image pickup device in accordance with the increase in the number of pixels leads to high costs in the semiconductor process. Conventionally, by increasing the pixel size, the number of pixels is increased even though the size is small. A solid-state image sensor has been generally used. Patent Documents 1 and 2 propose imaging lenses corresponding to such highly thinned solid-state imaging devices.
JP 2004-245893 A JP 2002-228925 A

  By the way, in a relatively large imaging device such as a lens interchangeable digital single-lens reflex camera, which tends to prioritize image quality over cost, 35 mm format (36 mm × 24 mm), APS format (about 24 mm × 16 mm), Four Thirds In many cases, a large-sized solid-state imaging device such as a format (about 18 mm × 13.5 mm) is used. Such a large solid-state image sensor has the same number of pixels as a smaller solid-state image sensor, which increases the light receiving area per pixel and is advantageous in terms of sensitivity and S / N ratio. This is because that. On the other hand, there is an attempt to use a large-sized solid-state imaging device as described above in a small-sized imaging device mounted on a video camera or a digital camera. However, since a lens that forms a subject image on the imaging surface of such a large solid-state imaging device is required to have optical performance such as telecentricity in order to suppress peripheral dimming, it is suitable for a small solid-state imaging device. The lenses shown in Patent Documents 1 and 2 have a problem that sufficient optical performance cannot be obtained. On the other hand, in order to ensure the compactness of video cameras and digital cameras, it is necessary to suppress the number of lenses and the total length as much as possible compared to interchangeable lenses for digital single lens reflex cameras.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a compact five-lens imaging lens and imaging device having optical performance compatible with a large solid-state imaging device. And

The imaging lens according to claim 1 is used to form a subject image on an imaging surface of a solid-state imaging device, and in order from the object side, a negative first lens, a positive second lens, a diaphragm, It consists of a negative third lens, a positive fourth lens, and a positive fifth lens, and satisfies the following conditions.
0.15 <T24 / T15 <0.55 (1)
0.03 <T1 / 2Y <0.09 (2)
However,
T24: length on the axis including the air gap from the second lens to the fourth lens T15: length on the axis including the air gap from the first lens to the fifth lens T1: the first lens On-axis thickness 2Y: diagonal length of imaging surface of solid-state imaging device

According to the present invention, a compact imaging lens is realized by adopting a five-lens configuration in which the lens on the most object side is a negative lens. Furthermore, by satisfying conditional expressions (1) and (2), it is possible to obtain optical performance suitable for a large-sized solid-state imaging device. More specifically, the conditional expression (1) is obtained by properly arranging the three lenses of the second lens, the third lens, and the fourth lens before and after the stop, thereby causing spherical aberration and off-axis aberration (non-axis aberration (non-axial aberration)). This is a conditional expression for appropriately correcting (point aberration, lateral chromatic aberration, etc.). That is, when the value of conditional expression (1) exceeds the lower limit, correction of excessive off-axis aberrations in the vicinity of the stop can be suppressed and generation of spherical aberration can be suppressed. On the other hand, when the value of conditional expression (1) is less than the upper limit, the three lenses of the second lens, the third lens, and the fourth lens can be arranged in the vicinity of the stop, and the entire area extends from the center to the periphery of the screen. Aberration correction is possible. More preferably, the range of the following formula should be satisfied.
0.22 <T24 / T15 <0.48 (1A)

Conditional expression (2) is a conditional expression for appropriately setting the axial thickness of the first lens to appropriately shorten the entire length of the imaging lens and correct aberrations. When the value of conditional expression (2) exceeds the lower limit, the occurrence of lateral chromatic aberration, astigmatism, and the like can be suppressed. On the other hand, when the value of conditional expression (2) is less than the upper limit, the overall lens length can be shortened. More preferably, the range of the following formula should be satisfied.
0.04 <T1 / 2Y <0.08 (2A)

  According to a second aspect of the present invention, in the invention of the first aspect, at least one aspherical surface is disposed on the second lens. By disposing at least one aspherical surface on the second lens, better aberration correction can be achieved.

  According to a third aspect of the present invention, in the invention of the first or second aspect, at least one aspheric surface is disposed on the fourth lens. By disposing at least one aspherical surface on the fourth lens, better aberration correction can be achieved.

  According to a fourth aspect of the present invention, in the invention of any one of the first to third aspects, the third lens and the fourth lens are cemented. By joining the third lens and the fourth lens, the overall length can be shortened, and in particular, good correction of longitudinal chromatic aberration and lateral chromatic aberration can be achieved.

The imaging lens of Claim 5 satisfies the following conditional expressions in the invention in any one of Claims 1-4, It is characterized by the above-mentioned.
0.4 <f2 / f <1.0 (3)
However,
f2: focal length of the second lens f: focal length of the entire imaging lens system

Conditional expression (3) is a conditional expression for appropriately setting the focal length of the second lens to appropriately shorten the entire imaging lens and correct aberrations. When the value of conditional expression (3) exceeds the lower limit, the focal length of the second lens can be appropriately maintained, and shortening of the total lens length can be achieved. On the other hand, when the value of conditional expression (3) is less than the upper limit, the focal length of the second lens does not become too large, and generation of higher-order spherical aberration and coma aberration can be suppressed. More preferably, the range of the following formula should be satisfied.
0.54 <f2 / f <0.9 (3A)

  An imaging apparatus according to a sixth aspect includes the imaging lens according to any one of the first to fifth aspects.

  According to the present invention, it is possible to provide a compact five-lens imaging lens and imaging device having optical performance compatible with a large solid-state imaging device.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. 1A and 1B are a perspective view as viewed from the front upper side and a perspective view as viewed from the lower back side of the digital camera equipped with the image pickup apparatus according to the present embodiment. FIG. It is a block diagram of an imaging device which has an imaging lens concerning a form of.

  In FIG. 1A, a digital camera DC includes a retractable lens barrel 80 that incorporates an imaging lens 101 and retracts with respect to a camera body 81, a finder window 82, a release button 83, and a flash light emitting unit 84. , A strap attaching portion 87, a USB terminal 88, and a lens cover 89. When the lens cover 89 is opened, a switch (not shown) is turned on, and the lens barrel 80 is moved forward to enter a shooting state. On the other hand, when the lens cover 89 is closed after shooting is finished, the switch (not shown) is turned off. The lens barrel 80 is retracted. Since the configuration for retracting the lens barrel 80 is well known, the following details are not described.

  Further, in FIG. 1B, the digital camera DC includes a finder eyepiece 91 and red and green display lamps that display AF and AE information to the photographer by light emission or blinking when the release button 83 is pressed. 92, a zoom button 93 for zooming up and down according to the operation of the photographer, a menu / set button 95 for various settings, a four-way switch 96 as a selection button, an image, other character information, and the like. A monitor LCD 112 to be displayed, a playback button 97 for playing back an image shot on the monitor LCD 112, a display button 98 for selecting display or deletion of an image displayed on the monitor LCD 112 or other character information, and a shot and recorded image Erasing button 99, tripod hole 71, and battery / card cover 72 that can be freely opened and closed. The photographer can display various menus on the monitor LCD 112 with the menu / set button 95, select with the selection button 96, and confirm the setting with the menu / set button 95. Inside the battery / card cover 72, a battery for supplying power to the digital camera DC and a card-type removable memory for recording captured images are loaded.

  Further, as illustrated in FIG. 2, the imaging apparatus 100 mounted on the digital camera DC includes an imaging lens 101, a solid-state imaging device 102 that is an APS format, an A / D conversion unit 103, a control unit 104, and an optical unit. System drive unit 105, timing generation unit 106, image sensor drive unit 107, image memory 108, image processing unit 109, image compression unit 110, image recording unit 111, monitor LCD 112, and FIG. The operation unit 113 including the above-described button group is configured.

The imaging lens 101 has a function of forming a subject image on the imaging surface of the solid-state imaging device 102. The imaging lens according to the present embodiment includes, in order from the object side, a negative first lens, a positive second lens, a diaphragm, a negative third lens, a positive fourth lens, and a positive fifth lens. And satisfy the following conditions.
0.15 <T24 / T15 <0.55 (1)
0.03 <T1 / 2Y <0.09 (2)
However,
T24: Length on the axis including the air gap from the second lens to the fourth lens T15: Length on the axis including the air gap from the first lens to the fifth lens T1: Thickness on the axis 2Y of the first lens : Diagonal length of imaging surface of solid-state image sensor

In addition, at least one aspherical surface is disposed on the second and fourth lenses, and the third lens and the fourth lens are joined. In addition, the following conditional expression is satisfied.
0.4 <f2 / f <1.0 (3)
However,
f2: focal length of the second lens f: focal length of the entire imaging lens system

  In the present embodiment, a relatively large total value (Δ1 + Δ2) of the lens-to-lens distance Δ1 between the first lens and the second lens and the lens-to-lens distance Δ2 between the fourth lens and the fifth lens can be secured relatively large. The total lens length can be shortened as much as possible.

  The solid-state image sensor 102 is an image sensor such as a CCD or CMOS, and includes an RGB color filter. The solid-state image sensor 102 photoelectrically converts incident light for each of R, G, and B and outputs an analog signal thereof. The A / D conversion unit 103 converts an analog signal into digital image data.

  The control unit 104 controls each unit of the imaging device 100. The control unit 104 includes a CPU (Central Processing Unit), a RAM (Random Access Memory), and a ROM (Read Only Memory), and various programs read out from the ROM and expanded in the RAM, and various in cooperation with the CPU. Execute the process.

  The optical system drive unit 105 controls the drive of the imaging lens 101 during zooming, focusing, exposure, and the like under the control of the control unit 104. The timing generator 106 outputs a timing signal for analog signal output. The image sensor drive unit 107 performs scanning drive control of the solid-state image sensor 102.

  The image memory 108 stores image data so as to be readable and writable. The image processing unit 109 performs various image processes on the image data. The image compression unit 110 compresses captured image data by a compression method such as JPEG (Joint Photographic Experts Group). The image recording unit 111 records image data on a recording medium such as a memory card set in a slot (not shown).

  The monitor LCD 112 is a color liquid crystal panel or the like, and displays image data after shooting, a through image before shooting, various operation screens, and the like. The operation unit 113 outputs information input by the user to the control unit 104 via the button group described above with reference to FIG.

  Here, the operation of the imaging apparatus 100 will be described. In subject photographing, subject monitoring (through image display) and image photographing execution are performed. In monitoring, an image of a subject obtained through the imaging lens 101 is formed on the light receiving surface (imaging surface) of the solid-state image sensor 102. The solid-state imaging device 102 disposed behind the imaging optical axis of the imaging lens 101 is scanned and driven by the timing generation unit 106 and the imaging device driving unit 107, and serves as a photoelectric conversion output corresponding to an optical image formed at regular intervals. Output analog signal for one screen.

  The analog signal is appropriately gain-adjusted for each primary color component of RGB, and then converted into digital data by the A / D conversion unit 103. The digital data is subjected to color process processing including pixel interpolation processing and γ correction processing by the image processing unit 109 to generate a luminance signal Y and color difference signals Cb, Cr (image data) as digital values, and the image memory. 108, the signal is periodically read out, the video signal is generated, and output to the monitor LCD 112. Note that the control unit 104, which is a white balance adjusting unit, adjusts the white balance so that the signal intensity of the blue wavelength component in the image signal is smaller than the signal intensity of the other colors.

  The monitor LCD 112 functions as an electronic viewfinder in monitoring, and displays captured images in real time. In this state, zooming, focusing, exposure, and the like of the imaging lens 101 are performed by driving the optical system driving unit 105 based on an input through the operation unit 113 that is performed according to the operation of the release button 83 of the photographer. Is set.

  In such a monitoring state, when the user operates the release button 83 at a timing at which still image shooting is desired, still image data is shot. In response to the operation of the release button 83, one frame of image data stored in the image memory 108 is read out and compressed by the image compression unit 110. The compressed image data is recorded in the removable memory by the image recording unit 111.

  Note that the description in the above embodiment and each example is an example of a suitable imaging lens and imaging apparatus according to the present invention, and the present invention is not limited to this. The imaging apparatus can also be installed in a video camera.

Next, examples suitable for the above-described embodiment will be described. However, the present invention is not limited to the following examples. The meaning of each symbol in the embodiment is as follows.
f: Focal length of the entire imaging lens system fB: Back focus F: F number 2Y: Diagonal length of the imaging surface of the solid-state imaging device R: Radius of curvature D: Spacing on the upper axis Nd: Refractive index νd of lens material with respect to d-line: lens material Abbe number of

In each embodiment, the surface described with “*” after each surface number is a surface having an aspheric shape, and the shape of the aspheric surface has the vertex of the surface as the origin and the X axis in the optical axis direction. The height in the direction perpendicular to the optical axis is represented by the following “Equation 1”. In the following (including the lens data in the table), a power of 10 (for example, 2.5 × 10 ⁻⁰² ) is expressed using E (for example, 2.5E-02).

ただし、
Ａｉ：ｉ次の非球面係数
Ｒ：曲率半径
Ｋ：円錐定数

However,
Ai: i-th order aspheric coefficient R: radius of curvature K: conic constant

Example 1
Table 1 shows lens data of Example 1. 3 is a cross-sectional view of the imaging lens of Example 1. FIG. In the figure, L1 is a negative first lens, L2 is a positive second lens, S is an aperture stop, L3 is a negative third lens, L4 is a positive fourth lens, L5 is a positive fifth lens, and I is An imaging surface is shown. The third lens L3 and the fourth lens L4 are cemented. F is a parallel plate that assumes an optical low-pass filter, an IR cut filter, a seal glass of a solid-state image sensor, and the like. FIG. 4 is an aberration diagram of spherical aberration (a), astigmatism (b), and distortion (c) of the imaging lens according to the first example. Here, in the spherical aberration diagram, g represents the amount of spherical aberration with respect to the g line, and d represents the amount of spherical aberration with respect to the d line. In the astigmatism diagram, a solid line S represents a sagittal surface, and a dotted line M represents a meridional surface.

(Example 2)
Table 2 shows lens data of Example 2. FIG. 5 is a cross-sectional view of the imaging lens of the second embodiment. In the figure, L1 is a negative first lens, L2 is a positive second lens, S is an aperture stop, L3 is a negative third lens, L4 is a positive fourth lens, L5 is a positive fifth lens, and I is An imaging surface is shown. The third lens L3 and the fourth lens L4 are cemented. F is a parallel plate that assumes an optical low-pass filter, an IR cut filter, a seal glass of a solid-state image sensor, and the like. FIG. 6 is an aberration diagram of spherical aberration (a), astigmatism (b), and distortion (c) of the imaging lens according to the second example. Here, in the spherical aberration diagram, g represents the amount of spherical aberration with respect to the g line, and d represents the amount of spherical aberration with respect to the d line. In the astigmatism diagram, a solid line S represents a sagittal surface, and a dotted line M represents a meridional surface.

(Example 3)
Table 3 shows lens data of Example 3. FIG. 7 is a cross-sectional view of the imaging lens of the third embodiment. In the figure, L1 is a negative first lens, L2 is a positive second lens, S is an aperture stop, L3 is a negative third lens, L4 is a positive fourth lens, L5 is a positive fifth lens, and I is An imaging surface is shown. The third lens L3 and the fourth lens L4 are cemented. F is a parallel plate that assumes an optical low-pass filter, an IR cut filter, a seal glass of a solid-state image sensor, and the like. FIG. 8 is an aberration diagram of spherical aberration (a), astigmatism (b), and distortion (c) of the imaging lens according to the third example. Here, in the spherical aberration diagram, g represents the amount of spherical aberration with respect to the g line, and d represents the amount of spherical aberration with respect to the d line. In the astigmatism diagram, a solid line S represents a sagittal surface, and a dotted line M represents a meridional surface.

Example 4
Table 4 shows lens data of Example 4. FIG. 9 is a cross-sectional view of the imaging lens of Example 4. In the figure, L1 is a negative first lens, L2 is a positive second lens, S is an aperture stop, L3 is a negative third lens, L4 is a positive fourth lens, L5 is a positive fifth lens, and I is An imaging surface is shown. The third lens L3 and the fourth lens L4 are cemented. F is a parallel plate that assumes an optical low-pass filter, an IR cut filter, a seal glass of a solid-state image sensor, and the like. FIG. 10 is an aberration diagram of spherical aberration (a), astigmatism (b), and distortion (c) of the imaging lens according to the fourth example. Here, in the spherical aberration diagram, g represents the amount of spherical aberration with respect to the g line, and d represents the amount of spherical aberration with respect to the d line. In the astigmatism diagram, a solid line S represents a sagittal surface, and a dotted line M represents a meridional surface.

  The values of conditional expressions (1) to (3) corresponding to the respective examples are summarized below.

It is the perspective view (a) seen from the front upper side of the digital camera carrying the imaging device concerning this Embodiment, and the perspective view (b) seen from the back lower side. It is a block diagram of an imaging device which has an imaging lens concerning this embodiment. 2 is a cross-sectional view of an imaging lens of Example 1. FIG. FIG. 6 is an aberration diagram of spherical aberration (a), astigmatism (b), and distortion (c) of the imaging lens according to Example 1; 6 is a cross-sectional view of an imaging lens of Example 2. FIG. FIG. 6 is an aberration diagram of spherical aberration (a), astigmatism (b), and distortion (c) of the imaging lens according to Example 2; 6 is a cross-sectional view of an imaging lens of Example 3. FIG. FIG. 6 is an aberration diagram of spherical aberration (a), astigmatism (b), and distortion aberration (c) of the imaging lens according to Example 3; 6 is a cross-sectional view of an imaging lens of Example 4. FIG. FIG. 6 is an aberration diagram of spherical aberration (a), astigmatism (b), and distortion aberration (c) of the imaging lens according to Example 4;

Explanation of symbols

71 Tripod hole 72 Card cover 80 Lens barrel 81 Camera body 82 Viewfinder window 83 Release button 84 Flash light emitting part 87 Strap attaching part 88 USB terminal 89 Lens cover 91 Viewfinder eyepiece 92 Display lamp 93 Zoom button 95 Set button 96 4 directions Switch 96 Selection button 97 Playback button 98 Display button 99 Erase button 100 Imaging device 101 Imaging lens 102 Solid-state imaging device 103 Conversion unit 104 Control unit 105 Optical system driving unit 106 Timing generation unit 107 Imaging device driving unit 108 Image memory 109 Image processing unit 110 Image compression unit 111 Image recording unit 112 Monitor LCD
113 Operation unit DC Digital camera L1 to L5 Lens S Aperture stop I Imaging surface F Optical low-pass filter or IR cut filter

Claims (6)

Used to form a subject image on the imaging surface of the solid-state imaging device, and in order from the object side, a negative first lens, a positive second lens, a stop, a negative third lens, and a positive first lens An imaging lens comprising four lenses and a positive fifth lens and satisfying the following conditions:
0.15 <T24 / T15 <0.55 (1)
0.03 <T1 / 2Y <0.09 (2)
However,
T24: length on the axis including the air gap from the second lens to the fourth lens T15: length on the axis including the air gap from the first lens to the fifth lens T1: the first lens On-axis thickness 2Y: diagonal length of imaging surface of solid-state imaging device   The imaging lens according to claim 1, wherein at least one aspheric surface is disposed on the second lens.   The imaging lens according to claim 1, wherein at least one aspheric surface is disposed on the fourth lens.   The imaging lens according to claim 1, wherein the third lens and the fourth lens are cemented. The imaging lens according to claim 1, wherein the following conditional expression is satisfied.
0.4 <f2 / f <1.0 (3)
However,
f2: focal length of the second lens f: focal length of the entire imaging lens system   An imaging apparatus comprising the imaging lens according to claim 1.

Images