JP2010181554A - Imaging lens and imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging lens having high optical performance, though it is made compact and is inexpensive. <P>SOLUTION: The imaging lens comprises, in order from an object side, a meniscus first lens having a convex surface directed toward the object side and having negative power, a second lens having a convex surface on the object side and positive power, a biconcave third lens having negative power, and a meniscus fourth lens having a convex surface directed toward an image side and having positive power. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an imaging lens used for an in-vehicle camera or a surveillance camera using an image sensor such as a CCD or CMOS, and mainly for an in-vehicle camera for taking images of the front, side, rear, etc. of an automobile. The present invention relates to an imaging lens used for the above.

  In recent years, image sensors such as CCDs and CMOSs have been greatly reduced in size and pixels. For this reason, the imaging device main body and the lens mounted thereon are also required to be small and light. On the other hand, in-vehicle cameras and surveillance cameras, for example, have high weather resistance, and can be used at night even though they can be used in a wide temperature range, such as in the mid-summer tropical region and outside air in cold winter areas. There is a need for a lens that has a small F-number, is bright, has high performance, and is inexpensive.

  Conventionally, as an imaging lens used for a vehicle-mounted camera, a surveillance camera, or the like, there are many 5 to 7 lenses. However, although the five- to seven-sheet structure has no problem in terms of optical performance, it is expensive and has the disadvantages of large and heavy dimensions. Therefore, it is conceivable to use an imaging lens having a four-lens configuration in order to achieve downsizing and cost reduction while providing performance that is not problematic in practice.

  As such an imaging lens, for example, those described in Patent Documents 1 to 4 below are known. In these Patent Documents 1 to 4, a lens optical system having a four-lens structure as a whole has a relatively small number of lenses.

Japanese Patent No. 3756114 Japanese Patent Application Laid-Open No. 60-037514 Japanese Patent Application Laid-Open No. 06-082695 JP-A-11-030745

  However, Patent Documents 1 to 4 do not satisfy all aspects of brightness, angle of view, and aberration in high dimensions, and further improvement in optical performance is desired in a four-lens optical system. .

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an imaging lens having high optical performance while being small and inexpensive, and an imaging apparatus including the imaging lens.

  The imaging lens of the present invention includes, in order from the object side, a first lens that is a meniscus lens having a negative power with a convex surface facing the object side, and a second lens having a positive power whose surface on the object side is a convex surface. And a third lens that is a biconcave lens and a fourth lens that is a meniscus lens having a positive power with the convex surface facing the image side.

  In the imaging lens of the present invention, it is preferable that a diaphragm is provided between the second lens and the third lens.

Further, when the focal length of the first lens is f1 and the focal length of the second lens is f2, it is preferable that the following conditional expression (1) is satisfied.
−5.0 <f1 / f2 <−3.0 (1)

Further, when the focal length of the first lens is f1 and the focal length of the third lens is f3, it is preferable that the following conditional expression (2) is satisfied.
3.3 <f1 / f3 <6.0 (2)

Further, when the radius of curvature of the object side surface of the fourth lens is R8 and the radius of curvature of the image side surface of the fourth lens is R9, it is preferable that the following conditional expression (3) is satisfied.
5.0 <R8 / R9 (3)

Further, it is preferable that the following conditional expression (4) is satisfied, where R1 is the radius of curvature of the object side surface of the first lens and f is the focal length of the entire system.
0.55 <R1 / f <0.70 (4)

Further, when the radius of curvature of the object side surface of the fourth lens is R8 and the radius of curvature of the image side surface of the fourth lens is R9, it is preferable that the following conditional expression (5) is satisfied.
0.9 <(R8 + R9) / (R8−R9) <1.5 (5)

  An imaging apparatus according to the present invention includes the imaging lens described above.

  According to the imaging lens of the present invention, in order from the object side, a first lens that is a meniscus lens having a negative power with a convex surface facing the object side, and a second lens having a positive power whose surface on the object side is a convex surface. Because it is composed of a lens, a third lens that is a biconcave lens having negative power, and a fourth lens that is a meniscus lens having positive power with the convex surface facing the image side, it is small and inexpensive, but high An imaging lens having optical performance can be realized.

  Since the image pickup apparatus of the present invention includes the image pickup lens of the present invention, the image pickup apparatus can be configured to be small and inexpensive, and can obtain a high-quality image.

Sectional drawing which shows the lens structure of the imaging lens concerning Example 1 of this invention. Sectional drawing which shows the lens structure of the imaging lens concerning Example 2 of this invention. Sectional drawing which shows the lens structure of the imaging lens concerning Example 3 of this invention. Sectional drawing which shows the lens structure of the imaging lens concerning Example 4 of this invention. Sectional drawing which shows the lens structure of the imaging lens concerning Example 5 of this invention. Each aberration diagram of the imaging lens according to Example 1 of the present invention Each aberration diagram of the imaging lens according to Example 2 of the present invention Each aberration diagram of the imaging lens according to Example 3 of the present invention Each aberration diagram of the imaging lens according to Example 4 of the present invention Each aberration diagram of the imaging lens according to Example 5 of the present invention The figure for demonstrating arrangement | positioning of the vehicle-mounted imaging device concerning embodiment of this invention

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a cross-sectional view illustrating a configuration of an imaging lens according to an embodiment of the present invention, and corresponds to the imaging lens of Example 1 described later.

  The imaging lens 1 includes a first lens L1 that is a meniscus lens having a negative power with a convex surface facing the object side in order from the object side along the optical axis Z, and a convex surface on the object side. A second lens L2 having a certain positive power, a third lens L3 that is a biconcave lens having a negative power, and a fourth lens L4 that is a meniscus lens having a positive power with a convex surface facing the image side are arranged. Being done. Note that the aperture stop St in FIG. 1 does not indicate the shape or size, but indicates the position on the optical axis Z.

  In FIG. 1, the imaging element 5 disposed on the image plane including the imaging position of the imaging lens 1 is also illustrated in consideration of the case where the imaging lens 1 is applied to the imaging device. The image pickup device 5 converts an optical image formed by the image pickup lens 1 into an electric signal, and includes, for example, a CCD image sensor.

  In addition, when applied to the imaging device, a cover glass, a low-pass filter, an infrared cut filter, or the like is disposed between the fourth lens L4 and the image plane in accordance with the configuration of the camera side on which the lens is mounted. Is preferred. For example, when the imaging lens 1 is used for a vehicle-mounted camera and used as a night vision camera for visual assistance at night, the blue light is cut from the ultraviolet light between the fourth lens L4 and the image plane. A simple filter may be inserted.

  Instead of arranging a low-pass filter or various filters that cut a specific wavelength range between the fourth lens L4 and the image plane, these various filters may be arranged between the lenses. Or you may give the coat | court which has the effect | action similar to various filters to the lens surface of either lens which the imaging lens 1 has.

  By adopting such a configuration, it is possible to exhibit sufficient optical performance even when all of the first to fourth lenses are configured with spherical lenses without using an expensive aspherical lens with a four-lens configuration. Therefore, an imaging lens having high optical performance while being small and inexpensive can be realized.

  Further, it is desirable that the imaging lens 1 satisfies any or all of the following conditional expressions.

When the focal length of the first lens is f1 and the focal length of the second lens is f2, it is preferable that the following conditional expression (1) is satisfied. Here, when the upper limit of conditional expression (1) is exceeded, spherical aberration and coma aberration increase, and it becomes difficult to obtain resolution at a high frequency. When the lower limit is exceeded, astigmatism increases.
−5.0 <f1 / f2 <−3.0 (1)
In addition, it is more preferable to satisfy conditional expression (1-1).

  −4.5 <f1 / f2 <−3.1 (1-1)

Further, when the focal length of the first lens is f1 and the focal length of the third lens is f3, it is preferable that the following conditional expression (2) is satisfied. Here, if the upper limit of conditional expression (2) is exceeded, astigmatism will increase, and if it falls below the lower limit, spherical aberration and coma will increase, making it difficult to achieve resolution at high frequencies.
3.3 <f1 / f3 <6.0 (2)
In addition, it is more preferable to satisfy conditional expression (2-1).

  3.4 <f1 / f3 <5.0 (2-1)

Further, when the radius of curvature of the object side surface of the fourth lens is R8 and the radius of curvature of the image side surface of the fourth lens is R9, it is preferable that the following conditional expression (3) is satisfied. Here, if the lower limit of conditional expression (3) is not reached, distortion will increase.
5.0 <R8 / R9 (3)
In addition, it is more preferable to satisfy conditional expression (3-1).

  6.0 <R8 / R9 (3-1)

Further, it is preferable that the following conditional expression (4) is satisfied, where R1 is the radius of curvature of the object side surface of the first lens and f is the focal length of the entire system. Here, if the upper limit of conditional expression (4) is exceeded, spherical aberration and coma aberration will be undercorrected, and if it falls below the lower limit, distortion will increase.
0.55 <R1 / f <0.70 (4)

Further, when the radius of curvature of the object side surface of the fourth lens is R8 and the radius of curvature of the image side surface of the fourth lens is R9, it is preferable that the following conditional expression (5) is satisfied. Here, if the upper limit of conditional expression (5) is exceeded, spherical aberration and coma aberration will be undercorrected, and astigmatism will increase, and if it falls below the lower limit, spherical aberration and coma aberration will increase. It becomes difficult to obtain resolution.
0.9 <(R8 + R9) / (R8−R9) <1.5 (5)
In addition, it is more preferable to satisfy conditional expression (5-1).

  1.0 <(R8 + R9) / (R8-R9) <1.4 (5-1)

  As for the aperture stop St, if the aperture stop St is on the object side of the second lens L2, the outer diameter of the first lens L1 can be reduced, but the effective diameters of the third lens L3 and the fourth lens L4 are increased. If the lens is arranged so that the luminous flux is not kicked, the length of the entire lens system becomes long. In addition, when it is located on the image side with respect to the third lens L3, the incident angle of off-axis light to the image surface becomes large, and depending on the sensor, the image is deteriorated and the peripheral light amount is reduced. Therefore, it is preferable to provide the aperture stop St between the second lens L2 and the third lens L3.

  The imaging lens 1 preferably has a distortion of ± 10% or less when the ideal image height is f tan θ. By suppressing the distortion to ± 10%, an image with little distortion can be obtained. Furthermore, by setting the distortion to ± 5% or less, image distortion can be further suppressed.

  Since the first lens L1 is the most object side lens, when used in a harsh environment such as an in-vehicle camera, the first lens L1 is resistant to surface deterioration due to wind and rain, temperature change due to direct sunlight, It is preferable to use a material that is resistant to chemicals such as detergents, that is, a material having high water resistance, weather resistance, acid resistance, chemical resistance, and the like. Further, the first lens L1 is preferably made of a hard material that is hard to break, and specifically, glass or transparent ceramics is preferably used. Ceramics have properties of higher strength and higher heat resistance than ordinary glass.

  When the imaging lens 1 is applied to, for example, a vehicle-mounted camera, it is required that the imaging lens 1 can be used in a wide temperature range from the outside air in a cold region to the interior of a tropical summer vehicle. Therefore, it is preferable that the material of all the lenses is glass. Specifically, it is preferable that it can be used in a wide temperature range of −40 ° C. to 125 ° C. In order to manufacture lenses at low cost, it is preferable that all the lenses are spherical lenses. However, when priority is given to optical performance over cost, aspherical lenses may be used.

  In the imaging lens 1, the light beam that passes outside the effective diameter between the first lens L <b> 1 and the second lens L <b> 2 becomes stray light and reaches the image plane, which may become a ghost. Since the light beam that passes outside the outermost peripheral light beam of the off-axis light beam may become stray light, it is preferable to block the stray light by providing a light shielding means between the first lens L1 and the second lens L2. As the light shielding means, for example, an opaque paint may be applied to a portion outside the effective diameter on the image side of the first lens L1, or an opaque plate material may be provided. Alternatively, an opaque plate material may be provided in the optical path of a light beam that becomes stray light to serve as a light shielding unit. The light shielding means for such a purpose may be arranged not only between the first lens L1 and the second lens L2, but also between other lenses as necessary. Furthermore, a hood-shaped object that prevents stray light may be disposed in front of the first lens L1 on the object side.

  Next, specific numerical examples of the imaging lens 1 according to the present invention will be described.

<Example 1>
FIG. 1 shows a lens configuration diagram of the imaging lens according to Example 1, and Table 1 shows lens data and various data. In the lens data of Table 1, the surface number indicates the i-th (i = 1, 2, 3,...) Surface number that sequentially increases toward the image side with the surface of the component closest to the object side as the first. The lens data in Table 1 includes the aperture stop St.

  In Table 1, Ri represents the radius of curvature of the i-th (i = 1, 2, 3,...) Surface, and Di represents the i-th surface between the i (i = 1, 2, 3,...) Surface and the i + 1-th surface. The surface interval on the optical axis Z is shown. Nej represents the refractive index with respect to the e-line of the j-th (j = 1, 2, 3,...) Optical element that sequentially increases toward the image side with the most optical element on the object side being first, and νdj is j The Abbe number for the d-line of the th optical element is shown. In Table 1, the unit of the radius of curvature and the surface interval is mm, and the radius of curvature is positive when convex on the object side and negative when convex on the image side.

  In the various data in Table 1, f is the focal length of the entire system, Bf is the back focus converted to air, and L is the distance on the optical axis Z from the object side surface of the first lens L1 of the entire system to the image plane (back The focus is air equivalent). The units in the various data in Table 1 are all mm. The meanings of symbols in Table 1 are the same for the examples described later.

<Example 2>
FIG. 2 shows a lens configuration diagram of the imaging lens according to Example 2, and Table 2 shows lens data and various data. ●

<Example 3>
FIG. 3 shows a lens configuration diagram of the imaging lens according to Example 3, and Table 3 shows lens data and various data.

<Example 4>
FIG. 4 shows a lens configuration diagram of the imaging lens according to Example 4, and Table 4 shows lens data and various data.

<Example 5>
FIG. 5 shows a lens configuration diagram of the imaging lens according to Example 5, and Table 5 shows lens data and various data.

  Aberration diagrams of spherical aberration, astigmatism, distortion (distortion aberration), and lateral chromatic aberration of the imaging lenses according to Examples 1 to 5 are shown in FIGS. The upper part of each figure shows the longitudinal aberration, and the lower part shows the lateral aberration. The lateral aberration at the bottom indicates coma.

  Each aberration diagram shows an aberration with the e-line (546.07 nm) as a reference wavelength, but the spherical aberration diagram and the lateral chromatic aberration diagram show the g-line (wavelength 435.83 nm) and the C-line (wavelength 656.27 nm). The aberration for is also shown. The distortion diagram shows the amount of deviation from the ideal image height ftan θ using the focal length f of the entire lens system and the incident angle θ of the light beam to the lens (variable treatment, 0 ≦ θ ≦ ω). Fno. On the vertical axis of the spherical aberration diagram. Is the F number, and ω on the vertical axis of the other aberration diagrams represents the half angle of view.

  As can be seen from FIGS. 6 to 10, the first to fifth embodiments are bright optical systems with an F value of 2.5, and each aberration is well corrected. It can be used.

  The above-described imaging lens 1 and the imaging lenses of Examples 1 to 5 have good optical performance in spite of the four-lens configuration, and can realize downsizing and cost reduction. It can be suitably used for a vehicle-mounted camera for taking a video of a side, rear, or the like.

  As a usage example, FIG. 11 shows a state in which the imaging lens and the imaging apparatus of the present embodiment are mounted on the automobile 100. In FIG. 11, an automobile 100 includes an outside camera 101 for imaging a blind spot range on the side surface on the passenger seat side, an outside camera 102 for imaging a blind spot range on the rear side of the automobile 100, and a rear surface of a rearview mirror. An in-vehicle camera 103 that is attached and captures the same field of view as the driver is provided. The outside camera 101, the outside camera 102, and the inside camera 103 are imaging devices, the imaging lens 1 according to the embodiment of the present invention, and an imaging device 5 that converts an optical image formed by the imaging lens 1 into an electrical signal. It has.

  As described above, since the imaging lens 1 according to the embodiment of the present invention is small and has good optical performance, the outside cameras 101 and 102 and the in-vehicle camera 103 can also be configured in a small size. A good image can be formed on the imaging surface. Further, since the imaging lens 1 can exhibit sufficient optical performance without using an aspheric lens, it can be manufactured at low cost, and therefore the outside cameras 101 and 102 and the in-vehicle camera 103 can also be manufactured at low cost.

  The present invention has been described with reference to the embodiment and examples. However, the present invention is not limited to the above embodiment and example, and various modifications can be made. For example, the values of the radius of curvature, the surface interval, and the refractive index of each lens component are not limited to the values shown in the above numerical examples, but can take other values.

  In the embodiment of the imaging device, the example applied to the in-vehicle camera has been described with reference to the drawings. However, the present invention is not limited to this application. For example, the present invention is applied to a mobile terminal camera, a surveillance camera, and the like. Is also applicable.

DESCRIPTION OF SYMBOLS 1 Image pick-up lens 5 Image pick-up element 100 Automobile 101,102 Outside camera 103 In-vehicle camera L1 1st lens L2 2nd lens L3 3rd lens L4 4th lens St Aperture stop Z Optical axis

Claims (8)

  In order from the object side, a first lens that is a meniscus lens having a negative power with a convex surface facing the object side, a second lens having a positive power whose surface on the object side is a convex surface, and a third lens that is a biconcave lens An imaging lens comprising: a lens; and a fourth lens that is a meniscus lens having a positive power with a convex surface facing the image side.   The imaging lens according to claim 1, further comprising a diaphragm between the second lens and the third lens. 3. The imaging lens according to claim 1, wherein the following conditional expression (1) is satisfied, where f1 is a focal length of the first lens and f2 is a focal length of the second lens.
−5.0 <f1 / f2 <−3.0 (1) The imaging according to any one of claims 1 to 3, wherein the following conditional expression (2) is satisfied, where f1 is a focal length of the first lens and f3 is a focal length of the third lens. lens.
3.3 <f1 / f3 <6.0 (2) 2. The following conditional expression (3) is satisfied, where R8 is the radius of curvature of the object side surface of the fourth lens and R9 is the radius of curvature of the image side surface of the fourth lens. 5. The imaging lens according to any one of items 1 to 4.
5.0 <R8 / R9 (3) 6. The following conditional expression (4) is satisfied, where R1 is the radius of curvature of the object side surface of the first lens and f is the focal length of the entire system. The imaging lens described.
0.55 <R1 / f <0.70 (4) 2. The following conditional expression (5) is satisfied, where R8 is a radius of curvature of the object side surface of the fourth lens and R9 is a radius of curvature of the image side surface of the fourth lens. The imaging lens according to any one of items 1 to 6.
0.9 <(R8 + R9) / (R8−R9) <1.5 (5)   An imaging apparatus comprising the imaging lens according to claim 1.

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