JP5693364B2 - Imaging lens - Google Patents

Description

  The present invention relates to a single-focus wide-angle imaging lens used in an imaging device including a solid-state imaging device such as a vehicle-mounted camera.

  Imaging lenses used in in-vehicle cameras often require visibility at the periphery of the screen compared to the center of the screen while ensuring a wide angle of view, so the image magnification at the periphery of the screen is large and imaging performance is good. Is required. In addition, since the mounting space is often limited, it is required to be small and lightweight.

  The following Patent Document 1 has been proposed as a single-focus wide-angle imaging lens that can possibly meet these demands. However, in the single focus lens described in Patent Document 1, in order to have high imaging performance by design, a lot of aspheric surfaces are used, and one glass lens and three resin lenses are in a poor balance of materials. Problems occur in actual use. Further, as a manufacturing problem, since the refractive index is not sufficiently high for a resin lens, the load applied to the lens surface becomes strong, so that manufacturing tolerances become severe. In particular, the tolerance between the second lens and the third lens is severe, which leads to a decrease in yield. Moreover, as a problem in actual use, first, there is a problem in the performance guarantee temperature. When a camera module is mounted on a car, it is required to satisfy performance in a wide temperature range from low to high. However, in the following patent, since the balance between the glass lens and the resin lens is poor as described above, the temperature range in which the performance can be guaranteed becomes narrow. The reason is that the resin lens has a larger chemical change and physical change due to temperature than the glass lens, and the shape deviates from the design according to the temperature change. The second problem is the problem of ghost flare. In Patent Document 1, the second lens object side surface is set as a concave surface by the power arrangement. Although this is a concave surface for correcting chromatic aberration of magnification, it tends to cause ghost flare in a wide-angle lens. This is because the light reflected by the object side surface of the second lens is reflected by the surface on the first lens image surface side and reaches the imaging surface. In actual use, a headlight or the like of an oncoming vehicle at night appears as a ghost on the imaging surface due to surface reflection of the lens.

JP 2010-54646 A

  The present invention has been made in view of the above points. The object of the present invention is to provide a large image of the periphery of the screen while having high optical performance by the four-lens configuration, the shape of a lens, the shape of an aspheric surface, etc. Is to provide a small and thin wide-angle imaging lens.

In order to achieve the above object, the lens of the present invention comprises, in order from the object side, a first lens formed of a glass material that is a meniscus lens having a negative refractive power with a convex surface facing the object side, and a surface on the imaging side. A second lens formed of a resin material that is a meniscus lens that has an aspherical surface and has a negative refractive power with the convex surface facing the object side, and a positive refractive power that does not have an aspherical surface and has the convex surface facing the object side Four lenses, a third lens made of a glass material having an aperture stop, and a fourth lens made of a resin material that is convex on both sides and has positive refractive power and is aspheric on both sides. A lens is disposed, and the following conditional expression is satisfied. However, 2 <Θ <90 (deg), h1 is the height from the center of the imaging surface where an object with a half field angle Θ-2 (deg) forms an image on the imaging surface, and h2 is the half field angle Θ-1 ( deg) is the height from the center of the imaging surface where the object is imaged on the imaging surface, h3 is the height from the center of the imaging surface where the object with the half angle of view Θ (deg) is imaged on the imaging surface , The focal length of the first lens is f1 (mm), the focal length of the second lens at the d line is f2 (mm), the focal length of the third lens at the d line is f3 (mm), and the first lens at the d line is f3 (mm). The focal length of the four lenses is f4 ( mm), the object side curvature radius of the first lens is r1 (mm), the image side curvature radius of the first lens is r2 (mm), and the center lens thickness of the first lens is Is d (mm), and the focal length of the optical system is f (mm) .

(H2-h1) / (h3-h2) ≦ 1.0 (1)
0.9 <| f2 / f4 | <1.1 (3)
1.2 <d / f (4)
3.4 <r1 / r2 <4.2 (5)
6.0 <| f1 / f | <9.0 (9)
2.3 <| f2 / f | <2.7 (10)
2.9 <| f3 / f | <4.0 (11)
Equation (1) means that an object appears large on the imaging surface as the angle of view widens (in other words, shifts from the center of the angle of view to the periphery of the screen). The above formula will be described using Example 1 as an example. For example, for an object with a half field angle of 20 deg to 21 deg, the difference in image formation position on the imaging surface is 14.9 (μm). An object having a half field angle of 21 deg to 22 deg is 15.0 (μm) on the imaging surface. As the angle of view widens in this way, the object appears larger on the imaging surface (see FIG. 5).

  (3) Designed to satisfy the conditions such as the formula, it can be used in low temperatures in the usage environment. It is possible to realize high quality camera modules in a wide temperature range up to high temperatures. High quality here means that optical performance and projection characteristics do not vary with temperature.
To do. If you deviate from the above lower limit and upper limit, the temperature will change and the resin lens will fluctuate.
Optical performance will change more. The above formula means that the second lens is a concave lens.
The power ratio (focal length ratio) of the fourth lens, which is a lens and a convex lens, is approximately 1: 1 (0.9).
~ Within 1.1), the change due to the temperature change is offset between the resin lenses. It is a thing. Glass lenses originally have little change with temperature, so The camera module as a whole realizes a high-quality camera module in a wide temperature range.

  The front camera is designed by satisfying the conditions of (4) and (5). It is possible to function as an in-vehicle camera module. The above imaging lens When used as a front camera, the 1st lens is affected by the moving stones Strong drop impact strength is required. In that case, if the first lens is thin, sufficient strength can be obtained. I can't. The above equation is an item that must be designed in view of the situation. Naturally As the noise becomes smaller, it is possible to obtain sufficient strength even if it is thin. The thickness d, the focal length f, and the curvature radius ratio of both surfaces of the first lens are used.

  If the lower limit of equation (9) is exceeded, the negative refracting power increases and correction of chromatic aberration of magnification is acceptable. Although it becomes easy, the curvature of the side surface of the first lens image becomes too small, making it difficult to manufacture. The If the upper limit is exceeded, the curvature of the side surface of the first lens object becomes small, so the effective diameter is large. The lens system becomes difficult to downsize, and the negative required to obtain a wide angle of view. The refractive power is supplemented only by the second lens image side surface, and the curvature becomes too small. When the lower limit value of the expression (10) is exceeded, the negative refractive power increases, so the curvature of the side surface of the second lens image Becomes too small. Accordingly, the curvature of the side surface of the third lens object is also small. It becomes too difficult to manufacture. If the upper limit is exceeded, the negative refractive power is insufficient. This makes it difficult to correct the chromatic aberration of magnification. If the upper limit of (11) is exceeded, positive bending Since the bending force is insufficient, it is difficult to correct chromatic aberration of magnification. If the lower limit is exceeded, the third len Since the curvature of the side surface of the object becomes too small, manufacturing becomes difficult. 4th lens In particular, since the aberration is greatly corrected on the image side surface, the upper limit of (12) is exceeded. Then, the positive refractive power becomes too small, and it becomes difficult to correct the aberration. Conversely, the lower limit is exceeded Then, since the curvature of the side surface of the fourth lens image becomes too small, the manufacture becomes difficult. The

  Further, the distance from the object side surface of the first lens to the image sensor is L (mm). When the maximum diameter φ (mm) through which the light beam passes on the object side surface of the first lens, It is preferable to satisfy the conditional expression.

0.95 <φ / L <1.05 (2)
  By designing to meet these conditions, a small, small-diameter camera module It can be realized. In a wide-angle lens, the optical total length is correlated with the first lens diameter. is there. If the focal length is constant and the first lens diameter and optical total length are increased, the correction of aberrations is easy. Therefore, high optical performance can be ensured. Conversely, the first lens diameter and the optical total length are shortened. If this occurs, it will be difficult to correct the aberrations, leading to a reduction in quality. Here the diameter and total length are parameters As mentioned above, there is a strong correlation between the two, and each individual small size is difficult. Because it is difficult. In other words, keep the diameter constant and the overall length short, and keep the overall length constant and the diameter small. Is not suitable for miniaturization. High optical performance is maintained by designing to satisfy the above formula Thus, it is possible to reduce the size.

  Further, it is preferable that a horizontal field angle and a vertical field angle in the imaging lens satisfy the following conditional expressions. However, 2W is the total field angle of the light beam incident on the maximum horizontal position on the imaging surface, and 2V is the total field angle of the light beam incident on the maximum vertical position on the imaging surface.

2W> 180 (deg) (6)
150 (deg) <2V <160 (deg) (7)
By designing so as to satisfy such a condition, it is possible to greatly capture an object at the periphery of the screen. Regarding the above formula (6), first, an in-vehicle camera is assumed as the camera module of the present invention. It is necessary to see the 180 deg direction that is a blind spot in the front camera. Regarding the above formula (7), the vertical angle of view must be in an area satisfying the above formula in order to enlarge the peripheral portion. An angle of view smaller than 150 deg is advantageous as a peripheral magnification, but it is difficult to maintain high optical performance. In particular, it is difficult to correct lateral chromatic aberration and the peripheral image performance tends to deteriorate. Conversely, if it exceeds 160 deg, the periphery becomes small, and the visibility of the periphery that is the object of the present invention is lowered.

  Furthermore, when the distance from the image side surface of the fourth lens to the imaging surface is fb (mm) and the focal length of the optical system is f (mm), it is preferable that the following conditional expression is satisfied.

fb / f > 2.0 (8)
By designing so as to satisfy such a condition, it is possible to secure a distance between the imaging surface and the lens. There are two adverse effects caused by deviating from the conditional expression. First, if this interval is shortened, it becomes difficult to insert a member such as a low-pass filter or an infrared cut filter. Furthermore, it becomes difficult to secure an adjustment margin when adjusting the tilt of the imaging lens and the imaging element. Secondly, the imaging element and the fourth resin lens are close to each other, and the fourth lens generates heat due to heat transmission and causes a composition change under the influence of heat generation of the imaging element. In particular, resin lenses may cause problems such as yellowing due to their low glass transition temperature.

  According to the present invention, it is possible to provide a wide-angle imaging lens that has a small size, a thin shape, and a large periphery, by appropriately setting the shape of the lens, the shape of an aspheric surface, etc. while having high optical performance by the four-lens configuration. As a result, a compact wide-angle imaging lens that can be mounted on a surveillance camera or a vehicle-mounted camera can be realized.

It is a figure which shows the lens structure of the imaging lens of this embodiment. It is a figure which shows the basic composition of the lens system in Example 1 of this embodiment. FIG. 6 is an aberration diagram showing spherical aberration and astigmatism in Example 1 of the present embodiment. It is a figure which shows the distortion which made the ideal image height in Example 1 of this embodiment into the three-dimensional projection system. It is a figure which shows the image magnification of the lens in Example 1 of this embodiment. It is a figure which shows the basic composition of the lens system in Example 2 of this embodiment. It is an aberration diagram showing spherical aberration and astigmatism in Example 2 of the present embodiment. It is a figure which shows the distortion which made the ideal image height in Example 2 of this embodiment into the stereoscopic projection system. It is a figure which shows the image magnification of the lens in Example 2 of this embodiment. It is a figure which shows the basic composition of the lens system in Example 3 of this embodiment. It is an aberration diagram showing spherical aberration and astigmatism in Example 3 of the present embodiment. It is a figure which shows the distortion which made the ideal image height in Example 3 of this embodiment into the three-dimensional projection system. It is a figure which shows the image magnification of the lens in Example 3 of this embodiment. It is a figure which shows the basic composition of the lens system in Example 4 of this embodiment. It is an aberration diagram showing spherical aberration and astigmatism in Example 4 of the present embodiment. It is a figure which shows the distortion which made the ideal image height in Example 4 of this embodiment into the three-dimensional projection system. It is a figure which shows the image magnification of the lens in Example 4 of this embodiment. It is a figure which shows the basic composition of the lens system in Example 5 of this embodiment. FIG. 10 is an aberration diagram showing spherical aberration and astigmatism in Example 5 of the present embodiment. It is a figure which shows the distortion which made the ideal image height in Example 5 of this embodiment into the three-dimensional projection system. It is a figure which shows the image magnification of the lens in Example 5 of this embodiment. It is a figure which shows the basic composition of the lens system in Example 6 of this embodiment. It is an aberrational figure which shows the spherical aberration and astigmatism in Example 6 of this embodiment. It is a figure which shows the distortion which made the ideal image height in Example 6 of this embodiment into the three-dimensional projection system. It is a figure which shows the image magnification of the lens in Example 6 of this embodiment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows the lens configuration of the embodiment in an optical section. In FIG. 1, reference numeral 100 </ b> A denotes a symbol for each component and a symbol for each surface, and reference numeral 100 </ b> B denotes a symbol for the interval D in each component, both of which indicate the imaging lens 100.

  In this embodiment, as shown by 100A in FIG. 1, in order from the object side, the first lens 110, the second lens 120, the third lens 130, the aperture stop 140, the fourth lens 150, the IRCF or the cover glass 160, and the CCD. This is a four-lens single-focus imaging lens 100 in which an imaging element 170 such as (Charge Coupled Device) or CMOS (Complementary Mental-Oxide Semiconductor device) is arranged.

  In the imaging lens embodying the present invention, the four lenses are, in order from the object side, the first lens 110 that is a meniscus lens having a negative refractive power with the convex surface facing the object side, and the negative lens with the convex surface facing the object side. A second lens 120 that is a meniscus lens having a refractive power of ## EQU2 ## a third lens 130 having a positive refractive power with the convex surface facing the object side, and a first lens having a positive refractive power with the convex surface facing the aperture stop and both sides. The four lenses 150 are arranged.

  In the imaging lens 100, the light incident from the object side is the object side R1 surface 1, the image surface side R2 surface 2 of the first lens 110, and the object side R3 surface 3 of the second lens 120, as indicated by 100A in FIG. , Image side R4 surface 4, object side R5 surface 5 of third lens 130, image side R6 surface 6, surface 7 of aperture stop 140, object side R7 surface 8 of fourth lens 150, image surface side R8 surface 9 Then, the light passes through the object side R9 surface 10 and the image surface side R10 surface 11 of the cover glass 160 in order, and is condensed on the imaging surface (imaging surface) 12 of the image sensor 170.

  Further, as indicated by 100B in FIG. 1, the distance between the R1 surface 1 and the R2 surface 2, which is the thickness of the first lens 110, is D1, and the R2 surface 2 of the first lens 110 and the R3 surface 3 of the second lens 120. The distance between the R3 surface 3 and the R4 surface 4 that is the thickness of the second lens 120 is D3, the distance between the R4 surface 4 of the second lens 120 and the R5 surface 5 of the third lens 130 is D4, The distance between the R5 surface 5 and the R6 surface 6 that is the thickness of the third lens 130 is D5, the distance between the R6 surface 6 of the third lens 130 and the surface 7 of the aperture stop 140 is D6, and the surface 7 of the aperture stop 140 and the fourth The distance between the R8 surface 8 of the lens 150 is D7, the distance between the R8 surface 8 and the R9 surface 9 which is the thickness of the fourth lens 150 is D8, the R surface 9 of the fourth lens 150 and the object side R9 surface of the cover glass 160. D9 is the distance between 10 and R9 is the thickness of the cover glass 160 10 and the distance between the R10 surface 11 D10, the distance between the R10 surface 11 of the cover glass 160 and the image plane 12 and D11.

  Here, when the second lens 120 and the fourth lens 150 are formed of a resin material, weight reduction and cost reduction can be realized, and an aspherical shape can be easily manufactured. Further, by forming the first lens 110 and the third lens 130 from a glass material, a material having a wide dispersion value can be selected, and as a result, it is possible to satisfactorily correct lateral chromatic aberration.

  In addition, the second lens 120 and the fourth lens 14 have an aspherical shape. By having an aspherical shape, aberration correction becomes easy, and it is possible to obtain a good resolution performance while being small.

  The aspheric shape of the lens described in the following numerical examples is positive in the direction from the object side to the image plane side, k is a conical coefficient, and A, B, C, and D are aspheric coefficients. , R is the central radius of curvature, h represents the height of the light beam, and c represents the reciprocal of the central radius of curvature. Where Z is the depth from the tangent plane to the surface vertex, A is the fourth-order aspheric coefficient, B is the sixth-order aspheric coefficient, C is the eighth-order aspheric coefficient, and D is the tenth-order aspheric coefficient. Each aspheric coefficient is shown.

  In the imaging lens embodying the present invention, the Abbe number of the material constituting the first lens 110 with respect to the d-line is preferably 40 or more, and the Abbe number of the material constituting the second lens 120 with respect to the d-line is 50 or more. The Abbe number for the d-line of the material constituting the three lenses 130 is set to 30 or less, and the Abbe number for the d-line of the material constituting the fourth lens 150 is set to 50 or more. The first lens 110 and the second lens 120 that are located on the object side of the aperture stop 140 and are negative lenses have a magnification that is generated in the first lens 110 and the second lens 120 as the Abbe number of each material constituting them increases. Chromatic aberration is reduced. Further, this is because the chromatic aberration of magnification can be corrected more favorably as the Abbe number of the material constituting the third lens 130 that is a positive lens is closer to the object side than the aperture stop 140.

  Examples 1 to 6 according to specific numerical values of the imaging lens 100 are shown below. In the numerical values of Examples 1 to 6, the focal length, the F number, the horizontal field angle, the vertical field angle, the image height, the total lens length, and the back focus (BF) are as shown in Table 1 below. Similarly, in the numerical values of Examples 1 to 6, the numerical data of the conditional expressions (2) to (12) are the values described in Table 2 below.

  Reference numerals 101 to 106 shown in FIGS. 2, 6, 10, 14, 18, and 22, which are drawings showing Examples 1 to 6, have the same configuration as the imaging lens 100 shown in FIG. 1. Therefore, the description of the code of each constituent element, the surface code, and the distance code shall be omitted. 7, 11, 15, 19, and 23 are the same as the description of the c-line, the d-line, and the g-line shown in FIG. Further, as is clear from FIGS. 5, 9, 13, 17, 21, and 25, all the examples satisfy the conditional expression (1) in the present invention. In Examples 1 to 6, the second lens 120 and the fourth lens 150 were formed of a resin material, and the first lens 110 and the third lens 130 were formed of a glass material.

<Example 1>
The basic configuration of the lens system in Embodiment 1 is shown in FIG. 2, each numerical data (setting value) is shown in Table 3, Table 4, and Table 5, and aberration diagrams showing spherical aberration and astigmatism are shown in FIG. Each is shown. FIG. 3 shows spherical aberration on the left and astigmatism on the right in Example 1. The vertical axis of the longitudinal aberration diagram is the pupil diameter normalized to 1, the vertical axis of the astigmatism diagram represents the half field angle ω, the solid line M is the value of the meridional image plane, and the broken line S is the sagittal image plane. Each value is shown. As can be seen from FIG. 3, according to the first embodiment, the spherical and astigmatism aberrations are corrected well, and the imaging lens 101 having excellent imaging performance can be obtained.

  The imaging lens 101 in Example 1 shows the lower limit of the relational expression (2) between the total length and the first lens diameter accompanying the downsizing. In this embodiment, the diameter of the first lens 110 is made as small as possible and the overall length is short.

  As shown in FIG. 2, the first lens 110 has a meniscus shape with a convex surface facing the object side, the second lens 120 has a meniscus shape with a convex surface facing the object side, the third lens 130 has a plano-convex shape, and the aperture stop 140 The fourth lens 150 disposed on the image side has a biconvex shape with convex surfaces facing both sides. The second lens 120 and the fourth lens 140 each have an aspheric surface.

  Table 4 shows the stop corresponding to each surface number of the imaging lens 101 in Example 1, the radius of curvature R, the interval D, the refractive index Nd, and the dispersion value νd of each lens. Table 5 shows the aspheric coefficient of the predetermined surface.

  FIG. 4 shows distortion in which the ideal image height is a three-dimensional projection method. The stereoscopic projection formula is as follows.

The image height formed by the optical system is the real image height, and this is Y. The ideal image height imaged by the stereoscopic projection system and Y _0. When θ is the angle of view and f is the focal length of the optical system, Y ₀ is expressed by the following equation.

Y ₀ = 2f × tan (θ / 2)
Further, the distortion D is, Y, it is revealed as follows by _{Y 0.}

D = (Y−Y ₀ ) / Y ₀
FIG. 5 shows the image magnification of the imaging lens 101. The horizontal axis represents the half field angle, and the vertical axis represents the image size.

<Example 2>
The basic configuration of the lens system in the second embodiment is shown in FIG. 6, each numerical data (setting value) is shown in Table 6, Table 7, and Table 8, and aberration diagrams showing spherical aberration and astigmatism are shown in FIG. Each is shown. FIG. 7 shows spherical aberration on the left and astigmatism on the right in Example 2. The vertical axis of the longitudinal aberration diagram is the pupil diameter normalized to 1, the vertical axis of the astigmatism diagram represents the half field angle ω, the solid line M is the value of the meridional image plane, and the broken line S is the sagittal image plane. Each value is shown. As can be seen from FIG. 7, according to the second embodiment, the imaging lens 102 having excellent imaging performance can be obtained in which various spherical and astigmatism aberrations are well corrected.

  The imaging lens 102 in Example 2 shows the upper limit of the relational expression (2) between the total length and the diameter of the first lens 110 due to the downsizing. This is an example with a long overall length in which the diameter of the first lens 110 is increased and aberrations are sufficiently corrected.

  As shown in FIG. 6, the first lens 110 has a meniscus shape with a convex surface facing the object side, the second lens 120 has a meniscus shape with a convex surface facing the object side, the third lens 130 has a plano-convex shape, and the aperture stop 140 The fourth lens 150 disposed on the image side has a biconvex shape with convex surfaces facing both sides. Each of the second lens 120 and the fourth lens 150 has an aspheric surface.

  Table 7 shows the stop corresponding to each surface number of the imaging lens 110 in Example 2, the radius of curvature R, the interval D, the refractive index Nd, and the dispersion value νd of each lens. Table 8 shows the aspheric coefficient of the predetermined surface.

  FIG. 8 shows distortion in which the ideal image height is a three-dimensional projection method. The three-dimensional projection formula is the same as in the first embodiment.

  FIG. 9 shows the image magnification of the imaging lens 102. The horizontal axis represents the half field angle, and the vertical axis represents the image size.

<Example 3>
The basic configuration of the lens system in Embodiment 3 is shown in FIG. 10, each numerical data (setting value) is shown in Table 9, Table 10, and Table 11, and the aberration diagram showing spherical aberration and astigmatism is shown in FIG. Each is shown. FIG. 11 shows spherical aberration on the left and astigmatism on the right in Example 3. The vertical axis of the longitudinal aberration diagram is the pupil diameter normalized to 1, the vertical axis of the astigmatism diagram represents the half field angle ω, the solid line M is the value of the meridional image plane, and the broken line S is the sagittal image plane. Each value is shown. As can be seen from FIG. 11, according to Example 3, the spherical and astigmatism aberrations are corrected well, and the imaging lens 103 with excellent imaging performance can be obtained.

  The imaging lens 103 in Example 3 indicates the upper limit of the relational expression (3) between the focal lengths of the second lens 120 and the fourth lens 150. The power balance of the second lens 120 and the fourth lens 150 is close to the upper limit value 1.1.

  As shown in FIG. 10, the first lens 110 has a meniscus shape with a convex surface facing the object side, the second lens 120 has a meniscus shape with a convex surface facing the object side, the third lens 130 has a plano-convex shape, and the aperture stop 140 The fourth lens 150 disposed on the image side has a biconvex shape with convex surfaces facing both sides. Each of the second lens 120 and the fourth lens 150 has an aspheric surface.

  Table 10 shows the stop corresponding to each surface number of the imaging lens 103 in Example 3, the radius of curvature R, the interval D, the refractive index Nd, and the dispersion value νd of each lens. Table 11 shows the aspheric coefficient of the predetermined surface.

  FIG. 12 shows distortion in which the ideal image height is a three-dimensional projection method. The three-dimensional projection formula is the same as in the first embodiment.

  FIG. 13 shows the image magnification of the imaging lens 103. The horizontal axis represents the half field angle, and the vertical axis represents the image size.

<Example 4>
The basic configuration of the lens system in the fourth embodiment is shown in FIG. 14, each numerical data (setting value) is shown in Table 12, Table 13, and Table 14, and the aberration diagram showing spherical aberration and astigmatism is shown in FIG. Each is shown. FIG. 15 shows spherical aberration on the left and astigmatism on the right in Example 4. The vertical axis of the longitudinal aberration diagram is the pupil diameter normalized to 1, the vertical axis of the astigmatism diagram represents the half field angle ω, the solid line M is the value of the meridional image plane, and the broken line S is the sagittal image plane. Each value is shown. As can be seen from FIG. 15, according to Example 4, the spherical and astigmatism aberrations are corrected well, and the imaging lens 104 with excellent imaging performance can be obtained.

  The imaging lens 104 in Example 4 shows the lower limit of the relational expression (3) between the focal lengths of the second lens 120 and the fourth lens 150. The power balance between the second lens 120 and the fourth lens 150 is close to the lower limit value 0.9.

  As shown in FIG. 14, the first lens 110 has a meniscus shape with a convex surface facing the object side, the second lens 120 has a meniscus shape with a convex surface facing the object side, the third lens 130 has a plano-convex shape, and the aperture stop 140 The fourth lens 150 disposed on the image side has a biconvex shape with convex surfaces facing both sides. Each of the second lens 120 and the fourth lens 150 has an aspheric surface.

  Table 13 shows the stop corresponding to each surface number of the imaging lens in Example 4, the radius of curvature R, the interval D, the refractive index Nd, and the dispersion value νd of each lens. Table 14 shows the aspheric coefficient of the predetermined surface.

  FIG. 16 shows distortion in which the ideal image height is a three-dimensional projection method. The three-dimensional projection formula is the same as in the first embodiment.

  FIG. 17 shows the image magnification of the imaging lens 104. The horizontal axis represents the half field angle, and the vertical axis represents the image size.

<Example 5>
The basic configuration of the lens system according to Embodiment 5 is shown in FIG. 18, the numerical data (setting values) are shown in Tables 15, 16, and 17, and the aberration diagrams showing spherical aberration and astigmatism are shown in FIG. Each is shown. FIG. 19 shows spherical aberration on the left and astigmatism on the right in Example 5. The vertical axis of the longitudinal aberration diagram is the pupil diameter normalized to 1, the vertical axis of the astigmatism diagram represents the half field angle ω, the solid line M is the value of the meridional image plane, and the broken line S is the sagittal image plane. Each value is shown. As can be seen from FIG. 19, according to Example 5, the spherical and astigmatism aberrations are corrected well, and the imaging lens 105 with excellent imaging performance can be obtained.

  The imaging lens 105 according to the fifth embodiment is an example of the projection characteristics that satisfy all the conditional expressions, but is particularly an example in which the focal length is increased and the distortion is small.

  As shown in FIG. 18, the first lens 110 has a meniscus shape with a convex surface facing the object side, the second lens 120 has a meniscus shape with a convex surface facing the object side, the third lens 130 has a plano-convex shape, and the aperture stop 140 The fourth lens 150 disposed on the image side has a biconvex shape with convex surfaces facing both sides. Each of the second lens 120 and the fourth lens 150 has an aspheric surface.

  Table 16 shows the stop corresponding to each surface number of the imaging lens 105 in Example 5, the radius of curvature R, the interval D, the refractive index Nd, and the dispersion value νd of each lens. Table 17 shows the aspheric coefficient of the predetermined surface.

  FIG. 20 shows distortion in which the ideal image height is a three-dimensional projection method. The three-dimensional projection formula is the same as in the first embodiment.

  FIG. 21 shows the image magnification of the imaging lens 105. The horizontal axis represents the half field angle, and the vertical axis represents the image size.

<Example 6>
The basic configuration of the lens system in the sixth embodiment is shown in FIG. 22, numerical data (setting values) are shown in Table 18, Table 19, and Table 20, and aberration diagrams showing spherical aberration and astigmatism are shown in FIG. Each is shown. FIG. 23 shows spherical aberration on the left and astigmatism on the right in Example 6. The vertical axis of the longitudinal aberration diagram is the pupil diameter normalized to 1, the vertical axis of the astigmatism diagram represents the half field angle ω, the solid line M is the value of the meridional image plane, and the broken line S is the sagittal image plane. Each value is shown. As can be seen from FIG. 23, according to Example 6, the spherical and astigmatism aberrations are satisfactorily corrected, and the imaging lens 106 having excellent imaging performance can be obtained.

  The imaging lens 106 in Example 6 shows an example of projection characteristics that satisfy all the conditional expressions, and is an example in which the focal length is shortened and distortion is large.

  As shown in FIG. 22, the first lens 110 has a meniscus shape with a convex surface facing the object side, the second lens 120 has a meniscus shape with a convex surface facing the object side, the third lens 130 has a plano-convex shape, and the aperture stop 140 The fourth lens 150 disposed on the image side has a biconvex shape with convex surfaces facing both sides. The second lens 120 and the fourth lens 140 each have an aspheric surface.

  Table 19 shows the stop corresponding to each surface number of the imaging lens 106 in Example 6, the radius of curvature R, the interval D, the refractive index Nd, and the dispersion value νd of each lens. Table 20 shows the aspheric coefficient of the predetermined surface.

  FIG. 24 shows distortion in which the ideal image height is a three-dimensional projection method. The three-dimensional projection formula is the same as in the first embodiment.

  FIG. 25 shows the image magnification of the imaging lens 106. The horizontal axis represents the half field angle, and the vertical axis represents the image size.

100, 100A, 100B, 101-106: imaging lens 110: first lens
120: Second lens 130: Third lens
140: Aperture stop 150: Fourth lens 160: Cover glass (or IRCF)
170: Imaging device (or imaging surface / imaging surface)

Claims (5)

In order from the object side, the first lens made of glass material, which is a meniscus lens having negative refractive power with the convex surface facing the object side, and the imaging side surface have an aspheric surface, and the convex surface faces the object side. a second lens made of a resin material is a meniscus lens having a negative refractive power and does not have a non-spherical surface, a third formed of a glass material having a positive refractive power with a convex surface on the object side Four lenses, a lens, an aperture stop, and a fourth lens made of a resin material that is convex on both sides and has positive refractive power and is aspheric on both sides, satisfy the following conditional expression: An imaging lens characterized by the above. However, 2 <Θ <90 (deg), h1 is the height from the center of the imaging surface where an object with a half angle of view Θ-2 (deg) forms an image on the imaging surface, and h2 is a half angle of view Θ-1 ( deg) is the height from the center of the imaging surface at which the object is imaged on the imaging surface, h3 is the height from the imaging surface center at which the object of the half field angle Θ (deg) is imaged on the imaging surface , the focal length of the first lens that put f1 (mm), the focal length of the second lens at the d-line f2 (mm), the focal length of the third lens at the d-line f3 (mm), d line the focal length of the definitive fourth lens f4 (mm), the object side surface curvature of the first lens radius r1 (mm), the image side surface of curvature radius of the first lens r2 (mm), the first lens The center lens thickness of the lens is d (mm), and the focal length of the optical system is f (mm) .
(H2-h1) / (h3-h2) ≦ 1.0 (1)
0.9 <| f2 / f4 | <1.1 (3)
1.2 <d / f (4)
3.4 <r1 / r2 <4.2 (5)
6.0 <| f1 / f | <9.0 (9)
2.3 <| f2 / f | <2.7 (10)
2.9 <| f3 / f | <4.0 (11)
2.3 <| f4 / f | <2.7 (12) When the distance from the object side surface of the first lens to the image sensor is L (mm) and the maximum diameter φ (mm) through which light passes on the object side surface of the first lens, the following conditional expression is satisfied. The imaging lens according to claim 1.
0.95 <φ / L <1.05 (2) The imaging lens according to claim 1 or 2 , wherein a horizontal angle of view of the imaging lens satisfies the following conditional expression. However, 2W is the total angle of view of the light rays incident on the maximum horizontal position on the imaging surface.
2W> 180 (deg) (6) The imaging lens according to any one of claims 1 to 3 , wherein a vertical angle of view of the imaging lens satisfies the following conditional expression. However, 2V is the full angle of view of light incident on the maximum vertical position on the imaging surface.
150 (deg) <2V <160 (deg) (7) The following conditional expression is satisfied, where fb (mm) is the distance from the image side surface of the fourth lens to the imaging surface, and f (mm) is the focal length of the optical system. Item 2. The imaging lens according to Item 1.
fb / f > 2.0 (8)

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