JP2007279632A - Super wide angle lens - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a super wide angle lens which is constituted of a small number of lenses, is bright and can secure a maximum viewing angle of ≥170°. <P>SOLUTION: The super wide angle lens is equipped with a first lens which is a negative meniscus having a convex surface formed on its object side, a second negative lens, a third positive lens, a diaphragm, a fourth positive lens and a fifth negative lens which are separated from each other or cemented with each other, and a sixth biconvex lens in order from the object side to an image side. An aspherical surface is formed at least on one surface of the third lens or the sixth lens. The super wide angle lens satisfies following conditions. (1) 0.4<¾f<SB>12</SB>¾/H<1.1, (2) 1.4<¾f<SB>1</SB>¾/¾f<SB>2</SB>¾<2.3, and (3) 0.2<d<SB>4</SB>/H<0.7, provided that f: focal distance of the lens entire system, f<SB>12</SB>: synthetic focal distance of the first lens and the second lens, f<SB>1</SB>: focal distance of the first lens, f<SB>2</SB>: focal distance of the second lens, d<SB>4</SB>: distance between the centers of the image side surface of the second lens and the object side surface of the third lens, and H: maximum image height. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a bright super-wide-angle lens having a field angle of 170 degrees or more and used for surveillance cameras and in-vehicle camera applications.

  The lens characteristics required for surveillance cameras and in-vehicle cameras include a wide shooting range, a response to a difference in brightness of a subject, and a deep depth of field. In order to satisfy these conditions, an ultra-wide-angle lens, in particular, a bright lens having a large aperture is used.

  As a conventional super wide-angle lens, for example, a lens described in Patent Document 1 is known.

  In the lens design in Patent Document 1, a lens arrangement of a negative front group, a diaphragm, and a positive rear group is adopted, and the negative front group is composed of negative lenses.

Furthermore, what is described in Patent Document 2 is known as an ordinary wide-angle lens having a similar structure.
JP 2004-29282 A JP 2004-177435 A

  On the other hand, in a field of recent surveillance cameras, in-vehicle cameras, etc., a wider range of photographing is required. In many cases, the maximum angle of view required in this case is 170 degrees or more. In the super-wide-angle lens design described in Patent Document 1, since the distance between the divergence front group rear surface and the convergence rear group front surface is set to be large, particularly when the angle of view is widened. The off-axis light beam greatly diverging from the last diverging surface of the negative group cannot be received at the forefront of the rear group. In other words, there is a limit to the realizable field angle range.

  Further, in the wide-angle lens with the design described in Patent Document 2, a negative meniscus first lens, a negative second lens, a positive third lens, a positive fourth lens, and a negative fifth lens from the object side. A cemented lens and a positive sixth lens are arranged. In this case, too, the distance between the divergent second lens and the convergent third lens is large, and the divergent first and second lenses are also arranged. Since the divergent power of the lens is not sufficient and its refractive power distribution is not suitable for super wide-angle lens applications, the maximum angle of view remains at about 70 degrees.

  SUMMARY OF THE INVENTION An object of the present invention is to solve the above-described problems and to provide a bright super wide-angle lens that can secure a maximum field angle of 170 degrees or more with a small number of lenses.

  To achieve this object, the super wide-angle lens according to claim 1 of the present invention includes a first lens that is a negative meniscus lens having a convex surface formed on the object side in order from the object side to the image side; A negative second lens, a positive third lens, a stop, a positive fourth lens and a negative fifth lens that are spaced apart from each other or cemented, and a biconvex sixth lens; An aspheric surface is formed on at least one surface of the third lens or the sixth lens, and the following conditions are satisfied.

(1) 0.4 <| f ₁₂ | / H <1.1
(2) 1.4 <| f ₁ | / | f ₂ | <2.3
(3) 0.2 <d ₄ /H<0.7
Where f ₁₂ is the combined focal length of the first lens and the second lens, f ₁ is the focal length of the first lens, f ₂ is the focal length of the second lens, and d ₄ is the second lens image side surface and the third lens object. The center-to-center distance, H, is the maximum image height.

  The super wide-angle lens according to claim 2 of the present invention is characterized in that, in the invention according to claim 1, the fourth lens and the fifth lens are cemented, and the following conditions are satisfied.

(4) | f ₄₅ | / H> 2.5
Here, f ₄₅ is the combined focal length of the fourth lens and the fifth lens.

  The super wide-angle lens according to claim 3 of the present invention is characterized in that, in the invention according to claim 2, the fourth lens and the fifth lens are cemented, and any one of the following expressions is satisfied. is there.

(5) | nd ₄ −nd _R | ≦ 0.05
(6) | nd ₅ −nd _R | ≦ 0.05
Where nd ₄ is the refractive index of the fourth lens material at the d-line, nd ₅ is the refractive index of the fifth lens material at the d-line, and nd _R is d of the adhesive material that joins the fourth lens and the fifth lens. The refractive index at the line.

  The super wide-angle lens according to claim 4 of the present invention is characterized in that, in the invention according to claim 1, the first lens material is glass and satisfies the following conditions.

_{(7) d 1 - {SAG} 1 + (ET 1/2)}> 0
Where d ₁ is the thickness of the central portion of the first lens in the optical axis direction, and SAG ₁ is the object of the first lens in the direction parallel to the optical axis when the image side is taken positively from the object side on the optical axis. coordinate difference between the first lens outermost periphery from the side center, ET ₁ is the thickness of the edge portion of the optical axis of the first lens.

  The super wide-angle lens according to claim 5 of the present invention is characterized in that, in the invention according to claim 1, the following conditions are satisfied.

(8) 1.1 <b _f /H<1.4
Where b _f is the back focus.

  The super wide-angle lens described in claim 6 of the present invention is characterized in that, in the invention described in claim 1, the following conditions are satisfied.

(9) ν ₂ −ν ₃ > 25
(10) ν ₄ −ν ₅ > 25
(11) ν ₆ > 45
Where ν ₂ , ν ₃ , ν ₄ , ν ₅ , and ν ₆ are Abbe numbers of the second, third, fourth, fifth, and sixth lens materials, respectively.

  The super wide-angle lens according to claim 7 of the present invention is characterized in that, in the invention according to claim 1, the following conditions are satisfied.

(12) 5.8 <TL / H <8.6
Here, TL is the total lens length.

  The invention described in claim 8 of the present invention is characterized in that, in the invention described in claim 1, the following conditions are satisfied.

(13) 1.5 <f ₄₅₆ /H<1.9
(14) 0.9 <f ₃ /H<3.1
(15) 1.0 <f ₆ /H<1.4
Here, f ₄₅₆ is a combined focal length of the fourth lens, the fifth lens, and the sixth lens, f ₃ is a focal length of the third lens, and f ₆ is a focal length of the sixth lens.

  The super wide-angle lens of the present invention includes, in order from the object side to the image side, a first lens that is a negative meniscus lens having a convex surface formed on the object side, a negative second lens, a positive third lens, A diaphragm, a positive fourth lens and a negative fifth lens that are spaced apart from each other or cemented together, and a biconvex sixth lens, and an aspheric surface on at least one surface of the third lens or the sixth lens This is an ultra-wide-angle lens characterized by having an F value of 2.0 or more and a maximum field angle of 170 degrees or more.

  FIG. 1 is an explanatory diagram showing a schematic arrangement of super-wide-angle lenses in the embodiment of the present invention. L1, L2, L3, L4, L5, and L6 are first, second, third, fourth, fifth, and sixth lenses, S is an aperture, C1 is a cover glass, and I is an image plane. In order from the object side to the image side, a first lens L1, which is a negative meniscus lens having a convex surface formed on the object side, a biconcave second lens L2, a biconvex third lens L3, an aperture S, A biconvex fourth lens L4; a biconcave fifth lens L5 cemented with the fourth lens image side surface; and a biconvex sixth lens L6, and an aspheric surface on the object side surface of the sixth lens L6. Is formed.

  In the present invention, the following conditional expressions (1), (2), and (3) are satisfied.

(1) 0.4 <| f ₁₂ | / H <1.1
(2) 1.4 <| f ₁ | / | f ₂ | <2.3
(3) 0.2 <d ₄ /H<0.7
Where f ₁ is the focal length of the first lens L 1, f ₂ is the focal length of the second lens L 2, f ₁₂ is the combined focal length of the first lens L 1 and the second lens L 2, and d ₄ is the side surface of the second lens L 2 image. And the center distance between the third lens L3 and the object side surface, H is the maximum image height.

  In the lens configuration of the present invention, light from a large incident angle is captured by the divergent first lens L1 and second lens L2, and is adjusted to a state close to parallel light by the third lens L3. The subject image is coupled to the image plane by performing mainly chromatic aberration correction with the L4 and the fifth lens L5 and mainly spherical aberration correction with the aspheric surface of the sixth lens L6. As the projection method, an equidistant projection method represented by the following equation is used.

(16) Y = fθ
Where Y is the image height, f is the focal length, and θ is the incident angle. In a general central projection method described by Y = f · tan θ, when the incident angle θ is close to 90 degrees as in the present invention, the value of tan θ approaches infinity and the value of f becomes very small. For this reason, the design requires a large number of lenses, and the size of the lens increases, which is not practical.

  In the conditional expression (1), the combined focal length range of the first lens L1 and the second lens L2 constituting the divergent lens group is defined. When the lower limit of conditional expression (1) is exceeded, the combined focal length is small and the refractive power of the divergent lens group is too strong. In this case, in particular, it becomes difficult to correct the coma that occurs off-axis by the lens group after the third lens L3. Furthermore, the tangential image surface at the periphery of the image surface is greatly curved to the positive side, leading to resolution degradation. If the upper limit of conditional expression (1) is exceeded, the refractive power of the divergent group will be too small. In this case, it is difficult to secure a sufficient maximum field angle and illuminance at the periphery of the image plane. Become.

  The conditional expression (2) defines the refractive power distribution of the first lens L1 and the second lens L2. Both lenses have strong negative refracting power. In particular, the first lens captures an off-axis light beam from a large incident angle, and the second lens L2 strongly refracts the off-axis light beam to move from an on-axis light beam to an off-axis light beam. The third lens L3 plays a role of being incident on the object side surface with a small incident angle. That is, by performing the refractive power distribution so that the refractive power of the second lens L2 is larger than the refractive power of the first lens L1, the incident angle of the light beam on the lens surface after the third lens L3 is suppressed, and the aberration is reduced. Image formation is performed on the image plane while suppressing generation. If the lower limit of conditional expression (2) is exceeded, the refractive power of the first lens L1 will be too strong, and if it exceeds the upper limit, the refractive power of the second lens L2 will be too strong. In addition, it is difficult to capture off-axis light from a large incident angle. In particular, when the lower limit of conditional expression (2) is exceeded, it is necessary to increase the curvature of the concave surface on the first lens L1 image side that is a negative meniscus lens, which makes it difficult to manufacture the lens. Further, when the strong refractive power is excessively concentrated on one side, the coma aberration generated in the off-axis light beam is extremely increased. However, when the upper limit of the conditional expression (2) is exceeded, the second lens L2 having an originally large refractive power. This means that the refractive power further increases, and it becomes particularly difficult to correct the large coma aberration generated in the off-axis light beam by passing through the second lens L2 in the lens group after the third lens L3.

  In the conditional expression (3), the distance range between the second lens L2 and the third lens L3 is defined. It is desirable that both the on-axis light beam and off-axis light beam that have passed through the second group image side surface are incident on the object side surface of the third lens L3 so that they are as divergent as possible and the end points of the respective light beams are as close as possible. This is particularly desirable for bright lenses with a large aperture. The reason is that if the light beam diverges too much, the curvature of the lens surface must be reduced in order to receive the light beam on the object side surface of the third lens L3, and it becomes difficult to obtain sufficient refractive power. . In general, when the light beam passes through the periphery of the lens surface, the amount of aberration such as spherical aberration and coma increases. If the end point of any of the above light beams, particularly off-axis light beam, is far away from the end point of the on-axis light beam and passes through the third lens L3 object side surface periphery, the amount of aberration generated by the off-axis light beam increases, In the case of a large-aperture lens, the above phenomenon appears remarkably. Conditional expression (3) shows an appropriate range for preventing the above phenomenon. In particular, when the lower limit of the conditional expression (3) is exceeded, the distance between the second lens and the third lens is too small, and there is a possibility that they may physically interfere with each other, which is not preferable.

  That is, the total sum of the refractive powers of the first lens L1 and the second lens L2 and their distribution are set appropriately, and the second lens L2 and the third lens L3 are configured so as to suppress the occurrence of aberrations on the object side of the third lens L3 as much as possible. By setting the distance between them, the aberration generation amount is in a range that can be corrected by the third lens L3 and subsequent lenses even with a large aperture. Therefore, the configuration of the present invention makes it possible to realize a super-wide-angle lens that is bright and has a full field angle of 170 degrees or more.

  The diaphragm S is provided between the third lens L3 and the fourth lens L4. This has not only an advantage in optical design but also an effect of blocking stray light unnecessary for image formation.

  As for the aspherical surface, an example in which an aspherical surface is provided on the object side surface of the sixth lens L6 in order to reduce the aberration generated to realize the super wide angle is shown. However, the third lens L3 is shown. Alternatively, an aspheric surface is provided on at least one of the surfaces of the sixth lens L6, so that there is an effect of reducing aberration.

  In the present invention, it is desirable that the fourth lens L4 and the fifth lens L5 are cemented to satisfy the following conditional expression (4).

(4) | f ₄₅ | / H> 2.5
Here, f ₄₅ is the combined focal length of the cemented lens.

  When the fourth lens L4 and the fifth lens L5 are joined, the assembly eccentricity error between them can be sufficiently suppressed by the joining process. This occurs when the cemented lens is incorporated in the super-wide-angle lens assembly process by sufficiently reducing the refractive power of the cemented lens under the conditions and setting the combined focal length within the range defined by conditional expression (4). It is possible to reduce the sensitivity of the optical performance due to the eccentricity and tilt, and to suppress the fluctuation of the optical performance due to the error. If the lower limit of conditional expression (4) is exceeded, the refractive power becomes too strong, and the optical performance fluctuation due to the manufacturing error increases.

  In addition, when the fourth lens and the fifth lens are cemented, it is desirable that either of the following conditional expressions (5) and (6) is satisfied.

(5) | nd ₄ −nd _R | ≦ 0.05
(6) | nd ₅ −nd _R | ≦ 0.05
Where nd ₄ is the refractive index of the material of the fourth lens L4 at the d-line, nd ₅ is the refractive index of the material of the fifth lens L5 at the d-line, and nd _R is the joint between the fourth lens L4 and the fifth lens L5. It is a refractive index in d line of adhesive material to do.

  When the fourth lens L4 and the fifth lens L5 are cemented and the refractive index of each lens material is greatly different from the refractive index of the adhesive material used for the cementing, the thickness of the adhesive layer The optical performance fluctuates due to the variation, and the peripheral resolution is deteriorated when focused on the center of the screen. When the refractive index of any one of the lens materials is close to the refractive index of the adhesive material, it is possible to suppress the optical performance variation, and the tolerance of the adhesive layer thickness in the fourth lens and fifth lens joining process can be reduced. It can be mitigated.

  In the present invention, it is desirable to use glass lenses for the first lens L1 and the second lens L2. The reason is that the use of a low dispersion material for both lenses is effective in reducing chromatic aberration. Therefore, the use of a glass material capable of selecting a low dispersion material over a plastic material improves optical performance. This is because it is effective. In particular, it is desirable to use a glass material for the first lens L1 and satisfy the following conditional expression (7).

_{(7) d 1 - {SAG} 1 + (ET 1/2)}> 0
However, d ₁ is the thickness of the central portion of the first lens L1 in the optical axis direction, and SAG ₁ is the first lens L1 in the direction parallel to the optical axis when the image side is taken positively from the object side on the optical axis. The coordinate difference between the center of the object side surface and the outermost periphery of the first lens L1, ET ₁ is the thickness of the edge portion of the first lens L1 in the optical axis direction.

  In addition to the above-described material characteristics for correcting chromatic aberration, the first lens L1 is in direct contact with the outside air, so that a material excellent in water resistance and weather resistance is desirable. In this respect, a glass material is more advantageous than a plastic material. Further, by defining the shape within the range of the conditional expression (7), the manufacture thereof, particularly the lens manufacture by molding is facilitated. If the conditional expression (7) is not satisfied, the ratio of the thickness of the central portion in the optical axis direction to the thickness of the edge portion in the optical axis direction of the first lens L1 is reduced, so that a crack at the time of lens molding Or it becomes easy to generate | occur | produce partly damage of a lens, and lens shaping | molding becomes difficult.

  In the present invention, it is desirable that the following conditional expression (8) is satisfied.

(8) 1.1 <b _f /H<1.4
Where b _f is the back focus.

  If the upper limit of conditional expression (8) is exceeded, the back focus will be too large. In that case, the space occupied by the lens is shortened, and the light beam must be refracted therein. Therefore, it is necessary to make the refractive power of the first lens L1 and the second lens L2 that are divergent groups too strong, and it becomes difficult to correct aberrations after the third lens L3. If the lower limit of conditional expression (8) is exceeded, the back focus is shortened, so that it is difficult to secure a space for inserting filters such as a low-pass filter.

  In the present invention, it is desirable that the following conditional expressions (9), (10), and (11) are satisfied.

(9) ν ₂ −ν ₃ > 25
(10) ν ₄ −ν ₅ > 25
(11) ν ₆ > 45
Here, ν ₂ , ν ₃ , ν ₄ , ν ₅ , and ν ₆ are Abbe numbers of the materials of the second lens L2, the third lens L3, the fourth lens L4, the fifth lens L5, and the sixth lens L6, respectively.

  By setting the conditional expressions (9), (10), and (11) in the above ranges, chromatic aberration can be suppressed particularly well. The reason is that when the lens group is composed of a plurality of lenses, it is necessary to ensure an Abbe number difference between the concave lens material and the convex lens material. In order to satisfactorily correct chromatic aberration between the second and third lenses, it is desirable to satisfy conditional expression (9), and in order to satisfactorily correct chromatic aberration between the fourth lens and the fifth lens, conditional expression is satisfied. It is desirable to satisfy (10). On the image side surface of the fifth lens L5, the off-axis light beam is refracted in a direction away from the optical axis, and converged by the sixth lens L6 to form an image on the image plane. That is, since the sixth lens L6 is a convergent group composed of a single lens, the lens material is made of a sufficiently low dispersion material in order to sufficiently suppress the occurrence of chromatic aberration when the light beam passes through the lens. There must be. Therefore, it is desirable to satisfy the conditional expression (11) in order to suppress the occurrence of chromatic aberration in the sixth lens L6.

  In the present invention, it is desirable that the following conditional expression (12) is satisfied.

(12) 5.8 <TL / H <8.6
Here, TL is the total lens length.

  By setting the conditional expression (12) in the range, it is possible to reduce the size of the lens while ensuring the optical performance with respect to the image sensor size. It is important to reduce the size of the lens so that it is not noticeable in cameras for in-vehicle use or surveillance. However, if the upper limit of conditional expression (12) is exceeded, the lens cannot be made sufficiently small with respect to the image sensor size. It is not preferable. If the lower limit of conditional expression (12) is exceeded, the lens will be reduced in size. However, in order to secure a wide angle of view, the focal lengths of the first lens L1 and the second lens L2 that are the diverging lens group must be made extremely small. Don't be. As a result, the amount of aberration, such as coma, mainly increases, making it difficult to correct aberrations in the third lens L3 and subsequent lenses. Therefore, it is desirable to satisfy conditional expression (12) in order to balance performance and miniaturization.

  In the present invention, it is desirable that the following conditional expressions (13), (14), and (15) are satisfied.

(13) 1.5 <f ₄₅₆ /H<1.9
(14) 0.9 <f ₃ /H<3.1
(15) 1.0 <f ₆ /H<1.4
Here, f ₄₅₆ is a combined focal length of the fourth lens L4, fifth lens L5, and sixth lens L6, f ₃ is a focal length of the third lens L3, and f ₆ is a focal length of the sixth lens L6.

  The lens group composed of the third lens L3 and the fourth lens L4, the fifth lens L5, and the sixth lens L6 after the stop S is common, and the field curvature generated in the first lens L1 and the second lens L2. It has a role to correct.

  By setting the conditional expression (13) within the range, it is possible to obtain an image in which spherical aberration and curvature of field are suppressed while keeping the distance between the optical axes from the stop S to the image plane short. If the upper limit of conditional expression (13) is exceeded, the refractive power of the lens group composed of the fourth lens L4, the fifth lens L5, and the sixth lens L6 becomes weak. It is disadvantageous. Further, since the refractive power of the lens group becomes weak, it is not possible to correct the curvature of field in which the tangential image plane that is greatly generated in the lens group including the first lens L1 and the second lens L2 is greatly curved to the positive side. , Resulting in lower resolution around the screen. If the lower limit of conditional expression (13) is exceeded, the refractive power of the lens group composed of the fourth lens L4, the fifth lens L5, and the sixth lens L6 becomes too strong. Spherical aberration increases, making it difficult to ensure optical performance. Furthermore, a large curvature that makes it difficult to manufacture the lens is required on any lens surface from the fourth lens L4 to the sixth lens L6.

  Further, by setting the conditional expression (14) in the range, coma aberration and field curvature are suppressed, and an image with uniform illuminance can be obtained over the entire effective screen of the image sensor. If the upper limit of conditional expression (14) is exceeded, the refractive power of the third lens L3 becomes too weak, so that the tangential image plane that occurs greatly in the lens group composed of the first lens and the second lens is large on the positive side. The curved curvature of field cannot be corrected and the resolution is lowered, which is not preferable. If the lower limit of conditional expression (14) is exceeded, the refractive power of the third lens L3 becomes too strong, and the coma aberration generated in the off-axis light beam that has passed through the third lens L3 increases.

Further, by setting the conditional expression (15) within the range, the incident angle to the image sensor is suppressed from the center to the periphery of the effective screen of the image sensor, and the illuminance is uniform over the entire effective screen of the image sensor. It is possible to obtain an image of If the upper limit of conditional expression (15) is exceeded, the refractive power of the sixth lens L6 becomes too weak. In this case, the off-axis light beam that has passed through the image plane side of the fifth lens L5 is lifted in the direction away from the optical axis to the side surface of the sixth lens object, but the off-axis light beam can be sufficiently refracted by the sixth lens. As a result, the incident angle of the light beam incident on the peripheral portion of the effective screen of the image sensor increases. The image sensor sensitivity when using a solid-state image sensor decreases as the incident angle increases, and the image plane illuminance decreases in proportion to cos ⁴ θ when the incident angle to the image plane is θ. In the above case, the amount of light sensed by the image sensor decreases, and the illuminance at the periphery of the screen relative to the illuminance at the center of the screen decreases, which is not preferable. When the lower limit of conditional expression (15) is exceeded, the refracting power of the sixth lens becomes too strong, and field curvature occurs in which the tangential image surface is greatly curved to the negative side at the periphery of the imaging screen. Even if an aspherical surface is used, if the curvature of field is too large, it is difficult to correct, or even if it can be corrected, the lens center part is convex and the peripheral part is concave. This is not preferable because it is difficult to manufacture.

  Next, design examples of the super-wide-angle lens will be described based on the first to eighth embodiments. Here, symbols used in each embodiment are as follows.

r: Paraxial radius of curvature d: Lens thickness or lens spacing on the optical axis n _d : Refractive index of d line ν _d : Abbe number of d line In each embodiment, the aspherical shape of the lens is the optical axis When an orthogonal coordinate system having a z-axis in the direction and an x-axis and a y-axis in the direction orthogonal to the optical axis is used, the following expression is used.

z = (h ² / r) / [1 + √ {1− (1 + K) (h / r) ² }] + A ₄ · h ⁴ + A ₆ · h ⁶ + A ₈ · h ⁸ + A ₁₀ · h ¹⁰
However, h = √ (x ² + y ² )
r: paraxial radius of curvature, K: conical constant,
A _p (p = 4, 6, 8, 10): High-order aspheric coefficients The notations of K and A _{p in} the table are defined as follows.

For example, “6.0023456E-4” represents 6.023456 × 10 ⁻⁴ .

  In each embodiment, one or two cover glasses are installed on the object side of the image plane I, but these cover glasses are not simply flat glasses, but are replaced by filters such as IR cut filters. It is also possible to do.

(Embodiment 1)
Next, a specific design example of the super wide-angle lens in the present invention reflecting the above configuration will be described below.

  Table 1 and Table 2 show numerical examples, Table 3 shows optical performance, FIG. 1 shows the lens configuration, and FIG.

  The explanatory view showing the schematic arrangement of the wide-angle lens of Embodiment 1 is the same as that shown in FIG. FIG. 2 is an explanatory diagram showing spherical aberration, astigmatism, and distortion of the wide-angle lens of FIG. As for distortion aberration, distortion based on the equidistant projection method is also shown. In the equidistant projection method, when there is no distortion, the image height Y is expressed by the following equation (16) using the focal length f and the angle of view θ.

(16) Y = fθ
Accordingly, the distortion Dist is expressed by the following equation (17), where Y ′ is the actual image height.

(17) Dist = (Y′−Y) / Y × 100 (%)
In this embodiment, an aspheric surface is used only on the object side surface of the sixth lens L6, and the fourth lens L4 and the fifth lens L5 are cemented. Each aberration is well corrected for an ultra-wide-angle lens.

(Embodiment 2)
Table 2 and Table 5 show numerical examples, Table 6 shows optical performance, FIG. 3 shows a lens configuration diagram, and FIG. 4 shows various aberration diagrams of the design example 2 of the super-wide-angle lens.

  FIG. 3 is an explanatory diagram showing a schematic arrangement of the wide-angle lens according to the second embodiment. 3, the same components as those in FIG. 1 are denoted by the same reference numerals, and detailed description thereof is omitted. FIG. 4 is an explanatory diagram showing spherical aberration, astigmatism, and distortion of the wide-angle lens of FIG. In the present embodiment, an aspheric surface is used only for the object side surface of the sixth lens L6, and the fourth lens L4 and the fifth lens L5 are joined, and the combined refractive power of the first lens L1 and the second lens L2 and In this example, the combined refractive power of the third lens L3, the fourth lens L4, the fifth lens L5, and the sixth lens L6 is increased, but each aberration is well corrected as an ultra-wide angle lens.

(Embodiment 3)
Table 3 and Table 8 show numerical examples, Table 9 shows optical performance, FIG. 5 shows a lens configuration diagram, and FIG. 6 shows various aberration diagrams of the design example 3 of the super-wide-angle lens.

  FIG. 5 is an explanatory diagram showing a schematic arrangement of the wide-angle lens according to the third embodiment. 5, the same components as those in FIG. 1 are denoted by the same reference numerals, and detailed description thereof is omitted. FIG. 6 is an explanatory diagram showing spherical aberration, astigmatism, and distortion of the wide-angle lens of FIG. In this embodiment, an aspheric surface is used only for the object side surface of the sixth lens L6, and the fourth lens L4 and the fifth lens L5 are cemented, and then the second lens L2 image side surface and the third lens L3 object side surface are used. In this example, the aberrations are corrected as a super-wide-angle lens.

(Embodiment 4)
Table 4 and Table 11 show numerical examples, Table 12 shows optical performance, FIG. 7 shows a lens configuration diagram, and FIG.

  FIG. 7 is an explanatory diagram showing a schematic arrangement of the wide-angle lens according to the fourth embodiment. In FIG. 7, the same components as those in FIG. FIG. 8 is an explanatory diagram showing spherical aberration, astigmatism, and distortion of the wide-angle lens of FIG. In this embodiment, an aspheric surface is used for the third lens L3 object side surface and the sixth lens L6 object side surface, and the fourth lens L4 and the fifth lens L5 are cemented. As a good correction.

(Embodiment 5)
With respect to design example 5 of the ultra-wide-angle lens, (Table 13) and (Table 14) show numerical examples thereof, (Table 15) shows optical performance, FIG. 9 shows the lens configuration diagram, and FIG. 10 shows various aberration diagrams.

  FIG. 9 is an explanatory diagram showing a schematic arrangement of the wide-angle lens according to the fifth embodiment. 9, the same components as those in FIG. 1 are denoted by the same reference numerals and detailed description thereof is omitted. In the present embodiment and thereafter, the design is such that two cover glasses are inserted, and C1 and C2 are respectively set from the object side surface. Either or both of these can be replaced with a filter, or can be replaced with a single sheet. FIG. 10 is an explanatory diagram showing spherical aberration, astigmatism, and distortion of the wide-angle lens of FIG. In this embodiment, the aspherical surface is used only on the image side surface of the sixth lens L6, and the fourth lens L4 and the fifth lens L5 are separated from each other. However, each aberration is well corrected as an ultra-wide angle lens. ing.

(Embodiment 6)
Table 6 and Table 17 show numerical examples, Table 18 shows optical performance, FIG. 11 shows a lens configuration diagram, and FIG.

  FIG. 11 is an explanatory diagram showing a schematic arrangement of the wide-angle lens according to the sixth embodiment. In FIG. 11, the same components as those in FIG. 9 are denoted by the same reference numerals, and detailed description thereof is omitted. FIG. 12 is an explanatory diagram showing spherical aberration, astigmatism, and distortion of the wide-angle lens of FIG. The present embodiment is an example in which an aspheric surface is used only on the image side surface of the sixth lens L6, the fourth lens L4 and the fifth lens L5 are spaced apart, and the total lens length is shortened compared with the sixth embodiment. Each aberration is well corrected for an ultra-wide-angle lens.

(Embodiment 7)
Table 7 and Table 20 show numerical examples, Table 21 shows optical performance, FIG. 13 shows a lens configuration diagram, and FIG. 14 shows various aberration diagrams of the super wide-angle lens design example 7.

  FIG. 13 is an explanatory diagram showing a schematic arrangement of the wide-angle lens according to the seventh embodiment. 13, the same components as those in FIG. 9 are denoted by the same reference numerals and detailed description thereof is omitted. FIG. 14 is an explanatory diagram showing spherical aberration, astigmatism, and distortion of the wide-angle lens of FIG. In this embodiment, an aspheric surface is used only on the image side surface of the sixth lens L6, the fourth lens L4 and the fifth lens L5 are cemented, and the refractive index of the material of the fourth lens L4 is substantially equal to the refractive index of the bonding adhesive. In this example, glass (BK7) that is equal and has excellent water resistance and weather resistance is used for the first lens L1. From the above, while the design takes into account water resistance, weather resistance, and manufacturing tolerance relaxation, each aberration is well corrected for an ultra-wide angle lens.

(Embodiment 8)
Table 8 and Table 23 show numerical examples, Table 24 shows optical performance, FIG. 15 shows a lens configuration diagram, and FIG. 16 shows various aberration diagrams of the super wide-angle lens design example 8.

  FIG. 15 is an explanatory diagram showing a schematic arrangement of the wide-angle lens according to the eighth embodiment. 15, the same components as those in FIG. 9 are denoted by the same reference numerals, and detailed description thereof is omitted. FIG. 16 is an explanatory diagram showing spherical aberration, astigmatism, and distortion of the wide-angle lens of FIG. In this embodiment, an aspheric surface is used only on the image side surface of the sixth lens L6, the fourth lens L4 and the fifth lens L5 are cemented, and the refractive index of the material of the fourth lens L4 is substantially equal to the refractive index of the bonding adhesive. Are equal. Accordingly, while manufacturing tolerance relaxation is also considered, a material having a very high refractive index is used as the material of the first lens L1 and the second lens L2, and the refractive power of the second lens L2 is set strongly. In addition, by using a material having a very high refractive index for other lens materials, each aberration is well corrected as an ultra-wide angle lens while realizing a maximum field angle of 200 degrees.

  The calculation results of the optical performance parameters corresponding to the conditional expressions (1) to (15) in the designs of the first to eighth embodiments are summarized in Table 25.

  In each of the embodiments, it is understood that conditional expressions (1) to (3) of Claim 1 are satisfied, thereby realizing optical performance as an ultra-wide angle lens. Conditions necessary to satisfy chromatic aberration correction, manufacturing tolerance relaxation, water resistance, and weather resistance can also be satisfied, and desired performance can be realized according to required specifications.

  The present invention is useful as an ultra-wide-angle lens that can ensure a maximum field angle of 170 degrees or more.

Explanatory drawing which shows schematic arrangement | positioning of the wide angle lens of Embodiment 1 of this invention. Explanatory drawing which shows the spherical aberration, astigmatism, and distortion of the wide-angle lens of Embodiment 1. Explanatory drawing which shows schematic arrangement | positioning of the wide angle lens of Embodiment 2. FIG. Explanatory drawing which shows the spherical aberration, astigmatism, and distortion of the wide angle lens of FIG. Explanatory drawing which shows schematic arrangement | positioning of the wide angle lens of Embodiment 3. FIG. Explanatory drawing which shows the spherical aberration, astigmatism, and distortion of the wide angle lens of FIG. Explanatory drawing which shows schematic arrangement | positioning of the wide angle lens of Embodiment 4. FIG. Explanatory drawing which shows spherical aberration, astigmatism, and distortion of the wide angle lens of FIG. Explanatory drawing which shows schematic arrangement | positioning of the wide angle lens of Embodiment 5. FIG. Explanatory drawing which shows spherical aberration, astigmatism, and distortion of the wide-angle lens of FIG. Explanatory drawing which shows schematic arrangement | positioning of the wide angle lens of Embodiment 6. FIG. Explanatory drawing which shows spherical aberration, astigmatism, and distortion of the wide angle lens of FIG. Explanatory drawing which shows schematic arrangement | positioning of the wide angle lens of Embodiment 7. FIG. Explanatory drawing which shows spherical aberration, astigmatism, and distortion of the wide angle lens of FIG. Explanatory drawing which shows schematic arrangement | positioning of the wide angle lens of Embodiment 8. FIG. Explanatory drawing showing spherical aberration, astigmatism and distortion of the wide angle lens of FIG.

Explanation of symbols

L1 1st lens L2 2nd lens L3 3rd lens L4 4th lens L5 5th lens L6 6th lens S Aperture C1 1st cover glass C2 2nd cover glass I Image surface

Claims (8)

Whether the first lens, which is a negative meniscus lens having a convex surface formed on the object side, the negative second lens, the positive third lens, and the stop are separated from each other in order from the object side to the image side Or a cemented positive fourth lens and negative fifth lens, and a biconvex sixth lens, and an aspherical surface is formed on at least one surface of the third lens or the sixth lens, and the following conditions: An ultra-wide-angle lens characterized by satisfying
(1) 0.4 <| f ₁₂ | / H <1.1
(2) 1.4 <| f ₁ | / | f ₂ | <2.3
(3) 0.2 <d ₄ /H<0.7
However,
f ₁₂ : Composite focal length of the first lens and the second lens f ₁ : Focal length of the first lens f ₂ : Focal length of the second lens d ₄ : Between the center of the second lens image side surface and the third lens object side surface Distance H: Maximum image height The super wide-angle lens according to claim 1, wherein the fourth lens and the fifth lens are cemented and satisfy the following conditions.
(4) | f ₄₅ | / H> 2.5
However,
f ₄₅ : Composite focal length of the fourth lens and the fifth lens The super wide-angle lens according to claim 2, wherein any one of the following expressions is satisfied.
(5) | nd ₄ −nd _R | ≦ 0.05
(6) | nd ₅ −nd _R | ≦ 0.05
However,
nd ₄ : Refractive index at the d-line of the fourth lens material nd ₅ : Refractive index at the d-line of the fifth lens material nd _R : Refraction at the d-line of the adhesive material that joins the fourth lens and the fifth lens rate The super wide-angle lens according to claim 1, wherein the first lens material is glass and satisfies the following conditions.
_{(7) d 1 - {SAG} 1 + (ET 1/2)}> 0
However,
d ₁ : thickness of the central portion of the first lens in the optical axis direction SAG ₁ : from the object side surface center of the first lens in the direction parallel to the optical axis when the image side is taken positively from the object side on the optical axis Coordinate difference between the outermost periphery of the first lens ET ₁ : thickness of the edge of the first lens in the optical axis direction The super wide-angle lens according to claim 1, wherein the following condition is satisfied.
(8) 1.1 <b _f /H<1.4
However,
b _f : Back focus The super wide-angle lens according to claim 1, wherein the following condition is satisfied.
(9) ν ₂ −ν ₃ > 25
(10) ν ₄ −ν ₅ > 25
(11) ν ₆ > 45
ν ₂ : Abbe number of the second lens material ν ₃ : Abbe number of the third lens material ν ₄ : Abbe number of the fourth lens material ν ₅ : Abbe number of the fifth lens material ν ₆ : Abbe number of the sixth lens material The super wide-angle lens according to claim 1, wherein the following condition is satisfied.
(12) 5.8 <TL / H <8.6
However,
TL: Total lens length The super wide-angle lens according to claim 1, wherein the following condition is satisfied.
(13) 1.5 <f ₄₅₆ /H<1.9
(14) 0.9 <f ₃ /H<3.1
(15) 1.0 <f ₆ /H<1.4
However,
f ₄₅₆ : Composite focal length of the fourth lens, fifth lens, and sixth lens f ₃ : Focal length of the third lens f ₆ : Focal length of the sixth lens

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