JP4899198B2 - Imaging optical system - Google Patents

Description

  The present invention relates to an imaging optical system of an imaging apparatus using a solid-state imaging device such as a small CCD image sensor or a CMOS image sensor of 1/2 inch or less.

  In order to reduce the size and weight of a digital camera, video, mobile phone, etc., it is necessary to reduce the size and weight of optical components mounted therein. For example, folding (clamshell type) and sliding (slide type) mobile phones are required to be thin in the thickness of the mobile phone body, and there is a limit to the space in which optical components such as an imaging lens can be mounted. Therefore, a reduction in the height of the optical component is required. In particular, in the case of a sub camera, the thickness of the mobile phone body is about the same as that of a liquid crystal panel, and the imaging device installed on the back surface of the liquid crystal panel needs to be further reduced in height. Further, in order to manufacture the imaging lens at low cost, it is also required that the imaging apparatus can be soldered by reflow mounting.

  As an imaging lens aiming at miniaturization and weight reduction as described above, it has a two-lens group of lenses, and by forming a resin lens on a flat glass or glass lens (hybrid type), solder reflow is possible Or shorten the overall length of the lens system (see Patent Documents 1 and 2).

  Further, as a similar imaging lens, a lens group having three lenses is provided, the first lens provides the refractive power of the entire lens system, and the second and third lenses exhibit the function of a correction lens. Some lens systems shorten the overall length of the lens system (see Patent Document 3).

  In addition, as a similar imaging lens, it has a three-lens lens group, the lens having the largest positive refractive power is made of a glass lens, and other lenses are made of a curable resin material to withstand a solder reflow process. Some have heat resistance and reduce image point position fluctuation at the time of temperature change (see Patent Document 4).

  Also, as a similar imaging lens, it has a four-lens lens group, and the fourth lens is arranged at a position that satisfies the conditional expression, thereby strengthening the correction effect of the fourth lens and shortening the overall length of the lens system. (See Patent Document 5).

Japanese Patent No. 3926380 JP 2009-157402 A JP 2009-265451 A JP 2008-203822 A JP 2009-210923 A

  However, since the imaging lenses such as Patent Documents 1 and 2 use glass as a base for the lens system, the lens shape is restricted by the glass shape, and it is difficult to make the lens system thinner than a certain thickness. In addition, when a glass wafer is used for mass production, the thickness of the glass wafer is required to be about 0.4 mm to 0.5 mm or more for securing the strength, so that it is more difficult to make the lens system thinner.

  In addition, although the imaging lenses such as Patent Documents 3, 4, and 5 are designed for the purpose of shortening the overall length of the lens system, the thickness of the single lens configured and the total thickness of the lens portion are shortened. Therefore, it cannot be said that it can sufficiently withstand the above-mentioned demand for downsizing. In addition, a glass lens is used in part, and if the lens portion is thick, the production cost may increase.

  Accordingly, an object of the present invention is to provide an inexpensive imaging optical system having a thin lens portion capable of accommodating a solid-state imaging device of 1/2 inch or less while maintaining the optical performance and having a short total length of the optical system.

In order to solve the above problems, an imaging optical system according to the present invention is an imaging optical system for a solid-state imaging device having an image plane size of 1/2 inch or less, and includes a plurality of single lenses, and the entire surface of the plurality of single lenses. More than half of the number has an aspherical surface, more than half of the plurality of single lenses are meniscus lenses, and are used between an object at infinity and a magnification of −0.10, and the F number is brighter than 4. The center thickness of each lens of the single lens is di, the total lens thickness from the object-side lens surface of the first lens to the image-side lens surface closest to the image side is L, and the object side of the first lens of the total lens length from the lens surface to the image plane and L _T, a focal length is f, the image height and y, those thickest among the center thickness of each lens and d _max, the thinnest ones and d _min, Let R _iF be the radius of curvature on the object side of each lens , The radius of curvature of the image side when the _{R iR,} the following conditional expression (1), (2), (3), (4), (5), (7), (9), and (10) It is characterized by satisfying.
di ≦ 0.40 (mm) (i ≧ 2) (1)
0.15 ≦ L / 2y ≦ 0.50 (2)
L / L _T ≦ 0.55 (3)
L / f ≦ 0.65 (4)
d _min / d _max ≧ 2/3 (5)
L _T /2y≦0.939 (7)
| R _iF | /di≧2.058 (i ≧ 1) (9)
| R _iR | /di≧2.157 (i ≧ 1) (10)
Here, the meniscus lens means a lens having the same sign of the radius of curvature before and after the lens (paraxial radius of curvature in the case of an aspheric surface). Further, in the center thickness di of each lens, i indicates a lens number from the object side, and is, for example, d2 in the case of the center thickness of the second lens (i = 2), and the center thickness of the third lens (i = 3). In the case of d3. Further, when the stop is disposed on the object side than the first lens or on the image side than the lens closest to the image side, the total lens thickness L of each lens is on the image side of the lens closest to the image side from the stop. The distance to the lens surface, or the distance from the lens surface on the object side of the first lens to the stop. Further, if the stop is disposed on the object side of the first lens, the total lens length L _T is a distance from the stop to the image plane. Furthermore, if the parallel flat plate between the most image close to the side lens and the image surface is arranged, the total lens length L _T, a part of the plane-parallel plate a distance equivalent air. Further, the conditional expression (2) defines the total lens thickness L to diameter 2y image plane, the conditional expression (3) defines the total lens thickness L to the lens total length L _T, the conditional expression (4) The total lens thickness L with respect to the focal length f is defined.
When the maximum center thickness d _max and the minimum center thickness d _min satisfy the conditional expression (5), the thickness of each lens can be kept thin and uniform. The conditional expression (7) defines the total lens length _{L T} to the image surface of the diameter 2y. Further, when the lens total length L _T and the image height y satisfy the conditional expression (7), a compact imaging optical system can be obtained. In Condition (7), at least the lens total length _{L T} is shorter than or equal to 0.939 times the image plane diameter 2y.
Further, when the curvature radii R _iF and R _{iR of} the respective lenses satisfy the conditional expressions (9) and (10), the curvature radii R _iF and R _iR are increased, and the lens does not have a strong surface. The center thickness di of the lens does not increase. Here, if | R _iF | / di is less than 2.058, or if | R _iR | / di is less than 2.157, the center thickness di of each lens is increased and the lens surface of the lens is increased. Power increases and higher order aberrations occur. Therefore, when such an imaging optical system is used, the image surface is bent and becomes non-uniform. Therefore, by satisfying conditional expressions (9) and (10), the occurrence of aberration can be prevented and the image surface can be made flat and uniform.

In the imaging optical system described above, the imaging optical system is configured by a plurality of single lenses, and more than half of the lens surfaces are aspherical, so that the configuration is simple and the number of lenses is small, and the imaging optical system can be made compact. it can. Note that if all lens surfaces are aspherical, the imaging optical system can have higher performance. Further, since the shape of each lens becomes a meniscus lens mainly in the imaging optical system, keeping short total lens length L _T, it can be particularly short total lens thickness L. In addition, when the center thickness di of each lens satisfies the conditional expression (1), the thickness of each lens can be reduced, and each lens can be disposed in a state where the air space between the lenses is maintained. The total lens thickness L can be shortened. Moreover, reducing the thickness or the total lens length L _T of the lens only, and it is possible to ensure a sufficient optical performance. In addition, by reducing the thickness of each lens unit, it is possible to reduce the influence on the optical performance due to water absorption when the material is resin. For example, when a material having a pencil hardness of 3H or more is used, a large number of thin lenses can be manufactured at a time by a casting method, and the lenses can be mass-produced at low cost. Furthermore, if a heat resistant resin is used for the lens, solder reflow mounting is also possible. In addition, when the total lens thickness L, the total lens length L _T , and the focal length f satisfy the above conditional expressions (2), (3), and (4), the amount of lens material used in the imaging optical system is reduced and the cost is reduced. The image pickup optical system can be made compact and have high performance. From the above, the total length of the imaging optical system is shortened, and the imaging apparatus including the optical system is small and can be easily incorporated into a mobile phone or the like. By setting the lower limit of L / 2y in the conditional expression (2), it is possible to prevent the total lens thickness L from being short and the exit pupil position from being too close to the image plane, or to secure the lens thickness and the inter-lens space. can do. As L / 2y, L / L _T , and L / f all decrease, the exit pupil position tends to be closer, and the lower limit setting in the conditional expression (2) may not be sufficient. In that case, an image sensor using a microlens with a wider tolerance of the exit pupil position may be used, or a field lens may be set in front of the image plane.

Here, the process leading to the present invention will be briefly described. FIG. 19A shows a conventional hybrid type imaging optical system. In the imaging optical system 101 shown in FIG. 19A, a glass base 31 is sandwiched between thin lenses 11 and 21. The refractive index n of the glass base 31 is 1.5168, and the thickness d is 0.4343. The thickness of each thin lens 11 and 21 is 0.0929. The optical path length of the parallel plane glass can be converted into the optical path length of air, and the thickness d _A of the air at that time is
d _A = (1− (n−1) / n) d (13)
Given in. If the values of the refractive index n and the thickness d are substituted, d _A is 0.2863. As a result, when replacing the glass base 31 shown in FIG. 19 (A) to the air, the total lens length _{L T} as shown in FIG. 19 (B) is 0.148 shortened. If the air interval is further shortened, the power of the entire lens is increased, and the height of the light beam incident on the thin lens 21 is changed to generate aberration. Thus, in order to shorten the total lens length L _T is as thin as possible portion of the glass or resin, and it is desirable to secure an air gap. However, if the dimensions are in mm in FIGS. 19A and 19B, for example, the lens thickness of 0.0929 mm is too thin in consideration of maintaining the shape of the individual thin lenses 11 and 21. there is a possibility. Therefore, it is considered that a certain thickness is required depending on the lens material. Further, the glass base 31 side of each thin lens 11 and 21 does not need to be a flat surface, and it is desirable to improve the optical performance as a spherical surface or an aspherical surface like the other surfaces in optical design. Based on the above consideration, in the imaging optical system 100 of the present invention, that to satisfy the above-described configuration, and so the total lens length L _T becomes shorter while maintaining the optical performance.

Further, in a specific aspect or aspect of the present invention, a diaphragm is provided on either the object side or the image side of the first lens , the image height is y, and the total thickness of each lens is L ′, When the number of lenses is j, the following conditional expressions (6a) , (6b), (6c), and (8) are satisfied.
L ′ / 2y ≦ 0.40 (6a)
L ′ / L _T ≦ 0.40 (6b)
L ′ / f ≦ 0.60 (6c)
L ′ = Σdi (i = 1, 2,..., J) (8)
Diaphragm Rino position is preferably an object side or the image side of the first lens. Here, the image side of the first lens means between the first lens and the second lens. Further, when an opaque film is applied on the lens surface as a diaphragm, it may be provided on the object-side lens surface or the image-side lens surface of the first lens. Instead of installing on the object side lens surface of the first lens, a stop may be installed just before the object side of the first lens. Further, an aperture may be provided on the object side of the second lens, that is, between the first lens and the second lens or on the lens surface on the object side of the second lens. As described above, by providing the stop on either the object side or the image side of the first lens, the imaging optical system can be made compact, the exit pupil position is appropriate, and the performance can be improved. However, a diaphragm for preventing flare and ghost may be provided between other surfaces and lenses. Further, the lens center thickness di and the total sum L ′ of the lens thicknesses satisfy the conditional expressions (6a) , (6b), (6c), and (8), so that the total lens thickness L and the total lens length L _T Even if the distance is short, the air gap between the lenses can be secured and sufficient aberration correction can be performed. At this time, the shape of each lens is mainly a meniscus lens, and there is no strong power lens surface, and the image surface is flat and uniform .

In another aspect of the present invention, when the air interval between the lenses is Air (i), and the thicker one of the center thicknesses di of the front and rear lenses adjacent to the air interval is Di, The condition (11) is satisfied.
Air (i) /Di≧0.3 (i ≧ 1) (11)
Here, the conditional expression (11) indicates the condition of the air interval Air (i) sandwiched between adjacent lenses. In this case, the air space Air (i) between the lenses, by satisfying the thicker thickness Di of the central thickness di of the front and rear of the lens adjacent to the air gap is the conditional expression (11), an air gap It is possible to realize an imaging optical system that is compact and that aberrations are favorably corrected while ensuring Air (i). Here, if the value of Air (i) / Di is smaller than 0.3, the imaging optical system becomes compact, but good aberration cannot be maintained.

According to still another aspect of the present invention, when the center thickness of the first lens is d1, the first lens closest to the object among the plurality of single lenses is a meniscus lens convex to the object side. Conditional expression (12) is satisfied.
d1 ≦ 0.40 (mm) (12)
In this case, when the center thickness d1 of the first lens satisfies the conditional expression (12), all the lenses constituting the imaging optical system can be made thinner and more compact. Conditional expression (12) is effective when it is not necessary for the first lens to also serve as a lens protection, that is, when it is not necessary to keep the first lens somewhat thick. In addition, when the first lens closest to the object side is a meniscus lens convex to the object side, when the first lens has a positive focal length f, the principal point of the lens can be positioned closer to the object side than the lens center. can shorten the total lens length L _T is facilitated. Moreover, the paraxial space which can be used spreads, the freedom degree of design increases, and the performance improvement of an optical system can be aimed at. On the other hand, when the first lens has a negative focal length f, it is suitable for collecting a light beam having a wide angle of view.

  In still another aspect of the present invention, the stop is formed by applying, printing, or sputtering an opaque film on a lens surface of a lens provided with the stop. In this case, a compact and inexpensive imaging optical system can be obtained by providing a stop on the lens surface of the lens.

  In still another aspect of the present invention, each lens is formed of a resin having a pencil hardness of 3H or higher. In this case, the lens can be formed in a thin shape by using a resin having a high hardness of pencil hardness of 3H or higher. In addition, since the pencil hardness is a high hardness of 3H or more, a large number of thin lenses can be manufactured at once by a casting method, and the lenses can be mass-produced at a low cost.

  In still another aspect of the present invention, each lens is formed of a resin having resistance to a solder reflow temperature of 250 ° C. or higher. In this case, it is possible to cope with the solder reflow process by using a heat resistant resin having a heat resistant temperature of 250 ° C. or higher for forming the lens.

It is a block diagram of the lens which comprises the imaging optical system which concerns on 1st Embodiment. (A) is an astigmatism diagram of the lens of Example 1, and (B) is a distortion diagram of the lens of Example 1. FIG. FIGS. 4A to 4D are coma aberration diagrams of the lens of Example 1. FIGS. It is a block diagram of the lens which comprises the imaging optical system which concerns on 2nd Embodiment. (A) is an astigmatism diagram of the lens of Example 2, and (B) is a distortion diagram of the lens of Example 2. FIG. FIGS. 4A to 4D are coma aberration diagrams of the lens of Example 2. FIGS. It is a block diagram of the lens which comprises the imaging optical system which concerns on 3rd Embodiment. (A) is an astigmatism diagram of the lens of Example 3, and (B) is a distortion diagram of the lens of Example 3. FIG. (A)-(D) are coma aberration diagrams of the lens of Example 3. FIG. It is a block diagram of the lens which comprises the imaging optical system which concerns on 4th Embodiment. (A) is an astigmatism diagram of the lens of Example 4, and (B) is a distortion diagram of the lens of Example 4. FIG. (A)-(D) are coma aberration diagrams of the lens of Example 4. FIG. It is a block diagram of the lens which comprises the imaging optical system which concerns on 5th Embodiment. (A) is an astigmatism diagram of the lens of Example 5, and (B) is a distortion diagram of the lens of Example 5. FIG. FIGS. 7A to 7D are coma aberration diagrams of the lens of Example 5. FIGS. It is a block diagram of the lens which comprises the imaging optical system which concerns on 6th Embodiment. (A) is an astigmatism diagram of the lens of Example 6, and (B) is a distortion diagram of the lens of Example 6. FIG. (A)-(D) are coma aberration diagrams of the lens of Example 6. FIG. (A), (B) is a figure explaining the principle of this invention.

[First Embodiment]
Hereinafter, an imaging optical system according to a first embodiment of the present invention will be described with reference to the drawings.
An imaging optical system 100 shown in FIG. 1 is incorporated in an imaging apparatus 1000 mounted on a digital camera, video, mobile phone, or the like, and projects an image on an object OS onto an imaging element 90. Here, such an imaging apparatus 1000 uses a solid-state imaging device such as a small CCD image sensor or a CMOS image sensor of 1/2 inch or less as the imaging device 90, and the total length of the imaging optical system 100 is the image plane of the imaging device 90. The diameter is 2y or less. The imaging optical system 100 is used between an object at infinity with a magnification of zero and a magnification of −0.10.

  As shown in FIG. 1, the imaging optical system 100 includes a first lens 10 disposed in order from the object OS side (left side in FIG. 1) toward the image plane PS side (right side in FIG. 1) of the imaging device 90. A second lens 20. That is, the first lens 10 is provided at a position closest to the object OS side, and the second lens 20 is provided adjacent to the image plane PS side of the first lens 10. In FIG. 1, the image plane PS is an imaging plane of the imaging optical system 100 that is a focal position obtained by combining the first and second lenses 10 and 20. In the imaging optical system 100, a cover glass CS associated with the imaging element 90 is provided on the image plane PS side of the second lens 20.

  In the imaging optical system 100, the first and second lenses 10 and 20 are each a single lens made of resin, the first lens 10 is a meniscus lens convex on the object OS side, and the second lens 20 is a biconvex lens. Yes. The convex or concave lens surfaces L11, L12, L21, and L22 constituting the first and second lenses 10 and 20 are all aspherical surfaces.

In the imaging optical system 100, the total lens thickness from the object-side lens surface L11 of the first lens 10 to the lens surface L22 on the image plane PS side of the second lens 20 closest to the imaging element 90 is L, and the first lens 10 of the total lens length from the object OS side lens surface L11 to the image plane PS and L _T, a focal length is f, the image height is taken as y, the following conditional expression (2), (3), (4 ) And (7) are satisfied.
0.15 ≦ L / 2y ≦ 0.50 (2)
L / L _T ≦ 0.55 (3)
L / f ≦ 0.65 (4)
L _T / 2y ≦ 1 (7)
Note that the total lens length L _T more compact, it is desirable to satisfy the following conditional expression (7-2).
L _T /2y≦0.9 (7-2)

The center thickness d1 of the first lens 10 and the center thickness d2 of the second lens 20 satisfy the following conditional expressions (12) and (1).
d1 ≦ 0.40 (mm) (12)
d2 ≦ 0.40 (mm) (1)
It should be noted that it is desirable to satisfy the following conditional expressions (12-1) and (1-1) in order to realize a more compact and less expensive material by using less materials.
d1 ≦ 0.35 (mm) (12-1)
d2 ≦ 0.35 (mm) (1-1)

Further, the following conditional expressions (6a), (6b), (6c), and (8) are assumed, where di is the center thickness of each lens, L ′ is the total thickness of each lens, and j is the number of lenses constituting the lens. Meet.
L ′ / 2y ≦ 0.40 (6a)
L ′ / L _T ≦ 0.40 (6b)
L ′ / f ≦ 0.60 (6c)
L ′ = Σdi (i = 1, 2,..., J) (8)

Further, when the thickest of the center thicknesses d1 and d2 of the first and second lenses 10 and 20 is the maximum center thickness _dmax and the thinnest is the minimum center thickness _dmin , the following conditional expression (5 Is satisfied.
d _min / d _max ≧ 2/3 (5)
In order to secure more performance, it is desirable to satisfy the following conditional expression (5-2).
d _min / d _max ≧ 0.7 (5-2)

Further, the curvature radii on the object OS side of the first and second lenses 10 and 20 are R _1F and R _2F, and the curvature radii on the image plane PS side are R _1R and R _2R , respectively, and the first lens 10 and the second lens. When air (1) is set to Air (1), and the thicker one of the center thicknesses d1 and d2 of the first and second lenses 10 and 20 adjacent to each other is D1, the following conditions are satisfied. Expressions (9), (10), and (11) are satisfied.
| R _iF | /di≧1.55 (i = 1, 2) (9)
| R _iR | /di≧1.55 (i = 1, 2) (10)
Air (1) /D1≧0.3 (11)
In addition, in order to exhibit an effect more, it is desirable to satisfy the following conditional expressions (9-2), (10-2), and (11-2).
| R _iF | /di≧1.75 (i = 1, 2) (9-2)
| R _iR | /di≧1.75 (i = 1, 2) (10-2)
Air (1) /D1≧0.35 (11-2)

  In the imaging optical system 100, a diaphragm 60 is provided on the lens surface L <b> 12 on the image plane PS side of the first lens 10. The diaphragm 60 is formed by applying any one of an opaque film, printing, and sputtering on the lens surface L12 on the image plane PS side of the first lens 10.

  In the present embodiment, the first and second lenses 10 and 20 are each formed of the same resin material. The resin has a pencil hardness of 3H or higher and has resistance to a solder reflow temperature of 250 ° C. or higher. Specifically, an organic / inorganic hybrid resin or the like is used.

  Hereinafter, a method for manufacturing the first and second lenses 10 and 20 will be described. The first and second lenses 10 and 20 are manufactured by a casting manufacturing method. In the casting method, a glass substrate is not necessary. Specifically, an ultraviolet curable resin, a thermosetting resin, or the like is poured into a mold having a lens molding surface, and the resin is cured by heating, ultraviolet irradiation, or the like. Since a high-hardness resin is used, the molding surface of the lens edge can be provided on the mold, and the lens and the edge are integrally molded, so that no spacer is required. If a mold having a large number of lens forming surfaces is used, a wafer-like lens group in which a large number of lenses are formed at a time can be obtained. If the wafer-like first lens 10 and the second lens 20 are overlapped and a wafer on which a large number of image sensors 90 are formed is overlapped, a large number of imaging systems can be formed at a time. What is necessary is just to cut out this and make it an individual imaging system.

According to the imaging optical system 100 described above, the imaging optical system 100 is configured by the first lens 10 and the second lens 20 that are two single lenses, and the lens surfaces L11, L1 of the first and second lenses 10, 20. Since L12, L21, and L22 are aspherical surfaces, the configuration is simple and the number of lenses is small, and the imaging optical system 100 can be made compact. Further, by the first lens 10 is a meniscus lens, maintaining short total lens length L _T, it can be particularly short total lens thickness L. Further, when the center thicknesses d1 and d2 of the first and second lenses 10 and 20 satisfy the conditional expressions (12) and (1), the thickness of each lens 10 and 20 is reduced, and the air gap is reduced. The lenses 10 and 20 can be arranged in a state where the lens is maintained, and the total lens thickness L can be shortened. Further, suppressing the total lens length L _T, and it is possible to ensure a sufficient optical performance. By reducing the thicknesses d1 and d2 of the individual lenses 10 and 20, the influence on the optical performance due to water absorption when the material is resin can be reduced. In addition, when a material having a pencil hardness of 3H or more is used, a large number of thin lenses can be manufactured at once by a casting method, and the lenses can be mass-produced at low cost. Furthermore, solder reflow mounting is also possible by using a heat resistant resin for each of the lenses 10 and 20. Further, when the total lens thickness L, the total lens length L _T , the focal length f, and the image height y satisfy the above conditional expressions (2), (3), and (4), the lens material used in the imaging optical system 100 The amount can be reduced, and the imaging optical system 100 can be made compact and high performance. From the above, the entire length of the imaging optical system 100 is shortened, and the imaging apparatus 1000 including the optical system 100 is small and can be easily incorporated into a mobile phone or the like.

Further, by providing the diaphragm 60 on the lens surface L12 on the image plane PS side of the first lens 10, the imaging optical system 100 can be made compact, the exit pupil position is appropriate, and the performance is high. Further, the maximum center thickness d _max , the minimum center thickness d _min , the center thicknesses d 1 and d 2 of the first and second lenses 10 and 20, and the total L ′ of the lens thicknesses are the conditional expressions (5), (6a), (6b), (6c), and by satisfying the (8), it is possible to maintain the thickness of each lens 10, 20 thin uniform, even short total lens thickness L and the total lens length _{L T} is the lens 10 , 20 can be ensured and sufficient aberration correction can be performed. Further, when the lens total length L _T and the image height y satisfy the conditional expression (7), a compact imaging optical system 100 can be obtained.

Further, when the radii of curvature R _iF and R _{iR of the} lenses 10 and 20 satisfy the conditional expressions (9) and (10), the radii of curvature R _iF and R _iR are increased, and a strong surface is provided. The center thicknesses d1 and d2 of the first and second lenses 10 and 20 are not increased. Therefore, by satisfying conditional expressions (9) and (10), the occurrence of aberration can be prevented and the image surface can be made flat and uniform. Further, the air distance Air (i) between the lenses 10 and 20 and the thicker thickness Di of the center thicknesses d1 and d2 of the first and second lenses 10 and 20 satisfy the conditional expression (11). In addition, it is possible to realize the imaging optical system 100 that is compact and has excellent aberration correction while ensuring the air interval Air (i).

[Example 1]
In the following, Example 1 in which the imaging optical system 100 shown in FIG. 1 is defined numerically will be described. Table 1 below shows lens data of the imaging optical system 100 of the first embodiment.

  In the upper column of Table 1, “surface number” is a number assigned to the surface of each lens in order from the object OS side. “R” indicates a radius of curvature, and “d” indicates an interval between the next surface. Furthermore, “n” represents the refractive index of the lens material at the d-line, and “ν” represents the Abbe number of the lens material.

本実施例１の場合、上記非球面式における各係数ｋ、α_１〜α_ｍの値については、表１の下欄に示す通りである。なお、表１の下欄において、非球面データは、１０のべき乗数を「Ｅ」を用いて表している。 In the first embodiment, the first and second lenses 10 and 20 are aspherical. The displacement amount Z from the surface apex in the optical axis direction of these aspherical shapes is such that c is the reciprocal of the radius of curvature, r is the height from the optical axis, k is the conical coefficient, and α _m is the 2m-order aspheric coefficient. Is represented by the following equation.

In the case of the first embodiment, the values of the coefficients k and α _{1 to} α _{m in} the aspheric formula are as shown in the lower column of Table 1. In the lower column of Table 1, the aspheric data represents a power of 10 using “E”.

  As a result of the specification of the imaging optical system 100 according to the first embodiment, as shown in the upper column of Table 1, the focal length f is f = 0.651 (mm), and the F number is Fno = 3.405. In this case, the image height y is y = 0.5 (mm).

In the imaging optical system 100, the value L / 2y of the condition (2) is 0.385, the value L / _{L T} of the condition (3) is 0.448, the condition The value L / f of (4) is 0.592, the value d _min / d _max of the conditional expression (5) is 0.833, and the value L _T / 2y of the conditional expression (7) is 0.860. The values of the conditional expressions (6a), (6b), and (6c), L ′ / 2y, L ′ / L _T , and L ′ / f were 0.330, 0.384, and 0.507, respectively. .

In the first lens 10, the value d1 of the conditional expression (12) is 0.15, the value | R _1F | / d1 of the conditional expression (9) is 2.058, and the conditional expression The value | R _1R | / d1 of (10) was 2.157, and the value Air (1) / D1 of the conditional expression (11) was 0.306.

In the second lens 20, the value d2 of the conditional expression (1) is 0.18, the value | R _2F | / d2 of the conditional expression (9) is 6.875, and the conditional expression The value | R _2R | / d2 of (10) was 2.573.

  2A shows the astigmatism of each color at the reference wavelength 588 nm and the other wavelengths 656 nm and 486 nm on the image plane PS of Example 1, and FIG. 2B shows the reference on the image plane PS. The distortion aberration of each color at a wavelength of 588 nm and other wavelengths of 656 nm and 486 nm is shown.

  3A to 3D are diagrams showing coma aberration at each image height on the image plane PS of the first embodiment. The right side of each figure shows sagittal coma aberration, and the left side shows meridional coma aberration.

[Second Embodiment]
Hereinafter, the imaging optical system according to the second embodiment will be described. The imaging optical system according to the second embodiment is a modification of the first embodiment, and parts that are not particularly described are the same as those in the first embodiment.

  As shown in FIG. 4, the imaging optical system 100 includes a first lens 10 disposed in order from the object OS side (left side in FIG. 4) toward the image plane PS side (right side in FIG. 4) of the imaging device 90. A second lens 20. The diaphragm 60 is provided on the lens surface L12 on the image plane PS side of the first lens 10.

  In the imaging optical system 100 shown in FIG. 4, the first and second lenses 10 and 20 are both meniscus lenses, and one of the first lenses 10 is convex on the object OS side. The convex or concave lens surfaces L11, L12, L21, and L22 constituting the first and second lenses 10 and 20 are all aspherical surfaces. The imaging optical system 100 satisfies the conditional expressions (1) to (12) as in the first embodiment.

  In the present embodiment, the first and second lenses 10 and 20 are made of the same type of resin material.

[Example 2]
A second embodiment in which the imaging optical system 100 shown in FIG. 4 is defined numerically will be described below. Table 2 below shows lens data of the imaging optical system 100 of Example 2. The symbols in Table 2 are the same as the symbols in Table 1.

  As a result of the imaging optical system 100 of the second embodiment, as shown in the upper column of Table 2, the focal length f is f = 3.936 (mm), and the F number is Fno = 3.175. The image height y at this time was y = 2.25 (mm).

In the imaging optical system 100, the value L / 2y of the condition (2) is 0.196, the value L / _{L T} of the condition (3) is 0.208, the condition The value L / f of (4) is 0.224, the value d _min / d _max of the conditional expression (5) is 1, and the value L _T / 2y of the conditional expression (7) is 0. 939. The values of the conditional expressions (6a), (6b), and (6c), L ′ / 2y, L ′ / L _T , and L ′ / f were 0.124, 0.133, and 0.142, respectively.

In the first lens 10, the value d1 of the conditional expression (12) is 0.28, the value | R _1F | / d1 of the conditional expression (9) is 4.780, and the conditional expression The value | R _1R | / d1 of (10) was 140.24, and the value Air (1) / D1 of the conditional expression (11) was 1.142.

In the second lens 20, the value d2 of the conditional expression (1) is 0.28, the value | R _2F | / d2 of the conditional expression (9) is 2.704, and the conditional expression The value | R _2R | / d2 of (10) was 3.654.

  FIG. 5A shows astigmatism of each color at the reference wavelength 588 nm on the image plane PS of Example 2 and other wavelengths 656 nm and 486 nm, and FIG. 5B shows the reference on the image plane PS. The distortion aberration of each color at a wavelength of 588 nm and other wavelengths of 656 nm and 486 nm is shown.

  6A to 6D show coma aberration diagrams at image heights on the image plane PS of the second embodiment. The right side of each figure shows sagittal coma aberration, and the left side shows meridional coma aberration.

[Third Embodiment]
The imaging optical system according to the third embodiment will be described below. The imaging optical system according to the third embodiment is a modification of the first embodiment, and parts that are not particularly described are the same as those in the first embodiment.

  As shown in FIG. 7, the imaging optical system 100 includes a first lens 10 disposed in order from the object OS side (left side in FIG. 7) toward the image plane PS side (right side in FIG. 7) of the imaging device 90. A second lens 20. The diaphragm 60 is provided on the lens surface L12 on the image plane PS side of the first lens 10.

  In the imaging optical system 100 shown in FIG. 7, the first and second lenses 10 and 20 are both meniscus lenses, and one of the first lenses 10 is convex on the object OS side. The convex or concave lens surfaces L11, L12, L21, and L22 constituting the first and second lenses 10 and 20 are all aspherical surfaces. The imaging optical system 100 satisfies the conditional expressions (1) to (12) as in the first embodiment.

  In the present embodiment, the first and second lenses 10 and 20 are made of resin materials having different refractive indexes and Abbe numbers, respectively.

Example 3
A third embodiment in which the imaging optical system 100 shown in FIG. 7 is defined numerically will be described below. Table 3 below shows lens data of the imaging optical system 100 of Example 3. The symbols in Table 3 are the same as the symbols in Table 1.

  As a result of the imaging optical system 100 of the third embodiment, as shown in the upper column of Table 3, the focal length f is f = 3.665 (mm), and the F number is Fno = 3.714. The image height y at this time was y = 2.25 (mm).

In the imaging optical system 100, the value L / 2y of the condition (2) is 0.194, the value L / _{L T} of the condition (3) is 0.214, the condition The value L / f of (4) is 0.238, the value d _min / d _max of the conditional expression (5) is 0.933, and the value L _T / 2y _{max of the} conditional expression (7) is set. Was 0.905. The values of the conditional expressions (6a), (6b), and (6c), L ′ / 2y, L ′ / L _T , and L ′ / f were 0.129, 0.142, and 0.158, respectively.

In the first lens 10, the value d1 of the conditional expression (12) is 0.30, and the value | R _1F | / d1 of the conditional expression (9) is 3.636. The value | R _1R | / d1 of (10) was 20.597, and the value Air (1) / D1 of the conditional expression (11) was 0.969.

In the second lens 20, the value d2 of the conditional expression (1) is 0.28, the value | R _2F | / d2 of the conditional expression (9) is 2.788, and the conditional expression The value | R _2R | / d2 of (10) was 3.426.

  FIG. 8A shows astigmatism of each color at the reference wavelength 588 nm on the image plane PS of Example 3 and other wavelengths 656 nm and 486 nm, and FIG. 8B shows the reference on the image plane PS. The distortion aberration of each color at a wavelength of 588 nm and other wavelengths of 656 nm and 486 nm is shown.

  FIGS. 9A to 9D show coma aberration diagrams at the image heights of the image plane PS of the third embodiment. The right side of each figure shows sagittal coma aberration, and the left side shows meridional coma aberration.

[Fourth Embodiment]
The imaging optical system according to the fourth embodiment will be described below. The imaging optical system according to the fourth embodiment is a modification of the first embodiment, and parts that are not particularly described are the same as those in the first embodiment.

  As shown in FIG. 10, the imaging optical system 100 includes a first lens 10 arranged in order from the object OS side (left side in FIG. 10) toward the image plane PS side (right side in FIG. 10) of the imaging device 90. A second lens 20 and a third lens 30 are provided. The diaphragm 60 is provided on the lens surface L12 on the image plane PS side of the first lens 10. In order to obtain a more compact and high-performance lens, a combination of three or more single lenses is desirable as in this embodiment.

  In the imaging optical system 100 shown in FIG. 10, the first, second, and third lenses 10, 20, and 30 are all meniscus lenses, and the first and third lenses 10 and 30 are objects. The OS side is convex. The convex or concave lens surfaces L11, L12, L21, L22, L31, and L32 constituting the first, second, and third lenses 10, 20, and 30 are all aspherical surfaces. The imaging optical system 100 satisfies the conditional expressions (1) to (12) as in the first embodiment.

  In the present embodiment, the first, second, and third lenses 10, 20, and 30 are each formed of the same resin material.

Example 4
A fourth embodiment in which the imaging optical system 100 shown in FIG. 10 is defined numerically will be described below. Table 4 below shows lens data of the imaging optical system 100 of Example 4. The symbols in Table 4 are the same as the symbols in Table 1.

  As a result of the imaging optical system 100 according to the fourth embodiment, as shown in the upper column of Table 4, the focal length f is f = 2.829 (mm), and the F number is Fno = 3.501. In this case, the image height y is y = 1.75 (mm).

In the imaging optical system 100, the value L / 2y of the condition (2) is 0.315, the value L / _{L T} of the condition (3) is 0.358, the condition The value L / f of (4) is 0.390, the value d _min / d _max of the conditional expression (5) is 1, and the value L _T / 2y of the conditional expression (7) is 0 .881. The values of the conditional expressions (6a), (6b), and (6c), L ′ / 2y, L ′ / L _T , and L ′ / f were 0.257, 0.292, and 0.318, respectively.

In the first lens 10, the value d1 of the conditional expression (12) is 0.30, the value | R _1F | / d1 of the conditional expression (9) is 3.184, and the conditional expression The value | R _1R | / d1 of (10) was 13.630, and the value Air (1) / D1 of the conditional expression (11) was 0.303.

In the second lens 20, the value d2 of the conditional expression (1) is 0.30, the value | R _2F | / d2 of the conditional expression (9) is 3.225, and the conditional expression The value | R _2R | / d2 of (10) was 6.161, and the value Air (2) / D2 of the conditional expression (11) was 0.374.

In the third lens 30, the value d3 of the conditional expression (1) is 0.30, the value | R _3F | / d3 of the conditional expression (9) is 2.965, and the conditional expression The value | R _3R | / d3 of (10) was 3.387.

  11A shows the astigmatism of each color at the reference wavelength 588 nm on the image plane PS of Example 4 and other wavelengths 656 nm and 486 nm, and FIG. 11B shows the reference on the image plane PS. The distortion aberration of each color at a wavelength of 588 nm and other wavelengths of 656 nm and 486 nm is shown.

  12A to 12D show coma aberration diagrams at image heights on the image plane PS of the fourth embodiment. The right side of each figure shows sagittal coma aberration, and the left side shows meridional coma aberration.

[Fifth Embodiment]
The imaging optical system according to the fifth embodiment will be described below. The imaging optical system according to the fifth embodiment is a modification of the first embodiment, and parts that are not particularly described are the same as those in the first embodiment.

  As shown in FIG. 13, the imaging optical system 100 includes a first lens 10 arranged in order from the object OS side (left side in FIG. 13) toward the image plane PS side (right side in FIG. 13) of the imaging device 90. A second lens 20 and a third lens 30 are provided. The diaphragm 60 is provided on the lens surface L12 on the image plane PS side of the first lens 10.

  In the imaging optical system 100 shown in FIG. 13, the first, second, and third lenses 10, 20, and 30 are all meniscus lenses, and the first and third lenses 10, 30 are object objects. The OS side is convex. The convex or concave lens surfaces L11, L12, L21, L22, L31, and L32 constituting the first, second, and third lenses 10, 20, and 30 are all aspherical surfaces. The imaging optical system 100 satisfies the conditional expressions (1) to (12) as in the first embodiment.

  In the present embodiment, the first and third lenses 10 and 30 are made of a resin material having a refractive index and an Abbe number different from those of the second lens 20.

Example 5
A fifth embodiment in which the imaging optical system 100 shown in FIG. 13 is defined numerically will be described below. Table 5 below shows lens data of the imaging optical system 100 of Example 5. The symbols in Table 5 are the same as the symbols in Table 1.

  As a result, the focal length f of the imaging optical system 100 of Example 5 is f = 2.799 (mm), and the F number is Fno = 2.777. In this case, the image height y is y = 1.75 (mm).

In the imaging optical system 100, the value L / 2y of the condition (2) is 0.299, the value L / _{L T} of the condition (3) is 0.345, the condition The value L / f of (4) is 0.373, the value d _min / d _max of the conditional expression (5) is 0.833, and the value L _T / 2y of the conditional expression (7) is 0.867. The values of the conditional expressions (6a), (6b), and (6c), L ′ / 2y, L ′ / L _T , and L ′ / f were 0.237, 0.274, and 0.297, respectively.

In the first lens 10, the value d1 of the conditional expression (12) is 0.30, the value | R _1F | / d1 of the conditional expression (9) is 2.842, and the conditional expression The value | R _1R | / d1 of (10) was 15.376, and the value Air (1) / D1 of the conditional expression (11) was 0.326.

In the second lens 20, the value d2 of the conditional expression (1) is 0.25, the value | R _2F | / d2 of the conditional expression (9) is 3.235, and the conditional expression The value | R _2R | / d2 of (10) was 6.565, and the value Air (2) / D2 of the conditional expression (11) was 0.418.

In the third lens 30, the value d3 of the conditional expression (12) is 0.28, the value | R _3F | / d3 of the conditional expression (9) is 2.644, and the conditional expression The value | R _3R | / d3 of (10) was 3.270.

  FIG. 14A shows the astigmatism of each color at the reference wavelength 588 nm and the other wavelengths 656 nm and 486 nm on the image plane PS of Example 5, and FIG. 14B shows the reference on the image plane PS. The distortion aberration of each color at a wavelength of 588 nm and other wavelengths of 656 nm and 486 nm is shown.

  FIGS. 15A to 15D show coma aberration diagrams at the respective image heights of the image plane PS according to the fifth embodiment. The right side of each figure shows sagittal coma aberration, and the left side shows meridional coma aberration.

[Sixth Embodiment]
The imaging optical system according to the sixth embodiment will be described below. The imaging optical system according to the sixth embodiment is a modification of the first embodiment, and parts that are not particularly described are the same as those in the first embodiment.

  As shown in FIG. 16, the imaging optical system 100 includes a first lens 10 arranged in order from the object OS side (left side in FIG. 16) toward the image plane PS side (right side in FIG. 16) of the imaging device 90. The second lens 20, the third lens 30, and the fourth lens 40 are provided. The diaphragm 60 is provided on the lens surface L11 of the first lens 10 on the object OS side.

  In the imaging optical system 100 shown in FIG. 16, the first, third, and fourth lenses 10, 30, and 40 are meniscus lenses, and the second lens 20 is a biconvex lens. Among these, the first and third lenses 10 and 30 are convex on the object OS side. The convex or concave lens surfaces L11, L12, L21, L22, L31, L32, and L42 constituting the first, second, third, and fourth lenses 10, 20, 30, and 40 are aspherical, and the lens surface L41 is It is a spherical surface. The imaging optical system 100 satisfies the conditional expressions (1) to (12) as in the first embodiment.

  In the present embodiment, the first and third lenses 10 and 30 and the second and fourth lenses 20 and 40 are made of resin materials having different refractive indexes and Abbe numbers, respectively.

Example 6
A sixth embodiment in which the imaging optical system 100 shown in FIG. 16 is defined numerically will be described below. Table 6 below shows lens data of the imaging optical system 100 of Example 6. The symbols in Table 6 are the same as the symbols in Table 1.

  As a result of the imaging optical system 100 of the sixth embodiment, as shown in the upper column of Table 6, the focal length f is f = 3.404 (mm), and the F number is Fno = 2.80. The image height y at this time was y = 2.25 (mm).

In the imaging optical system 100, the value L / 2y of the condition (2) is 0.436, the value L / _{L T} of the condition (3) is 0.487, the condition The value L / f of (4) is 0.576, the value d _min / d _max of the conditional expression (5) is 0.775, and the value L _T / 2y of the conditional expression (7) is 0.895. The values of the conditional expressions (6a), (6b), and (6c), L ′ / 2y, L ′ / L _T , and L ′ / f were 0.254, 0.284, and 0.336, respectively.

In the first lens 10, the value d1 of the conditional expression (12) is 0.25, and the value | R _1F | / d1 of the conditional expression (9) is 3.370. The value | R _1R | / d1 of (10) was 2.418, and the value Air (1) / D1 of the conditional expression (11) was 0.489.

In the second lens 20, the value d2 of the conditional expression (1) is 0.3218, the value | R _2F | / d2 of the conditional expression (9) is 5.551, and the conditional expression The value | R _2R | / d2 of (10) was 10.572, and the value Air (2) / D2 of the conditional expression (11) was 0.342.

In the third lens 30, the value d3 of the conditional expression (1) is 0.25, the value | R _3F | / d3 of the conditional expression (9) is 3.826, and the conditional expression The value | R _3R | / d3 of (10) was 3.626, and the value Air (3) / D3 of the conditional expression (11) was 1.708.

In the fourth lens 40, the value d4 of the conditional expression (1) is 0.3225, the value | R _4F | / d4 of the conditional expression (9) is 5.144, and the conditional expression The value | R _4R | / d4 of (10) was 4.145.

  FIG. 17A shows astigmatism of each color at the reference wavelength 588 nm on the image plane PS of Example 6 and other wavelengths 656 nm and 486 nm, and FIG. 17B shows the reference on the image plane PS. The distortion aberration of each color at a wavelength of 588 nm and other wavelengths of 656 nm and 486 nm is shown.

  18A to 18D show coma aberration diagrams at image heights on the image plane PS of the sixth embodiment. The right side of each figure shows sagittal coma aberration, and the left side shows meridional coma aberration.

In the first to sixth embodiments described above, the values of the conditional expressions (2) to (7) and (9) to (11) are collectively shown in Tables 7 to 9.

  While the imaging optical system according to the present embodiment has been described above, the imaging optical system according to the present invention is not limited to the above. For example, in the above embodiment, the lenses constituting the imaging optical system 100 are not limited to two, three, and four, but may be five or more.

  In the above embodiment, most of the lens surfaces constituting the imaging optical system 100 have an aspheric surface. However, more than half of the surfaces need only have an aspheric surface.

CS ... cover glass, L ... total lens thickness, L11, L12, L21, L22 , L31, L32, L41, L42 ... lens surface, L T _... total lens length, OS ... object, PS ... image surface,
d1, d2 ... center thickness, y ... image height, 10, 20, 30, 40 ... lens, 90 ... imaging element, 100 ... imaging optical system, 1000 ... imaging device

Claims (7)

An imaging optical system for a solid-state imaging device having an image plane size of 1/2 inch or less,
With multiple single lenses,
More than half of the total number of single lenses has an aspheric surface,
More than half of the plurality of single lenses are meniscus lenses,
Used between an object at infinity with a magnification of zero and a magnification of -0.10, the F number is brighter than 4,
The center thickness of each lens of the plurality of single lenses is di, the total lens thickness from the object-side lens surface of the first lens to the image-side lens surface of the lens closest to the image side is L, and the first lens the total lens length from the object-side lens surface of the lens to the image plane and L _T, a focal length is f, the image height and y, what the thickest of the center thickness of each lens and d _max, thinnest was a _{d min,} the curvature radius of the object side of the lens and _{R iF,} the radius of curvature of the image side when the _{R iR,} the following conditional expression (1), (2), (3), (4 ) , (5), (7), (9), and (10) .
di ≦ 0.40 (mm) (i ≧ 2) (1)
0.15 ≦ L / 2y ≦ 0.50 (2)
L / L _T ≦ 0.55 (3)
L / f ≦ 0.65 (4)
d _min / d _max ≧ 2/3 (5)
L _T /2y≦0.939 (7)
| R _iF | /di≧2.058 (i ≧ 1) (9)
| R _iR | /di≧2.157 (i ≧ 1) (10) A diaphragm provided on either the object side or the image side of the first lens;
The following conditional expressions (6a) , (6b), (6c), and (8) are satisfied, where y is the image height , L ′ is the total thickness of each lens, and j is the number of lenses constituting the lens. The imaging optical system according to claim 1.
L ′ / 2y ≦ 0.40 (6a)
L ′ / L _T ≦ 0.40 (6b)
L ′ / f ≦ 0.60 (6c)
L ′ = Σdi (i = 1, 2,..., J) (8) When the air space between the lenses is Air (i) and the thicker one of the center thicknesses di of the front and rear lenses adjacent to the air space is Di, the following conditional expression (11) is satisfied. The imaging optical system according to any one of claims 1 and 2.
Air (i) /Di≧0.3 (i ≧ 1) (11) When the center thickness of the first lens is d1, the first lens closest to the object side among the plurality of single lenses is a meniscus lens convex toward the object side, and satisfies the following conditional expression (12): The imaging optical system according to any one of claims 1 to 3, wherein the imaging optical system is characterized.
d1 ≦ 0.40 (mm) (12)   The said stop is formed by performing any one of application | coating, printing, and sputtering of an opaque film | membrane on the lens surface of the lens in which the said stop is provided. The imaging optical system according to one item.   6. The imaging optical system according to claim 1, wherein each lens is formed of a resin having a pencil hardness of 3H or more.   The imaging optical system according to any one of claims 1 to 6, wherein each lens is formed of a resin having resistance to a solder reflow temperature of 250 ° C or higher.

Images