Patent Grant
9323031
1. Field of the Invention
The present invention relates to an imaging lens used in an electronic camera, such as a digital camera, a video camera, a surveillance camera and an in-vehicle camera, and to an imaging apparatus on which the imaging lens is mounted.
2. Description of the Related Art
As an imaging lens consisting of a negative lens unit consisting of only a lens or lenses having negative refractive power and a positive lens unit arranged toward an image side of the negative lens unit, and which has positive refractive power, in this order from an object side, imaging lenses disclosed in Japanese Unexamined Patent Publication No. 2000-019391 (Patent Document 1), Japanese Patent No. 3062735 (Patent Document 2), Japanese Unexamined Patent Publication No. 11(1999)-142730 (Patent Document 3), Japanese Unexamined Patent Publication No. 2011-237750 (Patent Document 4), and Japanese Unexamined Patent Publication No. 5(1993)-323183 (Patent Document 5) have been proposed.
In the imaging lens disclosed in Patent Document 1, various aberrations are excellently corrected, but an F-number is 3.2, which means a slow lens, and an angle of view is about 64°, which is not very wide. In the imaging lens disclosed in Patent Document 2, various aberrations are excellently corrected, and an angle of view is about 117°, which is wide. However, it is difficult to suppress the size of the imaging lens in total length. In the imaging lens disclosed in Patent Document 3, various aberrations are excellently corrected, but an angle of view is 80° or less, which is not very wide. The imaging lens disclosed in Patent Document 4 is in small size, and an F-number is about 1.8, which means a fast lens. However, an angle of view is 40° or less, which is not wide. In the imaging lens disclosed in Patent Document 5, an angle of view is 131° or more, which is wide. However, a total length is long, and the imaging lens is not a fast lens.
In view of the foregoing circumstances, it is an object of the present invention to provide an imaging lens, the total length of which is short, and the size of which is small, and which is a fast lens with a wide angle of view and excellent optical performance.
An imaging lens of the present invention consists essentially of a front group consisting of a first lens having a negative meniscus shape with its convex surface facing an object side, a second lens having negative refractive power, a third lens having positive refractive power, a fourth lens having a negative meniscus shape with its concave surface facing an image side and a fifth lens having positive refractive power, and the front group having positive refractive power as a whole, a stop, and a rear group consisting of a sixth lens having positive refractive power and a seventh lens having a negative meniscus shape with its concave surface facing the object side, and the rear group having positive refractive power as a whole, in this order from the object side. Further, the following conditional formula (1) is satisfied:
0.6<|f12|/f<1.5 (1), where
f12: a combined focal length of the first lens and the second lens, and
f: a focal length of an entire system.
The imaging lens of the present invention consists essentially of seven lenses of the first lens through the seventh lens and the stop. However, the imaging lens may include a lens or lenses substantially without refractive power, an optical element, such as a cover glass, other than the lenses, a mechanism part, such as a lens flange, a lens barrel, an imaging device and a hand shake blur correction mechanism, and the like besides the seven lenses.
Further, in the present invention, the shape of a lens surface, such as a convex surface, a concave surface, a flat surface, biconcave, meniscus, biconvex, plano-convex and plano-concave, and the sign of refractive power of a lens, such as positive and negative, are considered in a paraxial region when an aspherical surface is included, unless otherwise mentioned. In the present invention, the sign of a curvature radius is positive when a surface shape is convex toward the object side, and negative when a surface shape is convex toward the image side.
It is desirable that the imaging lens of the present invention satisfies the following conditional formula (1-1) or (1-2):
0.7<|f12|/f<1.3 (1-1); or
0.8<|f12|/f<1.2
In the imaging lens of the present invention, it is desirable that the following conditional formula (2) is satisfied:
1.3<fa/f<1.9 (2), where
fa: a focal length of the front group, and
f: a focal length of an entire system.
In this case, it is more desirable that the following conditional formula (2-1) is satisfied:
1.4<fa/f<1.8 (2-1).
Further, in the imaging lens of the present invention, it is desirable that the following conditional formula (3) is satisfied:
0.5<fa/f5<1.4 (3), where
fa: a focal length of the front group, and
f5: a focal length of the fifth lens.
In this case, it is more desirable that the following conditional formula (3-1) or (3-2) is satisfied:
0.7<fa/f5<1.3 (3-1); or
0.8<fa/f5<1.2 (3-2).
Further, in the imaging lens of the present invention, it is desirable that the following conditional formula (4) is satisfied:
vd3<26.0 (4), where
vd3: an Abbe number of the third lens for d-line.
In this case, it is more desirable that the following conditional formula (4-1) is satisfied:
vd3<23.0 (4-1).
Further, in the imaging lens of the present invention, it is desirable that the following conditional formula (5) is satisfied:
3.5<L/Rr1<9.0 (5), where
L: a length from a vertex of an object-side surface of the first lens to a paraxial image formation position determined by the first lens through the seventh lens, and
Rr1: a paraxial curvature radius of an image-side surface of the first lens.
In this case, it is more desirable that the following conditional formula (5-1) is satisfied:
4.0<L/Rr1<7.0 (5-1).
Further, in the imaging lens of the present invention, it is desirable that the following conditional formula (6) is satisfied:
3.5<L/Rr2<10.0 (6), where
L: a length from a vertex of an object-side surface of the first lens to a paraxial image formation position determined by the first lens through the seventh lens, and
Rr2: a paraxial curvature radius of an image-side surface of the second lens.
In this case, it is more desirable that the following conditional formula (6-1) is satisfied:
4.5<L/Rr2<9.0 (6-1).
Further, in the imaging lens of the present invention, it is desirable that the following conditional formula (7) is satisfied:
0.4<f5/f6<1 (7), where
f5: a focal length of the fifth lens, and
f6: a focal length of the sixth lens.
In this case, it is more desirable that the following conditional formula (7-1) is satisfied:
0.55<f5/f6<0.85 (7-1).
An imaging apparatus of the present invention is an imaging apparatus on which the imaging lens of the present invention, as described above, is mounted.
According to the present invention, the imaging lens consists essentially of a front group consisting of a first lens having a negative meniscus shape with its convex surface facing an object side, a second lens having negative refractive power, a third lens having positive refractive power, a fourth lens having a negative meniscus shape with its concave surface facing an image side and a fifth lens having positive refractive power, and the front group having positive refractive power as a whole, a stop, and a rear group consisting of a sixth lens having positive refractive power and a seventh lens having a negative meniscus shape with its concave surface facing the object side, and the rear group having positive refractive power as a whole, in this order from the object side. Further, conditional formula (1) is satisfied. Therefore, the imaging lens with a short total length and in small size is structurable. Further, the imaging lens is structurable as a fast lens with a wide angle of view and excellent performance.
The imaging apparatus of the present invention includes the imaging lens of the present invention. Therefore, it is possible to structure the imaging apparatus in small size and with excellent optical performance. The imaging apparatus can obtain excellent images by using an imaging device.
Hereinafter, embodiments of the present invention will be described in detail with reference to drawings.
In
An imaging lens according to an embodiment of the present invention consists essentially of two lens groups of front group Ga having positive refractive power as a whole and rear group Gb having positive refractive power as a whole in this order from the object side, as lens groups. Further, aperture stop St is arranged between front group Ga and rear group Gb.
Front group Ga consists essentially of first lens L1 having a negative meniscus shape with its convex surface facing an object side, second lens L2 having negative refractive power, third lens L3 having positive refractive power, fourth lens L4 having a negative meniscus shape with its concave surface facing an image side and fifth lens L5 having positive refractive power in this order from the object side. Here, second lens L2 is an aspheric lens the object-side surface and the image-side surface of which are aspherical. In Example 2, which will be described later, front group Ga is structured in a similar manner to Example 1. However, Examples 3 through 7 differ from Example 1 in that first lens L1 instead of second lens L2 is an aspheric lens the object-side surface and the image-side surface of which are aspherical.
Rear group Gb consists essentially of sixth lens L6 having positive refractive power and seventh lens L7 having a negative meniscus shape with its concave surface facing the object side. In Examples 2 through 7, which will be described later, rear group Gb is structured in a similar manner to Example 1.
Aperture stop St illustrated in
When first lens L1 and second lens L2 have negative refractive power, it is possible to reduce an angle of incidence of rays in a peripheral part of the angle of view entering third lens L3 and lenses after third lens L3, and that is advantageous to widening an angle. When first lens L1 is a meniscus lens with its convex surface facing the object side, it is possible to suppress generation of astigmatism, a lateral chromatic aberration and excessive distortion.
When third lens L3 has positive refractive power, it is possible to cancel out various aberrations generated in first lens L1 and second lens L2, and especially a lateral chromatic aberrations, and that is advantageous to widening an angle.
When fourth lens L4 has negative refractive power, it is possible to correct a longitudinal chromatic aberration and a spherical aberration. Especially, when fourth lens L4 is a meniscus lens with its convex surface facing the object side, it is possible to suppress generation of astigmatism.
Fifth lens L5 together with sixth lens L6 carries main positive refractive power of the entire system. When fifth lens L5 and sixth lens L6 face each other with aperture stop St therebetween, it is possible to prevent generation of a coma aberration and a lateral chromatic aberration.
When seventh lens L7 has negative refractive power, it is possible to correct a longitudinal chromatic aberration, a lateral chromatic aberration and a spherical aberration. When seventh lens L7 has a meniscus shape with its concave surface facing the object side, it is possible to suppress generation of astigmatism. Further, since the shape of seventh lens L7 and the shape of fourth lens L4 are symmetrical with aperture stop St therebetween, it is possible to suppress generation of a coma aberration.
The imaging lens according to the embodiments of the present invention has the aforementioned structure, and satisfies the following conditional formula (1):
0.6<|f12|/f<1.5 (1), where
f12: a combined focal length of first lens L1 and second lens
L2, and
f: a focal length of an entire system.
If the value is lower than the lower limit of conditional formula (1), positive refractive power of third lens L3 and thereafter becomes strong, and curvature of field increases. If the value exceeds the upper limit of conditional formula (1), negative refractive power of first lens L1 and second lens L2 becomes weak, and that is disadvantageous to widening an angle. Further, a spherical aberration is insufficiently corrected, and that is not appropriate for a larger diameter.
To further enhance the aforementioned action and effect, it is desirable that the following conditional formula (1-1) is satisfied. It is more desirable that the following conditional formula (1-2) is satisfied:
0.7<|f12|/f<1.3 (1-1); and
0.8<|f12|/f<1.2
In the imaging lens according to an embodiment of the present invention, first lens L1 having a negative meniscus shape with its convex surface facing the object side, second lens L2 having negative refractive power, and third lens L3 having positive refractive power are arranged. Therefore, it is possible to widen an angle of view, and to excellently correct a lateral chromatic aberration.
Further, fourth lens L4 having a negative meniscus shape with its concave surface facing the image side, fifth lens L5 having positive refractive power, sixth lens L6 having positive refractive power and seventh lens L7 having a negative meniscus shape with its concave surface facing the object side are arranged. Therefore, it is possible to excellently correct a spherical aberration and a longitudinal chromatic aberration.
Therefore, according to the embodiment of the present invention, it is possible to reduce the total length, and to structure the imaging lens in small size. Further, it is possible to structure the imaging lens, as a fast lens having a wide angle of view and excellent optical performance.
Next, desirable structure of the imaging lens according to the embodiment of the present invention will be described.
It is desirable that second lens L2 has a negative meniscus shape with its convex surface facing the object side. Accordingly, it is possible to suppress generation of astigmatism, a lateral chromatic aberration and excessive distortion in a similar manner to first lens L1.
It is desirable that third lens L3 is a biconvex lens. Accordingly, it is possible to suppress generation of a spherical aberration and a coma aberration.
It is desirable that the following conditional formula (2) is satisfied:
1.3<fa/f<1.9 (2), where
fa: a focal length of front group Ga, and
f: a focal length of an entire system.
If the value is lower than the lower limit of conditional formula (2), the positive refractive power of front group Ga becomes too strong, and a spherical aberration is insufficiently corrected. If the value exceeds the upper limit of conditional formula (2), the positive refractive power of rear group Gb becomes too strong, and a lateral chromatic aberration increases. That is disadvantageous also to reduction of the total length.
To further enhance the aforementioned action and effect, it is desirable that the following conditional formula (2-1) is satisfied:
1.4<fa/f<1.8 (2-1).
It is desirable that the following conditional formula (3) is satisfied:
0.5<fa/f5<1.4 (3), where
fa: a focal length of front group Ga, and
f5: a focal length of fifth lens L5.
If the value is lower than the lower limit of conditional formula (3), the positive refractive power of fifth lens L5 becomes weak, and a spherical aberration is excessively corrected. If the value exceeds the upper limit of conditional formula (3), the positive refractive power of fifth lens L5 becomes strong, and a spherical aberration is insufficiently corrected.
To further enhance the aforementioned action and effect, it is desirable that the following conditional formula (3-1) is satisfied. It is more desirable that the following conditional formula (3-2) is satisfied:
0.7<fa/f5<1.3 (3-1); and
0.8<fa/f5<1.2 (3-2).
It is desirable that the following conditional formula (4) is satisfied:
vd3<26.0 (4), where
vd3: an Abbe number of third lens L3 for d-line.
If the value exceeds the upper limit of conditional formula (4), a lateral chromatic aberration increases.
To further enhance the aforementioned action and effect, it is desirable that the following conditional formula (4-1) is satisfied:
vd3<23.0 (4-1).
It is desirable that the following conditional formula (5) is satisfied:
3.5<L/Rr1<9.0 (5), where
L: a length from a vertex of an object-side surface of first lens L1 to a paraxial image formation position determined by first lens L1 through seventh lens L7, and
Rr1: a paraxial curvature radius of an image-side of first lens L1.
If the value is lower than the lower limit of conditional formula (5), negative refractive power becomes weak, and curvature of field increases. If the value exceeds the upper limit of conditional formula (5), the total length becomes long, and it becomes difficult to reduce size.
To further enhance the aforementioned action and effect, it is desirable that the following conditional formula (5-1) is satisfied:
4.0<L/Rr1<7.0 (5-1).
It is desirable that the following conditional formula (6) is satisfied:
3.5<L/Rr2<10.0 (6), where
L: a length from a vertex of an object-side surface of first lens L1 to a paraxial image formation position determined by first lens L1 through seventh lens L7, and
Rr2: a paraxial curvature radius of an image-side of second lens L2.
If the value is lower than the lower limit of conditional formula (6), negative refractive power becomes weak, and curvature of field increases. If the value exceeds the upper limit of conditional formula (6), the total length becomes long, and it becomes difficult to reduce size.
To further enhance the aforementioned action and effect, it is desirable that the following conditional formula (6-1) is satisfied:
4.5<L/Rr2<9.0 (6-1).
It is desirable that the following conditional formula (7) is satisfied:
0.4<f5/f6<1 (7), where
f5: a focal length of fifth lens L5, and
f6: a focal length of sixth lens L6.
If the value is lower than the lower limit of conditional formula (7), the positive refractive power of sixth lens L6 becomes weak, and a spherical aberration is excessively corrected. If the value exceeds the upper limit of conditional formula (7), the positive refractive power of sixth lens L6 increases, and a spherical aberration is insufficiently corrected, and astigmatism increases.
To further enhance the aforementioned action and effect, it is desirable that the following conditional formula (7-1) is satisfied:
0.55<f5/f6<0.85 (7-1).
Next, an imaging apparatus according to the present invention will be described.
As described above, the imaging lens 12 according to the embodiment of the present invention has sufficiently small size. Therefore, it is possible to make the surveillance camera 10 compact. Further, the surveillance camera 10 to which the imaging lens 12 of the present invention has been applied can perform imaging with higher image qualities.
The imaging lens according to the embodiment of the present invention is applicable not only to the surveillance camera but also to various kinds of electronic cameras, such as a digital camera, a video camera and an in-vehicle camera.
Next, specific examples of the imaging lens according to embodiments of the present invention will be described.
Table 1 through Table 3 show specific lens data corresponding to the structure of the imaging lens in Example 1, illustrated in
In the lens data of Table 1, the sign of * is attached to surface numbers of aspherical surfaces. As the curvature radius of an aspherical surface, a numerical value of a paraxial curvature radius is shown. In Example 1, the object-side surface and the image-side surface of second lens L2 are aspherical surfaces.
Table 2 shows values of paraxial focal length f (mm), back focus Bf, F-number (FNo.) and angle of view (2ω).
Table 3 shows aspherical surface data of the imaging lens in Example 1. Table 3 shows the surface numbers of aspherical surfaces and aspherical surface coefficients about the respective aspherical surfaces. Here, “E-n” (n: integer) in the numerical value of the aspherical surface coefficient means “×10−n”. The aspherical surface coefficients are values of coefficients KA, Am (m=3, 4, 5, . . . 20) in the following aspherical surface equation:
Zd=C·h2/{1+(1−KA·C2·h2)1/2}+ΣAm·hm, where
Zd: the depth of an aspherical surface (the length of a perpendicular from a point on the aspherical surface at height h to a plane that contacts with the vertex of the aspherical surface and is perpendicular to the optical axis),
h: height (a length from the optical axis to the lens surface),
C: a reciprocal of a paraxial curvature radius, and
KA, Am: aspherical surface coefficients (m=3, 4, 5, . . . 20).
The description methods of Tables 1 through 3, as described so far, are similar also in Tables 4 through 21, which will be described later.
In all of the following tables, mm is used as the unit of length, and degree (°) is used as the unit of angle. However, since an optical system is usable by proportionally enlarging or reducing the optical system, other appropriate units may be used.
In a similar manner to Example 1, Tables 4 through 6 show specific lens data of the imaging lens in Example 2. Further, Table 7 through 9 show specific lens data of the imaging lens in Example 3, and Tables 10 through 12 show specific lens data of the imaging lens in Example 4. Tables 13 through 15 show specific lens data of the imaging lens in Example 5, and Tables 16 through 18 show specific lens data of the imaging lens in Example 6. Tables 19 through 21 show specific lens data of the imaging lens in Example 7.
Table 22 shows conditions defined by the aforementioned conditional formulas (1) through (7), specifically, values of letter parts of the formulas for each of Examples 1 through 7. Table 22 shows values for d-line. As Table 22 shows, all of the imaging lenses in Examples 1 through 7 satisfy all of conditional formulas (1) through (7). Further, all of the imaging lenses in Examples 1 through 7 satisfy all of conditional formulas defining more desirable ranges than the ranges defined by conditional formulas (1) through (7). Accordingly, effects as described above in detail are achievable.
Similarly,
As the above numerical value data and the aberration diagrams show, various aberrations are excellently corrected and an imaging lens the size of which, as a whole, is small is realized in each of the examples. Further, in the imaging lenses in Examples 1 through 6, aberrations are excellently corrected not only in a visible range but also in a near-infrared range.
The present invention is not limited to the aforementioned embodiments nor examples, and various modifications are possible. For example, values of a curvature radius, a distance between surfaces, a refractive index and the like of each lens element are not limited to the values shown in the above examples of numerical values, but may be other values.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2012-088063 | Apr 2012 | JP | national |
This application is a Continuation of PCT International Application No. PCT/JP2013/002355 filed on Apr. 5, 2013, which claims priority under 35 U.S.C. §119(a) to Japanese Patent Application No. 2012-088063 filed on Apr. 9, 2012. Each of the above applications is hereby expressly incorporated by reference, in its entirety, into the present application.
| Number | Name | Date | Kind |
|---|---|---|---|
| 4256373 | Horimoto | Mar 1981 | A |
| 5434713 | Sato | Jul 1995 | A |
| 5861999 | Tada | Jan 1999 | A |
| 20110249349 | Asami | Oct 2011 | A1 |
| Number | Date | Country |
|---|---|---|
| 54-32319 | Mar 1979 | JP |
| 61-123810 | Jun 1986 | JP |
| 02-248910 | Oct 1990 | JP |
| 04-218012 | Aug 1992 | JP |
| 05-273459 | Oct 1993 | JP |
| 05-323183 | Dec 1993 | JP |
| 11-142730 | May 1999 | JP |
| 2000-019391 | Jan 2000 | JP |
| 3062735 | Jul 2000 | JP |
| 2011-237750 | Nov 2011 | JP |
| Entry |
|---|
| International Search Report PCT/JP2013/002355 dated Jul. 30, 2013. |
| Number | Date | Country | |
|---|---|---|---|
| 20150022908 A1 | Jan 2015 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2013/002355 | Apr 2013 | US |
| Child | 14507863 | US |
