JP7656449B2 - Imaging lens - Google Patents

Description

The present invention relates to an imaging lens that forms an image of a subject on a solid-state imaging element such as a CCD sensor or C-MOS sensor used in an imaging device.

In recent years, camera functions have been installed in a variety of products, including home appliances, information terminal devices, and automobiles. It is expected that development of various products incorporating camera functions will continue in the future.

The imaging lenses installed in such devices must be small yet have high resolution.

As a conventional imaging lens aiming at high performance, for example, the imaging lens described in Patent Document 1 below is known.

Patent Document 1 discloses an imaging lens that is composed of, in order from the object side, a first lens having negative refractive power, a second lens having positive refractive power, a third lens having positive refractive power, a fourth lens having negative refractive power, a fifth lens having positive refractive power, and a sixth lens having negative refractive power, and that is configured so that the angle of view of the imaging lens, the relationship between the focal length of the fifth lens and the focal length of the sixth lens, and the relationship between the paraxial radius of curvature of the object side surface of the third lens and the paraxial radius of curvature of the image side surface of the third lens satisfy certain conditions.

China Patent Publication No. 111007648

If one were to attempt to reduce the height and F-number of the lens configuration described in Patent Document 1, it would be extremely difficult to correct aberrations in the peripheral areas, and good optical performance would not be achieved.

The present invention was made in consideration of the above-mentioned problems, and aims to provide an imaging lens that has high resolution with well-corrected aberrations while satisfying the requirements for low height and low F-number in a well-balanced manner.

In addition, with regard to the terms used in this invention, the convex, concave, and flat surfaces of a lens are defined as referring to the paraxial shape. The refractive power is defined as referring to the paraxial refractive power. The pole is defined as a point on an aspheric surface other than on the optical axis where the tangent plane intersects the optical axis perpendicularly. The total optical length is defined as the distance on the optical axis from the object-side surface of the optical element located closest to the object to the imaging surface. Note that the total optical length and back focus are the distances obtained by converting the thickness of an IR cut filter, cover glass, etc., placed between the imaging lens and the imaging surface into air.

The imaging lens according to the present invention is composed of a first lens having negative refractive power, a second lens having positive refractive power, a third lens having positive refractive power, a fourth lens having negative refractive power, a fifth lens having positive refractive power, and a sixth lens having negative refractive power, which are arranged in this order from the object side to the image side, and the first lens is biconcave in the paraxial direction, the second lens has a convex surface on the object side in the paraxial direction, the fourth lens has a concave surface on the image side in the paraxial direction, the fifth lens has a convex surface on the object side in the paraxial direction, and the sixth lens has a concave surface on the image side in the paraxial direction.

The first lens has negative refractive power and is biconcave on the paraxial plane to suppress chromatic aberration, coma, astigmatism, and distortion.

The second lens has positive refractive power and is convex on the object side at the paraxial position, providing excellent correction for spherical aberration, coma, astigmatism, curvature of field, and distortion.

The third lens has a positive refractive power, which allows for a low profile and effectively corrects spherical aberration, coma, astigmatism, field curvature, and distortion.

The fourth lens has negative refractive power and is concave on the image side at the paraxial position, suppressing chromatic aberration, coma, astigmatism, field curvature, and distortion.

The fifth lens has positive refractive power and is convex on the object side at the paraxial line, suppressing spherical aberration, coma, astigmatism, curvature of field, and distortion.

The sixth lens has negative refractive power and is concave on the image side at paraxial position, which allows for good correction of chromatic aberration, astigmatism, curvature of field, and distortion. Also, by making the image side concave at paraxial position, it ensures a good back focus while maintaining a low height.

In addition, in an imaging lens having the above configuration, it is preferable that the object-side surface of the first lens is formed as an aspheric surface having a pole point at a position other than on the optical axis.

By forming an aspheric surface with a pole point at a position other than on the optical axis on the object-side surface of the first lens, better correction of astigmatism, field curvature, and distortion becomes possible.

In addition, in an imaging lens having the above configuration, it is preferable that the second lens has a concave surface on the image side in the paraxial direction.

By making the image-side surface of the second lens paraxially concave, it becomes possible to effectively correct coma, field curvature, and distortion.

In addition, in an imaging lens having the above configuration, it is preferable that the image-side surface of the fourth lens is formed as an aspheric surface having a pole point at a position other than on the optical axis.

By forming an aspheric surface with a pole point at a position other than on the optical axis on the image-side surface of the fourth lens, better correction of astigmatism, field curvature, and distortion becomes possible.

In addition, in the imaging lens having the above configuration, it is preferable that the sixth lens has a convex surface on the object side in the paraxial direction.

By making the object-side surface of the sixth lens a convex surface paraxially, it becomes possible to effectively correct astigmatism, field curvature, and distortion.

In addition, in the imaging lens having the above configuration, it is preferable that the object-side surface of the sixth lens is formed as an aspheric surface having a pole point at a position other than on the optical axis.

By forming an aspheric surface with a pole point at a position other than on the optical axis on the object-side surface of the sixth lens, better correction of astigmatism, field curvature, and distortion becomes possible.

In addition, in the imaging lens having the above configuration, it is preferable that the image-side surface of the sixth lens is formed as an aspheric surface having a pole point at a position other than on the optical axis.

By forming an aspheric surface with a pole point at a position other than on the optical axis on the image-side surface of the sixth lens, better correction of astigmatism, field curvature, and distortion becomes possible.

By adopting the above-mentioned configuration, the imaging lens of the present invention achieves a low height with a total-to-diagonal ratio (the ratio of the total optical length to the diagonal length of the effective imaging surface of the imaging element) of 1.05 or less, and a low F-number of 2.4 or less.

In addition, in the imaging lens having the above configuration, it is desirable to satisfy the following conditional expression (1).
(1) 5.75<f3/T3<14.50
Here, f3 is the focal length of the third lens, and T3 is the distance on the optical axis from the image-side surface of the third lens to the object-side surface of the fourth lens.

Satisfying the range of conditional expression (1) allows for a low profile and good correction of spherical aberration, coma, astigmatism, field curvature, and distortion.

In addition, in the imaging lens having the above configuration, it is desirable to satisfy the following conditional expression (2).
(2) -5.9<r1/r2<-0.9
Here, r1 is the paraxial radius of curvature of the object side surface of the first lens, and r2 is the paraxial radius of curvature of the image side surface of the first lens.

By satisfying the range of conditional expression (2), it becomes possible to achieve good correction of coma, astigmatism, and distortion.

In the imaging lens having the above configuration, it is desirable to satisfy the following conditional expression (3).
(3) 11<r4/(T2/T1)<255
where r4 is the paraxial radius of curvature of the image-side surface of the second lens, T2 is the distance on the optical axis from the image-side surface of the second lens to the object-side surface of the third lens, and T1 is the distance on the optical axis from the image-side surface of the first lens to the object-side surface of the second lens.

By satisfying the range of conditional expression (3), it is possible to achieve a low profile and to achieve good correction of coma, field curvature, and distortion.

In the imaging lens having the above configuration, it is desirable to satisfy the following conditional expression (4).
(4) -15<r6/T3<-3
Here, r6 is the paraxial radius of curvature of the image-side surface of the third lens, and T3 is the distance on the optical axis from the image-side surface of the third lens to the object-side surface of the fourth lens.

Satisfying the range of conditional expression (4) allows for a low profile and good correction of spherical aberration, coma, astigmatism, field curvature, and distortion.

Moreover, in the imaging lens having the above configuration, it is desirable to satisfy the following conditional expression (5).
(5) -35.5<r9/r10<-4.9
Here, r9 is the paraxial radius of curvature of the object side surface of the fifth lens, and r10 is the paraxial radius of curvature of the image side surface of the fifth lens.

By satisfying the range of conditional expression (5), it becomes possible to satisfactorily correct coma, astigmatism, curvature of field, and distortion.

In the imaging lens having the above configuration, it is desirable to satisfy the following conditional expression (6).
(6)-36<(T1/f1)×100<-9
Here, T1 is the distance on the optical axis from the image side surface of the first lens to the object side surface of the second lens, and f1 is the focal length of the first lens.

By satisfying the range of conditional expression (6), it is possible to achieve a low profile and good correction of chromatic aberration, coma, astigmatism, and distortion.

Moreover, in the imaging lens having the above configuration, it is desirable to satisfy the following conditional expression (7).
(7) -3.5<(T5/f6)×100<-0.5
Here, T5 is the distance on the optical axis from the image side surface of the fifth lens to the object side surface of the sixth lens, and f6 is the focal length of the sixth lens.

By satisfying the range of conditional expression (7), it is possible to achieve a low profile and good correction of chromatic aberration, astigmatism, curvature of field, and distortion.

Moreover, in the imaging lens having the above configuration, it is desirable to satisfy the following conditional expression (8).
(8) 0.7<T4/T5<4.5
Here, T4 is the distance on the optical axis from the image side surface of the fourth lens to the object side surface of the fifth lens, and T5 is the distance on the optical axis from the image side surface of the fifth lens to the object side surface of the sixth lens.

By satisfying the range of conditional expression (8), it is possible to achieve a low profile and good correction of coma, astigmatism, and distortion.

Moreover, in the imaging lens having the above configuration, it is desirable to satisfy the following conditional expression (9).
(9) -2.5<f1/f<-0.5
Here, f1 is the focal length of the first lens, and f is the focal length of the entire imaging lens system.

By satisfying the range of conditional expression (9), chromatic aberration, coma, astigmatism, and distortion can be effectively corrected.

In the imaging lens having the above configuration, it is desirable to satisfy the following conditional expression (10).
(10) 1<f2/f<8
Here, f2 is the focal length of the second lens, and f is the focal length of the entire imaging lens system.

By satisfying the range of conditional expression (10), it becomes possible to achieve good correction of spherical aberration, coma, astigmatism, curvature of field, and distortion.

Moreover, in the imaging lens having the above configuration, it is desirable to satisfy the following conditional expression (11).
(11)-7<r1/f<-1
Here, r1 is the paraxial radius of curvature of the object side surface of the first lens, and f is the focal length of the entire imaging lens system.

By satisfying the range of conditional expression (11), coma, astigmatism, and distortion can be effectively corrected.

Moreover, in the imaging lens having the above configuration, it is desirable to satisfy the following conditional expression (12).
(12) 0.40<r2/f<1.65
Here, r2 is the paraxial radius of curvature of the image-side surface of the first lens, and f is the focal length of the entire imaging lens system.

By satisfying the range of conditional expression (12), it becomes possible to satisfactorily correct coma, astigmatism, and distortion.

Moreover, in the imaging lens having the above configuration, it is desirable to satisfy the following conditional expression (13).
(13) -2.3<r2/r1/D1<-0.3
Here, r2 is the paraxial radius of curvature of the image-side surface of the first lens, r1 is the paraxial radius of curvature of the object-side surface of the first lens, and D1 is the thickness of the first lens on the optical axis.

By satisfying the range of conditional expression (13), it is possible to achieve a low profile and good correction of coma, astigmatism, and distortion.

Moreover, in the imaging lens having the above configuration, it is desirable to satisfy the following conditional expression (14).
(14) 20<r4/T2<450
Here, r4 is the paraxial radius of curvature of the image-side surface of the second lens, and T2 is the distance on the optical axis from the image-side surface of the second lens to the object-side surface of the third lens.

By satisfying the range of conditional expression (14), it is possible to achieve a low profile and to achieve good correction of coma, field curvature, and distortion.

Moreover, in the imaging lens having the above configuration, it is desirable to satisfy the following conditional expression (15).
(15) 15<r5/T2<250
Here, r5 is the paraxial radius of curvature of the object-side surface of the third lens, and T2 is the distance on the optical axis from the image-side surface of the second lens to the object-side surface of the third lens.

By satisfying the range of conditional expression (15), it is possible to achieve a low profile and good correction of spherical aberration, astigmatism, curvature of field, and distortion.

Moreover, in the imaging lens having the above configuration, it is desirable to satisfy the following conditional expression (16).
(16) -28.0<(r6/|r7|)×100<-0.2
Here, r6 is the paraxial radius of curvature of the image-side surface of the third lens, and r7 is the paraxial radius of curvature of the object-side surface of the fourth lens.

By satisfying the range of conditional expression (16), it becomes possible to achieve good correction of spherical aberration, coma, astigmatism, curvature of field, and distortion.

In the imaging lens having the above configuration, it is desirable to satisfy the following conditional expression (17).
(17) 3<|r7|/f<430
Here, r7 is the paraxial radius of curvature of the object side surface of the fourth lens, and f is the focal length of the entire imaging lens system.

By satisfying the range of conditional expression (17), coma, astigmatism, and distortion can be effectively corrected.

Moreover, in the imaging lens having the above configuration, it is desirable to satisfy the following conditional expression (18).
(18) 0.5<r8/f<3.0
Here, r8 is the paraxial radius of curvature of the image-side surface of the fourth lens, and f is the focal length of the entire imaging lens system.

By satisfying the range of conditional expression (18), it becomes possible to satisfactorily correct coma, astigmatism, curvature of field, and distortion.

Moreover, in the imaging lens having the above configuration, it is desirable to satisfy the following conditional expression (19).
(19) 1.8<r9/f<14.5
Here, r9 is the paraxial radius of curvature of the object side surface of the fifth lens, and f is the focal length of the entire imaging lens system.

By satisfying the range of conditional expression (19), it becomes possible to satisfactorily correct coma, astigmatism, curvature of field, and distortion.

Moreover, in the imaging lens having the above configuration, it is desirable to satisfy the following conditional expression (20).
(20) 8.5<r9/(T3+D4)<72.5
where r9 is the paraxial radius of curvature of the object-side surface of the fifth lens, T3 is the distance on the optical axis from the image-side surface of the third lens to the object-side surface of the fourth lens, and D4 is the thickness on the optical axis of the fourth lens.

By satisfying the range of conditional expression (20), it is possible to achieve a low profile and good correction of coma, astigmatism, and distortion.

Moreover, in the imaging lens having the above configuration, it is desirable to satisfy the following conditional expression (21).
(21)-1.2<r10/D5<-0.3
Here, r10 is the paraxial radius of curvature of the image-side surface of the fifth lens, and D5 is the thickness of the fifth lens on the optical axis.

By satisfying the range of conditional expression (21), it is possible to achieve a low profile and good correction of astigmatism, field curvature, and distortion.

Moreover, in the imaging lens having the above configuration, it is desirable to satisfy the following conditional expression (22).
(22) 5<r11/(T4+T5)<24
where r11 is the paraxial radius of curvature of the object-side surface of the sixth lens, T4 is the distance on the optical axis from the image-side surface of the fourth lens to the object-side surface of the fifth lens, and T5 is the distance on the optical axis from the image-side surface of the fifth lens to the object-side surface of the sixth lens.

By satisfying the range of conditional expression (22), it is possible to achieve a low profile and to achieve good correction of coma, astigmatism, curvature of field, and distortion.

The present invention makes it possible to obtain an imaging lens with high resolution and excellent correction of aberrations while satisfying the requirements for low height and low F-number in a well-balanced manner.

1 is a diagram showing a schematic configuration of an imaging lens according to a first embodiment of the present invention. 3A to 3C are diagrams illustrating spherical aberration, astigmatism, and distortion of the imaging lens according to the first embodiment of the present invention. FIG. 11 is a diagram showing a schematic configuration of an imaging lens according to a second embodiment of the present invention. 6A and 6B are diagrams illustrating spherical aberration, astigmatism, and distortion of the imaging lens according to the second embodiment of the present invention. FIG. 11 is a diagram showing a schematic configuration of an imaging lens according to a third embodiment of the present invention. 11A and 11B are diagrams illustrating spherical aberration, astigmatism, and distortion of the imaging lens according to Example 3 of the present invention. FIG. 11 is a diagram showing a schematic configuration of an imaging lens according to a fourth embodiment of the present invention. 11A and 11B are diagrams illustrating spherical aberration, astigmatism, and distortion of the imaging lens according to Example 4 of the present invention. FIG. 13 is a diagram showing a schematic configuration of an imaging lens according to a fifth embodiment of the present invention. 13A to 13C are diagrams illustrating spherical aberration, astigmatism, and distortion of the imaging lens according to the fifth embodiment of the present invention. FIG. 13 is a diagram showing a schematic configuration of an imaging lens according to a sixth embodiment of the present invention. 13A to 13C are diagrams illustrating spherical aberration, astigmatism, and distortion of an imaging lens according to a sixth embodiment of the present invention. FIG. 13 is a diagram showing a schematic configuration of an imaging lens according to a seventh embodiment of the present invention. 13A to 13C are diagrams illustrating spherical aberration, astigmatism, and distortion of the imaging lens according to Example 7 of the present invention. FIG. 13 is a diagram showing a schematic configuration of an imaging lens according to an eighth embodiment of the present invention. 13A to 13C are diagrams illustrating spherical aberration, astigmatism, and distortion of the imaging lens according to Example 8 of the present invention. FIG. 13 is a diagram showing a schematic configuration of an imaging lens according to a ninth embodiment of the present invention. 13A to 13C are diagrams illustrating spherical aberration, astigmatism, and distortion of the imaging lens according to Example 9 of the present invention.

The following describes in detail an embodiment of the present invention with reference to the drawings.

Figures 1, 3, 5, 7, 9, 11, 13, 15, and 17 each show a schematic configuration diagram of an imaging lens according to Examples 1 to 9 of an embodiment of the present invention. Details of the embodiment of the present invention will be described below with reference to Figure 1.

As shown in FIG. 1, the imaging lens according to the present invention is composed of a first lens L1 having negative refractive power, a second lens L2 having positive refractive power, a third lens L3 having positive refractive power, a fourth lens L4 having negative refractive power, a fifth lens L5 having positive refractive power, and a sixth lens L6 having negative refractive power, which are arranged in this order from the object side to the image side. The first lens L1 is biconcave in the paraxial direction, the second lens L2 has a convex surface on the object side in the paraxial direction, the fourth lens L4 has a concave surface on the image side in the paraxial direction, the fifth lens L5 has a convex surface on the object side in the paraxial direction, and the sixth lens L6 has a concave surface on the image side in the paraxial direction.

A filter IR, such as an infrared cut filter or cover glass, is disposed between the sixth lens L6 and the imaging surface IMG (i.e., the imaging surface of the image sensor). Note that this filter IR can be omitted.

The aperture stop ST is disposed between the second lens L2 and the third lens L3, which facilitates correction of distortion. Note that the position of the aperture stop ST is not limited to between the second lens L2 and the third lens L3. It may be disposed as appropriate according to the specifications of the image sensor.

The first lens L1 has negative refractive power and is biconcave paraxially. This suppresses chromatic aberration, coma, astigmatism, and distortion.

In addition, the aspheric surface formed on the object-side surface of the first lens L1 has a pole point at a position other than on the optical axis X. This effectively suppresses astigmatism, field curvature, and distortion.

The second lens L2 has positive refractive power and is a meniscus shape with a convex surface on the object side at the paraxial position. This provides good correction for spherical aberration, coma, astigmatism, curvature of field, and distortion.

The third lens L3 has positive refractive power and is biconvex on the paraxial plane. This allows for a low profile and excellent correction of spherical aberration, coma, astigmatism, curvature of field, and distortion.

The fourth lens L4 has negative refractive power and is a meniscus shape with a concave surface on the image side at paraxial position. Therefore, chromatic aberration, coma aberration, astigmatism, field curvature, and distortion aberration are well corrected. The shape of the fourth lens L4 is not limited to the shape according to the present numerical example 1. The shape of the fourth lens L4 may be a reverse meniscus shape, that is, a meniscus shape with a convex surface on the image side at paraxial position. Furthermore, the fourth lens L4 may be a biconcave shape at paraxial position. In this case, the negative refractive power on both sides is advantageous for correcting chromatic aberration.

In addition, the aspheric surface formed on the image-side surface of the fourth lens L4 has a pole point at a position other than on the optical axis X. This allows for better correction of astigmatism, field curvature, and distortion.

The fifth lens L5 has positive refractive power and is biconvex on the paraxial plane. This allows for good correction of spherical aberration, coma, astigmatism, curvature of field, and distortion.

The sixth lens L6 has negative refractive power and is a meniscus shape with a concave surface on the image side at paraxial position. This allows for good correction of chromatic aberration, astigmatism, curvature of field, and distortion. In addition, by making the image side concave at paraxial position, the back focus is ensured while maintaining a low height.

In addition, the aspheric surface formed on the object-side surface of the sixth lens L6 has a pole point at a position other than on the optical axis X. This allows for better correction of astigmatism, field curvature, and distortion.

Furthermore, the aspheric surface formed on the image-side surface of the sixth lens L6 has a pole point at a position other than on the optical axis X. This allows for better correction of astigmatism, field curvature, and distortion.

In the imaging lens according to this embodiment, it is preferable that each of the first lens L1 to the sixth lens L6 is composed of a single lens. A configuration consisting of only single lenses allows for extensive use of aspheric surfaces. In this embodiment, by forming appropriate aspheric surfaces on all lens surfaces, various aberrations are effectively corrected. In addition, since the number of steps can be reduced compared to the case of using cemented lenses, it is possible to manufacture the lens at low cost.

In addition, the imaging lens according to this embodiment uses plastic materials for all the lenses, making it easy to manufacture and enabling mass production at low cost.

The lens material used is not limited to plastic materials. It is possible to aim for even higher performance by using glass materials. Also, it is preferable to form all lens surfaces aspheric, but depending on the required performance, spherical surfaces, which are easier to manufacture, may be used.

The imaging lens of this embodiment exerts favorable effects by satisfying the following conditional expressions (1) to (22).
(1) 5.75<f3/T3<14.50
(2) -5.9<r1/r2<-0.9
(3) 11<r4/(T2/T1)<255
(4) -15<r6/T3<-3
(5) -35.5<r9/r10<-4.9
(6)-36<(T1/f1)×100<-9
(7) -3.5<(T5/f6)×100<-0.5
(8) 0.7<T4/T5<4.5
(9) -2.5<f1/f<-0.5
(10) 1<f2/f<8
(11)-7<r1/f<-1
(12) 0.40<r2/f<1.65
(13) -2.3<r2/r1/D1<-0.3
(14) 20<r4/T2<450
(15) 15<r5/T2<250
(16) -28.0<(r6/|r7|)×100<-0.2
(17) 3<|r7|/f<430
(18) 0.5<r8/f<3.0
(19) 1.8<r9/f<14.5
(20) 8.5<r9/(T3+D4)<72.5
(21)-1.2<r10/D5<-0.3
(22) 5<r11/(T4+T5)<24
however,
D1: thickness on the optical axis X of the first lens L1 D4: thickness on the optical axis X of the fourth lens L4 D5: thickness on the optical axis X of the fifth lens L5 T1: distance on the optical axis X from the image side surface of the first lens L1 to the object side surface of the second lens L2 T2: distance on the optical axis X from the image side surface of the second lens L2 to the object side surface of the third lens L3 T3: distance on the optical axis X from the image side surface of the third lens L3 to the object side surface of the fourth lens L4 T4: distance on the optical axis X from the image side surface of the fourth lens L4 to the object side surface of the fifth lens L5 T5: distance on the optical axis X from the image side surface of the fifth lens L5 to the object side surface of the sixth lens L6 f: focal length of the entire imaging lens system f1: first lens L 1 focal length f2: focal length f3 of the second lens L2: focal length f6 of the third lens L3: focal length r1 of the sixth lens L6: paraxial radius of curvature r2 of the object side surface of the first lens L1: paraxial radius of curvature r4 of the image side surface of the first lens L1: paraxial radius of curvature r5 of the image side surface of the second lens L2: paraxial radius of curvature r6 of the object side surface of the third lens L3: paraxial radius of curvature r7 of the image side surface of the third lens L3: paraxial radius of curvature r8 of the object side surface of the fourth lens L4: paraxial radius of curvature r9 of the image side surface of the fourth lens L4: paraxial radius of curvature r10 of the object side surface of the fifth lens L5: paraxial radius of curvature r11 of the image side surface of the fifth lens L5: paraxial radius of curvature of the object side surface of the sixth lens L6 It is not necessary to satisfy all of the above conditional expressions, and by satisfying each conditional expression alone, it is possible to obtain the action and effect corresponding to each conditional expression.

Moreover, the imaging lens of this embodiment exerts more preferable effects by satisfying the following conditional expressions (1a) to (22a).
(1a) 6.5<f3/T3<12.5
(2a) -5.7<r1/r2<-1.2
(3a) 16<r4/(T2/T1)<210
(4a) -13.5<r6/T3<-4.5
(5a) -30.0<r9/r10<-5.8
(6a) -30.0<(T1/f1)×100<-13.5
(7a) -2.9<(T5/f6)×100<-1.1
(8a) 1.1<T4/T5<3.6
(9a) -2.0<f1/f<-0.9
(10a) 2.0.<f2/f<6.5
(11a) -5.9<r1/f<-1.5
(12a) 0.60<r2/f<1.50
(13a) -2.0<r2/r1/D1<-0.5
(14a) 30<r4/T2<370
(15a) 21<r5/T2<200
(16a) -23.0<(r6/|r7|)×100<-0.4
(17a) 4.5<|r7|/f<350.0
(18a) 0.9<r8/f<2.3
(19a) 2.4<r9/f<12.0
(20a) 9.5<r9/(T3+D4)<52.5
(21a) -1.0<r10/D5<-0.5
(22a)7<r11/(T4+T5)<20
However, the symbols in each conditional expression are the same as those in the previous paragraph. Note that only the lower limit value or only the upper limit value of each of the conditional expressions (1a) to (22a) may be applied to the corresponding conditional expressions (1) to (22).

In this embodiment, the aspheric shape used for the aspheric surface of the lens surface is expressed by Equation 1, where Z is the axis in the optical axis direction, H is the height in the direction perpendicular to the optical axis, R is the paraxial radius of curvature, k is the conic coefficient, and A4, A6, A8, A10, A12, A14, A16, A18, and A20 are aspheric coefficients.

Next, examples of the imaging lens according to this embodiment are shown. In each example, f is the focal length of the entire imaging lens system, Fno is the F-number, ω is the half angle of view, ih is the maximum image height, and TTL is the total optical length. Also, i is the surface number counted from the object side, r is the paraxial radius of curvature, d is the distance between lens surfaces on the optical axis (surface spacing), Nd is the refractive index of the d-line (reference wavelength), and νd is the Abbe number for the d-line. Note that aspheric surfaces are indicated by adding an asterisk (*) after the surface number i.

(Example 1)

Basic lens data is shown in Table 1 below.

The imaging lens of Example 1 achieves a total length to diagonal ratio of 0.94 and an F-number of 2.2. In addition, as shown in Table 10, it satisfies conditional expressions (1) to (22).

Figure 2 shows the spherical aberration (mm), astigmatism (mm), and distortion (%) for the imaging lens of Example 1. The spherical aberration diagram shows the amount of aberration for each wavelength of the F-line (486 nm), d-line (588 nm), and C-line (656 nm). The astigmatism diagram also shows the amount of aberration for the d-line (solid line) at the sagittal image surface S, and the amount of aberration for the d-line (dashed line) at the tangential image surface T (the same applies to Figures 4, 6, 8, 10, 12, 14, 16, and 18). As shown in Figure 2, it can be seen that each aberration is well corrected.

(Example 2)

Basic lens data is shown in Table 2 below.

The imaging lens of Example 2 achieves a total length to diagonal ratio of 0.95 and an F-number of 2.2. In addition, as shown in Table 10, it satisfies conditional expressions (1) to (22).

Figure 4 shows the spherical aberration (mm), astigmatism (mm), and distortion (%) for the imaging lens of Example 2. As shown in Figure 4, it can be seen that each aberration is well corrected.

(Example 3)

Basic lens data is shown in Table 3 below.

The imaging lens of Example 3 achieves a total length to diagonal ratio of 0.96 and an F-number of 2.2. In addition, as shown in Table 10, it satisfies conditional expressions (1) to (22).

Figure 6 shows the spherical aberration (mm), astigmatism (mm), and distortion (%) for the imaging lens of Example 3. As shown in Figure 6, it can be seen that each aberration is well corrected.

(Example 4)

Basic lens data is shown in Table 4 below.

The imaging lens of Example 4 achieves a total length to diagonal ratio of 0.94 and an F-number of 2.2. In addition, as shown in Table 10, it satisfies conditional expressions (1) to (22).

Figure 8 shows the spherical aberration (mm), astigmatism (mm), and distortion (%) for the imaging lens of Example 4. As shown in Figure 8, it can be seen that each aberration is well corrected.

(Example 5)

Basic lens data is shown in Table 5 below.

The imaging lens of Example 5 achieves a total length to diagonal ratio of 0.94 and an F-number of 2.2. In addition, as shown in Table 10, it satisfies conditional expressions (1) to (22).

Figure 10 shows the spherical aberration (mm), astigmatism (mm), and distortion (%) for the imaging lens of Example 5. As shown in Figure 10, it can be seen that each aberration is well corrected.

(Example 6)

Basic lens data is shown in Table 6 below.

The imaging lens of Example 6 achieves a total length to diagonal ratio of 0.94 and an F-number of 2.2. In addition, as shown in Table 10, it satisfies conditional expressions (1) to (22).

Figure 12 shows the spherical aberration (mm), astigmatism (mm), and distortion (%) for the imaging lens of Example 6. As shown in Figure 12, it can be seen that each aberration is well corrected.

(Example 7)

Basic lens data is shown in Table 7 below.

The imaging lens of Example 7 achieves a total length to diagonal ratio of 0.95 and an F-number of 2.2. In addition, as shown in Table 10, it satisfies conditional expressions (1) to (22).

Figure 14 shows the spherical aberration (mm), astigmatism (mm), and distortion (%) for the imaging lens of Example 7. As shown in Figure 14, it can be seen that each aberration is well corrected.

(Example 8)

Basic lens data is shown in Table 8 below.

The imaging lens of Example 8 achieves a total length to diagonal ratio of 0.71 and an F-number of 2.2. In addition, as shown in Table 10, it satisfies conditional expressions (1) to (22).

Figure 16 shows the spherical aberration (mm), astigmatism (mm), and distortion (%) for the imaging lens of Example 8. As shown in Figure 16, it can be seen that each aberration is well corrected.

(Example 9)

Basic lens data is shown in Table 9 below.

The imaging lens of Example 9 achieves a total length to diagonal ratio of 0.95 and an F-number of 2.2. In addition, as shown in Table 10, it satisfies conditional expressions (1) to (22).

Figure 18 shows the spherical aberration (mm), astigmatism (mm), and distortion (%) for the imaging lens of Example 9. As shown in Figure 18, it can be seen that each aberration is well corrected.

Table 10 shows the values of conditional expressions (1) to (22) for Examples 1 to 9.

When the imaging lens according to the present invention is applied to a product equipped with a camera function, it contributes to the reduction in the height and F-number of the camera, while also improving its performance.

ST Aperture diaphragm L1 First lens L2 Second lens L3 Third lens L4 Fourth lens L5 Fifth lens L6 Sixth lens IR Filter IMG Imaging surface

Claims (6)

Arranged in order from the object side to the image side,
a first lens having a negative refractive power;
a second lens having a positive refractive power;
a third lens having a positive refractive power;
a fourth lens having a negative refractive power;
a fifth lens having a positive refractive power;
and a sixth lens having a negative refractive power,
the first lens is paraxially biconcave;
the second lens has a convex surface on the object side in a paraxial direction, and the fourth lens has a concave surface on the image side in a paraxial direction,
the fifth lens has a convex surface on the object side in a paraxial direction, the sixth lens has a concave surface on the image side in a paraxial direction,
An imaging lens characterized by satisfying the following conditional expressions (1), (2), and (7') :
(1) 5.75<f3/T3<14.50
(2) -5.9<r1/r2<-0.9
(7')-3.5<(T5/f6)×100≦-1.70
however,
f3: focal length of the third lens T3: distance on the optical axis from the image side surface of the third lens to the object side surface of the fourth lens r1: paraxial radius of curvature of the object side surface of the first lens r2: paraxial radius of curvature of the image side surface of the first lens T5: distance on the optical axis from the image side surface of the fifth lens to the object side surface of the sixth lens f6: focal length of the sixth lens The imaging lens according to claim 1, characterized in that the second lens has a concave surface on the image side in the paraxial direction. The imaging lens according to claim 1, characterized in that the sixth lens has a convex surface on the object side in the paraxial direction. 2. The imaging lens according to claim 1, wherein the following conditional expression (3) is satisfied:
(3) 11<r4/(T2/T1)<255
however,
r4: paraxial radius of curvature of the image-side surface of the second lens T2: distance on the optical axis from the image-side surface of the second lens to the object-side surface of the third lens T1: distance on the optical axis from the image-side surface of the first lens to the object-side surface of the second lens 2. The imaging lens according to claim 1, wherein the following conditional expression (4) is satisfied:
(4) -15<r6/T3<-3
however,
r6: paraxial radius of curvature of the image-side surface of the third lens T3: distance on the optical axis from the image-side surface of the third lens to the object-side surface of the fourth lens 2. The imaging lens according to claim 1, wherein the following conditional expression (5) is satisfied:
(5) -35.5<r9/r10<-4.9
however,
r9: paraxial radius of curvature of the object side surface of the fifth lens r10: paraxial radius of curvature of the image side surface of the fifth lens