Patent Description:
In recent years, imaging units such as on-vehicle cameras, monitoring cameras, and cameras for mobile devices have been widely spreading. These imaging units are requested to ensure a wide field angle, while achieving satisfactory resolution performance of the surroundings, with a small size and at low costs. Examples of wide-angle imaging lenses that satisfy such requests include those as described in the following PTLs <NUM> to <NUM>.

Further previously proposed arrangements are disclosed in <CIT>, <CIT>, and <CIT>.

PTL <NUM> makes a proposal for a wide-angle imaging lens constituted by five lenses in five groups. However, although the imaging lens described in PTL <NUM> achieves a field angle larger than <NUM>° as an entire field angle, a rear group rearward of a stop has a two-lens configuration including a positive lens and a negative lens. Accordingly, the imaging lens fails in fully correcting a chromatic aberration. It is difficult to obtain the satisfactory resolution performance over the surroundings.

PTL <NUM> makes a proposal for a wide-angle imaging lens constituted by six lenses in five groups. The wide-angle imaging lens described in PTL <NUM> attains a photographing field angle of <NUM>° or more. But the wide-angle imaging lens is constituted solely by glass lenses, and also includes a cemented lens. This contributes to advantages in terms of the chromatic aberration or sensitivity, but involves using a cementing agent or performing processing. It is therefore difficult to reduce costs. Moreover, in particular, regarding the on-vehicle cameras, in recent years, there has been rapid advancement in attempts to perform automatic operation such as a parking assistance function by white line recognition, as applications of automatic recognition techniques to the imaging units. Such cameras are requested not to suffer from changes in optical characteristics of the cameras even if temperature changes occur in tough environment where a vehicle travels. Plastic lenses allow for lower costs and smaller weight as compared to glass lenses. But the plastic lenses are subjected to significant changes in refractive indexes in accordance with temperature changes. Moreover, expansion and subtraction because of large linear expansion coefficients cause changes in surface shapes, contributing to degradation in the optical characteristics. Therefore, imaging lenses constituted solely by the glass lenses have been mainly utilized so far, for the imaging lenses for the above-described applications.

PTL <NUM> makes a proposal for a configuration including six lenses in four groups, with a third lens group being a cemented lens of glass lenses, to restrain the changes in the optical characteristics accompanying the temperature changes. However, the configuration utilizes three glass lenses out of the six lenses. Furthermore, because the third lens group is the cemented lens of the two glass lenses, it is necessary to use the cementing agent or to perform the processing for cementing. It is therefore difficult to reduce costs. Moreover, with the cemented lens of the two plastic lenses included, there is a concern that a shape of a cemented surface changes in accordance with the temperature change, causing a cemented joint to peel off easily. Furthermore, the plastic lenses are disposed near an imaging element that serves as a source of heat generation. This makes the configuration more likely to be affected by the temperature changes.

Accordingly, there has been a desire for development of a single-focus wide-angle imaging lens that balances size reduction and a wide field angle, e.g., the photographing angle of <NUM>° or more, and restrains changes in the optical characteristics due to the temperature changes at low costs.

It is therefore desirable to provide an imaging lens that makes it possible to achieve size reduction and cost reduction while providing a wide field angle and high image quality, and an imaging unit. Moreover, it is desirable to provide an imaging lens that makes it possible to restrain changes in optical characteristics due to temperature changes at low costs, and an imaging unit.

This invention is defined by claim <NUM>. Further respective aspects and features of the invention are defined in the appended claims.

In the other imaging lens or the other imaging unit according to the embodiments of the disclosure, with a six-lens configuration as a whole, optimization of a configuration of each lens is attained, mainly by lens materials and power distribution.

According to the imaging lens or the imaging unit of the embodiments of the disclosure, with the six-lens configuration as a whole, the optimization of the configuration of each lens is attained, mainly by the lens shapes and the power distribution. Hence, it is possible to achieve the size reduction and the cost reduction while providing the wide field angle and the high image quality.

According to the other imaging lens or the imaging unit of the embodiments of the disclosure, with the six-lens configuration as a whole, the optimization of the configuration of each lens is attained, mainly by the lens materials and the power distribution. Hence, it is possible to restrain the changes in the optical characteristics due to the temperature changes at the low costs.

It is to be noted that effects of the disclosure are not necessarily limited to the effects described above, and may include any of effects that are described herein.

In the following, some embodiments of the disclosure are described in detail with reference to the drawings. It is to be noted that description is made in the following order.

<FIG> illustrates a cross-sectional configuration of an imaging lens <NUM> according to a first configuration example of one embodiment of the disclosure. <FIG> illustrates a cross-sectional configuration of an imaging lens <NUM> according to a second configuration example. <FIG> illustrates a cross-sectional configuration of an imaging lens <NUM> according to a third configuration example. <FIG> illustrates a cross-sectional configuration of an imaging lens <NUM> according to a fourth configuration example. <FIG> illustrates a cross-sectional configuration of an imaging lens <NUM> according to a fifth configuration example. Described later are Numerical Examples in which specific numerical values are applied to each of the configuration examples. In the figures such as <FIG>, a reference character IMG denotes an image plane, and a reference character Z1 denotes an optical axis.

In the followings, a configuration of an imaging lens according to this embodiment is described in association with the configuration examples illustrated in the figures such as <FIG> as appropriate. However, the technology according to the disclosure is not limited to the configuration examples as illustrated in the figures.

The imaging lens according to this embodiment includes a negative front group Gf, an aperture stop S, and a positive rear group Gr, in the order from object side to image side. The front group Gf includes a negative first lens L1, a negative second lens L2, and a positive third lens L3. The rear group Gr includes a positive fourth lens L4, a negative fifth lens L5, and a positive sixth lens L6. That is, the imaging lens according to this embodiment includes substantially six lenses.

Description is given next on workings and effects of the imaging lens according to this embodiment. Described together are preferable configurations in the imaging lens according to this embodiment.

It is to be noted that effects described herein are merely exemplified. Effects of the technology are not limited to the effects described herein. Effects of the technology may further include other effects than the effects described herein.

According to the imaging lens of this embodiment, with a configuration of six single lenses as a whole, it is possible to obtain satisfactory optical characteristics with the small number of lenses, while downsizing and restraining costs. Moreover, as described below, optimization of a configuration of each lens is attained, mainly by lens shapes and power distribution. This makes it possible to achieve size reduction and cost reduction while providing a wide field angle and high image quality. Moreover, as described below, the optimization of the configuration of each lens is attained, mainly by the lens materials and the power distribution. This makes it possible to restrain changes in the optical characteristics due to temperature changes at low costs.

In the imaging lens according to this embodiment, in order to achieve the size reduction and the cost reduction while providing the wide field angle and the high image quality, it is preferable that the first lens L1 have a meniscus shape with a convex surface facing the object side. It is preferable that the second lens L2 have the meniscus shape with a convex surface facing the object side. It is preferable that the third lens L3 have a biconvex shape. It is preferable that the fifth lens L5 include a concave surface facing the image side. It is preferable that the sixth lens L6 include a concave surface facing the image side.

Furthermore, according to the invention at least the following conditional expressions (<NUM>) and (<NUM>) are satisfied, <MAT> <MAT> <MAT> where.

The conditional expression (<NUM>) as mentioned above is an expression that represents a condition that provides a configuration suitable for a balance between the wide field angle and the size reduction of the first lens L1. Falling below a lower limit of the conditional expression (<NUM>) causes refractive power of the first lens L1 to be lowered. This causes difficulty in providing the wide field angle, and causes an increase in a diameter of the first lens L1. In contrast, exceeding an upper limit of the conditional expression (<NUM>) causes the refractive power of the first lens L1 to become too strong. This causes difficulty in correcting an off-axis aberration. Accordingly, allowing the imaging lens to satisfy the conditional expression (<NUM>) allows for appropriate regulation of allocation of the refractive power of the first lens L1, leading to the balance between the wide field angle and the size reduction.

The conditional expression (<NUM>) as mentioned above is an expression that regulates the radius of curvature of the surface on the image side of the first lens L1. Falling below a lower limit of the conditional expression (<NUM>) causes refractive power of the surface on the image side of the first lens L1 to become too strong. This causes occurrence of the off-axis aberration, while causing difficulty in processing of the surface on the image side, resulting in an increase in manufacture costs. Accordingly, allowing the imaging lens to satisfy the conditional expression (<NUM>) allows for rationalization of the refractive power of the surface on the image side of the first lens L1, making it possible to restrain the manufacture costs.

The conditional expression (<NUM>) as mentioned above is an expression that regulates the radius of curvature of the second lens L2. Falling below a lower limit of the conditional expression (<NUM>) causes the second lens L2 to become a biconcave lens with a concave surface facing the object side, and to have large refractive power. This causes degradation in optical performance due to lens eccentricity caused by variations in manufacture. In contrast, exceeding an upper limit of the conditional expression (<NUM>) causes the radii of curvature of the surface on the object side and the surface on the image side of the second lens L2 to be too close. This causes refractive power of the second lens L2 to be lowered, causing difficulty in achieving the wide field angle. Accordingly, allowing the imaging lens to satisfy the conditional expression (<NUM>) allows for rationalization of the refractive power of the second lens L2, making it possible to achieve the wide field angle and reduction in sensitivity to eccentricity.

It is to be noted that it is more preferable to limit the upper limits and the lower limits of the conditional expressions (<NUM>), (<NUM>), and (<NUM>) as follows. <MAT> <MAT> <MAT>.

Moreover, in the imaging lens according to this embodiment, it is preferable that Abbe numbers with respect to d line of the first lens L1, the second lens L2, the fourth lens L4, and the sixth lens L6 are equal to or larger than <NUM>, and that the Abbe numbers of the third lens L3 and the fifth lens L5 are equal to or smaller than <NUM>. Satisfying the conditions as mentioned above makes it possible to satisfactorily correct a chromatic aberration.

In the imaging lens according to this embodiment, in order to restrain the changes in the optical characteristics due to the temperature changes at low costs, it is preferable that the first lens L1 and the sixth lens L6 be made of glass. Moreover, it is preferable that each of the second lens to the fifth lens be made of plastics.

Out of the first lens L1 to the sixth lens L6, the sixth lens L6 is the closest to the imaging element <NUM>. Glass has smaller changes in characteristics in accordance with the temperature, than plastics have. Allowing the sixth lens L6 to be made of glass makes it possible to restrain the optical characteristics from being affected by a temperature rise due to heat generation of the imaging element <NUM>. Moreover, allowing the first lens L1 that is exposed to outside air to be made of glass makes it possible to enhance environment resistance. Furthermore, allowing both the negative first lens L1 and the positive sixth lens L6 to be glass lenses allows for mutual cancellation of the changes in the optical characteristics due to the temperature characteristics. This makes it possible to reduce the changes in the optical characteristics as a whole.

In order to restrain the changes in the optical characteristics due to the temperature changes, furthermore, it is preferable that the following conditional expression (<NUM>) is satisfied. In particular, in order to restrain changes in focal positions accompanying the temperature changes, according to the present invention the conditional expressions (<NUM>) and (<NUM>) are satisfied. Moreover, in order to restrain changes in a field angle accompanying the temperature changes, it is preferable that the conditional expression (<NUM>) be satisfied. <MAT> <MAT> <MAT> where.

The conditional expression (<NUM>) as mentioned above is an expression that regulates a ratio of refractive power of each lens to refractive power of the lens entire system. Falling below a lower limit of the conditional expression (<NUM>) causes an increase in the refractive power of each lens, and causes higher sensitivity to the eccentricity. Moreover, there occur larger changes in the refractive power due to the temperature changes, in particular in plastic lenses having larger changes in linear expansion coefficient values and refractive indexes due to the temperature changes than glass has. Accordingly, caused are the changes in the focal positions, and the degradation in the optical characteristics such as resolution performance.

The conditional expression (<NUM>) as mentioned above is an expression that regulates composite refractive power of the second lens L2 to the fifth lens L5 that are constituted by plastic lenses. Falling below a lower limit of the conditional expression (<NUM>) causes the composite refractive power to be strong. This causes an increase in changes in the refractive power due to the temperature changes, resulting in the degradation in the optical characteristics such as the changes in the focal positions.

The conditional expression (<NUM>) as mentioned above is an expression that represents a condition that reduces an angle of a light ray that enters the imaging element <NUM>, and reduces changes in the field angle in a case where the focal position is shifted due to the temperature changes. Exceeding an upper limit or falling below a lower limit of the conditional expression (<NUM>) causes the angle of the light ray that enters the imaging element <NUM> to be steep (causes an angle of a light ray with respect to an imaging plane to be small). This causes the changes in the field angle on occasions of the temperature changes.

Moreover, it is more preferable that the upper limits and the lower limits of the conditional expressions (<NUM>) to (<NUM>) be limited as follows, <MAT> <MAT> <MAT>.

Moreover, in a case with use of a member such as plastics having large linear expansion coefficients, instead of metals, for a lens holder member, expansion and contraction occur due to temperature changes of the holder member. Accordingly, it is more preferable that the conditional expression (<NUM>) be limited as follows, <MAT>.

The imaging lens according to this embodiment is applicable to, for example, an imaging unit such as an on-vehicle camera, a monitoring camera, and a camera for a mobile device. In the case of the application to the imaging unit, as illustrated in <FIG>, the imaging element <NUM> such as CCD (Charge Coupled Devices) and CMOS (Complementary Metal Oxide Semiconductor) is disposed in the vicinity of the image plane IMG of the imaging lens. The imaging element <NUM> outputs an imaging signal (an image signal) that corresponds to an optical image formed by the imaging lens. In this case, as illustrated in the figures such as <FIG>, for example, a filter such as an infrared ray cutoff filter and a low pass filter may be disposed between the sixth lens L6 and the image plane IMG. In addition, optical members such as sealing glass for protection of the imaging element may be disposed.

<FIG> and <FIG> provide a configuration example of on-vehicle cameras, as an application example to the imaging unit. <FIG> illustrates one example of exemplary disposition of the on-vehicle cameras. <FIG> illustrates one network configuration example of the on-vehicle cameras.

For example, as illustrated in <FIG>, disposed are an on-vehicle camera <NUM> in front (forward) of a vehicle <NUM>, on-vehicle cameras <NUM> and <NUM> on the right and on the left, and, furthermore, an on-vehicle camera <NUM> in the rear (rearward). The on-vehicle cameras <NUM> to <NUM> are coupled to an in-vehicle network <NUM>, as illustrated in <FIG>. To the in-vehicle network <NUM>, also coupled are an ECU (Electrical Control Unit) <NUM>, a display <NUM>, and a speaker <NUM>. The constituent blocks are each able to communicate mutually through the in-vehicle network <NUM>.

An angle of image acquisition of the on-vehicle camera <NUM> provided in front of the vehicle <NUM> is, for example, in a range denoted by "a" in <FIG>. An angle of image acquisition of the on-vehicle camera <NUM> is, for example, in a range denoted by "b" in <FIG>. An angle of image acquisition of the on-vehicle camera <NUM> is, for example, in a range denoted by "c" in <FIG>. An angle of image acquisition of the on-vehicle camera <NUM> is, for example, in a range denoted by "d" in <FIG>. The on-vehicle cameras <NUM> to <NUM> each output images acquired, to the ECU <NUM>. As a result, the ECU <NUM> is able to acquire an image around <NUM> degrees (omnidirectionally), i.e., frontward, rightward, leftward, and rearward of the vehicle <NUM>.

The ECU <NUM> includes a signal processor <NUM>, as illustrated in <FIG>. The on-vehicle camera <NUM> includes a camera module <NUM> and a signal processor <NUM>, as illustrated in <FIG>. The signal processors <NUM> and <NUM> are each constituted by an LSI (Large Scale Integration), e.g., an image processor LSI. The camera module <NUM> includes an imaging lens <NUM> and an imaging element <NUM>. To the imaging lens <NUM>, the imaging lens according to this embodiment as illustrated in the figures such as <FIG> is applicable. The other on-vehicle cameras <NUM>, <NUM>, and <NUM> may have substantially similar configurations.

The signal processor <NUM> of the on-vehicle camera <NUM> converts a signal from the imaging element <NUM> to a signal in a form transmittable as the image signal to the in-vehicle network <NUM>. The signal processor <NUM> transmits the signal converted, to the signal processor <NUM> of the ECU <NUM>. The other on-vehicle cameras <NUM>, <NUM>, and <NUM> perform substantially similar processing.

The signal processor <NUM> of the ECU <NUM> receives the images from the plurality of the on-vehicle cameras <NUM> to <NUM>, composites the images, generates a high-field-angle image (a panorama image), and sends the image to the display <NUM>. The display <NUM> displays the image thus sent.

Each of the signal processors <NUM> of the on-vehicle cameras <NUM> to <NUM> may also have a function of receiving a signal from the camera module <NUM>, and making a detection of an object in the image (e.g., a vehicle, a person, a bicycle, and an obstacle ahead) with use of the image signal received. The signal processor <NUM> may also have a function of performing signal processing such as measurement of a distance to the object, and generation of a warning signal on the basis of the distance to the object. A result of the signal processing and the image signal in this case are transmitted, through the in-vehicle network <NUM>, to the signal processor <NUM> of the ECU <NUM>, the display <NUM>, and the speaker <NUM>.

The signal processor <NUM> of the ECU <NUM> may generate a signal for a brake control of the vehicle, or generate a signal for a speed control, as necessary, on the basis of the result of the signal processing in each of the signal processors <NUM> of the on-vehicle cameras <NUM> to <NUM>. Moreover, on receiving the warning signal, the display <NUM> displays a warning image, to give a warning to a driver. Furthermore, on receiving the warning signal, the speaker <NUM> provides a warning sound, to give the warning to the driver.

Description is given next on specific Numerical Examples of the imaging lens according to this embodiment. Here, described are Numerical Examples in which specific numerical values are applied to the imaging lenses <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> of the respective configuration examples as illustrated in <FIG>, <FIG>, <FIG>, <FIG>, and <FIG>.

It is to be noted that meanings of symbols and other legends illustrated in the following tables and description are as follows. The term "surface number" stands for the number of the i-th surface counted from the object side toward the image side. The term "Ri" stands for a value (mm) of a paraxial radius of curvature of the i-th surface. The term "Di" stands for a value (mm) of an axial surface interval (a lens center thickness, or an air interval) between the i-th surface and the (i+<NUM>)-th surface. The term "Ni" stands for a value of a refractive index at the d line (wavelength <NUM>) of, for example, a lens starting at the i-th surface. The term "vi" stands for a value of the Abbe number at the d line of, for example, the lens starting at the i-th surface. A part whose value of "Ri" is "∞" stands for a flat plane, or a stop plane (the aperture stop S). A surface represented as "STO" in the "surface number" means that the surface is the aperture stop S. The term "f" stands for the focal length of the lens entire system. The term "Fno" stands for an F number (maximum aperture). The term "ω" stands for a half field angle.

Some of the lenses used in each Numerical Example include an aspherically formed lens surface. A surface represented as "ASP" in the "surface number" means that the surface is an aspherical surface. An aspherical shape is defined by the following expression. It is to be noted that in each table described later that summarizes aspherical surface coefficients, the term "E-n" is exponential notation with base of <NUM>. That is, the term "E-n" means "minus n-th power of <NUM>". For example, "<NUM>. 12345E-<NUM>" means "<NUM>×(minus 5th power of <NUM>)".

In the expression of the aspherical surface as mentioned above, a distance in a direction of an optical axis from a vertex of a lens surface is denoted by "x". A height in a direction perpendicular to the optical axis is denoted by "y". A paraxial curvature (<NUM>/R) at a lens vertex is denoted by "c". A conical constant (a conic constant) is denoted by "κ". The terms "A4","A6", "A8", "A10", "A12", "A14", and "A16" denote respectively the 4th, 6th, 8th, 10th, 12nd, 14th, and 16th aspherical surface coefficients.

All the imaging lenses <NUM> to <NUM> to which the following Numerical Examples are applied have configurations that satisfy the basic lens configuration as described above. All the imaging lenses <NUM> to <NUM> include the negative front group Gf, the aperture stop S, and the positive rear group Gr, in this order from the object side toward the image side. The front group Gf includes the negative first lens L1, the negative second lens L2, and the positive third lens L3. The rear group Gr includes the positive fourth lens L4, the negative fifth lens L5, and the positive sixth lens L6. In other words, all the imaging lenses <NUM> to <NUM> include substantially six lenses.

The first lens L1 has the meniscus shape with the convex surface facing the object side. The second lens L2 has the meniscus shape with the convex surface facing the object side. The third lens L3 has the biconvex shape. The fifth lens L5 includes the concave surface facing the image side. The sixth lens L6 includes the concave surface facing the image side.

The aperture stop S is disposed between the third lens L3 and the fourth lens L4. The filter FL is disposed between the sixth lens L6 and the image plane IMG.

[Table <NUM>] summarizes lens data of Numerical Example <NUM> in which specific numerical values are applied to the imaging lens <NUM> illustrated in <FIG>. In the imaging lens <NUM>, both sides of each of the second lens L2 to the sixth lens L6 are the aspherical surfaces. [Table <NUM>] summarizes values of the aspherical surface coefficients A4, A6, A8, A10, A12, A14, and A16 in the aspherical surfaces, together with values of the conical coefficient κ. Moreover, [Table <NUM>] summarizes the focal length f of the entire system, the F number Fno, the half field angle ω, and a value of a lens total length.

In this Numerical Example <NUM>, the first lens L1 is a glass lens. The second lens L2 to the sixth lens L6 are all plastic lenses.

Various aberrations in Numerical Example <NUM> described above are illustrated in <FIG> illustrates, as the various aberrations, a spherical aberration and astigmatism (field curvature) in a focusing state at a finite distance (<NUM>). Each of the aberration diagrams illustrates the aberration with the d line (<NUM>) serving as a reference wavelength. In the spherical aberration diagram, a solid line denotes the aberration with respect to the d line. An alternate long and short dash line denotes the aberration with respect to g line (<NUM>). A broken line denotes the aberration with respect to C line (<NUM>). In the astigmatism diagram, a solid line denotes a value of the aberration in a sagittal image plane, and a broken line denotes a value of the aberration in a meridional image plane. The same applies to aberration diagrams in the following other Numerical Examples.

As seen from each of the above-described aberration diagrams, it is evident that the imaging lens <NUM> is satisfactorily corrected in the various aberrations, and has optimal imaging performance.

[Table <NUM>] summarizes lens data of Numerical Example <NUM> in which specific numerical values are applied to the imaging lens <NUM> illustrated in <FIG>. In the imaging lens <NUM>, both sides of each of the second lens L2 to the sixth lens L6 are the aspherical surfaces. [Table <NUM>] summarizes the values of the aspherical surface coefficients A4, A6, A8, A10, A12, A14, and A16 in the aspherical surfaces, together with the values of the conical coefficient κ. Moreover, [Table <NUM>] summarizes the focal length f of the entire system, the F number Fno, the half field angle ω, and the value of the lens total length.

In this Numerical Example <NUM>, the first lens L1 is a glass lens. Moreover, the second lens L2 to the sixth lens L6 are all plastic lenses.

Various aberrations in Numerical Example <NUM> described above are illustrated in <FIG>. As seen from each of the aberration diagrams, it is evident that the imaging lens <NUM> is satisfactorily corrected in the various aberrations, and has the optimal imaging performance.

[Table <NUM>] summarizes lens data of Numerical Example <NUM> in which specific numerical values are applied to the imaging lens <NUM> illustrated in <FIG>. In the imaging lens <NUM>, both sides of each of the second lens L2, and the fourth lens L4 to the sixth lens L6 are the aspherical surfaces. Moreover, the surface on the object side (the fifth surface) of the third lens L3 is the aspherical surface. [Table <NUM>] summarizes the values of the aspherical surface coefficients A4, A6, A8, A10, A12, A14, and A16 in the aspherical surfaces, together with the values of the conical coefficient κ. Moreover, [Table <NUM>] summarizes the focal length f of the entire system, the F number Fno, the half field angle ω, and the value of the lens total length.

In this Numerical Example <NUM>, the first lens L1 and the fourth lens L4 are glass lenses. Moreover, the second lens L2 and the third lens L3, and the fifth lens L5 and the sixth lens L6 are plastic lenses.

In this Numerical Example <NUM>, the first lens L1 and the sixth lens L6 are glass lenses. Moreover, the second lens L2 to the fifth lens L5 are all plastic lenses.

In this Numerical Example <NUM>, the first lens L1 and the sixth lens are glass lenses. Moreover, the second lens L2 to the fifth lens L5 are all plastic lenses.

[Table <NUM>] summarizes values regarding each of the conditional expressions as mentioned above, with respect to each of Numerical Examples. As is evident from [Table <NUM>], the imaging lenses of all Examples satisfy the conditional expressions (<NUM>) to (<NUM>). The conditional expressions (<NUM>) and (<NUM>) are satisfied by at least the imaging lenses of Examples <NUM> and <NUM>.

It is to be noted that regarding the conditional expression (<NUM>), summarized are values of fi/f (min). fi/f (min) represents a minimum value, out of values of the ratio (fi/f) of the focal length fi of the i-th lens (i=<NUM> to <NUM>) to the focal length f of the lens entire system.

The technology according to the disclosure is not limited to the description of the embodiment and Examples as mentioned above, and may be modified and implemented in a variety of ways.

For example, shapes and numerical values of each part as described in each of the forgoing Numerical Examples are merely examples of embodiments to carry out the technology, and the technical scope of the technology should never be restrictively interpreted on the basis of them.

Moreover, in the embodiment and Examples as described above, description is given on the configuration that includes substantially six lenses. However, an alternative configuration may be possible that further includes a lens that is substantially devoid of refractive power.

Claim 1:
An imaging lens (<NUM>) for use in an on-vehicle camera (<NUM>), comprising a negative front group; a stop; and a positive rear group, the negative front group, the stop, and the positive rear group being disposed in order from object side toward image side,
the front group including
a negative first lens having a meniscus shape with a convex surface facing the object side,
a negative second lens having the meniscus shape with a convex surface facing the object side, and
a positive third lens having a biconvex shape, and
the rear group including
a positive fourth lens,
a negative fifth lens with a concave surface facing the image side, and
a positive sixth lens,
wherein the half field angle of the imaging lens is <NUM> degrees or greater,
wherein both surfaces of each of the second, third, fourth, fifth, and sixth lenses are aspherical,
wherein the imaging lens further satisfies the following condition, <MAT>
where R3 is a radius of curvature of the surface on the object side of the second lens, and R4 is a radius of curvature of a surface on the image side of the second lens,
wherein the imaging lens further satisfies the following condition, <MAT>
where f1 is a focal length of the first lens, and f is a focal length of a lens entire system, wherein the imaging lens further satisfies the following condition, <MAT>
where fi is a focal length of the i-th lens (i=<NUM> to <NUM>) (a focal length of each of the first lens to the sixth lens) , and
wherein the first lens and the sixth lens are made of glass, and the imaging lens satisfies the following condition, <MAT>
where fp is a composite focal length of the second to the fifth lenses.