JP7010749B2 - Imaging lens unit - Google Patents

Description

The present invention relates to an image pickup lens used in a surveillance camera, an in-vehicle camera, or the like, and more particularly to an image pickup lens unit having a five-group, six-element configuration in which a junction lens is used in the rear group and a horizontal angle of view of more than 100 degrees.

In recent years, surveillance cameras, in-vehicle cameras, and the like have become widespread. As an image pickup lens mounted on a surveillance camera or an in-vehicle camera (hereinafter referred to as an in-vehicle camera or the like), a fixed-focus wide-angle lens having a bright F value is used. In particular, a wide-angle lens with a field of view exceeding 100 degrees is desired.
On the other hand, for surveillance cameras, in-vehicle cameras, etc., it is necessary to take into consideration the use in cold regions to tropical regions, and stable performance is desired in the temperature range from low temperature to high temperature.

When designing a wide-angle lens, a lens group with negative power as a whole in the front group, which is called retrofocus to ensure sufficient back focus, has positive power as a whole in the rear group. A lens configuration composed of a lens group is often used (see Patent Documents 1 and 2).

Japanese Unexamined Patent Publication No. 2016-114648 Japanese Patent No. 5042767

Applications for in-vehicle optical systems include viewing applications for simply securing a field of view, and sensing applications for linking with a safety assurance system represented by automatic braking. In particular, in order to be used for sensing applications, high optical accuracy such as flatness of the image plane is required in addition to measures against ghost and flare, not to mention chromatic aberration, in addition to compactness and compactness. Moreover, since an in-vehicle camera or the like is used in a harsh environment, it is required to have durability against changes in environmental temperature (hereinafter referred to as environmental resistance).

Patent Document 1 proposes an imaging optical system having a 5-group, 5-element structure capable of maintaining high resolution in a wide temperature range from low temperature to high temperature. In the present invention, the front group and the rear group are configured with the aperture in between, but the focus shift of the optical system is such that the second lens close to the aperture of the front group is a convex lens and the third lens close to the aperture of the rear group. We are trying to achieve this purpose by using a concave lens. However, in such a configuration, it is necessary to secure a sufficient distance between the first lens and the second lens in the front group, and as a result, the total length becomes long, which may be disadvantageous for a compact design.

Patent Document 2 discloses an optical system of 5 groups and 6 elements, with the front group having 3 elements in 3 groups and the rear group having 3 elements in 2 groups. However, as a condition for use in a wide temperature range, it is merely described as a glass material having a small linear expansion coefficient. Therefore, there is a limit to the temperature range that can be compensated, and there is also a limit when higher image quality is required.

An object of the present invention is to provide an image pickup lens suitable for an in-vehicle camera or the like, which is low in cost and has excellent mass productivity, and in particular, an image pickup lens that can be used for sensing applications.

In order to achieve the above object, an image pickup lens unit in which a plurality of lenses are incorporated in a lens barrel made of resin, and the front group (hereinafter referred to as the first lens group) in which the lenses have a negative refractive force in order from the object side. The first lens group is composed of a rear group (hereinafter referred to as a second lens group) having a positive refractive force across the aperture, and the first lens group has a negative refractive force from the object side. It is composed of a meniscus lens (first lens) having a convex surface on the object side and a meniscus lens (second lens) having a negative refractive force and forming a convex surface on the object side.
The second lens group includes a biconvex lens (third lens) having a positive refractive power, a biconvex lens (fourth lens) having a positive refractive power, and a biconvex lens (fourth lens) having a positive refractive power from the object side. The fifth lens) and the concave lens (sixth lens) having a negative refractive force are included, and the first to sixth lenses are provided in the lens barrel with the third lens and the fourth lens of the second lens group. An image pickup lens unit characterized in that the first lens to the third lens are incorporated from the object side of the lens barrel, and the fourth lens to the sixth lens are incorporated from the image plane side, with the space between them as a reference position.

In the present invention, in a so-called reverse telefocus type (retrofocus type) wide-angle lens composed of a first lens group and a second lens group with a diaphragm in between, the second group is compared with the first group composed of two lenses. It is composed of 4 lenses. In such a configuration, by arranging the reference position for incorporating the lens into the lens barrel between the third lens and the fourth lens in the second group, temperature compensation for ensuring imaging performance in a wide temperature range is obtained. It enables easy optical design.

It is desirable that both end lenses of the first lens and the sixth lens are fastened to the lens barrel by a retainer. By pressing each lens from the object side and the imaging side with the retainer, it is possible to prevent the lens from loosening in a wide temperature range against changes in the lens barrel length due to linear expansion of the resin lens barrel. Therefore, it is desirable that the retainer is made of an elastic body.

A lens in which the fifth lens and the sixth lens of the second lens group are joined, and the distance between the sixth lens and the fourth lens, which have a larger diameter than the fifth lens, is defined by an interval ring. It is desirable to be there. In the 6-lens image pickup lens of the present invention, in order to improve the imaging performance and the assembly accuracy, it is desirable to join the 5th lens and the 6th lens, and in that case, join them together. From the viewpoint of protecting the existing lens, by restricting the position of the fourth lens and the sixth lens by the interval ring, it is possible to form a structure in which the load on the lens joint surface is not applied.

According to the present invention, the first to sixth lenses composed of two first lens groups and four second lens groups are formed into a resin barrel with a reference position between the third lens and the fourth lens. By arranging the lens, stable optical performance can be obtained by alleviating the fluctuation of the focal length of the lens and the expansion / contraction of the lens barrel due to the temperature change from low temperature to high temperature.

It is a perspective view which shows the camera which has the lens unit which concerns on one Embodiment of this invention. It is sectional drawing of the lens unit shown in FIG. It is a breaking perspective view of the lens unit shown in FIG. It is a perspective sectional view which shows the lens barrel of the lens unit shown in FIG. It is a schematic diagram which shows the lens arrangement in a numerical example. It is a lens aberration diagram of the numerical example 1. FIG. It is a MTF characteristic diagram of the numerical example 1. FIG. It is a lens aberration diagram of the numerical example 2. FIG. It is a MTF characteristic diagram of the numerical example 2. FIG. It is a lens aberration diagram of the numerical example 3. FIG. It is a MTF characteristic diagram of the numerical example 3. FIG. It is a lens aberration diagram of the numerical example 4. FIG. It is a MTF characteristic diagram of the numerical example 4. FIG. It is a lens aberration diagram of the numerical example 5. It is a MTF characteristic diagram of the numerical example 5.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a camera 100 including a lens unit 10 according to an embodiment of the present invention. The lens unit 10 is composed of a resin barrel 2 and a plurality of lenses 1 (first lens 11 to sixth lens 16) incorporated in the lens barrel 2.

As shown in FIG. 2, the plurality of lenses 1 are a second lens 12 to a fifth lens 15 (hereinafter referred to as an intermediate lens group 1a) and a first lens arranged on both sides of the intermediate lens group 1a in the optical axis direction. 11 and a sixth lens 16 (hereinafter, each of which is referred to as both end lenses 1b) are included. The intermediate lens group 1a is press-fitted into the lens barrel 2 and incorporated therein. Both end lenses 1b include a first lens 11 on the most subject (object) side and a sixth lens 16 on the most image plane (sensor) side, respectively, and are fastened to the inside of the lens barrel 2 by a retainer 3.

The material of the lens 1 is not particularly limited, and for example, a glass lens, a thin-walled glass lens, a resin lens, or the like is used, and the lens 1 is used in an appropriate combination depending on the intended use. The number, diameter, thickness, and the like of the lens 1 may be different as long as they can be incorporated into the lens barrel 2.

The lens barrel 2 is a resin-made tubular member that houses the lens 1 inside, and has openings at both ends on the object side and the image plane side.

The lens barrel 2 is preferably designed by simulating the minimum necessary press-fitting pressure (pressure generated in the lens in the direction perpendicular to the optical axis) that can hold the lens in the lens barrel within the operating environment temperature range. The press-fitting pressure is preferably 20 to 70 MPa, more preferably 20 to 60 MPa. By setting the press-fitting pressure, the adverse effect on the lens 1 is suppressed, and glass materials having different linear expansion coefficients can be used. The operating environment temperature range of the lens barrel 2 is −40 to + 105 ° C, more preferably −40 to + 125 ° C. It should be noted that this temperature range may be applied to other members including the lens 1.

Such a lens barrel 2 is made of resin in terms of ease of molding by injection molding (mold molding), lightness, and cost. For example, polycarbonate (PC) resin, polyphenylene sulfide (PPS) resin, or the like is preferable. In particular, PPS resin has high rigidity and strength and is preferably used. Further, for example, glass fiber may be mixed in the resin in order to obtain higher strength and lower line expansion.

As shown in FIGS. 2 and 3, the first lens 11 and the sixth lens 16 are attached to the end of the lens barrel 2 by the retainer 3. The retainer 3 is an annular member, and is attached to the end portions of the lens barrel 2 on the object side and the image plane side in parallel with the optical axis direction, and both ends of the first lens 11 and the sixth lens 16 at the end portion of the lens barrel 2. The lenses 1b are fastened so as to be sandwiched between the lens barrels 2. The retainer 3 may not only hold the both end lenses 1b but also hold the intermediate lens group 1a inward of the lens barrel 2. That is, the second lens 12 and the fifth lens 15 with which both end lenses 1b abut can be pressed inward of the lens barrel 2. Further, the intermediate lens group 1a can hold down the entire lens 1 when the adjacent lenses are in contact with the spacing ring 6 as described later.

The method of fastening the retainer 3 to the lens barrel 2 is not particularly limited as long as the lens to be fastened does not play, and for example, threads are cut on the inner peripheral surface side of the retainer 3 and the outer peripheral surface sides of both ends of the lens barrel 2. Examples thereof include a method of screwing with a screw, and a method of fitting the retainer 3 and the lens barrel 2 and then screwing from the outside with a screw (not shown).

The retainer 3 is preferably formed of an elastic body in order to absorb linear expansion due to a change in environmental temperature and apply a stable pressing force in the optical axis direction to the lens unit. Both end lenses 1b can be pressed into the lens barrel 2 by the stress due to the elastic deformation of the retainer 3 to be more reliably fixed. Examples of the elastic body include a metal material such as aluminum and a resin material such as PPS. Further, the retainer 3 may be provided with a holding portion (for example, a leaf spring) that presses both end lenses 1b inward from the opening side.

As shown in FIG. 4, of the inner surface of the lens barrel 2, the inner peripheral surface of the portion where the press-fitted intermediate lens group 1a is incorporated is provided with a protruding portion 5 for receiving the press-fitted lens, and has a substantially circumferential circumference. It should have a surface shape (polygonal shape). The protruding portion 5 projects in a string shape (D-shaped, arc-shaped) in the lens barrel 2 in order to maintain the outer diameter of the press-fitted lens 1. The height of the protruding portion 5 in the protruding direction is 0.115 mm to 0.105 mm, and the thickness thereof is preferably equal to or larger than the edge of the lens. Further, the larger the contact area between the protrusion 5 and the lens, the better. If the contact area is large, the stress will be low and the lens will be held reliably, and if it is small, the stress will be large and the protruding portion will be plastically deformed, which may cause lens play.

It is not necessary to provide the protrusions 5 over the entire inner surface of the lens barrel 2, but at least one protrusion 5 may be provided in order to maintain the outer diameter of the lens 1, and more preferably, the protrusions 5 are provided at predetermined intervals in the inner peripheral direction. Is good. For example, it is preferable to provide three or four places at predetermined intervals so that the inner circumference of the lens barrel 2 is divided into three or four equal parts. Further, by providing the projecting portions 5 at predetermined intervals, even if the outer peripheral surface of the lens 1 and the projecting portion 5 are in contact with each other, the outer peripheral surface of the lens 1 and the lens barrel may be provided due to the spacing between the projecting portions 5. A gap is created between the inner peripheral surface of 2 and the inner peripheral surface of 2. Therefore, the space between the adjacent lenses 1 is not sealed, and the pressure can be released, so that the shape of the lens barrel 2 can be further suppressed from being deformed.

The protrusion 5 is provided for each lens of the intermediate lens group 1a to be press-fitted, and the shape and installation location may be different depending on the diameter of the lens. Further, the protruding portion 5 may be integrally molded with the lens barrel 2 by resin molding or the like, or may be formed by attaching another member to the lens barrel 2.

As shown in FIG. 4, the lens barrel 2 has a thick portion 2a and a thin portion 2b because the outer peripheral surface on which the intermediate lens group 1a is press-fitted has a different thickness corresponding to the outer diameter of the lens. .. In the thin portion 2b, a recess 8 is formed on the outer peripheral surface of the region including the portion where the protrusion 5 is formed on the inner peripheral surface of the lens barrel 2. The recess 8 can be provided by, for example, lightening the outer peripheral surface of the lens barrel 2 in the region including the portion where the protrusion 5 is formed. It is preferable that the concave portion 8 corresponds to the arrangement location and the number of arrangements of the protrusion 5 in the lens barrel 2.

Conventionally, when the intermediate lens group 1a is press-fitted into the lens barrel 2, since the rigidity of the lens barrel 2 is large, a large stress is generated due to the difference between the inner diameter of the lens barrel 2 and the outer diameter of the lens 1 to be press-fitted. However, by providing the recess 8, the rigidity of the lens barrel 2 at the lens accommodating portion can be relaxed and the press-fitting pressure of the lens 1 can be reduced. As a result, a lens such as a resin lens or a thin-walled glass lens, which has conventionally generated a large load due to press-fitting and is distorted and deteriorated in optical performance, is press-fitted into the lens barrel 2 as an intermediate lens group 1a for use. Can be done.

The diaphragm 4 is provided between the second lens 12 and the third lens 13, and is a member that controls the amount of light entering the lens by opening a predetermined aperture. The diaphragm 4 includes an aperture diaphragm that limits the amount of transmitted light and determines an F value that is an index of brightness, or a light-shielding diaphragm that blocks light rays that cause ghosts and aberrations. In this embodiment, the aperture 4 may be arranged between the space ring 6 arranged between the second lens 12 and the third lens 13 and the object surface side of the third lens 13, and this may result in this. It has the effect of maintaining the lens spacing. The material of the diaphragm 4 is preferably made of metal from the viewpoint of durability and the like, and examples of the metal include stainless steel and aluminum, and stainless steel is preferable.

In addition to the above, the lens barrel 2 may have a reference position 9, an interval ring 6, and the like.

The reference position 9 serves as a reference for the arrangement of the lens when the intermediate lens group 1a is press-fitted into the lens barrel 2, and refers to the contact point of the lens surface on which the lens is first arranged. In this embodiment, the reference position 9 is a substantially intermediate position (third) of the entire lens in order to make a compromise between the amount of change in the lens 1 and the amount of change in the lens barrel 2 with respect to the linear expansion of the lens barrel 2. It is preferable to provide it at a position (position between the lens 13 and the fourth lens 14). There is also an effect that providing the reference position 9 at a substantially intermediate position of the lens makes the lens unit 10 more compact than providing it at the aperture position or on one side of the entire lens. The reference position 9 may be appropriately changed depending on the number of lenses, performance, and the like, but distortion is less likely to occur when the number of lenses before and after the reference position 9 is the same.

As shown in FIG. 4, the reference position 9 has a roof in which the third lens contact reference surface 93 and the fourth lens contact reference surface 94 are inclined toward the image plane side and the object side, respectively, in the lens barrel 2. It is formed so as to project into a mold. The third lens 13 and the fourth lens 14 abut against the third lens contact reference surface 93 and the fourth lens contact reference surface 94, respectively, and are held at appropriate positions. The reference position 9 forms at least one projecting portion or step portion projecting in the circumferential direction of the lens barrel 2, and the inner peripheral surface is circular. The reason why the third lens contact reference surface 93 and the fourth lens contact reference surface 94 are inclined respectively is to prevent internal reflection that affects the image pickup, and to prevent internal reflection, and to the lens barrel 2. This is to facilitate pulling out the mold during integral molding.

The fluctuation of the focal length of the lens that occurs when the ambient temperature changes from the low temperature side (-40 ° C) to the high temperature side (+ 125 ° C) with respect to the reference temperature (about 20 ° C) of the lens unit based on the reference position 9. The optical design is performed so that the expansion and contraction of the lens barrel 2 can be optically compensated. At this time, since it is arranged at a substantially intermediate position of the entire lens, it is possible to perform a compensation design considering a small amount of change rather than setting a reference on the object side or the image plane side end portion, so that the optical design becomes easy. , More stable optical performance can be obtained. The optical design will be described later. On the other hand, if the reference position 9 does not satisfy the above conditions, it becomes difficult to design an optical device that satisfies the temperature compensation within the temperature range to be used.

For example, when the first lens 11 to the sixth lens 16 are installed in the lens barrel 2, first, the third lens 13 from the object side of the lens barrel 2 is incorporated in the reference position 9, and the fourth lens 14 from the image plane side. Incorporate. Next, it is preferable to incorporate the first lens 11 and the second lens 12 from the object side of the lens barrel 2, and the fifth lens 15 and the sixth lens 16 from the image plane side. At this time, the first lens group having a negative refractive power including the first lens 11 and the second lens 12 is an aperture with the second lens group having a positive refractive power including the third lens 13 to the sixth lens 16. It is configured by sandwiching the aperture 4 that has been made. In this way, when there is an imbalance in the optical axis lengths of the first lens group and the second lens group in the entire lens, the ambient temperature changes when the reference position 9 is provided at a substantially intermediate position of the entire lens. Fluctuations in the focal length of the lens and expansion / contraction of the lens barrel 2 that occur in some cases can be optically compensated, and the optical performance is stabilized.

A spacing ring 6 is provided between the second lens 12 and the third lens 13 and the fourth lens 14 and the fifth lens 15 arranged at intervals to maintain the spacing between adjacent lenses. .. The space ring 6 is a member arranged in the lens barrel 2, and the outer peripheral surface of the space ring 6 comes into contact with the inner peripheral surface of the lens barrel 2. The interval ring 6 is preferably made of metal because the amount of change with respect to temperature change is small and the rigidity is high. The metal spacing ring 6 can ensure stable optical performance in a wide temperature range. Examples of the material of such an interval ring 6 include aluminum, titanium, stainless steel, and the like, and aluminum is particularly preferable from the viewpoint of weight reduction and low cost.

The fifth lens 15 and the sixth lens 16 are bonded lenses (hereinafter referred to as bonded lenses). The bonded lens is preferably protected by arranging a fifth lens 15 having a diameter smaller than that of the sixth lens 16 on the object side so that stress in the optical axis direction due to a temperature change does not act on the bonded surface. Further, by laminating the 5th lens 15 and the 6th lens 16, the occurrence of chromatic aberration is improved, and even if the number of lenses is increased, the influence of the deviation generated when the lens is assembled is small, that is, the built-in sensitivity is reduced. It can be designed to be lower. It is preferable that the distance between the junction lens and the fourth lens 14 is defined by the distance ring 6.

<Explanation of optical system>
Next, the optical system of the present invention will be described with reference to FIGS. 1 and 5. The lens unit 10 has a lens configuration of 6 elements in 5 groups, and has a first lens group (L1) having a negative power as a whole and a second lens group (L1) having a positive power as a whole across the diaphragm 4. It is a retrofocus format composed of L2), and has a configuration that can be miniaturized while ensuring sufficient back focus.

As shown in FIG. 5, the first lens group (L1) is composed of two meniscus-type concave lenses, a first lens 11 and a second lens 12, in order from the object side. The second lens group (L2) is composed of a third lens 13, a fourth lens 14, a convex lens of the fifth lens 15, and a sixth lens 16 which is a concave lens from the object side. Since the fifth lens 15 and the sixth lens 16 are bonded lenses, the second lens group (L2) is composed of four elements in three groups. This junction lens is a convex lens having a positive power as a whole by laminating a set of lenses of a convex fifth lens 15 and a concave sixth lens 16. Therefore, the three groups constituting the second lens group (L2) all have a lens configuration in which positive power is arranged.

When the image pickup lens unit of the present invention is used as an in-vehicle lens unit, it is necessary to secure high imaging performance in a temperature range of about -40 ° C to + 120 ° C in consideration of use in cold regions and tropical regions. There is.

When plastic (PPS) is used as the material of the lens barrel, a resin with excellent environmental stability is selected and used, and the relative distance between the lens and the image sensor changes in the linear expansion of the resin lens barrel. However, it is desirable to design the optical system so that the image can be formed correctly.

One of the features of the present invention is the total length ratio between the first lens group and the second lens group.
Distance from the aperture to the side surface of the object in the first lens group (Df),
When the distance (Dr) from the aperture to the side surface of the image plane of the second lens group is 0.346 <Df / Dr <0.509 equation (1)
It is desirable to be satisfied.

When the total length ratio is less than the lower limit of the equation (1), the total length of the second lens group becomes too long as compared with the first lens group, and the linear expansion of the lens barrel due to a temperature change can be compensated by the optical system. become unable. On the contrary, when the upper limit is exceeded, the lens spacing of the second lens group cannot be optimized, or the spacing between the two lenses of the first lens group becomes large, which makes it difficult to design miniaturization.

<First lens group>
As an image pickup lens, when the focal length of the entire image pickup optical system is f and the focal length of the first lens group is f1.
1.070 <| f1 / f | <1.249 Equation (2)
0.995 <| f1 / Df | <1.176 Equation (3)
It is desirable to be satisfied with that.

In the present invention, as shown in the above-mentioned equation (1), the total length ratio of the first lens group is set small. Under this condition, in order to obtain excellent imaging performance, it is desirable to satisfy the equations (2) and (3) with respect to the focal length of the first lens group. The parameters of the equations (2) and (3) are related to the focal length of the first lens group. Within this range, excellent image quality can be realized up to the periphery of the field of view as shown in Examples described later.

<Second lens group>
As an image pickup lens, when the focal length of the entire image pickup optical system is f and the focal length of the second lens group is f2.
0.967 <| f2 / f | <1.108 Equation (4)
0.361 <| f2 / Dr | <0.471 Equation (5)
It is desirable to be satisfied with that.
Similar to the first lens group described above, in order to obtain excellent imaging performance, it is desirable that the focal lengths of the second lens group also satisfy the equations (4) and (5). The parameters of the equations (4) and (5) are related to the focal length of the second lens group. Within this range, excellent image quality can be realized up to the periphery of the field of view as shown in Examples described later.

Hereinafter, each lens will be described individually.

<First lens>
Since the first lens 11 is a lens located closest to the object and captures the light incident first, the quality of the design of this lens affects the overall aberration correction. Therefore, the first lens 11 uses a glass material having a small linear expansion coefficient so as to facilitate the design of the operating environment temperature characteristics, and has a meniscus shape having a convex surface on the object side.

<Second lens>
The second lens 12 has a meniscus shape having a convex surface on the object side similar to the first lens, and is arranged close to the first lens 11. By arranging the second lens 12 close to the first lens 11, it is possible to prevent the aperture of the first lens 11 required to obtain a desired incident angle of view from becoming larger.

As the glass material of the second lens 12, a highly dispersed glass material is selected and both sides are aspherical, thereby contributing to the imaging performance that can secure a high MTF.

<Third lens>
It is desirable that the first third lens 13 of the second lens group (L2) across the diaphragm 4 is selected and used as a glass material having a high refractive index and a high dispersion like the second lens. Further, a higher MTF can be secured by bringing the dispersion characteristics of the adjacent lenses of the first lens group (L1) and the second lens group (L2) closer to each other with the aperture 4 in between.
For example, in each embodiment described later, it is desirable to select a glass material in which the dispersion value of the second lens 12 is 31.18 and the dispersion of the third lens 13 is 37.37, and the dispersion values of both are smaller than 40. An optical system can be obtained.

<4th lens>
It is desirable that the fourth lens 14 is a biconvex lens having the most power, and a glass material having a negative refractive index temperature coefficient (dn / dt) and a large linear expansion coefficient is selectively used. This makes it possible to change the optical characteristics of the lens alone according to the temperature change of the lens barrel 2 so that the entire optical system can be correctly imaged on the surface of the image pickup sensor.

It is desirable that the fourth lens 14 uses a low-dispersion glass material so that chromatic aberration is not adversely affected even when the optical characteristics change according to the temperature change. In the examples described later,
The temperature coefficient (D line) of the fourth lens glass material is 20 to 40 ° C., and the temperature coefficient of refractive index (D line) is −6.6 × 10 ^-6 ° C (dn ^/ dt). As for ⁷ / ° C.)), 141 ones were used. By selecting such a glass material, an optical design capable of temperature compensation can be made, and high imaging performance can be maintained in a wide environmental temperature range of -40 ° C to 120 ° C. In addition, the fourth lens 14 is a biconvex lens that obtains the largest power for this optical system, and contributes to improving the imaging performance of the optical system itself by asphericalizing the object side and the image plane side. is doing.

<5th-6th lens>
The fifth and sixth lenses 15 and 16 improve the occurrence of chromatic aberration by bonding (joining) two lenses, and even if the number of lenses increases, the influence of the deviation that occurs when the lenses are assembled. Is designed to be small, that is, the built-in sensitivity is low.

The aspherical surfaces used in the wide-angle lenses (first lens 11 to sixth lens 16) according to the present embodiment are all represented by the following aspherical surfaces. In the formula, h is the height in the direction perpendicular to the optical axis, Z is the amount of displacement (sag amount) in the optical axis direction at the height h, r is the radius of curvature of the reference sphere (paraxial radius of curvature), and k is the conical coefficient. Further, A, B, C, and D represent 4, 6, 8, and 10th-order aspherical coefficients, respectively. And these numerical values are shown as a table for each numerical example.
In the table showing the aspherical coefficient, "E-04" means " ^{x10 -4} ".

(Numerical example)
As a numerical example, the following optical system quantities are provided, the built-in reference position is arranged between the third and fourth lenses of the second lens group L2, and the first lens and the sixth lens are arranged from the object side and the image plane side. Five examples were created and evaluated on the premise that the lens was pressed down. The lens configuration is schematically shown in FIG. The same members as those described above are designated by the same reference numerals, and the description thereof will be omitted.
At this time, a cover glass (CG) 97 and an IR (infrared) cut filter (IRCF) 96 are installed in front of the image plane (imaging sensor plane) 98. The solid line transmitted through each lens indicates the peripheral luminous flux, and the broken line indicates the central luminous flux. Moreover, each numerical value of the lens 1 was shown below.
Focal length f = 5.325mm
FNo. = 1.6
Horizontal angle of view = 112 degrees

Numerical value As Example 1, an optical system with 6 elements in 5 groups having the following lens data was designed. The surface number in Table 1 is the number of each surface of the lens constituting the optical system, and is the investment number sequentially indicated from the object side, and the curvature R indicates the radius of curvature of each lens surface. Yes, the spacing indicates the spacing between the surfaces on the optical axis. In the table, aspherical lenses are shown as aspherical lenses, and the others are spherical lenses.
Further, nd in the table is a numerical value indicating refraction at the d line (wavelength 589.29 nm), and νd is a numerical value indicating the dispersion characteristic at the d line (wavelength 589.29 nm).
Table 2 shows Numerical Example 1 of the aspherical surface numbers 5, 6, 10, and 11. The aberration characteristic diagram of the first embodiment is shown in FIG. 6, and the MTF characteristic diagram is shown in FIG. 7.

As Numerical Example 2, an optical system having 6 elements in 5 groups having the following lens data was designed. The aberration characteristic diagram of the second embodiment is shown in FIG. 8, and the MTF characteristic diagram is shown in FIG.

As Numerical Example 3, an optical system having 6 elements in 5 groups having the following lens data was designed. The aberration characteristic diagram of the third embodiment is shown in FIG. 10, and the MTF characteristic diagram is shown in FIG.

As Numerical Example 4, an optical system having 6 elements in 5 groups having the following lens data was designed. The aberration characteristic diagram of the fourth embodiment is shown in FIG. 12, and the MTF characteristic diagram is shown in FIG.

As Numerical Example 5, an optical system having 6 elements in 5 groups having the following lens data was designed. The aberration characteristic diagram of Example 5 is shown in FIG. 14, and the MTF characteristic diagram is shown in FIG.

For the above-mentioned numerical examples 1 to 5, the parameter conditional expressions (1) to (6) shown in the text are summarized in Table 11 below.

As shown in Table 11, in a wide-angle lens having an angle of view exceeding 100 degrees, as can be seen from the aberration characteristic diagram and the MTF characteristic diagram shown in FIGS. 6 to 15, the image pickup lens of the present invention has excellent optical performance. It can be seen that it has.

1 Lens 1a Intermediate lens group 1b Both end lenses 2 Lens barrel 2a Thick part 2b Thin part 3 Retainer 4 Aperture 5 Protrusion 6 Spacing ring 8 Concave 9 Reference position 10 Lens unit 100 Camera L1 1st lens group L2 2nd lens group

Claims (6)

An image pickup lens unit in which multiple lenses are built into the lens barrel.
The lens is composed of a first lens group having a negative refractive power and a second lens group having a positive refractive power across an aperture in order from the object side.
The first lens group has a meniscus lens (first lens) having a negative refractive power from the object side and forming a convex surface on the object side, and a meniscus lens (first lens) having a negative refractive power and forming a convex surface on the object side. Consists of a meniscus lens (second lens),
The second lens group includes a biconvex lens (third lens) having a positive refractive power, a biconvex lens (fourth lens) having a positive refractive power, and a biconvex lens (fourth lens) having a positive refractive power from the object side. A fifth lens) and a concave lens (sixth lens) having a negative refractive power are included.
The first to sixth lenses are placed in the lens barrel with a reference position between the third lens and the fourth lens of the second lens group, and the first to third lenses are on the object side of the lens barrel. Therefore, the 4th to 6th lenses are incorporated from the image plane side .
An image pickup lens unit characterized in that the following conditional expression is satisfied when the distance from the diaphragm to the side surface of the object of the first lens group is Df and the focal length of the first lens group is f1 .
0.995 <| f1 / Df | <1.176 When the distance from the diaphragm to the side surface of the object of the first lens group (Df) and the distance from the diaphragm to the side surface of the image plane of the second lens group (Dr), the following conditional expression is satisfied. , The image pickup lens unit according to claim 1.
0.346 <Df / Dr <0.509 The imaging lens unit according to claim 1 or 2 , wherein the following conditional expression is satisfied when the focal length of the entire imaging optical system is f and the focal length of the first lens group is f1 .
1.070 <| f1 / f | <1.249 The imaging lens unit according to any one of claims 1 to 3, wherein the following conditional expression is satisfied when the focal length of the entire imaging optical system is f and the focal length of the second lens group is f2. ..
0.967 <| f2 / f | <1.108 2. The image pickup lens unit described in any one.
0.361 <| f2 / Dr | <0.471 It is a lens in which the fifth lens and the sixth lens of the second lens group are joined, and is the fifth lens.
The distance between the 6th lens and the 4th lens, which have a larger diameter than the lens, is defined by a metal spacing ring.
The image pickup lens unit according to any one of claims 1 to 5.

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