JP2008134494A - Super wide angle optical system and imaging lens device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a super wide angle optical system suitable for monitoring, which has little aberration variation due to temperature change and further little chromatic aberration even in a near infrared region. <P>SOLUTION: The super wide angle optical system is equipped with a first group G1 where a meniscus negative lens turning its convex surface toward an object side and a positive lens are arranged from the object side and which is a diverging system as a whole, and a second group G2 where a positive lens, a negative lens and a positive lens are arranged from the object side and which is an imaging system as a whole. The meniscus negative lens is a glass lens, and a negative aspherical plastic lens L2 is arranged in the first group G1, and a positive aspherical plastic lens L7 is arranged in the second group G2, so that the optical system is equipped with even-numbered plastic lenses. (1) Assuming that the focal length of the entire optical system is f and the focal length of the first group is f1, -3≥f1/f≥-30 is satisfied, and (2) assuming that the focal length of the plastic lens having negative power in the first group is fm, the focal length of the plastic lens having positive power in the second group is fp, and g=¾fp/fm¾, 0.6<g<1.7 is satisfied. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a wide-angle and small-sized super-wide-angle optical system, and an imaging lens device including the super-wide-angle optical system, and more particularly to an ultra-wide-angle with little aberration in the near-infrared region and less focal position shift due to temperature change. The present invention relates to an optical system and an imaging lens system.

  Conventionally, when an ultra-wide-angle optical system is used, a wide range area can be imaged with a single imaging device, and an imaging device using such an ultra-wide-angle optical system is used for surveillance cameras and in-vehicle cameras. ing.

  Such an ultra-wide-angle optical system is employed in, for example, an in-vehicle camera used in a car back monitor device or the like. Such an in-vehicle camera has a wide angle of view and is required to be downsized so as not to obstruct the driver's field of view, to hinder the design of the vehicle body, or to protrude from the vehicle body when attached to the vehicle body. In addition, in the in-vehicle camera, it is desirable that the objects at both ends are imaged larger than those at the center in order to ensure the visibility of the peripheral part of the wide field of view, and the equidistant projection or stereoscopic projection is suitable as the projection method It is.

  As such an ultra-wide-angle optical system, an approximately afocal system of about 2 times having a meniscus negative lens in which the first lens is convex on the object surface is often used as the first group. With this configuration, the principal ray incident angle of each angle of view incident on the subsequent second group is reduced. In addition, the first group is generally divided into a partial system having a negative refractive power and a partial system having a positive refractive power, and a partial system having a negative refractive power is disposed on the object side. Light rays with a large tilt angle exceeding 90 degrees are converted into light beams with a smaller tilt angle.

  In the super wide-angle optical system, the light beam whose tilt angle is weakened in the first group is imaged in a finite image circle by the second group having a positive refractive power and an imaging function.

An example in which such an ultra-wide-angle optical system is used is disclosed in Patent Document 1. This super-wide-angle optical system is a negative optical power that is arranged in order from the object side, an ultra-wide-angle optical system that forms an optical image of a subject on the light-receiving surface of an image sensor that converts an optical image into an electrical signal. A first group including a negative meniscus lens having a convex surface on the object surface side, and a second group having a positive optical power. In this example, the first group includes at least one aspherical surface, the vicinity of the optical axis of the image side surface of the first lens is a concave surface having the optical axis as a central axis, and the entire optical total length T ( mm), half angle of view θ, and focal length ftot (mm) of the entire system, 10 mm <T × sin θ <30 mm and 7 <T / ftot <20 are satisfied.
JP 2006-119368 A

  By the way, in the above-mentioned in-vehicle camera, in addition to the above-mentioned various conditions, in consideration of use outdoors such as a vehicle, it is required that the aberration in a wide temperature range is small. In addition, when taking a picture at night, it is desirable that the chromatic aberration in the visible light region is small and the chromatic aberration is small up to the near infrared region where the CCD sensor or the like has sensitivity.

  However, in the above-described conventional super-wide-angle optical system, sufficient studies have not been made on the removal of the focal position variation with respect to the environmental temperature change and the removal of chromatic aberration in the near infrared region.

  Therefore, in the present invention, an ultra-wide-angle optical system and an imaging lens that have a wide angle of view, a small size, pan focus, equidistant projection, or three-dimensional projection, little aberration variation due to temperature change, and little chromatic aberration even in the near infrared region. An object is to provide an apparatus.

In order to solve the above problems, the present invention employs the following means. That is, the invention described in claim 1 includes a meniscus negative lens and a positive lens having a convex surface facing the object side from the object side, and a first group which is a diverging system as a whole, and a positive lens from the object side, A negative lens and a positive lens, and a second group that is an imaging system as a whole, and the meniscus negative lens of the first group is a glass lens, and at least one negative non-negative lens is included in the first group A super-wide-angle optical system characterized in that at least one positive aspheric plastic lens is arranged in the spherical plastic lens, the second group is provided with an even number of plastic lenses as a whole, and the following conditions are satisfied. is there. (1) When the focal length of the entire optical system is f and the focal length of the first group is f1, −3 ≧ f1 / f ≧ −30 (2) The focal length of the negative power plastic lens in the first group When the focal length of the positive-power plastic lens in the second lens unit is fp and g = | fp / fm |, 0.6 <g <1.7

  In the present invention, the projection system is realized by using the first group as a divergent system and securing a certain incident angle. When the first group exceeds the upper limit of (1) and becomes larger than −3, the first group has a strong refractive power, which is advantageous for the projection system, but the positive curvature of field becomes remarkable. . In addition, astigmatism caused by a large incident angle on the stronger surface of the meniscus lens cannot be corrected. On the other hand, when the first group exceeds the lower limit of (1) and becomes smaller than −30, the effect of reducing the tilt angle of the off-axis light beam of this group is weakened, and a light beam having a large tilt angle enters the subsequent group. As a result, the aberrations increase dramatically and the projection system collapses.

  In addition, since the plastic lens has a large variation in refractive power due to temperature, it is used as an aberration correcting element that has almost no refractive power. However, when the projection system is actively controlled by an aspheric plastic lens as in the present invention, the refractive power of the plastic material inevitably becomes strong.

  Therefore, it is necessary to compensate for the movement of the focal position due to the change in the refractive index. For this reason, it is conceivable to combine lenses made of materials having different refractive index temperature change rates as in the case of removing chromatic aberration. However, plastic as an optical material is not so free to be selected, and such focal position compensation is not possible. Therefore, even if the same material is used, a means for compensating the focal position movement is required.

  The present invention employs a method in which positive and negative lenses are arranged separately in the front group (first group) and the rear group (second group). Since the front group is a divergent system in order to obtain a desired projection method, a strong negative plastic lens is arranged on the object side of the front group. Further, since the rear group forms an image of divergent light from the front group, it requires a strong positive refractive power, and therefore a strong positive plastic lens is disposed on the image side. It should be noted that this condition does not preclude the placement of another plastic lens having an action opposite to those for correcting aberrations.

  The inventors have found the condition (2) as a condition for compensating the focal position due to temperature. Further, by setting the focal lengths of the two positive and negative plastic lenses in (2), it is possible to cancel out the temperature fluctuations of the refractive powers of both the negative plastic lens and the positive plastic lens.

  The invention according to claim 2 is the super wide-angle optical system according to claim 1, wherein the total angle of view (2ω) is 160 degrees or more. In order to be used for a surveillance camera or the like, an optical system having as wide an angle of view as possible is required in order to minimize the number of optical systems such as lenses. When the angle of view of the optical system is less than 160 degrees, a plurality of optical systems are required to capture a wide monitoring area. If the total angle of view is 160 degrees or more as in the super wide-angle optical system according to the present invention, it is possible to meet the demand for use in a surveillance camera or the like.

  The invention described in claim 3 is the super-wide-angle optical system according to claim 1 or 2, wherein the projection method of the super-wide-angle optical system is equidistant projection or stereoscopic projection in which the peripheral image is larger than the central image. It is characterized by that. When monitoring, the central part of the field of view is easy to visually recognize, so it is desirable that the peripheral part that is difficult to visually recognize is imaged large. If a projection method such as equisolid angle projection or orthographic projection is adopted, the surrounding image becomes small, which is not suitable for monitoring. An equidistant projection or three-dimensional projection optical system can enlarge a peripheral image and is suitable for monitoring.

  According to a fourth aspect of the present invention, in the super wide-angle optical system according to any one of the first to third aspects, L ≦ 14f when the total length of the optical system is L and the focal length of the optical system is f. Features. When the total length L exceeds 14f, the total length of the optical system becomes long, and the size reduction required for the in-vehicle camera or the like cannot be achieved.

  According to a fifth aspect of the present invention, in the super wide-angle optical system according to the fourth aspect, the total length is more than 10.0 mm and less than 15.0 mm. If the total length is 10 mm or less, it will be difficult to realize as an optical system, and if the total length is 15 mm or more, the demand for miniaturization cannot be met.

  The invention according to claim 6 is the super wide-angle optical system according to any one of claims 1 to 5, characterized in that a cemented optical system that performs axial achromaticity is arranged in the second group. The achromatic joint surface is arranged in the second group because the second group has a high axial marginal ray, and for the reason described later, the junction surface at a position where the paraxial marginal ray is high greatly affects the axial chromatic aberration. It is for exerting.

  According to a seventh aspect of the present invention, in the super wide-angle optical system according to the sixth aspect, the cemented optical system is arranged at a high position of a paraxial marginal ray. Placing at a high position of the paraxial marginal ray is because the contribution of axial chromatic aberration is proportional to the square of the paraxial marginal ray passing through the surface, so the joint surface at the high position of the paraxial marginal ray is achromatic. It is because it has a big influence on

  According to an eighth aspect of the present invention, in the super wide-angle optical system according to the sixth or seventh aspect, the cemented optical system has a low refractive index and low dispersion glass for a positive lens and a high refractive index and high dispersion for a negative lens. The glass is used. As described above, when a positive lens having a low refractive index and a low dispersion and a negative lens having a high refractive index and a high dispersion are used, chromatic aberration is satisfactorily canceled.

  A ninth aspect of the invention is characterized in that, in the super wide-angle optical system according to the eighth aspect of the invention, the junction surface is a diverging surface and a telephoto type arrangement is adopted. If the joint surface is a diverging surface, chromatic spherical aberration is strongly corrected.

  According to a tenth aspect of the present invention, when the plastic aspherical lens is used in the super wide-angle optical system according to any one of the first to ninth aspects, a temperature change is compensated by a combination of powers and at the same time a chromatic aberration up to the near infrared region. It is characterized by having reduced. When super-wide-angle optical systems are used for monitoring applications, it is assumed that they will be used outdoors, and environmental temperatures are expected to be used from low to high temperatures. Is desired. In addition, when night field use is taken into account for monitoring purposes, it is desired that the electronic imaging device has good optical characteristics in the near-infrared region where the sensitivity is high.

  According to an eleventh aspect of the present invention, the super-wide-angle optical system according to any one of the first to tenth aspects is provided, and the super-wide-angle optical system can form an optical image of a subject on a predetermined imaging surface. The imaging lens device is characterized by that. The imaging lens device is used, for example, in an in-vehicle monitoring device, and a CCD imaging device, a CMOS imaging device, and the like are arranged on an imaging plane, and image information is electrically transmitted from these imaging devices. For this reason, the super-wide-angle optical system forms an image of a monitoring area, which is a subject, on the imaging surface as an optical image.

  According to the present invention, the chromatic aberration with respect to the temperature change is canceled out by the negative power plastic lens and the positive power plastic lens, and as a whole, it is possible to obtain an ultra-wide-angle optical system in which the change in chromatic aberration with respect to the temperature change is small.

  In addition, according to the present invention, in a surveillance camera such as a vehicle-mounted camera, a wide range can be imaged with one optical system, and it is not necessary to arrange a large number of optical systems, thereby reducing costs.

Examples of the super wide-angle optical system according to the present invention will be described below. The super wide-angle optical system according to this example is configured to satisfy the following conditions: Used for a wide-angle lens for a small image sensor (2ω> 160 degrees).
2. Projection method (equal distance projection or stereoscopic projection) in which the peripheral image is larger than the central image
3. A plastic aspherical lens is used, and the power combination compensates for temperature changes (athermal) and at the same time reduces chromatic aberration up to the near infrared region. That is, in consideration of nighttime monitoring, chromatic aberration with respect to the s-line (852.11 nm) and t-line (1013.98 nm) in the near infrared region is considered.
4). The total length is short with respect to the image sensor size (focal length f). The total length is about 14 f.

The super wide-angle optical system according to the embodiment has the following configuration.
I. In order from the object side, a first group G1 having a meniscus negative lens having a convex surface and a positive lens, and a second group G2 including three or more positive, negative, and positive lenses are provided.
II. The first lens L1 on the object side of the first group is a glass lens having a spherical surface, and an even number of plastic lenses disposed in the optical system.
Further, the super wide-angle optical system according to this example has the following characteristics in the configuration.

a. The first group is a divergent system.
In wide-angle lenses, there are many examples in which the first group is a double afocal system having a meniscus negative lens with the first lens convex toward the object surface. (This is to reduce the chief ray incident angle of each angle of view incident on the second group.) The first group is generally divided into a subsystem having a negative refractive power and a subsystem having a positive refractive power. Divided. A sub-system having a negative refractive power is arranged on the object side, and a light beam having a large tilt angle exceeding 90 degrees is converted into a light beam having a smaller tilt angle by its diverging action. Thereafter, the light beam having a reduced inclination angle is imaged in a finite image circle by the second group having a positive refractive power and an imaging function.
However, in this example, a desired projection method is obtained by making the first group a divergent system and changing the incident angle to some extent.
Therefore, when the total focal length of the optical system is f and the focal length of the first group is f1, the following condition (1) is satisfied.
−3 ≧ f1 / f ≧ −30 Condition (1)
In this example, when the total focal length of the optical system is f and the total length is L, the following condition (1) ′ is satisfied: −0.5 ≧ f1 / L ≧
-2.0 Condition (1) '

  If the upper limit specified in the condition (1) is exceeded and the first lens unit has a stronger refractive power, it is advantageous to cope with the projection method, but the field curvature becomes remarkable. In addition, astigmatism caused by a large incident angle on the stronger surface of the meniscus cannot be corrected. On the other hand, when the first group exceeds the lower limit of (1) and becomes smaller than −30, the effect of reducing the tilt angle of the off-axis light beam of this group is weakened, and a light beam having a large tilt angle enters the subsequent group. As a result, the aberrations increase dramatically and the projection system collapses.

  If the upper limit defined by the condition (1) ′ is exceeded, the first lens unit has a stronger refractive power, which is advantageous for the projection system, but the positive curvature of field becomes remarkable. . In addition, astigmatism caused by a large incident angle on the stronger surface of the meniscus cannot be corrected. When the lower limit is exceeded, the effect of reducing the tilt angle of the off-axis light beam of this group is weakened, and a light beam having a large tilt angle is incident on the subsequent group, leading to a drastic increase in aberrations and collapse of the projection method.

b. Use an even number of plastic lenses to compensate for temperature-dependent chromatic aberration.
Plastic has a larger refractive index change due to temperature than glass, but compensates for temperature change by reducing the sum of the power of plastic. In this case, two (even) lenses are arranged in pairs as positive and negative to cancel the change in refractive index. (Conditions for plastic lenses)

  Conventionally, plastic lenses have been used as an aberration correction element that has almost no refractive power because the refractive power variation with temperature is large. However, when the projection system is actively controlled by an aspheric plastic lens as in the present invention, the refractive power of the plastic lens inevitably becomes strong.

  Therefore, it is necessary to compensate for the movement of the focal position due to the change in refractive index. As a means for this, for example, it is conceivable to combine lenses made of materials having different refractive index temperature change rates as in the case of removing chromatic aberration.

  However, plastic as an optical material is not so selective, and such focal position compensation is impossible. Therefore, even if the same material is used, a means for compensating the focal position movement is required.

  As a means for this, a method of arranging the positive and negative lenses separately in the front group and the rear group can be considered. Since the front group needs to be a divergent system in order to obtain a desired projection method, a strong negative plastic lens is disposed on the object side of the front group. Further, since the rear group forms an image of divergent light from the front group, a strong positive refractive power is required, and it is desirable to dispose a strong positive plastic lens on the image side. This condition does not preclude the placement of a plastic lens having the opposite action to correct aberrations.

Then, the following condition (2) is adopted as a condition for compensating the focal position due to temperature.
When the focal length of the positive plastic lens in the image forming group is fp, the focal length of the negative plastic lens in the diverging group is fm, and g = | fp / fm |
0.6 <g <1.7
Here, g = | fp / fm |, that is, the absolute value of the ratio of the focal length of the positive plastic lens to that of the negative plastic lens. Condition (2)
Under these conditions, temperature fluctuations in refractive power of both the negative plastic lens and the positive plastic lens can be canceled each other.
c. The second group G2 includes three positive, negative, and positive lenses from the object side.
By configuring the second group in this way, the overall length can be shortened with respect to the focal length. By adopting this configuration, the second group can be made shorter than the configuration including three negative, positive, and positive lenses from the object side. Thereby, the following condition (3) is satisfied.
10.0 mm <total length <15.0 mm Condition (3)
d. In the second group, a cemented lens for performing on-axis achromatism is arranged. The direction of the achromatic cemented surface of the cemented lens may be convex or concave toward the stop side. In addition, this cemented lens is arranged at a position close to the stop, that is, at a high position of the paraxial marginal ray in order to correct spherical aberration. Further, it is desirable to use a low refractive index and low dispersion glass for the positive lens and a high refractive index and high dispersion glass for the negative lens. As a result, the cemented surface becomes a divergent surface and strongly corrects chromatic spherical aberration.

  In particular, when the direction of the cemented surface is concave toward the stop, the cemented lens has a positive and negative so-called telephoto type arrangement. In this arrangement, the image side principal point is significantly biased toward the object side, and as a result, the effect of shortening the overall length is exhibited.

  If the direction of the cemented surface is convex toward the stop, the cemented lens has a negative and positive so-called retrofocus type arrangement. In this arrangement, the principal point on the image side is remarkably biased toward the image side, and as a result, the total length becomes long.

e. In the first group, one or more negative plastic lenses are arranged. By making this plastic lens an aspherical surface, the projection system can be controlled better.

f. In the second group, one or more positive plastic lenses are arranged. By making this plastic lens an aspherical surface, it is possible to achieve compactness while correcting aberrations.

g. It shall not be equipped with a focus adjustment moving mechanism such as focusing. Cost reduction and failure reduction can be achieved.

Examples 1 to 4 described below will be described. First, Table 1 summarizes the configuration of each example.

In addition, Table 2 shows the refractive index (−15 ° C., 25 ° C.) of the d-line of the two types of plastic lenses used in the examples (Plastic 1 and Plastic 2 in the table) and general optical glass BK7. Table 3 shows the Abbe number at 25 ° C. Furthermore, FIG. 1 shows the refractive index variation due to the temperature change of each material.

The aberration diagrams shown below are at + 25 ° C. In the astigmatism diagram, ΔS represents sagittal and ΔM represents a meridional image plane. Focal length shift with temperature was calculated for paraxial rays. Distortion is for equidistant projection. In each of the embodiments, aberration correction is satisfactorily performed, and the focal point movement is within an allowable value with respect to a temperature change. The aspheric coefficient is obtained by the following equation.

Here, x is a sag amount in the optical axis direction of the surface. R is a radius of curvature. Further, H = y 2 + z 2, which indicates that the surface shape is a rotationally symmetric shape. K is a conic constant, and − (eccentricity) ^ 2. A, B, and C are fourth-order, sixth-order, and eighth-order aspherical coefficients, respectively, and represent the distance from the conical curve of the surface shape.

Example 1 FIG. 2 is a cross-sectional view showing a lens arrangement of the super wide-angle optical system of Example 1. FIG. This super-wide-angle optical system includes a first lens L1 to a seventh lens L7 in order from the object side (left side in FIG. 1). The first lens L1 to the fourth lens form the first group G1, the fifth lens L5 to the seventh lens L7 form the second group G2, and a diaphragm surface between the first group G1 and the second group G2. Is formed.

The first group G1 forms a divergent system as a whole. In the first group G1, the first lens L1 is a glass meniscus lens (negative), the second lens L2 is an aspheric plastic lens (negative), the third lens L3 is a glass lens (negative), and a fourth lens. Is a glass lens (positive).

The second group G2 forms an imaging system as a whole. In the second group G2, the fifth lens L5 is a glass lens (positive), and the sixth lens is a glass lens (negative). The fifth lens L5 and the sixth lens L6 are joined for achromatic color. A lens is formed. This cemented lens is disposed at a position close to the stop, that is, at a high position of the paraxial marginal ray in order to correct spherical aberration. Then, a low refractive index and low dispersion glass is used for the positive lens, and a high refractive index and high dispersion glass is used for the negative lens.

Furthermore, a plastic aspherical lens is disposed as the seventh lens in the second group G2. In this example, the temperature variation of the refractive power of the second lens L2 (negative plastic lens) and the temperature variation of the refractive power of the seventh lens L7 (positive plastic lens) cancel each other, so that the refractive power as a whole is reduced. Temperature fluctuation is reduced.

This super-wide-angle optical system forms an image on an image plane (not shown) as a whole with the first group G1 and the second group G2. Table 4 shows the lens configuration of the super wide-angle optical system. “Plasta” in the configuration means the plastic 1 in Tables 2 and 3.

The second lens and the seventh lens are aspherical lenses, the second surface of the second lens L2, the first surface and the second surface of the seventh lens L7 are aspherical surfaces, and their aspherical coefficients. Is shown in Table 5.

With this configuration, in this example, an ultra-wide-angle optical system with equidistant projection could be obtained. As shown in Table 1, this super wide-angle optical system has an overall focal length of 1.00 mm, F / no. The angle of view is 3.00, the angle of view is 180.00 °, and the total length is 14.00 mm, which satisfies the above-described conditions (1), (1) ′, (2), and (3).

FIG. 3 shows the spherical aberration SA and sine condition SC of the obtained super-wide-angle optical system, FIG. 4 shows the chromatic aberration, FIG. 5 shows the focal distance due to temperature change, and FIG. 6 shows the astigmatism. The aberration is shown in FIG.

According to each figure, the super-wide-angle optical system according to the present embodiment has less spherical aberration, coma, astigmatism, chromatic aberration, distortion, etc., and has optical performance suitable for use in a surveillance camera. I understand. In particular, the super-wide-angle optical system of this example has little chromatic aberration in the s-line and t-line in the near-infrared region other than the visible region as shown in FIG. 4, and the focal length due to the temperature characteristic as shown in FIG. The position fluctuation could be reduced.

Example 2 FIG. 8 is a cross-sectional view illustrating a lens arrangement of an ultra-wide-angle optical system according to Example 2. This super wide-angle optical system includes a first lens L1 to a seventh lens L7 in order from the object side. The first lens L1 to the fourth lens form the first group G1, the fifth lens L5 to the seventh lens L7 form the second group G2, and a diaphragm surface between the first group G1 and the second group G2. Is formed.

The first group G1 forms a divergent system as a whole. In the first group G1, the first lens L1 is a glass meniscus lens (negative), the second lens L2 is an aspheric plastic lens (negative), the third lens L3 is a glass lens (negative), and a fourth lens. Is a glass lens (positive).

The second group G2 forms an imaging system as a whole. In the second group G2, the fifth lens L5 is a glass lens (positive), and the sixth lens is a glass lens (negative). The fifth lens L5 and the sixth lens L6 are joined for achromatic color. A lens is formed. This cemented lens is disposed at a position close to the stop, that is, at a high position of the paraxial marginal ray in order to correct spherical aberration. Then, a low refractive index and low dispersion glass is used for the positive lens, and a high refractive index and high dispersion glass is used for the negative lens.

Furthermore, a plastic aspherical lens is disposed as the seventh lens in the second group G2. In this example, the temperature variation of the refractive power of the second lens L2 (negative plastic lens) and the temperature variation of the refractive power of the seventh lens L7 (positive plastic lens) cancel each other, so that the refractive power as a whole is reduced. Temperature fluctuation is reduced.

This super-wide-angle optical system forms an image on an image plane (not shown) as a whole with the first group G1 and the second group G2. Table 6 shows the lens configuration of the super wide-angle optical system. “Plasta” in the configuration means the plastic 1 in Tables 2 and 3.

The second lens and the seventh lens are aspherical lenses, the second surface of the second lens L2, the first surface and the second surface of the seventh lens L7 are aspherical surfaces, and their aspherical coefficients. Is shown in Table 7.

With this configuration, in this example, an ultra-wide-angle optical system with equidistant projection could be obtained. As shown in Table 1, this super wide-angle optical system has an overall focal length of 1.00 mm, F / no. The angle of view was 3.00, the field angle was 180.00 °, and the total length was 13.36 mm, which satisfied the above-described conditions (1), (1) ′, (2), and (3).

FIG. 9 shows the spherical aberration SA and sine condition SC of the obtained super-wide-angle optical system, FIG. 10 shows the chromatic aberration, FIG. 11 shows the focal distance due to temperature change, and FIG. 12 shows the astigmatism. The aberration is shown in FIG.

According to each figure, the super-wide-angle optical system according to the present embodiment has less spherical aberration, coma, astigmatism, chromatic aberration, distortion, etc., and has optical performance suitable for use in a surveillance camera. I understand. In particular, the super-wide-angle optical system of this example has little chromatic aberration in the s-line and t-line in the near-infrared region in addition to the visible region as shown in FIG. 10, and the focal length due to the temperature characteristics as shown in FIG. The position fluctuation could be reduced.

Example 3 FIG. 14 is a cross-sectional view illustrating a lens arrangement of an ultra-wide-angle optical system according to Example 3. This super wide-angle optical system includes a first lens L1 to a seventh lens L7 in order from the object side. The first lens L1 to the fourth lens form the first group G1, the fifth lens L5 to the seventh lens L7 form the second group G2, and a diaphragm surface between the first group G1 and the second group G2. Is formed.

The first group G1 forms a divergent system as a whole. In the first group G1, the first lens L1 is a glass meniscus lens (negative), the second lens L2 is an aspheric plastic lens (negative), the third lens L3 is a glass lens (negative), and a fourth lens. Is a glass lens (positive).

The second group G2 forms an imaging system as a whole. In the second group G2, the fifth lens L5 is a glass lens (positive), and the sixth lens is a glass lens (negative). The fifth lens L5 and the sixth lens L6 are joined for achromatic color. A lens is formed. This cemented lens is disposed at a position close to the stop, that is, at a high position of the paraxial marginal ray in order to correct spherical aberration. Then, a low refractive index and low dispersion glass is used for the positive lens, and a high refractive index and high dispersion glass is used for the negative lens.

Furthermore, a plastic aspherical lens is disposed as the seventh lens in the second group G2. In this example, the temperature variation of the refractive power of the second lens L2 (negative plastic lens) and the temperature variation of the refractive power of the seventh lens L7 (positive plastic lens) cancel each other, so that the refractive power as a whole is reduced. Temperature fluctuation is reduced.

This super-wide-angle optical system forms an image on an image plane (not shown) as a whole with the first group G1 and the second group G2. Table 8 shows the lens configuration of the super wide-angle optical system.

The second lens and the seventh lens are aspherical lenses, the second surface of the second lens L2, the first surface and the second surface of the seventh lens L7 are aspherical surfaces, and their aspherical coefficients. Is shown in Table 9.

With this configuration, in this example, an ultra-wide-angle optical system with equidistant projection could be obtained. As shown in Table 1, this super wide-angle optical system has an overall focal length of 1.00 mm, F / no. The angle of view is 3.00, the angle of view is 180.00 °, and the total length is 14.00 mm, which satisfies the above-described conditions (1), (1) ′, (2), and (3).

FIG. 15 shows the spherical aberration SA and sine condition SC of the obtained ultra-wide-angle optical system, FIG. 16 shows the chromatic aberration, FIG. 17 shows the focal distance due to temperature change, and FIG. 18 shows the astigmatism. The aberration is shown in FIG.

According to each figure, the super-wide-angle optical system according to the present embodiment has less spherical aberration, coma, astigmatism, chromatic aberration, distortion, etc., and has optical performance suitable for use in a surveillance camera. I understand. In particular, the super-wide-angle optical system of this example has little chromatic aberration in the s-line and t-line in the near-infrared region in addition to the visible region as shown in FIG. 16, and the focal length due to the temperature characteristics as shown in FIG. The position fluctuation could be reduced.

Example 4 FIG. 20 is a cross-sectional view showing a lens arrangement of an ultra wide-angle optical system of Example 4. This super wide-angle optical system includes a first lens L1 to a sixth lens L6 in order from the object side. The first lens L1 to the third lens constitute the first group G1, the fourth lens L4 to the sixth lens L6 constitute the second group G2, and the diaphragm surface between the first group G1 and the second group G2. Is formed.

The first group G1 forms a divergent system as a whole. In the first group G1, the first lens L1 is a glass meniscus lens (negative), the second lens L2 is an aspheric plastic lens (negative), and the third lens L3 is an aspheric plastic lens (positive). is there.

The second group G2 forms an imaging system as a whole. In the second group G2, the fourth lens L4 is a glass lens (positive), the fifth lens is an aspheric plastic lens (negative), and the sixth lens is an aspheric plastic lens (positive). Further, in this example, a cover glass is disposed on the image side of the second group G2. The super wide-angle optical system forms an image on an image forming surface (not shown) as a whole with the first group G1 and the second group G2. Table 10 shows the lens configuration of the super wide-angle optical system.

  The second lens L2, the third lens L3, the fifth lens L5, and the sixth lens L6 are aspherical lenses. Table 11 shows these aspherical coefficients.

With this configuration, in this example, an ultra-wide-angle optical system with equidistant projection could be obtained. As shown in Table 1, this super wide-angle optical system has an overall focal length of 0.96 mm, F / no. It is 2.40, the angle of view is 200.00 °, and the total length is 14.00 mm, which satisfies the above-described conditions (1), (1) ′, (2), and (3).

FIG. 21 shows the spherical aberration SA and sine condition SC of the obtained super-wide-angle optical system, FIG. 22 shows the chromatic aberration, FIG. 23 shows the focal distance due to temperature change, and FIG. 24 shows the astigmatism. The aberration is shown in FIG.

According to each figure, the super-wide-angle optical system according to the present embodiment has less spherical aberration, coma, astigmatism, chromatic aberration, distortion, etc., and has optical performance suitable for use in a surveillance camera. I understand. In particular, the super-wide-angle optical system of this example has little chromatic aberration in the s-line and t-line in the near-infrared region other than the visible region as shown in FIG. The position fluctuation could be reduced.

  The super wide-angle optical system according to the above example is preferably used by being mounted on an in-vehicle camera. However, the present invention is not limited to this, and a portable information terminal device such as a camera-equipped mobile phone, a digital camera, a video camera, a house / building, etc. It can also be applied to surveillance cameras for moving bodies such as buildings, airplanes other than automobiles, and ships.

It is a graph which shows the temperature change of the refractive index of the plastic lens used for the Example. 1 is a diagram illustrating a schematic lens configuration of an ultra-wide angle optical system according to Example 1. FIG. 6 is a graph showing spherical aberration and sine conditions of the super wide-angle optical system according to Example 1. 3 is a graph showing chromatic aberration of the super wide-angle optical system according to Example 1. 6 is a graph showing movement of a focal position due to a temperature change of the super wide-angle optical system according to Example 1. 3 is a graph showing astigmatism of the super wide-angle optical system according to Example 1. 6 is a graph showing distortion aberration with respect to equidistant projection of the super wide-angle optical system according to Example 1. FIG. 6 is a diagram illustrating a schematic lens configuration of an ultra-wide-angle optical system according to Example 2. 6 is a graph showing spherical aberration and sine conditions of the super wide-angle optical system according to Example 2. 6 is a graph showing chromatic aberration of the super wide-angle optical system according to Example 2. 10 is a graph showing movement of a focal position due to a temperature change of the super wide-angle optical system according to Example 2. 6 is a graph showing astigmatism of the super wide-angle optical system according to Example 2. 6 is a graph showing distortion aberration with respect to equidistant projection of the super wide-angle optical system according to Example 2. 6 is a diagram illustrating a schematic lens configuration of an ultra-wide-angle optical system according to Example 3. FIG. 10 is a graph showing spherical aberration and sine conditions of the super wide-angle optical system according to Example 3. 10 is a graph showing chromatic aberration of the super wide-angle optical system according to Example 3. 10 is a graph showing movement of a focal position due to a temperature change of the super wide-angle optical system according to Example 3. 6 is a graph showing astigmatism of the super wide-angle optical system according to Example 3. 10 is a graph showing distortion aberration with respect to equidistant projection of the super wide-angle optical system according to Example 3. FIG. 10 is a diagram illustrating a schematic lens configuration of an ultra-wide-angle optical system according to Example 4. 10 is a graph showing spherical aberration and sine conditions of the super wide-angle optical system according to Example 4. 10 is a graph showing chromatic aberration of the super wide-angle optical system according to Example 4. 10 is a graph showing movement of a focal position due to a temperature change of the super wide-angle optical system according to Example 4. 10 is a graph showing astigmatism of the super wide-angle optical system according to Example 4. 10 is a graph showing distortion aberration with respect to equidistant projection of the super wide-angle optical system according to Example 4.

Explanation of symbols

G1 1st group G2 2nd group L1 1st lens L2 2nd lens L3 3rd lens L4 4th lens L5 5th lens L6 6th lens L7 7th lens

Claims (11)

A meniscus negative lens and a positive lens with a convex surface facing the object side are arranged from the object side, and the first group which is a diverging system as a whole, and a positive lens, a negative lens and a positive lens are arranged from the object side as a whole A first group meniscus negative lens as a glass lens, at least one negative aspheric plastic lens in the first group, and at least 1 in the second group. An ultra-wide-angle optical system in which a single positive aspherical plastic lens is arranged and an even number of plastic lenses are provided as a whole, and the following conditions are satisfied. (1) When the focal length of the entire optical system is f and the focal length of the first group is f1, −3 ≧ f1 / f ≧ −30 (2) The focal length of the negative power plastic lens in the first group When the focal length of the positive-power plastic lens in the second lens unit is fp and g = | fp / fm |, 0.6 <g <1.7 The super wide-angle optical system according to claim 1, wherein the total angle of view (2ω) exceeds 160 degrees. The super-wide-angle optical system according to claim 1 or 2, wherein the projection method of the super-wide-angle optical system is equidistant projection or stereoscopic projection in which a peripheral image is larger than a central image. The super-wide-angle optical system according to any one of claims 1 to 3, wherein L≤14f, where L is the total length of the optical system and f is the focal length of the optical system. 5. The super wide-angle optical system according to claim 4, wherein the total length is more than 10.0 mm and less than 15.0 mm. The super-wide-angle optical system according to any one of claims 1 to 5, wherein a cemented optical system that performs axial achromatism is disposed in the second group. The super-wide-angle optical system according to claim 6, wherein the bonding optical system is disposed at a high position of a paraxial marginal ray. 8. The super-wide-angle optical system according to claim 6, wherein the cemented optical system uses a glass having a low refractive index and a low dispersion for a positive lens and a glass having a high refractive index and a high dispersion for a negative lens. 9. The super-wide-angle optical system according to claim 8, wherein the joining surface is a diverging surface and is arranged in a telephoto type. 10. The super-wide-angle optical system according to claim 1, wherein when a plastic aspherical lens is used, a change in temperature is compensated by a combination of power, and at the same time, chromatic aberration to the near infrared region is reduced. An imaging lens apparatus comprising the super wide-angle optical system according to claim 1, wherein the super-wide angle optical system is capable of forming an optical image of a subject on a predetermined imaging surface. .