JP6840216B2 - Optical system and imaging device - Google Patents

Description

The present invention relates to an optical system and an image pickup device, and more particularly to an optical system suitable for an image pickup device using a solid-state image pickup element such as a digital still camera or a digital video camera, and an image pickup device provided with the optical system.

In recent years, an image pickup device using a solid-state image sensor such as a CCD or CMOS has become widespread. For example, in addition to an image pickup device that can be carried by a user such as a single-lens reflex camera, a mirrorless single-lens camera, and a digital still camera, a surveillance image pickup device, an in-vehicle image pickup device, and the like (hereinafter, simply referred to as "surveillance image pickup device and the like". ), A fixed-installation type image pickup device that is installed and fixed to a building or a vehicle body and used for a specific purpose is also becoming widespread. The performance and miniaturization of all image pickup devices have been remarkably advanced, and the optical systems used in these image pickup devices are also required to have higher performance and miniaturization.

In recent years, the number of pixels of sensors has increased, high resolution is required, and there is a demand for an imaging lens that is compact and lightweight, has a wide imaging range, and can handle low illuminance. In addition, surveillance imagers, security imagers, in-vehicle imagers, etc. installed indoors and outdoors are required to have reliability that can withstand long-term use, and at the same time, they are equipped with actuators that adjust focus from the viewpoint of cost reduction. It is common to use a non-fixed focus imaging lens. In the case of such an image pickup lens, it is necessary not only to secure the performance at room temperature, but also to maintain little fluctuation in the focal position even if the operating environment temperature changes, and to maintain good performance in both a high temperature environment and a low temperature environment. .. As an optical system satisfying such a requirement, for example, the optical systems shown in Patent Documents 1 to 3 exist. All of these optical systems are known as imaging lenses having a relatively wide angle of view configured by arranging a negative lens on the object side, and aiming at high performance and miniaturization.

Patent Document 1 discloses a wide-angle optical system composed of five lenses, a negative lens, a negative lens, a positive lens, a negative lens, and a positive lens, in this order from the object side. The optical system described in Patent Document 1 has good optical performance and a wide angle of view, and further adopts an optical system using a plastic lens to reduce the weight, compactness, and cost of the optical system. ing.

Patent Document 2 discloses an optical system composed of a negative lens, a positive lens, a positive lens, a negative lens, and a positive lens in order from the object side. The optical system described in Patent Document 2 is composed entirely of a spherical glass lens to achieve a bright optical system having a relatively large aperture ratio of Fno2.0 to Fno4.0, and at the same time, is environmentally resistant to fluctuations in the operating environment temperature. Is increasing.

Patent Document 3 discloses an optical system composed of five lenses, a negative lens, a positive lens, a negative lens, a positive lens, and a positive lens, in order from the object side. The optical system described in Patent Document 3 sets the relative refractive index change (dN / dT) of the glass material of the lens arranged before and after the diaphragm within a predetermined range, so that the optical system is focused even if the operating environment temperature changes. The position does not fluctuate much, and it has good environmental resistance in either a high temperature environment or a low temperature environment.

Japanese Unexamined Patent Publication No. 2003-307674 JP-A-2010-107532 Japanese Unexamined Patent Publication No. 2016-114648

However, in the optical system disclosed in Patent Document 1, when it is assumed that the optical system is used in a wide temperature environment such as a monitoring imager installed indoors or outdoors, the optical system is configured according to a change in the operating environment temperature. If the plastic lens is altered or deformed, the refractive index may change, resulting in a decrease in resolution, and there is a problem that good optical performance cannot be obtained.

Further, all the optical systems disclosed in Patent Document 2 employ spherical glass lenses to achieve a bright optical system having a relatively large aperture ratio and enhance environmental resistance. However, it is necessary to make the existence of the image pickup device inconspicuous from the viewpoint of a person on the subject side to be observed, and the optical system is also required to be miniaturized. In particular, it is required to reduce the outer diameter of the lens arranged on the subject side (object side) most, but the optical system disclosed in Patent Document 2 cannot be sufficiently miniaturized. Further, in order to improve visibility in a dark environment, it is necessary to use a lens having a large aperture ratio (Fno is bright), but the optical system disclosed in Patent Document 2 cannot secure sufficient brightness. Further, the half angle of view of the optical system is about 22 degrees, and the angle is not sufficiently widened. Therefore, when the optical system is applied to a monitoring imaging device or the like, there is a problem that the range that can be imaged by one monitoring imaging device is narrow.

Further, the optical system disclosed in Patent Document 3 has little fluctuation in the focal position even when the operating environment temperature changes, and has good environmental resistance in either a high temperature environment or a low temperature environment. When composed of "negative lens, positive lens, negative lens, positive lens, positive lens" in order from the object side, the incident light beam from the object side is alternately combined with divergence and convergence, so that chromatic aberration is reduced. From the viewpoint, good characteristics can be obtained. However, when the lenses are arranged in series to manufacture the optical system disclosed in Patent Document 3, the eccentric sensitivity becomes high, so that it becomes difficult to adjust the arrangement of the lenses, and the variable magnification optical system is manufactured. This is not preferable because it becomes difficult to secure stable optical performance. Further, a bright optical system having a large aperture ratio is required in order to improve visibility in a dark environment, but the Fno of the optical system is about 2.0, and sufficient brightness cannot be secured. Further, the half angle of view of the optical system is about 30 degrees, and the angle is not sufficiently widened. Therefore, as in Patent Document 2, there is a problem that the range that can be imaged is narrow in the optical system.

As can be understood from the above, the subject of the present invention is to realize a small diameter of the lens arranged on the most object side, and at the same time to widen the angle of view of 45 degrees or more, and Fno is 1.6. The purpose is to provide a bright optical system.

As a result of diligent research to solve the above problems, we came up with the idea that the above problems can be solved by adopting the optical system having the configuration described below.

<Optical system according to the present invention>
The optical system according to the present invention has a first lens having a negative refractive power and having a concave image side surface in order from the object side, and a meniscus shape having a positive or negative refractive power and convex toward the image side. It has a second lens, a third lens having a positive refractive power and a biconvex shape, a fourth lens having a negative refractive power, and a fifth lens having a positive or negative refractive power. It is also characterized by satisfying the above conditions.

R11 / f <6.0 ... (1)
However, R11: the radius of curvature of the near axis of the side surface of the object of the first lens.
f: The focal length of the entire optical system.

<Imaging device according to the present invention>
The image pickup apparatus according to the present invention is characterized by including the above-mentioned optical system and an image pickup element that receives an optical image formed by the optical system and converts it into an electrical image signal.

According to the present invention, it is possible to realize a small diameter of the lens arranged on the most object side, and at the same time realize a wide angle of a half angle of view of 45 degrees or more, and provide a bright optical system having an Fno of about 1.6. Can be done.

It is sectional drawing which shows the lens structure example of the optical system of Example 1 of this invention. It is a spherical aberration diagram, astigmatism diagram, and distortion diagram of the optical system of the first embodiment at infinity focusing. It is sectional drawing which shows the lens structure example of the optical system of Example 2 of this invention. It is a spherical aberration diagram, astigmatism diagram, and distortion diagram of the optical system of the second embodiment at infinity focusing. It is sectional drawing which shows the lens structure example of the optical system of Example 3 of this invention. 3 is a spherical aberration diagram, an astigmatism diagram, and a distortion aberration diagram when the optical system of the third embodiment is in focus at infinity. It is sectional drawing which shows the lens structure example of the optical system of Example 4 of this invention. It is a spherical aberration diagram, astigmatism diagram, and distortion diagram of the optical system of the fourth embodiment at infinity focusing. It is sectional drawing which shows the lens structure example of the optical system of Example 5 of this invention. 5 is a spherical aberration diagram, an astigmatism diagram, and a distortion diagram of the optical system of the fifth embodiment at infinity focusing. It is sectional drawing which shows the lens structure example of the optical system of Example 6 of this invention. 6 is a spherical aberration diagram, an astigmatism diagram, and a distortion aberration diagram when the optical system of the sixth embodiment is in focus at infinity. It is sectional drawing which shows the lens structure example of the optical system of Example 7 of this invention. FIG. 5 is a spherical aberration diagram, an astigmatism diagram, and a distortion diagram of the optical system of the seventh embodiment at infinity focusing.

Hereinafter, embodiments of the optical system and the image pickup apparatus according to the present invention will be described.

1. 1. Optical system 1-1. Configuration of Optical System The optical system according to the present invention includes "a first lens having a negative refractive power and a concave image side surface", "a second lens having a meniscus shape convex on the image side", and "positive". It is basically composed of a "third lens having a refractive power", a "fourth lens having a negative refractive power", and a "fifth lens having a positive or negative refractive power". Hereinafter, two specific configurations included in this concept are as follows. First, the configuration of the optical system according to the present invention will be described, and the contents related to the conditional expression required therethrough will be described later.

The optical system according to the present invention has, in order from the object side, "a first lens having a negative refractive power and a concave image side surface" and "a first lens having a negative refractive power and convex toward the image side". It is composed of a "second lens", a "third lens having a positive refractive power", a "fourth lens having a negative refractive power", and a "fifth lens having a positive or negative refractive power". (Hereinafter, referred to as "first configuration").

Further, as the optical system according to the present invention, in order from the object side, "a first lens having a negative refractive power and a concave image side surface" and "a first lens having a positive or negative refractive power and convex toward the image side". A second lens with a positive refractive power, a third lens with a biconvex shape, a fourth lens with a negative refractive power, and a positive or negative refractive power. It is also possible to adopt a lens having a "fifth lens having a lens" and satisfying the following conditional expression (1) (hereinafter, referred to as a "second configuration").

The optical system according to the present invention described above is intended to maintain the lens diameter of the first lens closest to the object side to a small diameter and at the same time to increase the angle. In such a case, the negative refractive power of the first lens G1 has to be increased, but it becomes difficult to reduce the diameter of the first lens in order to increase the negative refractive power. Therefore, by adopting a meniscus shape with a convex image side surface for the second lens G2, it is expected that a part of the negative refractive power originally required for the first lens G1 will be shared with the second lens G2. This makes it possible to widen the angle as it is. As a result, the diameter of the lens placed closest to the object can be reduced, the effect of making the presence of the image pickup device inconspicuous in the surveillance image pickup device, etc. can be exhibited, and the half angle of view can be widened to 45 degrees or more. Moreover, it is possible to obtain a bright image having an Fno of about 1.6. Then, in order to improve visibility in a dark environment, it is preferable that Fno is brighter than 2.0. When this lens configuration is adopted, the image side surface of the first lens is concave, and the second lens has a meniscus shape convex toward the image side, so that it is inevitable between the first lens and the second lens. Therefore, a biconvex air lens is formed. Each lens and the conditional expression will be described below.

(1) First Lens As described above, the first lens is not particularly limited as long as it has a negative refractive power and the image side surface is concave. Here, since the image side surface of the first lens is concave, the air lens inevitably formed between the image side of the first lens and the second lens having a convex meniscus shape on the image side is the first lens and the second lens. By providing a biconvex air lens between them, spherical aberration and image plane aberration can be corrected more satisfactorily. Therefore, from the viewpoint that the optical performance of the optical system can be improved, it is preferable that the image side surface of the first lens is concave.

(2) Second Lens The second lens in the above-mentioned first configuration has a negative refractive power and has a meniscus shape convex on the image side, and as long as the meniscus shape is provided, other specific lenses are provided. The lens configuration is not particularly limited. When the second lens has this shape, a biconvex air lens is inevitably formed between the first lens and the second lens. At this time, if the conditional expression (1) is satisfied, it becomes easier to widen the angle and further reduce the diameter of the first lens.

Then, as the second lens in the above-mentioned second configuration, on the premise that the conditional expression (1) described later is satisfied, a lens having a positive or negative refractive power and having a convex meniscus shape on the image side shall be used. Can be done. In this second configuration, when the second lens has a negative refractive power, the same effect as that of the first configuration can be obtained. When the second lens has a positive refractive power, it becomes difficult to share the negative refractive power of the first lens with the second lens. However, a lens having a negative refractive power as strong as possible is used as the first lens in the range where the diameter can be reduced, and the shape of the third lens having a positive refractive power is a biconvex shape. By satisfying (1), the effect of the present invention can be obtained even when the refractive power of the second lens is positive.

In order to ensure better optical performance of the second lens described above, it is preferable that at least one of the object side surface and the image side surface of the second lens is an aspherical surface. This is because the coma aberration and curvature of field can be satisfactorily corrected by providing the second lens with an aspherical surface.

(3) Third Lens As long as the third lens has a positive refractive power, other specific lens configurations are not particularly limited. As the third lens, it is preferable to use a biconvex lens having both convex surfaces. The third lens having both convex surfaces can disperse the positive refractive power between the side surface of the object and the side surface of the image, which makes it easy to satisfy the conditional expression (1) described later, and at the same time, suppresses deterioration of coma due to eccentricity. , It becomes easy to secure good optical performance.

Further, it is preferable that at least one of the object side surface and the image side surface of the third lens is an aspherical surface. This is because by making at least one surface of the third lens an aspherical surface, spherical aberration can be satisfactorily corrected and better optical performance can be obtained.

(4) Fourth Lens and Fifth Lens As described above, the fourth lens is not particularly limited in other specific lens configurations as long as it has a negative refractive power. However, the fourth lens preferably has a meniscus shape that is convex toward the object side. This is because the curvature of field can be satisfactorily corrected and good optical performance can be ensured.

As long as the fifth lens has a positive or negative refractive power, other specific lens configurations are not particularly limited. Whether to select positive or negative refractive power as the refractive power of the fifth lens satisfies the conditional expression described later in consideration of the aberration of the light beam receiving the refractive power from the first lens to the fourth lens. Can be selected arbitrarily. However, in order to secure more stable optical performance, it is preferable that the fifth lens has a positive refractive power. The fifth lens, like the fourth lens, preferably has a meniscus shape that is convex toward the object. This is because the curvature of field can be satisfactorily corrected and good optical performance can be ensured.

It is also preferable to bond the fourth lens and the fifth lens described above and use the lens as a bonded lens. The arrangement of lenses can be easily adjusted when manufacturing an optical system, and the eccentric sensitivity can be lowered. This is because a stronger synthetic refractive power can be obtained by using a bonded lens as compared with the refractive power when the lens is not used as a bonded lens, which can contribute to the improvement of the optical performance of the optical system according to the present invention.

(5) Lens Glass Material It is preferable that the first to fifth lenses constituting the optical system according to the present invention are all glass lenses. Compared to plastic, it has high thermal stability and small expansion and contraction due to temperature fluctuations. Therefore, by using glass lenses for all the lenses, fluctuations in the focal position can be satisfactorily suppressed even if the operating environment temperature changes.

(6) Aperture In the optical system according to the present invention, the location of the diaphragm (aperture diaphragm) is not particularly limited. For example, it can be arranged between the second lens and the third lens, between the third lens and the fourth lens, and the like. However, as the diaphragm is arranged closer to the image plane of the optical system, the incident angle of the imaged light with respect to the image plane becomes larger, and it becomes difficult to properly incident the image light on the photodiode arranged in the image sensor. As a result, it becomes difficult to secure proper exposure, which is not preferable because uneven sensitivity (shading unevenness) and peripheral coloring occur. Therefore, it is preferable to arrange the diaphragm between the second lens and the third lens.

1-2. Conditional expression Next, the conditions that the optical system according to the present invention should be satisfied with, or the conditions that are preferable to be satisfied, will be described.

1-2-1. Conditional expression (1)
In the optical system according to the present invention, in order from the object side, "a first lens having a negative refractive power and a concave image side surface" and "a first lens having a positive or negative refractive power and convex toward the image side". A second lens having a shape, a third lens having a positive refractive power and a biconvex shape, a fourth lens having a negative refractive power, and a second lens having a positive or negative refractive power. If it has "5 lenses", it is required to satisfy the following conditional expression (1).

R11 / f <6.0 ... (1)
However, R11: is the radius of curvature of the paraxial axis of the side surface of the object of the first lens.
f: The focal length of the entire optical system.

The conditional expression (1) is an expression that defines the ratio of the paraxial radius of curvature R11 of the side surface of the object of the first lens to the focal length f of the entire optical system. The numerical range of the conditional expression (1) is defined for the following reasons. When the value of R11 / f in the conditional expression (1) is 6.0 or more, it means that the paraxial radius of curvature R11 on the side surface of the object of the first lens becomes large. In such a case, the paraxial radius of curvature of the image side surface of the first lens becomes small, and when the light reflected on the image surface is incident on the image side surface of the first lens, the reflected light is likely to be re-incident on the image surface. The risk of ghost images is increased. Therefore, the range of the conditional expression (1) is defined from the viewpoint of ensuring good optical performance.

Then, although only the upper limit value is specified in the above-mentioned conditional expression (1), it is not necessary to specify the lower limit value from the viewpoint of those skilled in the art. However, if the lower limit is set, it is empirically 3. When the value of R11 / f is less than 3, the paraxial radius of curvature R11 on the side surface of the object of the first lens becomes excessively small, and it is possible to avoid the above-mentioned formation of the ghost image, but the curvature of field is curved. Becomes large, and it becomes difficult to secure the imaging performance. From this, more preferably, 3 <R11 / f <6.

Further, in order to reduce the curvature of field and ensure that the image formation of the ghost image is avoided, the lower limit of the conditional expression (1) is preferably 3.5, more preferably 4.0. The upper limit of the conditional expression (1) is preferably 5.8, more preferably 5.7.

1-2-2. Conditional expression (2)
The conditional expression (2) shown below defines the half angle of view w of the entire optical system in the optical system according to the present invention.

45 ° <w <90 ° ・ ・ ・ (2)
However, w: is a half angle of view of the entire optical system.

The reason why the half angle of view of the entire optical system is defined in this way is that the surface reflection ghost that occurs near the center of the image plane is assumed to use a wide-angle lens to some extent in the optical system according to the present invention. This is to avoid the occurrence. If the half angle of view w of the entire optical system is 45 ° or less, the purpose of widening the angle of 45 ° or more of the present invention is lost, which is not preferable. On the other hand, the reason why the half angle of view of the entire optical system is less than 90 ° is that it is difficult to secure a half angle of view of 90 ° or more in the case of a normally used wide-angle lens. For the above reasons, the range of the half angle of view w of the entire optical system is defined.

Then, the range of the half angle of view w in the conditional expression (2) is a conditional expression in order to more surely avoid the occurrence of the surface reflection ghost generated near the center of the image plane and surely achieve the wide angle. The lower limit of (2) is preferably 50 °, more preferably 55 °. The upper limit of the conditional expression (2) is preferably 80 °, more preferably 75 °, and even more preferably 70 °.

1-2-3. Conditional expression (3) and conditional expression (4)
It is preferable that the optical system according to the present invention simultaneously satisfies the conditional expression (3) and the conditional expression (4) described below.

Conditional expression (3): The conditional expression (3) is as follows.
1.0 << | f1 / f | <3.0 ... (3)
However, f1: the focal length of the first lens.
f: The focal length of the entire optical system.

This conditional expression (3) is an expression that defines the ratio of the focal length f of the entire optical system to the focal length f1 of the first lens. When the conditional expression (3) becomes 3.0 or more, it means that the negative refractive power of the first lens becomes weak, and it becomes difficult to realize a small diameter of the first lens arranged on the object side most. On the other hand, if the negative refractive power of the first lens is strengthened so that the conditional expression (3) becomes 1.0 or less, it becomes difficult to correct the curvature of field, which leads to performance deterioration, which is not preferable. Therefore, the conditional expression (3) is defined as described above.

The upper limit of the conditional expression (3) is preferably 2.5 as a range in which the diameter of the first lens arranged closest to the object is surely reduced and the curvature of field is surely corrected. It is preferably 2.3, and more preferably 2.2. The lower limit of the conditional expression (3) is preferably 1.2, preferably 1.3, and more preferably 1.5.

Conditional expression (4): The conditional expression (4) is as follows.
0.01 <d _{1-2 /} f <1.5 ... (4)
However, f: is the focal length of the entire optical system.
d _1-2 : The air distance between the first lens and the second lens on the optical axis.

The conditional expression (4) includes an air gap d _1-2 on the optical axis between the first lens and the second lens, and defines a ratio between the focal length f1 of the first lens, the present inventors This is an equation that defines the distance between the first lens and the second lens on the optical axis with respect to the focal length of the entire optical system according to the above. The distance between the first lens and the second lens on the optical axis as used herein means the surface distance of the air lens formed between the first lens and the second lens. By satisfying the conditional expression (4), various aberrations can be satisfactorily corrected by the air lens formed between the first lens and the second lens, and an optical system having good optical performance can be obtained. Further, by satisfying the conditional expression (4), the surface spacing of the air lens is within an appropriate range, and the optical system can be compactly configured. _{When d 1-2} / f of the conditional expression (4) is 0.01 or less, it becomes difficult to obtain the aberration correction effect by the air lens formed between the first lens and the second lens. In this case, in particular, it becomes difficult to correct curvature of field, and good optical performance cannot be obtained. On the other hand, when d _1-2 / f of the conditional expression (4) becomes 1.5 or more, the surface spacing of the air lens becomes too large, so that the total length of the optical system becomes long and the optical system becomes miniaturized. It becomes difficult. Therefore, the conditional expression (4) is defined as described above.

The upper limit of the conditional expression (4) is preferably 1.2 as a reliable range in which the surface spacing of the air lens is within a more appropriate range and the optical system can be compactly configured. , 1.0 is more preferable. The lower limit of the conditional expression (4) is preferably 0.2, more preferably 0.5.

1-2-4. Conditional expression (5)
The conditional expression (5) is an expression that defines the ratio between the focal length of the second lens and the focal length of the first lens. By satisfying the conditional expression (5) shown below, better optical performance can be obtained in the optical system according to the present invention, and it becomes easy to further reduce the size of the optical system.

5 <f2 / f1 <100 ... (5)
However, f1: the focal length of the first lens.
f2: The focal length of the second lens.

In the conditional expression (5), the cases where the value of f2 / f1 is 100 or more are the case where the negative refractive power of the first lens is excessively strong and the case where the negative refractive power of the second lens is excessively weak. It can be assumed that this is the case. In the former case, a bright image cannot be obtained, and it becomes difficult to obtain good optical performance, which is not preferable. In the latter case, the effect of dispersing the negative refractive power assumed between the first lens and the second lens becomes weaker, and in order to secure the performance of a wide angle of view, the lens diameter of the first lens is increased. It is not preferable because the diameter cannot be reduced. On the other hand, when the value of f2 / f1 is 5 or less, there are cases where the negative refractive power of the first lens becomes excessively weak and cases where the negative refractive power of the second lens becomes excessively strong. I can imagine. In the former case, if it is attempted to secure the performance of a wide angle of view, the lens diameter of the first lens cannot be reduced, which is not preferable. In the latter case, a bright image cannot be obtained, and it becomes difficult to obtain good optical performance, which is not preferable. Therefore, the conditional expression (5) is defined as described above.

Then, the negative refractive power of the first lens and the negative refractive power of the second lens are in a good balance range, and the conditional expression (5) is set as a range in which a stable and brighter image can be obtained. The upper limit of is preferably 50, more preferably 35. The lower limit of the conditional expression (5) is preferably 10 and more preferably 15.

1-2-5. Conditional expression (6), conditional expression (7), conditional expression (8)
The optical system according to the present invention preferably simultaneously satisfies the conditional expression (6), the conditional expression (7), and the conditional expression (8) described below.

Conditional expression (6): Conditional expression (6) is an expression that defines the ratio of the focal length of the entire optical system to the focal length of the third lens. By satisfying the conditional expression (6), the positive refractive power of the third lens is within an appropriate range, and better optical performance can be obtained. Further, it becomes easy to further reduce the size of the optical system. The conditional expression (6) is as follows.

1.0 <f3 / f <3.0 ... (6)
However, f3: the focal length of the third lens.
f: The focal length of the entire optical system.

When the value of f3 / f in the conditional expression (6) is 1.0 or less, the refractive power of the third lens becomes too strong. In this case, it becomes difficult to correct coma aberration and curvature of field, and it becomes difficult to secure good optical performance. Further, since the eccentric sensitivity becomes high, it is necessary to assemble the lens with high accuracy, and the productivity is lowered. On the other hand, when the value of f3 / f in the conditional expression (6) is 3.0 or more, the astringent effect of the incident luminous flux in the third lens becomes weak, and the total length of the optical system becomes long. Therefore, it is not preferable in order to reduce the size of the optical system. Therefore, the conditional expression (6) is defined as described above.

Then, in order to make the refractive power of the third lens more appropriate, secure better optical performance, and surely set the range of eccentric sensitivity that does not adversely affect productivity, the conditional equation (6) The upper limit is preferably 2.7, preferably 2.5, more preferably 2.3, and even more preferably 2.0. The lower limit of the conditional expression (6) is preferably 1.2, more preferably 1.3.

Conditional expression (7): Conditional expression (7) is an expression that defines the Abbe number with respect to the d-line of the third lens. By satisfying the conditional expression (7), it becomes easy for the optical system according to the present invention to obtain good optical performance. Further, the temperature coefficient of the refractive index of the glass material satisfying the conditional expression (7) is often negative. If the third lens is constructed using a glass material having a negative temperature coefficient of refractive index, it is possible to suppress fluctuations in the focusing position of the optical system due to changes in the ambient temperature. Therefore, the optical system can be made more suitable as the optical system of the above-mentioned stationary image pickup apparatus that is often used outdoors. This point will be described later. The conditional expression (7) is as follows.

νd3> 40.0 ・ ・ ・ (7)
νd3: Abbe number with respect to the d line (587.56 nm) of the third lens.

When the numerical value of the conditional expression (7) is 40.0 or less, axial chromatic aberration and chromatic aberration of magnification are deteriorated, and the optical performance of the optical system according to the present invention is deteriorated, which is not preferable. In addition, most of the glass materials having the numerical value of the conditional expression (7) of 40.0 or less have a positive temperature coefficient of refractive index, and suppress the fluctuation of the focusing position of the optical system due to the above-mentioned change in the atmospheric temperature. It becomes difficult. Therefore, the conditional expression (7) is defined as described above.

Then, although only the lower limit value is specified in the above-mentioned conditional expression (7), it is not necessary to specify the upper limit value from the viewpoint of those skilled in the art. However, if the upper limit is set, it is empirically 90.0.

Then, from the viewpoint of suppressing deterioration of axial chromatic aberration and chromatic aberration of magnification and ensuring better optical performance, more preferably 40.0 <νd3 <90.0, still more preferably 60.0 <νd3 <. It is 90.0.

Conditional formula (8): Conditional formula (8) is a formula that defines the ^{relative refractive index temperature coefficient (1 × 10-6} / K) at the d-line (587.56 nm) under the environment of 20 ° C. of the third lens. .. The lens expands and contracts due to changes in the environmental temperature. As a result, the refractive index of the lens changes, the focal length in the optical system fluctuates, and the resolution tends to decrease. Therefore, in the optical system according to the present invention, in order to maintain high resolution in a wide range of environmental temperatures from low temperature to high temperature, a third lens considered to have the greatest influence on the change in the refractive index of the lens in a high temperature environment and a low temperature environment is used. Conditional expression (8) was specified as the target. The conditional expression (8) is as follows.

dn3 / dT <6.0 × ^10-6 / K ・ ・ ・ (8)
^{dn3 / dT: The relative refractive index temperature coefficient (1 × 10-6} / K) at the d-line (587.56 nm) under the 20 ° C. environment of the third lens.

When the value of dn3 / dT in this conditional expression (8) becomes 6.0 × 10 ^-6 / K or more, the d-line of the material constituting the third lens, which is a positive lens arranged at the position closest to the aperture, When the relative refractive index change due to temperature becomes too small, the temperature characteristic ability deteriorates such that the fluctuation of the focal length in a high temperature environment and a low temperature environment becomes large, and the image resolution is lowered, which is not preferable. Therefore, the conditional expression (8) is defined as described above. The relative refractive index change with temperature is defined as the temperature change of the refractive index in the air having the same temperature as the lens material. The same applies hereinafter.

Then, although only the upper limit value is specified in the above-mentioned conditional expression (8), it is not necessary to specify the lower limit value from the viewpoint of those skilled in the art. However, if the lower limit is set, it is empirically -8.0 x ^10-6 / K. Then, from the viewpoint of suppressing deterioration of axial chromatic aberration and chromatic aberration of magnification and ensuring better optical performance, dn3 / dT <0.0, more preferably −6.0 × ^10-6. / K <(dn3 / dT) <0.0.

1-2-6. Conditional expression (9)
The conditional expression (9) is "relative refractive index temperature coefficient (1 x ^10-6 / K) at d-line (587.56 nm) under 20 ° C. environment of the third lens" and "20 ° C. environment of the second lens". Below, it is an equation that defines the ratio with the relative refractive index temperature coefficient (1 × ^{10-6 / K) at the d-line (587.56 nm).} In the case of the optical system according to the present application, the third lens is arranged as the positive lens at the position closest to the aperture, and the second lens is arranged as the negative lens at the position closest to the aperture. By satisfying this conditional expression (9), a higher resolution can be obtained even in a high temperature atmosphere or a low temperature atmosphere. The conditional expression (9) is as follows.

-5.0 <(dn3 / dT) / (dn2 / dT) <20.0 ... (9)
^{However, dn3 / dT: the relative refractive index temperature coefficient (1 × 10 -6} / K) at the d line (587.56 nm) under the environment of 20 ° C. of the third lens.
^{dn2 / dT: The relative refractive index temperature coefficient (1 × 10-6} / K) at the d line (587.56 nm) under the 20 ° C. environment of the second lens.

The values of (dn3 / dT) / (dn2 / dT) in the conditional expression (9) are positive values as long as the respective values of dn3 / dT and dn2 / dT satisfy the range of the conditional expression (9). It can be a negative number. However, in the optical system of the present invention, when the second lens has a negative refractive power and the third lens has a positive refractive power, and the relative refractive index temperature coefficients are different between positive and negative, Temperature characteristics tend to deteriorate. On the other hand, the relative refractive index temperature coefficient (dn3 / dT) of the third lens having a positive refractive power according to the above-mentioned conditional equation (8) has a negative value. In such a case, it is more preferable that the relative refractive index temperature coefficient (dn3 / dT) of the second lens is also a negative value in order to suppress fluctuations in the temperature characteristics. On the other hand, when the value of the conditional expression (9) is 20.0 or more, the difference between the relative refractive index temperature coefficient of the third lens and the relative refractive index temperature coefficient of the second lens becomes too large, the temperature characteristic. Is not preferable because it deteriorates. Therefore, the conditional expression (9) is defined as described above.

In this conditional expression (9), it is most preferable that both the "relative refractive index temperature coefficient of the third lens" and the "relative refractive index temperature coefficient of the second lens" are negative values. Then, in order to obtain extremely stable and high resolution even in a high temperature atmosphere or a low temperature atmosphere, more preferably −5 <(dn3 / dT) / (dn2 / dT) <15, and further preferably 0 <(dn3). / DT) / (dn2 / dT) <5.

1-2-7. Conditional expression (10)
The conditional expression (10) is an expression that defines the ratio between the focal length of the entire optical system and the focal length of the fourth lens having a negative refractive power. By satisfying the conditional expression (10), better optical performance can be imparted to the optical system according to the present invention, and it becomes easy to further reduce the size of the optical system. The conditional expression (10) is as follows.

1.0 << | f4 / f | <3.5 ... (10)
However, f4: the focal length of the fourth lens.
f: The focal length of the entire optical system.

When the value of | f4 / f | in the conditional expression (10) is 1.0 or less, the refractive power of the fourth lens becomes too strong, and it becomes difficult to correct the curvature of field. Therefore, it becomes difficult to obtain good optical performance. On the other hand, when the value of | f4 / f | in the conditional expression (10) is 3.5 or more, the refractive power of the fourth lens is weak and the divergence effect of the incident luminous flux in the fourth lens is weakened. Therefore, in order to secure a desired image height, it is necessary to increase the overall length of the optical system, and it becomes difficult to reduce the size of the optical system. Therefore, the conditional expression (10) is defined as described above.

In the conditional expression (10), the upper limit of the conditional expression (10) is preferably 3.0 in order to obtain extremely stable and high resolution even in a high temperature atmosphere or a low temperature atmosphere. It is preferably 8 and more preferably 2.5. The lower limit of the conditional expression (10) is preferably 1.2, preferably 1.5, and more preferably 1.8.

1-2-7. Conditional expression (11), conditional expression (12)
In the optical system according to the present invention, it is preferable that the conditional expressions (11) and the conditional expressions (12) described below are simultaneously satisfied on the premise that the fourth lens and the fifth lens are joined.

Conditional formula (11): Conditional formula (11) is a formula that defines the ratio of the combined focal length when the fourth lens and the fifth lens are joined to the focal length of the entire optical system. .. By satisfying the conditional expression (11), better optical performance can be imparted to the optical system according to the present invention, and it becomes easy to further reduce the size of the optical system. The conditional expression (11) is as follows.

f45 / f <200 ... (11)
However, f45: the combined focal length of the fourth lens and the fifth lens.
f: The focal length of the entire optical system.

In the conditional expression (11), if the value of f45 / f is not smaller than 200, the synthetic refractive power as a bonding lens is weakened, and the significance of bonding the fourth lens and the fifth lens is lost. It is not preferable because it cannot contribute to the improvement of the optical performance of the optical system according to the invention. Therefore, the conditional expression (11) is defined as described above. Although only the upper limit value is specified in the above-mentioned conditional expression (11), it is considered unnecessary to specify the lower limit value from the viewpoint of those skilled in the art.

Then, in the optical system according to the present invention, from the viewpoint of imparting better optical performance and facilitating further miniaturization of the optical system, -200 <f45 / f <0, more preferably -150 <. f45 / f <0.

Conditional formula (12): Conditional formula (12) is based on "the average coefficient of linear expansion of the glass material used for the fourth lens from -30 ° C to 70 ° C" and "from -30 ° C of the glass material used for the fifth lens". This is an equation that defines the ratio with the "average coefficient of linear expansion at 70 ° C." It is preferable that all the first to fifth lenses constituting the optical system according to the present invention are glass lenses. When the fourth lens and the fifth lens are joined, an organic component (adhesive) is interposed between the fourth lens and the fifth lens. The organic component has a higher coefficient of linear expansion than glass, and its volume is likely to change due to changes in the operating environment temperature. By satisfying the conditional expression (12), a stable bonding state between the fourth lens and the fifth lens can be obtained even when the operating environment temperature changes. The conditional expression (12) is as follows.

｜ α4-α5 ｜ ＜ 50 × ^10-7 / K ・ ・ ・ (12)
^{However, α4: the average linear expansion coefficient (1 × 10 -7} / K) of the glass material used for the fourth lens from −30 ° C. to 70 ° C.
^{α5: The average coefficient of linear expansion (1 × 10 -7} / K) of the glass material used for the fifth lens from −30 ° C. to 70 ° C.

The difference between the average linear expansion coefficient of the glass material used for the fourth lens from -30 ° C to 70 ° C and the average linear expansion coefficient of the glass material used for the fifth lens from -30 ° C to 70 ° C is 50 × 10 ^{−. If it is 7} or more, the possibility that the joint portion is peeled off due to the expansion / contraction behavior due to the temperature change in the assumed usage environment of -30 ° C to 70 ° C increases, which is not preferable. Therefore, the conditional expression (12) is defined as described above.

2. 2. Imaging Device Next, the imaging device according to the present invention will be described. The image pickup apparatus according to the present invention is characterized by including the above-mentioned optical system according to the present invention and an image pickup element that receives an optical image formed by the optical system and converts it into an electrical image signal.

Here, the image pickup device and the like are not particularly limited, and a solid-state image pickup device and the like such as a CCD sensor (Charge Coupled Device) and a CMOS sensor (Complementary Metal Oxide Semiconductor) can also be used. The image pickup device according to the present invention is suitable for an image pickup device using these solid-state image pickup elements such as a digital camera and a video camera. Further, the image pickup device may be a lens-fixed image pickup device in which the lens is fixed to a housing, or may be an interchangeable lens type image pickup device such as a single-lens reflex camera or a mirrorless single-lens camera. Of course.

In particular, the imaging device according to the present invention is suitable for a fixed-installation type imaging device that is installed and fixed to a building, a vehicle body, or the like and is used for a specific purpose, such as a monitoring imaging device or the like. Imaging devices for these purposes are required to make the presence of the imaging device inconspicuous from the subject side. The optical system according to the present invention realizes a small diameter of the lens arranged on the object side and a wide angle of view of 45 degrees or more at the same time, and obtains a bright image with Fno of about 1.6. Can be done. Therefore, the surveillance imager or the like provided with the optical system according to the present invention has an inconspicuous appearance, but can image a wide range, and can obtain a clear image even in a low light amount such as at night, which is ideal performance. Will be prepared.

Next, the present invention will be specifically described with reference to Examples. However, the present invention is not limited to the following examples. The optical systems of each of the examples listed below are imaging optical systems used in imaging devices (optical devices) such as digital cameras, video cameras, and silver salt film cameras, and in particular, are stationary type such as surveillance imaging devices. It can be preferably applied to an imaging device. Further, in each lens cross-sectional view, the left side is the object side and the right side is the image plane side when viewed from the drawing.

(1) Configuration of Optical System The optical system of Example 1 is shown in FIG. As can be understood from FIG. 1, the optical system has a negative refractive power in order from the object side, and has a first lens G1 having a concave image side surface and a negative refractive power, and is convex toward the image side. It is composed of a second lens G2 having a meniscus shape, a third lens G3 having a positive refractive power, a fourth lens G4 having a negative refractive power, and a fifth lens G5 having a positive refractive power. .. Then, as the fifth lens G5 having a positive refractive power at this time, a lens having a meniscus shape convex on the object side is used. Further, the fourth lens G4 and the fifth lens G5 in the first embodiment are bonded lenses, and their combined refractive power is negative.

In the first embodiment, the aperture diaphragm SP is arranged between the second lens G2 and the third lens G3. This aperture diaphragm SP limits the diameter (light amount) of the light flux incident on the image plane IP side from the object side. An optical block G is arranged between the fifth lens G5 and the image plane IP. This optical block G corresponds to an optical filter, a face plate, a crystal low-pass filter, an infrared cut filter, and the like.

When the image pickup apparatus is configured using the optical system of the first embodiment, the image plane IP corresponds to the image pickup plane of the solid-state image pickup device. As the solid-state image sensor, a photoelectric conversion element such as the above-mentioned CCD sensor or CMOS sensor can be used. In the image pickup apparatus, the light incident from the object side of the image pickup lens of the present embodiment is finally imaged on the image pickup surface of the solid-state image pickup device. Then, the light received by the solid-state image sensor is photoelectrically converted and output as an electric signal to generate a digital image corresponding to the image of the subject. Digital images can be recorded on recording media such as HDDs (Hard Disk Devices), memory cards, optical disks, and magnetic tapes. When the image pickup device is a silver halide film camera, the image plane IP corresponds to the film plane. When the image pickup device is a silver halide film camera, the image plane IP corresponds to the film plane. Since the notation of SP, IP, G, etc. is the same in the cross-sectional views of each lens shown in the following examples, the description thereof will be omitted below.

(2) Numerical Example An numerical example to which a specific numerical value of the optical system adopted in the first embodiment is applied will be described. Table 1 shows the lens data of the optical system. In Table 1 (1A), "plane number" is the number of the lens surface counted from the object side to the image surface side, and "r (mm)" is the radius of curvature of the lens surface (however, the value of r is ∞). The surface indicates that the surface is a flat surface.), “D” is the distance between the i-th (i is a natural number) lens surface from the object side and the i + 1th lens surface on the optical axis. “Nd” indicates the refractive index with respect to the d line (wavelength λ = 587.56 nm), and “νd” indicates the Abbe number with respect to the d line. However, if the lens surface is aspherical, "*" is added before the surface number in the table below. When the surface is aspherical, the radius of curvature of the paraxial axis is shown in the column of "r". And "INF" in the table represents infinity.

Table 1 (1B) shows various data of the optical system. Specifically, the focal length (mm), F number (Fno value), half angle of view (w / °), image height (mm), total lens length (mm), back focus (BF / mm) of the optical system. Is shown. Here, the total length of the lens is the distance on the optical axis from the object side surface of the first lens to the image surface side of the lens arranged closest to the image plane side in the subsequent lens group, here, the back focus. It is the added value. The back focus is a value obtained by air-converting the distance from the image side surface of the fifth lens G5 to the paraxial image plane.

Table 1 (1C) shows the aspherical coefficient of the aspherical surface (*) shown in Table 1 (1A) when the shape is defined by the following formula. The aspherical coefficient can be expressed by the following aspherical equation with the displacement in the optical axis direction at the position of the height h from the optical axis as a plane vertex reference. In Table 1 (1C), " ^Ea " means "x10-a".

Table 1 (1E) shows the focal length (f1) of the first lens, the focal length (f2) of the second lens, the focal length (f3) of the third lens, and the focal length of the third lens constituting the optical system adopted in the first embodiment. The focal lengths of the four lenses (f4), the focal lengths of the fifth lens (f5), and the combined focal lengths of the fourth lens and the fifth lens (f45) are listed.

z = ch ² / [1 + {1- (1 + k) c ² h ² } ^1/2 ] + A4h ⁴ + A6h ⁶ + A8h ⁸ + A10h ¹⁰・ ・ ・
However, c is the curvature (1 / r), h is the height from the optical axis, k is the conical coefficient (conic constant), and A4, A6, A8, A10 ... are the aspherical coefficients of each order. Further, the notation "E ± m" (m represents an integer) in the numerical values of the aspherical coefficient and the cornic constant ^{means "× 10 ± m} ".

^{Table 1 (1D) shows the relative refractive index temperature coefficient (unit: 1 × 10-6} / K) at the d-line (587.56 nm) under the 20 ° C. environment of the glass materials used for the second and third lenses. ^{The average linear expansion coefficient (unit: 1 × 10 -7} / K) of the glass material used for the 4th lens and the 5th lens at -30 ° C to 70 ° C is shown.

Further, Table 8 shows the numerical values of the above conditional expressions (1) to (13) of the optical system. Since the matters concerning each of these tables are the same in each of the tables shown in other examples, the duplicated description below will be omitted.

Then, FIG. 2 shows a longitudinal aberration diagram of the optical system of the first embodiment at infinity focusing. The longitudinal aberration diagram shown in FIG. 2 shows spherical aberration (SA / mm), astigmatism (AST / mm), and distortion (DIS /%) in order from the left side when facing the drawing.

The vertical axis of this spherical aberration diagram represents an F number (Fno). Further, the spherical aberration at the d line (wavelength 587.56 nm) is shown by a solid line, the spherical aberration at the C line (wavelength 656.27 nm) is shown by a long broken line, and the spherical aberration at the g line (wavelength 435.84 nm) is shown by a short broken line.

The vertical axis of the astigmatism diagram represents the image height (y). It also shows astigmatism of the sagittal ray ΔS (solid line) and the meridional ray ΔM (broken line) on the d-line (wavelength 587.56 nm).

The vertical axis of the distortion diagram represents the image height (y). Further, the distortion at the d line (wavelength 587.56 nm) is shown by a solid line. Since the matters related to these longitudinal aberration diagrams are the same in the longitudinal aberration diagrams shown in other examples, the duplicated description below will be omitted.

(1) Configuration of Optical System The optical system of Example 2 is shown in FIG. As can be understood from FIG. 3, the optical system has a negative refractive power in order from the object side, and has a first lens G1 having a concave image side surface and a negative refractive power, and is convex toward the image side. It is composed of a second lens G2 having a meniscus shape, a third lens G3 having a positive refractive power, a fourth lens G4 having a negative refractive power, and a fifth lens G5 having a positive refractive power. .. A double-sided convex lens is used for the fifth lens G5 having a positive refractive power at this time. Further, the fourth lens G4 and the fifth lens G5 in the second embodiment are bonded lenses, and their combined refractive power is negative. In the second embodiment, the aperture diaphragm SP is arranged between the second lens G2 and the third lens G3, as in the first embodiment.

(2) Numerical Example An numerical example to which a specific numerical value of the optical system adopted in the second embodiment is applied will be described. Hereinafter, since the same as in Example 1, duplicated description will be omitted as much as possible. Table 2 (2A) is the lens data of the optical system, Table 2 (2B) is various data of the optical system, and Table 2 (2C) is the aspherical aspherical surface shown in Table 2 (2A). Table 2 (2D) shows the relative refractive index temperature coefficient of the glass material used for the second lens and the third lens, and the average linear expansion coefficient of the glass material used for the fourth lens and the fifth lens. Table 2 (2E) shows the focal lengths (f1 to f5) of the first to fifth lenses and the combined focal lengths of the fourth lens and the fifth lens (f45) similar to those in the first embodiment. .. Further, Table 8 shows the numerical values of the above conditional expressions (1) to (13) of the optical system. Further, FIG. 4 shows a longitudinal aberration diagram of the optical system at infinity focusing.

(1) Configuration of Optical System The optical system of Example 3 is shown in FIG. As can be understood from FIG. 5, the optical system has a negative refractive power in order from the object side, and has a first lens G1 having a concave image side surface and a negative refractive power, and is convex toward the image side. It is composed of a second lens G2 having a meniscus shape, a third lens G3 having a positive refractive power, a fourth lens G4 having a negative refractive power, and a fifth lens G5 having a positive refractive power. .. Then, as the fifth lens G5 having a positive refractive power at this time, a lens having a meniscus shape convex on the object side is used. Further, the fourth lens G4 and the fifth lens G5 in the third embodiment are bonded lenses, and their combined refractive power is positive. In the third embodiment, the aperture diaphragm SP is arranged between the second lens G2 and the third lens G3, as in the first embodiment.

(2) Numerical Example An numerical example to which a specific numerical value of the optical system adopted in the third embodiment is applied will be described. Hereinafter, since the same as in Example 1, duplicated description will be omitted as much as possible. Table 3 (3A) shows the lens data of the optical system, Table 3 (3B) shows various data of the optical system, and Table 3 (3C) shows the aspherical aspherical surface shown in Table 3 (3A). Table 3 (3D) shows the relative refractive index temperature coefficient of the glass material used for the second lens and the third lens, and the average linear expansion coefficient of the glass material used for the fourth lens and the fifth lens. Table 3 (3E) shows the focal lengths (f1 to f5) of the first to fifth lenses and the combined focal lengths of the fourth lens and the fifth lens (f45) similar to those in the first embodiment. .. Further, Table 8 shows the numerical values of the above conditional expressions (1) to (13) of the optical system. Further, FIG. 6 shows a longitudinal aberration diagram of the optical system at infinity focusing.

(1) Configuration of Optical System The optical system of Example 4 is shown in FIG. As can be understood from FIG. 7, the optical system has a negative refractive power in order from the object side and from the object side, and has a negative refractive power with the first lens G1 having a concave image side surface. A second lens G2 having a convex meniscus shape on the image side, a third lens G3 having a positive refractive power, a fourth lens G4 having a negative refractive power, and a fifth lens G5 having a positive refractive power. It is composed of. A double-sided convex lens is used for the fifth lens G5 having a positive refractive power at this time. Further, the fourth lens G4 and the fifth lens G5 in the fourth embodiment are used without being bonded, and the combined refractive power thereof is positive. In the fourth embodiment, the aperture diaphragm SP is arranged between the second lens G2 and the third lens G3, as in the first embodiment.

(2) Numerical Example An numerical example to which the specific numerical value of the optical system adopted in the fourth embodiment is applied will be described. Hereinafter, since the same as in Example 1, duplicated description will be omitted as much as possible. Table 4 (4A) shows the lens data of the optical system, Table 4 (4B) shows various data of the optical system, and Table 4 (4C) shows the aspherical aspherical surface shown in Table 4 (4A). Table 4 (4D) shows the relative refractive index temperature coefficient of the glass material used for the second lens and the third lens, and the average linear expansion coefficient of the glass material used for the fourth lens and the fifth lens. Table 4 (4E) shows the focal lengths (f1 to f5) of the first to fifth lenses and the combined focal lengths of the fourth lens and the fifth lens (f45) similar to those in the first embodiment. .. Further, Table 8 shows the numerical values of the above conditional expressions (1) to (13) of the optical system. Further, FIG. 8 shows a longitudinal aberration diagram of the optical system at infinity focusing.

(1) Configuration of Optical System The optical system of Example 5 is shown in FIG. As can be understood from FIG. 9, the optical system has a first lens G1 having a negative refractive power and a concave image side surface and a positive refractive power in order from the object side, and is convex toward the image side. It is composed of a second lens G2 having a meniscus shape, a third lens G3 having a positive refractive power, a fourth lens G4 having a negative refractive power, and a fifth lens G5 having a positive refractive power. .. A double-sided convex lens is used for the fifth lens G5 having a positive refractive power at this time. Further, the fourth lens G4 and the fifth lens G5 in the fifth embodiment are used without being joined, and the combined refractive power thereof is positive. In the fourth embodiment, the aperture diaphragm SP is arranged between the second lens G2 and the third lens G3, as in the first embodiment.

(2) Numerical Example An numerical example to which a specific numerical value of the optical system adopted in the fifth embodiment is applied will be described. Hereinafter, since the same as in Example 1, duplicated description will be omitted as much as possible. Table 5 (5A) shows the lens data of the optical system, Table 5 (5B) shows various data of the optical system, and Table 5 (5C) shows the aspherical aspherical surface shown in Table 5 (5A). Table 5 (5D) shows the relative refractive index temperature coefficient of the glass material used for the second lens and the third lens, and the average linear expansion coefficient of the glass material used for the fourth lens and the fifth lens. Table 5 (5E) shows the focal lengths (f1 to f5) of the first to fifth lenses and the combined focal lengths of the fourth lens and the fifth lens (f45) similar to those in the first embodiment. .. Further, Table 8 shows the numerical values of the above conditional expressions (1) to (13) of the optical system. Further, FIG. 10 shows a longitudinal aberration diagram of the optical system at infinity focusing.

(1) Configuration of Optical System The optical system of Example 6 is shown in FIG. As can be understood from FIG. 11, the optical system has a negative refractive power in order from the object side, and has a first lens G1 having a concave image side surface and a negative refractive power, and is convex toward the image side. It is composed of a second lens G2 having a meniscus shape, a third lens G3 having a positive refractive power, a fourth lens G4 having a negative refractive power, and a fifth lens G5 having a positive refractive power. .. Then, as the fifth lens G5 having a positive refractive power at this time, a lens having a meniscus shape convex on the object side is used. Further, the fourth lens G4 and the fifth lens G5 in the sixth embodiment are bonded lenses, and their combined refractive power is negative.

(2) Numerical Examples Next, numerical examples to which specific numerical values of the optical system are applied will be described. Table 6 (6A) shows the lens data of the optical system, Table 6 (6B) shows various data of the optical system, and Table 6 (6C) shows the aspherical aspherical surface shown in Table 6 (6A). Table 6 (6D) shows the relative refractive index temperature coefficient of the glass material used for the second lens and the third lens, and the average linear expansion coefficient of the glass material used for the fourth lens and the fifth lens. Table 6 (6E) shows the focal lengths (f1 to f5) of the first to fifth lenses and the combined focal lengths of the fourth lens and the fifth lens (f45) similar to those of the first embodiment. .. Further, Table 8 shows the numerical values of the above conditional expressions (1) to (13) of the optical system. Further, FIG. 12 shows a longitudinal aberration diagram of the optical system at infinity focusing.

(1) Configuration of Optical System The optical system of Example 7 is shown in FIG. As can be understood from FIG. 13, the optical system has a negative refractive power in order from the object side, and has a first lens G1 having a concave image side surface and a negative refractive power, and is convex toward the image side. It is composed of a second lens G2 having a meniscus shape, a third lens G3 having a positive refractive power, a fourth lens G4 having a negative refractive power, and a fifth lens G5 having a positive refractive power. .. Then, as the fifth lens G5 having a positive refractive power at this time, a lens having a meniscus shape convex on the object side is used. Further, the fourth lens G4 and the fifth lens G5 in the seventh embodiment are bonded lenses, and their combined refractive power is negative.

(2) Numerical Examples Next, numerical examples to which specific numerical values of the optical system are applied will be described. Table 7 (7A) is the lens data of the optical system, Table 7 (7B) is various data of the optical system, and Table 7 (7C) is the aspherical aspherical surface shown in Table 7 (7A). Table 7 (7D) shows the relative refractive index temperature coefficient of the glass material used for the second lens and the third lens, and the average linear expansion coefficient of the glass material used for the fourth lens and the fifth lens. Table 7 (7E) shows the focal lengths (f1 to f5) of the first to fifth lenses and the combined focal lengths of the fourth lens and the fifth lens (f45) similar to those in the first embodiment. .. Further, Table 8 shows the numerical values of the above conditional expressions (1) to (13) of the optical system. Further, FIG. 14 shows a longitudinal aberration diagram of the optical system at infinity focusing.

The optical system according to the present invention enables wide-angle observation / imaging by widening the half-angle of view of 45 degrees or more while reducing the diameter of the lens placed closest to the object, and has an Fno of about 1.6. Allows you to get a bright image of. Therefore, a monitoring image pickup device or the like that employs this optical system can exert an effect of making the existence of the image pickup device inconspicuous when viewed from the subject side to be observed.

G1 to G5 1st to 5th lenses SP Aperture G Optical block IP image plane

Claims (13)

In order from the object side, a first lens having a negative refractive power and a concave image side surface, a second lens having a positive or negative refractive power and a convex meniscus shape on the image side, and a positive refractive power. It is composed of a biconvex third lens, a fourth lens having a negative refractive power, and a fifth lens having a positive or negative refractive power, and is characterized by satisfying the following conditions. Optical system.
3 <R11 / f <6.0 ... (1)
0.01 <d _{1-2 /} f <1.5 ... (4)
1.0 << | f4 / f | <3.5 ... (10)
However, R11: the radius of curvature of the near axis of the side surface of the object of the first lens.
f: Focal length of the entire optical system
f4: Focal length of the fourth lens
d _1-2 : The air distance between the first lens and the second lens on the optical axis . The optical system according to claim 1, which satisfies the following conditional expression.
45 ° <w <90 ° ・ ・ ・ (2)
However, w: is a half angle of view of the entire optical system. The optical system according to claim 1 or 2, which satisfies the following conditional expression.
1.0 << | f1 / f | <3.0 ... (3)
However, f1: the focal length of the first lens. The optical system according to any one of claims 1 to 3, wherein the second lens has a negative refractive power and satisfies the following conditional expression.
5 <f2 / f1 <100 ... (5)
However, f1: the focal length of the first lens f2: the focal length of the second lens. The optical system according to any one of claims 1 to 4, which satisfies the following conditional expression.
1.0 <f3 / f <3.0 ... (6)
νd3> 40.0 ・ ・ ・ (7)
(Dn3 / dT) <6.0 × ^10-6 / K ・ ・ ・ (8)
However, f3: the focal length of the third lens νd3: the Abbe number dn3 / dT with respect to the d line (587.56 nm) of the third lens: at the d line (587.56 nm) under the 20 ° C. environment of the third lens. Relative index temperature coefficient (1 × ^10-6 / K)
Is. The optical system according to claim 5, which satisfies the following conditional expression.
-5.0 <(dn3 / dT) / (dn2 / dT) <20.0 ... (9)
^{However, dn2 / dT: the relative refractive index temperature coefficient (1 × 10-6} / K) at the d line (587.56 nm) under the 20 ° C. environment of the second lens.
Is. The optical system according to any one of claims 1 to 6, wherein the second lens has at least one aspherical surface. The optical system according to any one of claims 1 to 7, wherein the third lens has at least one aspherical surface. The optical system according to any one of claims 1 to 8, wherein the fourth lens has a meniscus shape convex on the object side, and the fifth lens has a meniscus shape convex on the object side. The optical system according to any one of claims 1 to 9, wherein the first to fifth lenses are all glass lenses. The optical system according to any one of claims 1 to 10, wherein the fourth lens and the fifth lens are joined to each other and satisfy the following conditional expression.
f45 / f <200 ... (11)
｜ α4-α5 ｜ ＜ 50 × ^10-7 / K ・ ・ ・ (12)
However, f45: the combined focal length of the fourth lens and the fifth lens.
^{α4: Average linear expansion coefficient (1 × 10 -7} / K) of the glass material used for the fourth lens from −30 ° C. to 70 ° C.
^{α5: Average linear expansion coefficient (1 × 10 -7} / K) of the glass material used for the fifth lens from −30 ° C. to 70 ° C.
Is. The optical system according to any one of claims 1 to 11, wherein the fifth lens has a positive refractive power. An image pickup apparatus comprising the optical system according to any one of claims 1 to 12 and an image pickup element that receives an optical image formed by the optical system and converts it into an electrical image signal. ..

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