JP2012208148A - Image pickup optical system and image pickup device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that the influence of various aberration, especially the influence of comatic aberration, increases if an F number is made smaller and the size of an optical system is reduced in a conventional optical system.SOLUTION: An image pickup optical system includes, in order from an object side, a first lens having positive refractive power, a second lens having negative refractive power, a third lens having positive refractive power, a fourth lens having positive refractive power and a fifth lens having negative refractive power, has a diaphragm arranged closest to the object, and satisfies the following conditional expression (1) -4.0<(r6+r7)/(r6-r7)<-0.51, where r6 is a paraxial curvature radius of the third lens at the object side and r7 is a paraxial curvature radius of the third lens at the image side.

Description

  The present invention relates to an imaging optical system and an imaging apparatus using the imaging optical system.

  In recent years, with the thinning of mobile phones, there has been a demand for camera modules in which the length of the optical system in the optical axis direction is made as thin as possible. In addition, with the recent increase in the size and the number of pixels of an image sensor, a lens having a high resolution is required. In order to meet this requirement, a single-focus optical system composed of five aspheric lenses has been proposed (Patent Documents 1 and 2).

JP 2007-264180 A JP 2010-48996 A

  The optical systems of Patent Document 1 and Patent Document 2 have high optical performance, and the F number (FNO) is also small to some extent. However, these optical systems have a long overall optical system length and a large maximum effective diameter of the lens. Therefore, if the F number of these optical systems is further reduced and the size of the optical system is reduced, the influence of various aberrations, particularly the influence of coma aberration, will increase. As a result, it is difficult to realize an optical system in which various aberrations are well corrected while being compact.

  The present invention has been made in view of the above, and although it is a relatively small F-number optical system, the overall length of the optical system is short, the lens diameter is kept small, and various aberrations, particularly coma aberration, are corrected well. It is an object of the present invention to provide an image pickup optical system and an image pickup apparatus using the same.

In order to solve the above-described problems and achieve the object, the imaging optical system of the present invention includes, in order from the object side, a first lens having a positive refractive power, a second lens having a negative refractive power, and a positive lens. It consists of a third lens having a refractive power, a fourth lens having a positive refractive power, and a fifth lens having a negative refractive power, and a stop is disposed closest to the object side, and satisfies the following conditional expression (1): Features.
−4.0 <(r6 + r7) / (r6-r7) <− 0.51 (1)
However,
r6 is the paraxial radius of curvature of the object side surface of the third lens,
r7 is the paraxial radius of curvature of the image side surface of the third lens,
It is.

Moreover, according to the preferable aspect of this invention, it is desirable to satisfy the following conditional expressions (2).
1.21 <φL5edmax / φst <6.52 (2)
However,
φL5edmax is the effective diameter of the fifth lens,
φst is the aperture diameter,
It is.

Moreover, according to the preferable aspect of this invention, it is desirable to satisfy the following conditional expressions (3).
-10.8 <R9 / d9 <-1.6 (3)
However,
R9 is the paraxial radius of curvature of the image side surface of the fourth lens,
d9 is the air space on the optical axis of the fourth lens and the fifth lens,
It is.

  According to a preferred aspect of the present invention, it is desirable that the third lens is a meniscus lens having a convex surface directed toward the object side.

Moreover, according to a preferable aspect of the present invention, it is desirable that the following conditional expression (4) is satisfied.
-12.7 <r3 / f1 <-1.6 (4)
However,
r3 is the paraxial radius of curvature of the first lens image side surface,
f1 is the focal length of the first lens,
It is.

Moreover, according to the preferable aspect of this invention, it is desirable to satisfy the following conditional expressions (5).
1.3 <r7 / f (5)
However,
r7 is the paraxial radius of curvature of the third lens image side surface,
f is the focal length of the entire imaging optical system,
It is.

Moreover, according to the preferable aspect of this invention, it is desirable to satisfy the following conditional expressions (6).
0.4 <r6 / f <2.1 (6)
However,
r6 is the paraxial radius of curvature of the third lens object side surface,
f is the focal length of the entire imaging optical system,
It is.

Moreover, according to a preferable aspect of the present invention, it is desirable that the following conditional expression (7) is satisfied.
1.1 <f3 / f4 <7.6 (7)
However,
f3 is the focal length of the third lens,
f4 is the focal length of the fourth lens,
It is.

Moreover, according to the preferable aspect of this invention, it is desirable to satisfy the following conditional expressions (8).
1.0 <(r10 + r11) / (r10−r11) <3.4 (8)
However,
r10 is the paraxial radius of curvature of the object side surface of the fifth lens;
r11 is a paraxial radius of curvature of the image side surface of the fifth lens;
It is.

Moreover, according to a preferable aspect of the present invention, it is desirable that the following conditional expression (9) is satisfied.
0.4 <f1 / f <1.8 (9)
However,
f1 is the focal length of the first lens,
f is the focal length of the entire imaging optical system,
It is.

Moreover, according to the preferable aspect of this invention, it is desirable to satisfy the following conditional expressions (10).
−1.5 <f5 / f <−0.3 (10)
However,
f5 is the focal length of the fifth lens,
f is the focal length of the entire imaging optical system,
It is.

  According to a preferred aspect of the present invention, it is desirable that the first lens is a biconvex lens.

  According to a preferred aspect of the present invention, it is desirable that the second lens is a meniscus lens having a convex surface directed toward the object side.

  According to a preferred aspect of the present invention, it is desirable that the fourth lens is a meniscus lens having a concave surface facing the object side, and the shape of the object side surface is a concave shape from the central portion to the peripheral portion.

  In addition, an image pickup apparatus of the present invention includes the above-described image pickup optical system and an image pickup element.

  According to a preferred aspect of the present invention, it is desirable that the imaging optical system and the imaging element are integrated.

  According to a preferred aspect of the present invention, it is desirable that the imaging optical system is integrated with the autofocus mechanism.

  According to the present invention, there is provided an imaging optical system in which the overall length of the optical system is short, the lens diameter is kept small, and various aberrations, particularly coma aberration, are favorably corrected, while the optical system has a relatively small F number. The used imaging device can be provided.

It is sectional drawing which follows the optical axis which shows the optical structure at the time of infinity object point focusing of the imaging optical system concerning Example 1 of this invention. It is a figure which shows the spherical aberration (SA), astigmatism (AS), distortion aberration (DT), and lateral chromatic aberration (CC) at the time of an infinite object point focusing of the imaging optical system concerning Example 1. FIG. It is sectional drawing which follows the optical axis which shows the optical structure at the time of infinity object point focusing of the imaging optical system concerning Example 2 of this invention. It is a figure which shows the spherical aberration (SA), astigmatism (AS), distortion aberration (DT), and lateral chromatic aberration (CC) at the time of an infinite object point focusing of the imaging optical system concerning Example 2. FIG. It is sectional drawing which follows the optical axis which shows the optical structure at the time of infinity object point focusing of the imaging optical system concerning Example 3 of this invention. It is a figure which shows the spherical aberration (SA), astigmatism (AS), distortion aberration (DT), and lateral chromatic aberration (CC) at the time of an infinite object point focusing of the imaging optical system concerning Example 3. FIG. It is sectional drawing which follows the optical axis which shows the optical structure at the time of infinity object point focusing of the imaging optical system concerning Example 4 of this invention. It is a figure which shows the spherical aberration (SA), astigmatism (AS), distortion aberration (DT), and lateral chromatic aberration (CC) at the time of an infinite object point focusing of the imaging optical system concerning Example 4. FIG. It is sectional drawing which follows the optical axis which shows the optical structure at the time of infinity object point focusing of the imaging optical system concerning Example 5 of this invention. It is a figure which shows the spherical aberration (SA), astigmatism (AS), distortion aberration (DT), and lateral chromatic aberration (CC) at the time of an infinite object point focusing of the imaging optical system concerning Example 5. FIG. It is a front perspective view which shows the external appearance of the digital camera 40 incorporating the optical system by this invention. 2 is a rear perspective view of the digital camera 40. FIG. 2 is a cross-sectional view showing an optical configuration of a digital camera 40. FIG. 1 is a front perspective view of a state in which a cover of a personal computer 300 that is an example of an information processing apparatus in which an optical system of the present invention is incorporated as an objective optical system is opened. FIG. 2 is a cross-sectional view of a photographing optical system 303 of a personal computer 300. FIG. 2 is a side view of a personal computer 300. FIG. 1A and 1B are diagrams showing a mobile phone that is an example of an information processing apparatus in which the optical system of the present invention is built in as a photographing optical system. FIG. 3A is a front view of the mobile phone 400, FIG. 2 is a cross-sectional view of a photographing optical system 405. FIG.

The imaging optical system of the embodiment will be described. The imaging optical system according to the present embodiment includes, in order from the object side, a first lens having a positive refractive power, a second lens having a negative refractive power, a third lens having a positive refractive power, and a positive refractive power. It consists of a fourth lens and a fifth lens having a negative refractive power, and is characterized in that the stop is disposed closest to the object side and satisfies the following conditional expression (1).
−4.0 <(r6 + r7) / (r6-r7) <− 0.51 (1)
However,
r6 is the paraxial radius of curvature of the object side surface of the third lens,
r7 is the paraxial radius of curvature of the image side surface of the third lens,
It is.

  In the imaging optical system of the present embodiment, the refractive power arrangement is positive / negative / positive / positive / negative in order from the object side. By adopting such a refractive power arrangement, the position of the principal point of the imaging optical system can be positioned on the object side. As a result, the total length of the optical system can be sufficiently shortened with respect to the focal length of the entire imaging optical system, so that the total length of the optical system can be shortened.

  Moreover, the fourth lens has a positive refracting power, and the optical system is composed of a total of five lenses, so that the divergence of the off-axis light beam can be suppressed by the fourth lens. Therefore, the diameter of the fifth lens can be reduced while ensuring the telecentricity of the optical system.

  In the imaging optical system of the present embodiment, the exit pupil can be separated from the image plane by disposing the stop closest to the object side. As a result, the effective diameter of the lens can be reduced while ensuring the telecentricity of the optical system.

  Furthermore, the imaging optical system of the present embodiment satisfies the conditional expression (1). Conditional expression (1) is a preferable conditional expression for satisfactorily correcting coma aberration while shortening the total length of the optical system when the F-number is reduced. By satisfying conditional expression (1), in the optical system with a small F-number, the total length of the optical system can be shortened, and coma can be corrected well.

  When the object side surface of the third lens is convex and falls below the lower limit value of the conditional expression (1), the radius of curvature of the image side surface of the third lens decreases and the positive refractive power decreases. The refractive power becomes too strong. As a result, since the principal point position is located on the image side, it is difficult to shorten the overall length of the optical system. If the upper limit of conditional expression (1) is exceeded, the negative refractive power on the image side surface of the third lens will be small. As a result, since the incident angle of the off-axis light beam on the side surface of the third lens image is increased, it is difficult to correct the coma aberration.

Here, it is preferable that the following conditional expression (1 ′) is satisfied instead of conditional expression (1).
-2.6 <(r6 + r7) / (r6-r7) <-0.8 (1 ')
Further, it is more preferable to satisfy the following conditional expression (1 ″) instead of conditional expression (1).
-2.2 <(r6 + r7) / (r6-r7) <-1 (1 ")

Moreover, it is preferable that the imaging optical system of this embodiment satisfies the following conditional expression (2).
1.21 <φL5edmax / φst <6.52 (2)
However,
φL5edmax is the effective diameter of the fifth lens,
φst is the aperture diameter,
It is.

  Conditional expression (2) is a conditional expression regarding the effective diameter and aperture diameter of the fifth lens, and is a preferable conditional expression for satisfactorily correcting the downsizing of the optical system and the curvature of field. By satisfying the conditional expression (2), it is possible to reduce the size of the optical system and correct the field curvature.

  When the upper limit value of conditional expression (2) is exceeded, the effective diameter of the fifth lens becomes larger than the aperture diameter. In this case, it becomes easy to ensure telecentricity, but it is difficult to reduce the size of the optical system. If the lower limit of conditional expression (2) is not reached, the effective diameter of the fifth lens becomes smaller than the aperture diameter. In this case, since the interval between the on-axis light beam and the off-axis light beam in the fifth lens is narrowed, it becomes difficult to correct coma and distortion, particularly field curvature.

Here, it is preferable that the following conditional expression (2 ′) is satisfied instead of conditional expression (2).
1.86 <φL5edmax / φst <4.24 (2 ′)
Further, it is more preferable that the following conditional expression (2 ″) is satisfied instead of conditional expression (2).
2.20 <φL5edmax / φst <3.59 (2 ″)

Conditional expression (2) can be expressed by using the lens diameter of the fifth lens instead of the effective diameter of the fifth lens. In this case, it is preferable that the imaging optical system of the present embodiment satisfies the following conditional expression (2-1).
1.41 <φL5max / φst <6.72 (2-1)
However,
φL5max is the diameter of the fifth lens,
φst is the aperture diameter,
It is.

  The effect of conditional expression (2-1) is the same as that of conditional expression (2).

Here, it is preferable that the following conditional expression (2-1 ′) is satisfied instead of conditional expression (2-1).
2.06 <φL5max / φst <4.44 (2-1 ′)
Moreover, it is more preferable to satisfy the following conditional expression (2-1 ″) instead of conditional expression (2-1).
2.40 <φL5max / φst <3.79 (2-1 ”)

Moreover, it is preferable that the imaging optical system of this embodiment satisfies the following conditional expression (3).
-10.8 <R9 / d9 <-1.6 (3)
However,
R9 is the paraxial radius of curvature of the image side surface of the fourth lens,
d9 is the air space on the optical axis of the fourth lens and the fifth lens,
It is.

  Conditional expression (3) is a conditional expression regarding the paraxial curvature radius of the image side surface of the fourth lens and the air space on the optical axis of the fourth lens and the fifth lens, and is a preferable conditional expression for favorably correcting the aberration. It is. By satisfying conditional expression (3), the occurrence of coma, astigmatism, field curvature, and distortion can be corrected satisfactorily.

  When the upper limit of conditional expression (3) is exceeded, the air space between the fourth lens and the fifth lens becomes small. Here, if it is considered that an air lens exists between the fourth lens and the fifth lens, the refractive power of the air lens becomes weak, so that it is difficult to satisfactorily correct field curvature and distortion. Below the lower limit of conditional expression (3), the paraxial radius of curvature of the image side surface of the fourth lens becomes smaller. In this case, since the angle of the incident light ray on the image side surface of the fourth lens becomes large, coma occurs, and astigmatism cannot be sufficiently corrected.

Here, it is preferable that the following conditional expression (3 ′) is satisfied instead of conditional expression (3).
−7.0 <R9 / d9 <−2.4 (3 ′)
Further, it is more preferable that the following conditional expression (3 ″) is satisfied instead of conditional expression (3).
−5.9 <R9 / d9 <−2.8 (3 ″)

  In the imaging optical system of the present embodiment, the third lens is preferably a meniscus lens having a convex surface directed toward the object side. When the optical system has a large aperture, the occurrence of axial chromatic aberration becomes significant. Therefore, by making the third lens into a meniscus shape with the convex surface facing the object side, axial chromatic aberration can be corrected well even if the optical system has a large aperture.

Moreover, it is preferable that the imaging optical system of this embodiment satisfies the following conditional expression (4).
-12.7 <r3 / f1 <-1.6 (4)
However,
r3 is the paraxial radius of curvature of the first lens image side surface,
f1 is the focal length of the first lens,
It is.

  Conditional expression (4) is a preferable conditional expression for satisfactorily correcting spherical aberration and coma. By satisfying conditional expression (4), spherical aberration and coma aberration can be favorably corrected.

  If the upper limit of conditional expression (4) is exceeded, the paraxial radius of curvature of the image side surface of the first lens will be too small. In this case, since the incident angle of the off-axis light beam on the first lens image side surface becomes steep, correction of coma becomes difficult. If the lower limit value of conditional expression (4) is not reached, the paraxial radius of curvature of the image side surface of the first lens becomes large, making it difficult to correct spherical aberration.

Here, it is preferable to satisfy the following conditional expression (4 ′) instead of conditional expression (4).
−8.3 <r3 / f1 <−2.6 (4 ′)
It is more preferable to satisfy the following conditional expression (4 ″) instead of conditional expression (4).
−7.0 <r3 / f1 <−3.0 (4 ″)

Moreover, it is preferable that the imaging optical system of this embodiment satisfies the following conditional expression (5).
1.3 <r7 / f (5)
However,
r7 is the paraxial radius of curvature of the third lens image side surface,
f is the focal length of the entire imaging optical system,
It is.

  Conditional expression (5) is a preferable conditional expression for correcting various aberrations, particularly coma, while shortening the overall length of the optical system. By satisfying conditional expression (5), coma can be corrected well.

  When the upper limit of conditional expression (5) is exceeded, the paraxial radius of curvature of the image side surface of the third lens increases. Here, in order to shorten the overall length of the optical system, if the distance between the second lens and the third lens is reduced, the image side surface of the second lens is a concave surface, so the periphery of the second lens and the third lens. The interval at the part is too small. For this reason, since the shape of the image side surface of the second lens and the shape of the object side surface of the third lens are limited, it is difficult to correct aberrations, particularly coma. Below the lower limit of conditional expression (5), the paraxial radius of curvature of the image side surface of the third lens becomes small. In this case, since the light incident angle on the object side surface of the third lens becomes steep, the coma aberration generated in the third lens becomes large.

Here, it is preferable that the following conditional expression (5 ′) is satisfied instead of conditional expression (5).
2.1 <r7 / f <133.3 (5 ′)
Further, it is more preferable that the following conditional expression (5 ″) is satisfied instead of conditional expression (5).
2.5 <r7 / f <112.8 (5 ")

Moreover, it is preferable that the imaging optical system of this embodiment satisfies the following conditional expression (6).
0.4 <r6 / f <2.1 (6)
However,
r6 is the paraxial radius of curvature of the third lens object side surface,
f is the focal length of the entire imaging optical system,
It is.

  Conditional expression (6) is a preferable conditional expression for correcting various aberrations, particularly coma, while shortening the total length of the optical system. By satisfying conditional expression (6), it is possible to correct various aberrations, particularly coma, while shortening the overall length of the optical system.

  If the upper limit of conditional expression (6) is exceeded, the paraxial radius of curvature of the object side surface of the third lens will increase. Here, when the image side surface of the second lens is a concave surface on the image side, the distance between the second lens and the third lens in the peripheral portion is narrowed. Therefore, if an attempt is made to reduce the distance between the second lens and the third lens in order to shorten the overall length of the optical system, the shape of the image side surface of the second lens and the shape of the object side surface of the third lens are limited. It becomes difficult to correct aberrations, particularly coma. If the lower limit value of conditional expression (6) is not reached, the paraxial radius of curvature of the object side surface of the third lens becomes small. In this case, since the incident angle of the light beam on the object side surface of the third lens becomes steep, coma aberration generated in the third lens increases.

Here, it is preferable to satisfy the following conditional expression (6 ′) instead of conditional expression (6).
0.7 <r6 / f <1.4 (6 ′)
It is more preferable to satisfy the following conditional expression (6 ″) instead of conditional expression (6).
0.8 <r6 / f <1.1 (6 ")

Moreover, it is preferable that the imaging optical system of this embodiment satisfies the following conditional expression (7).
1.1 <f3 / f4 <7.6 (7)
However,
f3 is the focal length of the third lens,
f4 is the focal length of the fourth lens,
It is.

  Conditional expression (7) is a preferable conditional expression for appropriately distributing the refractive power distribution of the third lens and the fourth lens. By satisfying conditional expression (7), the refractive power distribution of the third lens and the fourth lens can be made appropriate. As a result, it is possible to satisfactorily correct the aberration of the off-axis light beam and to mitigate the deterioration of the eccentric sensitivity due to the shortening of the total length of the optical system.

  If the upper limit value of conditional expression (7) is exceeded, the refractive power of the fourth lens will be too large compared to the third lens. As a result, since the refractive power is biased toward the fourth lens, the manufacturing error sensitivity of the fourth lens is increased. If the lower limit value of conditional expression (7) is not reached, the refractive power of the third lens becomes large, and the exit angle of the off-axis light beam emitted from the third lens becomes small. For this reason, the height of the light beam cannot be sufficiently increased in the fourth lens. In this case, the difference in beam height between the off-axis light beam in the third lens and the off-axis light beam in the fourth lens becomes small. As a result, it becomes difficult to correct coma and higher-order field curvature.

Here, it is preferable that the following conditional expression (7 ′) is satisfied instead of conditional expression (7).
1.7 <f3 / f4 <5.0 (7 ′)
Further, it is more preferable to satisfy the following conditional expression (7 ″) instead of conditional expression (7).
2.0 <f3 / f4 <4.2 (7 ")

Moreover, it is preferable that the imaging optical system of this embodiment satisfies the following conditional expression (8).
1.0 <(r10 + r11) / (r10−r11) <3.4 (8)
However,
r10 is the paraxial radius of curvature of the object side surface of the fifth lens;
r11 is a paraxial radius of curvature of the image side surface of the fifth lens;
It is.

  Conditional expression (8) is a preferable conditional expression for reducing the size of the fifth lens, maintaining the telecentricity of the optical system, and correcting the coma aberration satisfactorily. If the conditional expression (8) is satisfied, the distance between the fifth lens and the image plane in the periphery of the image plane can be sufficiently secured, so that the telecentricity of the optical system can be maintained. In addition, the effective diameter of the fifth lens can be reduced, and coma can be corrected well.

  If the upper limit value of conditional expression (8) is exceeded, the position of the principal point of the fifth lens will be closer to the object side, and the back focus length will be shortened. As a result, it becomes difficult to reduce the effective diameter of the fifth lens while maintaining the telecentricity of the optical system. If the lower limit value of conditional expression (8) is not reached, the paraxial radius of curvature of the image side surface of the fifth lens becomes smaller. In this case, since the incident angle of the off-axis light beam with respect to the image side surface of the fifth lens becomes large, it is difficult to correct coma.

Here, it is preferable that the following conditional expression (8 ′) is satisfied instead of conditional expression (8).
1.1 <(r10 + r11) / (r10−r11) <2.2 (8 ′)
Further, it is more preferable that the following conditional expression (8 ″) is satisfied instead of conditional expression (8).
1.3 <(r10 + r11) / (r10-r11) <1.9 (8 ")

Moreover, it is preferable that the imaging optical system of this embodiment satisfies the following conditional expression (9).
0.4 <f1 / f <1.8 (9)
However,
f1 is the focal length of the first lens,
f is the focal length of the entire imaging optical system,
It is.

  Conditional expression (9) is a preferable condition for shortening the overall length of the optical system and achieving good aberration correction. By satisfying conditional expression (9), various aberrations can be favorably corrected while shortening the total length of the optical system.

  If the upper limit of conditional expression (9) is exceeded, the refractive power of the first lens will be weakened, making it difficult to shorten the overall length of the optical system. If the lower limit of conditional expression (9) is not reached, the refractive power of the first lens will become strong, and various aberrations will increase, making it difficult to correct aberrations. Also, the manufacturing sensitivity is lowered.

Here, it is preferable that the following conditional expression (9 ′) is satisfied instead of conditional expression (9).
0.6 <f1 / f <1.2 (9 ′)
Further, it is more preferable that the following conditional expression (9 ″) is satisfied instead of conditional expression (9).
0.7 <f1 / f <1.0 (9 ")

Moreover, it is preferable that the imaging optical system of this embodiment satisfies the following conditional expression (10).
−1.5 <f5 / f <−0.3 (10)
However,
f5 is the focal length of the fifth lens,
f is the focal length of the entire imaging optical system,
It is.

  Conditional expression (10) is a preferable condition for correcting various aberrations, particularly lateral chromatic aberration, while shortening the overall length of the optical system. By satisfying conditional expression (10), it is possible to satisfactorily correct lateral chromatic aberration while shortening the overall length of the optical system.

  If the upper limit value of conditional expression (10) is exceeded, the negative refractive power of the fifth lens will become weak. In this case, since it becomes difficult to position the principal point on the object side of the optical system, it becomes difficult to shorten the entire length of the optical system. If the lower limit value of conditional expression (10) is not reached, the negative refractive power of the fifth lens becomes strong, so that it is difficult to correct various aberrations generated from the first lens to the fourth lens, particularly lateral chromatic aberration. .

Here, it is preferable that the following conditional expression (10 ′) is satisfied instead of conditional expression (10).
−0.9 <f5 / f <−0.5 (10 ′)
Further, it is more preferable that the following conditional expression (10 ″) is satisfied instead of conditional expression (10).
−0.8 <f5 / f <−0.6 (10 ″)

  In the imaging optical system of the present embodiment, the first lens is preferably a biconvex lens. By making the shape of the first lens a biconvex shape, the occurrence of coma aberration is reduced and the overall length of the optical system can be shortened.

  In the imaging optical system of the present embodiment, the second lens is preferably a meniscus lens having a convex surface directed toward the object side. By making the shape of the second lens a meniscus shape with a convex surface facing the object side, chromatic aberration can be corrected well, and off-axis aberrations such as coma and curvature of field can be corrected well.

  In the imaging optical system of the present embodiment, it is preferable that the fourth lens is a meniscus lens having a concave surface facing the object side, and the shape of the object side surface is a concave shape from the central portion to the peripheral portion. By making the shape of the fourth lens into a meniscus shape with the concave surface facing the object side, the occurrence of coma aberration can be suppressed.

  Moreover, it is preferable that the imaging apparatus of this embodiment is provided with said imaging optical system and an image pick-up element. Although the optical system has a relatively small F number, it is possible to realize an imaging apparatus using an imaging optical system in which the overall length of the optical system is short, the lens diameter is kept small, and various aberrations, particularly coma aberration, are well corrected.

  In the imaging apparatus of the present embodiment, it is preferable that the imaging optical system and the imaging element are integrated. By integrating the imaging optical system and the imaging element, an optical image by the imaging optical system can be converted into an electrical signal. In addition, by selecting an electronic image sensor that can reduce the change in image brightness between the center and the periphery of the image, a small and high-performance imaging device can be provided.

  In the imaging apparatus of the present embodiment, it is preferable that the imaging optical system is integrated with the autofocus mechanism. By integrating the autofocus mechanism, it is possible to focus at any subject distance.

  Hereinafter, embodiments of an imaging optical system and an imaging apparatus will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments. Further, the positive / negative of the refractive power is based on the paraxial radius of curvature. Further, the stop (the aperture stop in the embodiment) is located closest to the object side. However, as described above, the stop is located on the object side of the image side surface of the first lens, more specifically, between the object side surface and the image side surface of the first lens. It is assumed that such a diaphragm position is also included in “arrange the diaphragm closest to the object”.

  Next, the image pickup optical system according to the first embodiment will be described. FIG. 1 is a cross-sectional view along the optical axis showing the optical configuration of the imaging optical system according to the first embodiment when focusing on an object point at infinity.

  FIG. 2 is a diagram illustrating spherical aberration (SA), astigmatism (AS), distortion (DT), and lateral chromatic aberration (CC) when the imaging optical system according to the example 1 is focused on an object point at infinity. FIY represents the image height. The symbols in the aberration diagrams are the same in the examples described later.

  As shown in FIG. 1, the imaging optical system according to the first embodiment has an aperture stop S, a first lens L1 having a positive refractive power, a second lens L2 having a negative refractive power, and a positive refractive power in order from the object side. It has a third lens L3, a fourth lens L4 having a positive refractive power, and a fifth lens L5 having a negative refractive power. In all the following examples, CG represents a cover glass and I represents an image pickup surface of an image pickup element in the lens cross section.

  The first lens L1 is a biconvex positive lens. The second lens L2 is a negative meniscus lens having a convex surface facing the object side. The third lens L3 is a positive meniscus lens having a convex surface facing the object side. The fourth lens L4 is a positive meniscus lens having a convex surface facing the image side. The fifth lens L5 is a negative meniscus lens having a convex surface facing the object side.

  The aspheric surfaces are provided on both surfaces of all of the first lens L1 to the fifth lens L5.

  Next, an imaging optical system according to Example 2 will be described. FIG. 3 is a cross-sectional view along the optical axis showing the optical configuration of the imaging optical system according to the second embodiment when focusing on an object point at infinity.

  FIG. 4 is a diagram illustrating spherical aberration (SA), astigmatism (AS), distortion (DT), and lateral chromatic aberration (CC) when the imaging optical system according to the example 2 is focused on an object point at infinity.

  As shown in FIG. 3, the imaging optical system according to the second embodiment has an aperture stop S, a first lens L1 having a positive refractive power, a second lens L2 having a negative refractive power, and a positive refractive power in order from the object side. It has a third lens L3, a fourth lens L4 having a positive refractive power, and a fifth lens L5 having a negative refractive power.

  The first lens L1 is a biconvex positive lens. The second lens L2 is a negative meniscus lens having a convex surface facing the object side. The third lens L3 is a positive meniscus lens having a convex surface facing the object side. The fourth lens L4 is a positive meniscus lens having a convex surface facing the image side. The fifth lens L5 is a negative meniscus lens having a convex surface facing the object side.

  The aspheric surfaces are provided on both surfaces of all of the first lens L1 to the fifth lens L5.

  Next, an imaging optical system according to Example 3 will be described. FIG. 5 is a cross-sectional view along the optical axis showing the optical configuration of the imaging optical system according to the third embodiment when focusing on an object point at infinity.

  FIG. 6 is a diagram illustrating spherical aberration (SA), astigmatism (AS), distortion (DT), and lateral chromatic aberration (CC) when the imaging optical system according to the example 3 is focused on an object point at infinity.

  As shown in FIG. 5, the imaging optical system according to the third embodiment has an aperture stop S, a first lens L1 having a positive refractive power, a second lens L2 having a negative refractive power, and a positive refractive power in order from the object side. It has a third lens L3, a fourth lens L4 having a positive refractive power, and a fifth lens L5 having a negative refractive power.

  The first lens L1 is a biconvex positive lens. The second lens L2 is a negative meniscus lens having a convex surface facing the object side. The third lens L3 is a positive meniscus lens having a convex surface facing the object side. The fourth lens L4 is a positive meniscus lens having a convex surface facing the image side. The fifth lens L5 is a negative meniscus lens having a convex surface facing the object side.

  The aspheric surfaces are provided on both surfaces of all of the first lens L1 to the fifth lens L5.

  Next, an imaging optical system according to Example 4 will be described. FIG. 7 is a cross-sectional view along the optical axis showing the optical configuration of the imaging optical system according to the fourth example when focusing on an object point at infinity.

  FIG. 8 is a diagram illustrating spherical aberration (SA), astigmatism (AS), distortion (DT), and lateral chromatic aberration (CC) when the imaging optical system according to the example 4 is focused on an object point at infinity.

  As shown in FIG. 7, the imaging optical system according to the fourth embodiment has an aperture stop S, a first lens L1 having a positive refractive power, a second lens L2 having a negative refractive power, and a positive refractive power in order from the object side. It has a third lens L3, a fourth lens L4 having a positive refractive power, and a fifth lens L5 having a negative refractive power.

  The first lens L1 is a biconvex positive lens. The second lens L2 is a negative meniscus lens having a convex surface facing the object side. The third lens L3 is a positive meniscus lens having a convex surface facing the object side. The fourth lens L4 is a positive meniscus lens having a convex surface facing the image side. The fifth lens L5 is a negative meniscus lens having a convex surface facing the object side.

  The aspheric surfaces are provided on both surfaces of all of the first lens L1 to the fifth lens L5.

  Next, an imaging optical system according to Example 5 will be described. FIG. 9 is a cross-sectional view along the optical axis showing the optical configuration of the imaging optical system according to the fifth example when focusing on an object point at infinity.

  FIG. 10 is a diagram illustrating spherical aberration (SA), astigmatism (AS), distortion (DT), and lateral chromatic aberration (CC) when the imaging optical system according to the fifth example is focused on an object point at infinity.

  As shown in FIG. 9, the imaging optical system according to the fifth embodiment has an aperture stop S, a first lens L1 having a positive refractive power, a second lens L2 having a negative refractive power, and a positive refractive power in order from the object side. It has a third lens L3, a fourth lens L4 having a positive refractive power, and a fifth lens L5 having a negative refractive power.

  The first lens L1 is a biconvex positive lens. The second lens L2 is a negative meniscus lens having a convex surface facing the object side. The third lens L3 is a positive meniscus lens having a convex surface facing the object side. The fourth lens L4 is a positive meniscus lens having a convex surface facing the image side. The fifth lens L5 is a negative meniscus lens having a convex surface facing the object side.

  The aspheric surfaces are provided on both surfaces of all the lenses of the first lens L1 to the fifth lens L5.

  Next, numerical data of optical members constituting the imaging optical system of each of the above embodiments will be listed. In the numerical data of each embodiment, r1, r2,... Are the curvature radii of the lens surfaces, d1, d2,... Are the thickness or air spacing of each lens, and nd1, nd2,. Are the Abbe number of each lens, Fno. Indicates the F number, f indicates the focal length of the entire system, and * indicates an aspherical surface.

The aspherical shape is expressed by the following equation when the optical axis direction is z, the direction orthogonal to the optical axis is y, the conical coefficient is K, and the aspherical coefficients are A4, A6, A8, and A10. .
z = (y ² / r) / [1+ {1− (1 + K) (y / r) ² } ^1/2 ]
+ A4y ⁴ + A6y ⁶ + A8y ⁸ + A10y ¹⁰
E represents a power of 10. The symbols of these specification values are common to the numerical data of the examples described later.

Numerical example 1
Unit mm

Surface data Surface number rd nd νd
1 (Aperture) ∞ 0.00
2 * 1.899 0.58 1.53463 56.22
3 * -14.108 0.11
4 * 5.542 0.30 1.61417 25.64
5 * 1.608 0.26
6 * 3.352 0.44 1.53463 56.22
7 * 13.743 0.52
8 * -2.408 0.58 1.53463 56.22
9 * -0.976 0.28
10 * 7.126 0.49 1.53463 56.22
11 * 1.124 0.64
12 ∞ 0.30 1.51633 64.14
13 ∞ Variable
Image plane ∞ 0.

Aspheric data 2nd surface
K = -0.881
A4 = 1.12361e-02, A6 = 9.43523e-03, A8 = 1.63446e-03, A10 = -9.07244e-03
Third side
K = -9.467
A4 = -1.80144e-02, A6 = 1.30386e-01, A8 = -1.72430e-01, A10 = 6.26790e-02
4th page
K = -111.241
A4 = -9.47939e-02, A6 = 2.85846e-01, A8 = -3.68682e-01, A10 = 1.54520e-01
5th page
K = -8.353
A4 = 1.25573e-03, A6 = 1.68775e-01, A8 = -2.03500e-01, A10 = 7.82501e-02
A12 = 3.79830e-04
6th page
K = -34.149
A4 = 2.96394e-02, A6 = -7.12671e-02, A8 = 8.63678e-02, A10 = -2.96344e-02
7th page
K = -75.222
A4 = -7.45335e-03, A6 = -1.17206e-02, A8 = -1.86648e-02, A10 = 1.51514e-02
8th page
K = -0.475
A4 = -8.25793e-03, A6 = 3.60363e-02, A8 = -1.56741e-02, A10 = -4.83613e-03,
A12 = 9.31825e-04
9th page
K = -2.258
A4 = -1.52094e-02, A6 = -1.06658e-02, A8 = 2.63124e-02, A10 = -5.33786e-03,
A12 = -4.77232e-04
10th page
K = -578.778
A4 = -4.00372e-02, A6 = 6.31511e-03, A8 = 4.42722e-04, A10 = -1.48309e-04,
A12 = 7.78440e-06, A14 = -1.91115e-09
11th page
K = -7.065
A4 = -4.94843e-02, A6 = 1.19528e-02, A8 = -2.45907e-03, A10 = 2.22435e-04,
A12 = -5.53516e-06, A14 = -1.13545e-07

Various image heights 2.9
fb (in air) 1.21
Total length (in air) 4.76

Focal length
f = 3.82

Numerical example 2
Unit mm

Surface data Surface number rd nd νd
1 (Aperture) ∞ -0.21
2 * 2.466 0.82 1.53463 56.22
3 * -17.844 0.13
4 * 7.183 0.30 1.61417 25.64
5 * 2.175 0.46
6 * 5.332 0.63 1.53463 56.22
7 * 28.938 0.81
8 * -2.856 0.64 1.53463 56.22
9 * -1.315 0.26
10 * 9.157 0.87 1.53463 56.22
11 * 1.575 0.86
12 ∞ 0.30 1.51633 64.14
13 ∞ 0.47
Image plane ∞ 0.

Aspheric data 2nd surface
K = -0.865
A4 = 4.98470e-03, A6 = 1.70004e-03, A8 = -2.33550e-05, A10 = -6.65461e-04
Third side
K = -74.210
A4 = -6.69903e-03, A6 = 2.93033e-02, A8 = -2.36324e-02, A10 = 4.79004e-03
4th page
K = -121.991
A4 = -3.91275e-02, A6 = 6.97216e-02, A8 = -4.85969e-02, A10 = 1.08383e-02
5th page
K = -8.352
A4 = 1.42166e-03, A6 = 4.17708e-02, A8 = -2.61007e-02, A10 = 5.50884e-03
6th page
K = -45.007
A4 = 1.22715e-02, A6 = -1.95254e-02, A8 = 9.76919e-03, A10 = -1.50533e-03
7th page
K = -620.583
A4 = -4.84435e-03, A6 = -2.75959e-03, A8 = -2.93339e-03, A10 = 7.95875e-04
8th page
K = 0.084
A4 = -7.53214e-03, A6 = 8.40059e-03, A8 = -1.70900e-03, A10 = -2.73910e-04,
A12 = -4.70115e-05
9th page
K = -1.888
A4 = -7.41935e-03, A6 = -3.19839e-03, A8 = 3.26570e-03, A10 = -4.51553e-04,
A12 = -7.44909e-06
10th page
K = -367.084
A4 = -1.66804e-02, A6 = 1.59274e-03, A8 = 4.94652e-05, A10 = -1.48995e-05,
A12 = -1.28361e-07, A14 = 2.97799e-08
11th page
K = -6.595
A4 = -1.86693e-02, A6 = 2.62509e-03, A8 = -2.99140e-04, A10 = 1.64284e-05,
A12 = -3.17449e-07, A14 = -7.92194e-09

Various image heights 3.8
fb (in air) 1.52
Total length (in air) 6.45

Focal length
f = 5.13

Numerical Example 3
Unit mm

Surface data Surface number rd nd νd
1 (Aperture) ∞ -0.21
2 * 2.467 0.76 1.53463 56.22
3 * -18.189 0.14
4 * 7.242 0.31 1.61417 25.64
5 * 2.179 0.47
6 * 5.215 0.60 1.53463 56.22
7 * 26.025 0.82
8 * -2.810 0.69 1.53463 56.22
9 * -1.305 0.24
10 * 7.730 0.89 1.53463 56.22
11 * 1.519 0.86
12 ∞ 0.30 1.51633 64.14
13 ∞ 0.49
Image plane ∞ 0.

Aspheric data 2nd surface
K = -0.815
A4 = 5.45292e-03, A6 = 1.44720e-03, A8 = 6.89583e-05, A10 = -5.42168e-04
Third side
K = -93.607
A4 = -6.37568e-03, A6 = 2.95462e-02, A8 = -2.32960e-02, A10 = 4.92034e-03
4th page
K = -116.116
A4 = -3.87946e-02, A6 = 6.99601e-02, A8 = -4.86438e-02, A10 = 1.09437e-02
5th page
K = -8.295
A4 = 1.93077e-03, A6 = 4.17066e-02, A8 = -2.63609e-02, A10 = 5.54659e-03
6th page
K = -45.445
A4 = 1.22938e-02, A6 = -1.94574e-02, A8 = 9.77219e-03, A10 = -1.49434e-03
7th page
K = -661.852
A4 = -4.70020e-03, A6 = -2.60080e-03, A8 = -2.84935e-03, A10 = 8.45016e-04
8th page
K = 0.054
A4 = -7.50810e-03, A6 = 8.58817e-03, A8 = -1.65161e-03, A10 = -2.51153e-04,
A12 = -3.83267e-05
9th page
K = -1.883
A4 = -8.16929e-03, A6 = -3.29436e-03, A8 = 3.27140e-03, A10 = -4.47868e-04,
A12 = -4.63228e-06
10th page
K = -232.895
A4 = -1.64616e-02, A6 = 1.62192e-03, A8 = 5.08558e-05, A10 = -1.64509e-05,
A12 = -3.29742e-07, A14 = 6.89537e-08
11th page
K = -6.364
A4 = -1.93238e-02, A6 = 2.69864e-03, A8 = -3.00378e-04, A10 = 1.63198e-05,
A12 = -3.42117e-07, A14 = -7.20261e-09

Various image heights 3.9
fb (in air) 1.55
Total length (in air) 6.47

Focal length
f = 5.11

Numerical Example 4
Unit mm

Surface data Surface number rd nd νd
1 (Aperture) ∞ -0.18
2 * 2.741 0.52 1.53463 56.22
3 * -14.448 0.20
4 * 4.952 0.30 1.61417 25.64
5 * 1.812 0.25
6 * 4.282 0.59 1.53463 56.22
7 * 500.000 0.84
8 * -2.262 0.70 1.53463 56.22
9 * -1.153 0.37
10 * 5.007 0.61 1.53463 56.22
11 * 1.320 0.75
12 ∞ 0.30 1.51633 64.14
13 ∞ 0.80
Image plane ∞ 0.

Aspheric data 2nd surface
K = -1.279
A4 = -1.79037e-03, A6 = -8.03611e-04, A8 = 1.02410e-03
Third side
K = -6.609
A4 = -1.57927e-02, A6 = 5.05025e-02, A8 = -4.07441e-02, A10 = 1.26222e-02
4th page
K = -64.772
A4 = -6.44405e-02, A6 = 1.49442e-01, A8 = -1.18136e-01, A10 = 3.30511e-02
5th page
K = -8.807
A4 = -5.75049e-03, A6 = 7.65993e-02, A8 = -5.89296e-02, A10 = 1.36525e-02
6th page
K = -44.123
A4 = 3.34671e-02, A6 = -4.13955e-02, A8 = 3.10495e-02, A10 = -5.81840e-03,
A12 = -6.08447e-04
7th page
K = -531.932
A4 = 5.34756e-03, A6 = 2.51172e-03, A8 = -1.41412e-02, A10 = 6.90857e-03,
A12 = -3.90127e-04
8th page
K = -0.220
A4 = -1.30213e-02, A6 = 2.01165e-02, A8 = -3.29704e-03, A10 = -2.85694e-04,
A12 = -3.91144e-04, A14 = 8.96023e-05
9th page
K = -1.592
A4 = 1.24602e-03, A6 = -1.09644e-02, A8 = 7.49208e-03, A10 = -1.93250e-04,
A12 = -2.67655e-04, A14 = 1.30913e-05
10th page
K = -103.807
A4 = -2.01088e-02, A6 = 1.88936e-03, A8 = 2.03766e-04, A10 = -3.98138e-05,
A12 = 2.01700e-06, A14 = -2.88183e-08
11th page
K = -5.909
A4 = -2.77692e-02, A6 = 4.79349e-03, A8 = -6.73609e-04, A10 = 5.54594e-05,
A12 = -2.17374e-06, A14 = 2.81129e-08

Various image heights 3.9
fb (in air) 1.75
Total length (in air) 6.13

Focal length
f = 4.88

Numerical Example 5
Unit mm

Surface data Surface number rd nd νd
1 (Aperture) ∞ -0.31
2 * 1.780 0.62 1.53463 56.22
3 * -19.519 0.10
4 * 9.592 0.30 1.61417 25.64
5 * 1.880 0.28
6 * 3.592 0.43 1.53463 56.22
7 * 10.750 0.49
8 * -2.305 0.63 1.53463 56.22
9 * -0.949 0.27
10 * 5.894 0.43 1.53463 56.22
11 * 1.097 0.62
12 ∞ 0.30 1.51633 64.14
13 ∞ 0.47
Image plane ∞ 0.

Aspheric data 2nd surface
K = -0.947
A4 = 1.73926e-02, A6 = 1.73904e-02, A8 = -4.66447e-03
Third side
K = 0.076
A4 = -1.11541e-02, A6 = 1.72217e-01, A8 = -2.32228e-01, A10 = 8.61042e-02
4th page
K = -34.106
A4 = -1.02241e-01, A6 = 3.53432e-01, A8 = -4.68458e-01, A10 = 1.88533e-01
5th page
K = -8.046
A4 = -6.98161e-04, A6 = 2.11680e-01, A8 = -2.73586e-01, A10 = 1.15204e-01
6th page
K = -37.662
A4 = 2.04232e-02, A6 = -9.25024e-02, A8 = 8.94440e-02, A10 = -3.01788e-02
7th page
K = -94.854
A4 = -8.84589e-03, A6 = -1.83717e-02, A8 = -2.34008e-02, A10 = 1.35782e-02
8th page
K = -0.651
A4 = -4.37690e-03, A6 = 3.74029e-02, A8 = -1.63020e-02, A10 = -9.45924e-03,
A12 = 2.37869e-03
9th page
K = -2.207
A4 = -6.80801e-03, A6 = -2.32755e-02, A8 = 3.07158e-02, A10 = -7.09722e-03,
A12 = -2.22422e-04
10th page
K = -508.945
A4 = -3.78877e-02, A6 = 1.19698e-03, A8 = 1.02665e-03, A10 = -1.62292e-04,
A12 = 5.03180e-06
11th page
K = -7.412
A4 = -4.98596e-02, A6 = 1.19625e-02, A8 = -3.04503e-03, A10 = 3.63173e-04,
A12 = -1.93274e-05

Various image heights 2.9
fb (in air) 1.28
Total length (in air) 4.82

Focal length
f = 3.88

The values corresponding to the conditional expressions in each example are shown below.

[Conditional Expressions] Example 1 Example 2 Example 3 Example 4 Example 5
(r6 + r7) / (r6-r7) -1.65 -1.45 -1.50 -1.02 -2.00
R9 / d9 -3.51 -4.98 -5.39 -3.12 -3.51
r3 / f1 -4.47 -4.36 -4.44 -3.33 -6.36
r7 / f 3.60 5.65 5.10 102.52 2.77
r6 / f 0.88 1.04 1.02 0.88 0.93
f3 / f4 3.04 3.04 3.08 2.24 3.81
(r10 + r11) / (r10-r11) 1.37 1.42 1.49 1.72 1.46
f1 / f 0.83 0.80 0.80 0.89 0.79
f5 / f -0.67 -0.72 -0.73 -0.73 -0.67
φL5edmax / SDIA 2.74 2.60 2.64 3.26 2.42

  The imaging (imaging) optical system according to the present invention as described above is an example of an imaging apparatus that captures an image of an object with an electronic imaging element such as a CCD or CMOS, particularly a digital camera, video camera, or information processing apparatus. It can be used for personal computers, telephones, mobile terminals, especially mobile phones that are convenient to carry. The embodiment is illustrated below.

  FIGS. 11 to 13 are conceptual diagrams of a configuration in which the imaging optical system according to the present invention is incorporated in a photographing optical system 41 of a digital camera. 11 is a front perspective view showing the appearance of the digital camera 40, FIG. 12 is a rear perspective view thereof, and FIG. 13 is a cross-sectional view showing an optical configuration of the digital camera 40.

  In this example, the digital camera 40 includes a photographing optical system 41 having a photographing optical path 42, a finder optical system 43 having a finder optical path 44, a shutter 45, a flash 46, a liquid crystal display monitor 47, and the like. Then, when the photographer presses the shutter 45 disposed on the upper part of the camera 40, photographing is performed through the photographing optical system 41, for example, the imaging optical system 48 of the first embodiment in conjunction therewith.

  The object image formed by the photographing optical system 41 is formed on the image pickup surface of the CCD 49. The object image received by the CCD 49 is displayed as an electronic image on the liquid crystal display monitor 47 provided on the back of the camera via the image processing means 51. Further, the image processing means 51 is provided with a memory or the like, and can record a captured electronic image. This memory may be provided separately from the image processing means 51, or may be configured to perform recording and writing electronically using a flexible disk, memory card, MO, or the like.

  Further, a finder objective optical system 53 is disposed on the finder optical path 44. The finder objective optical system 53 includes a cover lens 54, a first prism 10, an aperture stop 2, a second prism 20, and a focusing lens 66. An object image is formed on the imaging surface 67 by the finder objective optical system 53. This object image is formed on the field frame 57 of the Porro prism 55 which is an image erecting member. Behind the Porro prism 55, an eyepiece optical system 59 for guiding the image formed into an erect image to the observer eyeball E is disposed.

According to the digital camera 40 configured as described above, an electronic imaging apparatus having a compact and thin imaging optical system in which the number of components of the photographing optical system 41 is reduced can be realized. The present invention is not limited to the above-described retractable digital camera, but can also be applied to a folding digital camera that employs a bending optical system.
Further, an autofocus mechanism 500 integrated with the photographing optical system 41 is provided. By mounting the autofocus mechanism 500, it is possible to focus at any subject distance.

In addition, it is desirable that the photographing optical system 41 and the electronic image sensor chip (electronic image sensor) are integrated.
By integrating the electronic image pickup element, an optical image obtained by the image pickup optical system can be converted into an electric signal. In addition, it is possible to provide a small and high-performance digital camera (imaging device) by selecting an electronic image sensor that can reduce a change in image brightness between the central portion and the peripheral portion of the image.

  Next, a personal computer which is an example of an information processing apparatus in which the imaging optical system of the present invention is incorporated as an objective optical system is shown in FIGS. 14 is a front perspective view of the personal computer 300 with the cover open, FIG. 15 is a sectional view of the photographing optical system 303 of the personal computer 300, and FIG. 16 is a side view of FIG. As shown in FIGS. 14 to 16, the personal computer 300 includes a keyboard 301, information processing means and recording means, a monitor 302, and a photographing optical system 303.

  Here, the keyboard 301 is for an operator to input information from the outside. The information processing means and recording means are not shown. The monitor 302 is for displaying information to the operator. The photographing optical system 303 is for photographing an image of the operator himself or a surrounding area. The monitor 302 may be a liquid crystal display element, a CRT display, or the like. Examples of the liquid crystal display element include a transmissive liquid crystal display element that illuminates from the back with a backlight (not shown), and a reflective liquid crystal display element that reflects and displays light from the front. Further, in the drawing, the photographing optical system 303 is built in the upper right of the monitor 302. However, the imaging optical system 303 is not limited to the place, and may be anywhere around the monitor 302 or the keyboard 301.

  The photographic optical system 303 includes, on the photographic optical path 304, the objective optical system 100 including, for example, the imaging optical system according to the first embodiment, and the electronic imaging element chip 162 that receives an image. These are built in the personal computer 300.

A cover glass 102 for protecting the objective optical system 100 is disposed at the tip of the mirror frame.
The object image received by the electronic image sensor chip 162 is input to the processing means of the personal computer 300 via the terminal 166. Finally, the object image is displayed on the monitor 302 as an electronic image. FIG. 14 shows an image 305 taken by the operator as an example. The image 305 can also be displayed on a communication partner's personal computer from a remote location via the processing means. The Internet and telephone are used for image transmission to remote places.
Further, an autofocus mechanism 500 integrated with the objective optical system 100 (imaging optical system) is provided. By mounting the autofocus mechanism 500, it is possible to focus at any subject distance.

It is desirable that the objective optical system 100 (imaging optical system) and the electronic imaging element chip 162 (electronic imaging element) are integrated.
By integrating the electronic image pickup element, an optical image obtained by the image pickup optical system can be converted into an electric signal. In addition, a small and high-performance personal computer (imaging device) can be provided by selecting an electronic imaging device that can reduce the change in image brightness between the central portion and the peripheral portion of the image.

  Next, FIG. 17 shows a telephone, which is an example of an information processing apparatus in which the imaging optical system of the present invention is incorporated as a photographing optical system, particularly a portable telephone that is convenient to carry. 17A is a front view of the mobile phone 400, FIG. 17B is a side view, and FIG. 17C is a cross-sectional view of the photographing optical system 405. As shown in FIGS. 17A to 17C, the mobile phone 400 includes a microphone unit 401, a speaker unit 402, an input dial 403, a monitor 404, a photographing optical system 405, an antenna 406, and processing. Means.

  Here, the microphone unit 401 is for inputting an operator's voice as information. The speaker unit 402 is for outputting the voice of the other party. An input dial 403 is used by an operator to input information. The monitor 404 is for displaying information such as a photographed image of the operator himself or the other party, a telephone number, and the like. The antenna 406 is for transmitting and receiving communication radio waves. The processing means (not shown) is for processing image information, communication information, input signals, and the like.

  Here, the monitor 404 is a liquid crystal display element. Further, in the drawing, the arrangement positions of the respective components, in particular, are not limited thereto. The photographing optical system 405 includes the objective optical system 100 disposed on the photographing optical path 407 and an electronic image sensor chip 162 that receives an object image. As the objective optical system 100, for example, the imaging optical system of Example 1 is used. These are built in the mobile phone 400.

A cover glass 102 for protecting the objective optical system 100 is disposed at the tip of the mirror frame.
The object image received by the electronic imaging element chip 162 is input to an image processing unit (not shown) via the terminal 166. Finally, the object image is displayed as an electronic image on the monitor 404, the monitor of the communication partner, or both. The processing means includes a signal processing function. When transmitting an image to a communication partner, this function converts information on the object image received by the electronic image sensor chip 162 into a signal that can be transmitted.
Further, an autofocus mechanism 500 integrated with the objective optical system 100 (imaging optical system) is provided. By mounting the autofocus mechanism 500, it is possible to focus at any subject distance.

Further, it is desirable to integrate the objective optical system 100 (imaging optical system) and the electronic imaging element chip 162 (electronic imaging element).
By integrating the electronic image pickup device, an optical image by the image pickup optical system can be converted into an electric signal. In addition, it is possible to provide a small and high-performance mobile phone (imaging device) by selecting an electronic imaging device that can reduce a change in image brightness between the central portion and the peripheral portion of the image.

  The present invention can take various modifications without departing from the spirit of the present invention.

  As described above, the present invention is suitable for an imaging optical system in which various aberrations, particularly coma aberration, are corrected well, and an imaging apparatus using the imaging optical system.

L1 1st lens L2 2nd lens L3 3rd lens L4 4th lens L5 5th lens CG Cover glass I Imaging surface S Aperture stop 40 Digital camera 41 Imaging optical system 42 Imaging optical path 43 Viewfinder optical system 44 Viewfinder optical path 45 Shutter 46 Flash 47 LCD monitor 48 Lens 49 CCD
DESCRIPTION OF SYMBOLS 50 Image pick-up surface 51 Processing means 53 Finder objective optical system 55 Porro prism 57 Field frame 59 Eyepiece optical system 66 Focusing lens 67 Imaging surface 100 Objective optical system 102 Cover glass 162 Electronic image pick-up element chip | tip 166 Terminal 300 Personal computer 301 Keyboard 302 Monitor 303 Imaging Optical System 304 Imaging Optical Path 305 Image 400 Mobile Phone 401 Microphone Unit 402 Speaker Unit 403 Input Dial 404 Monitor 405 Imaging Optical System 406 Antenna 407 Imaging Optical Path 500 Autofocus Mechanism

Claims (17)

In order from the object side, a first lens having a positive refractive power, a second lens having a negative refractive power, a third lens having a positive refractive power, a fourth lens having a positive refractive power, and a negative refractive power. Of the fifth lens,
The iris is placed on the most object side,
An imaging optical system that satisfies the following conditional expression (1):
−4.0 <(r6 + r7) / (r6-r7) <− 0.51 (1)
However,
r6 is the paraxial radius of curvature of the object side surface of the third lens;
r7 is the paraxial radius of curvature of the image side surface of the third lens;
It is. The imaging optical system according to claim 1, wherein the following conditional expression (2) is satisfied.
1.21 <φL5edmax / φst <6.52 (2)
However,
φL5edmax is the effective diameter of the fifth lens,
φst is the diameter of the diaphragm,
It is. The imaging optical system according to claim 1, wherein the following conditional expression (3) is satisfied.
-10.8 <R9 / d9 <-1.6 (3)
However,
R9 is the paraxial radius of curvature of the image side surface of the fourth lens,
d9 is the air spacing on the optical axis of the fourth lens and the fifth lens,
It is.   The imaging optical system according to any one of claims 1 to 3, wherein the third lens is a meniscus lens having a convex surface directed toward the object side. The imaging optical system according to any one of claims 1 to 4, wherein the following conditional expression (4) is satisfied.
-12.7 <r3 / f1 <-1.6 (4)
However,
r3 is the paraxial radius of curvature of the first lens image side surface;
f1 is the focal length of the first lens,
It is. The imaging optical system according to claim 1, wherein the following conditional expression (5) is satisfied.
1.3 <r7 / f (5)
However,
r7 is the paraxial radius of curvature of the third lens image side surface;
f is the focal length of the entire imaging optical system,
It is. The imaging optical system according to any one of claims 1 to 6, wherein the following conditional expression (6) is satisfied.
0.4 <r6 / f <2.1 (6)
However,
r6 is the paraxial radius of curvature of the side surface of the third lens object;
f is the focal length of the entire imaging optical system,
It is. The imaging optical system according to any one of claims 1 to 7, wherein the following conditional expression (7) is satisfied.
1.1 <f3 / f4 <7.6 (7)
However,
f3 is the focal length of the third lens,
f4 is the focal length of the fourth lens,
It is. The imaging optical system according to any one of claims 1 to 8, wherein the following conditional expression (8) is satisfied.
1.0 <(r10 + r11) / (r10−r11) <3.4 (8)
However,
r10 is the paraxial radius of curvature of the object side surface of the fifth lens;
r11 is the paraxial radius of curvature of the image side surface of the fifth lens;
It is. The imaging optical system according to any one of claims 1 to 19, wherein the following conditional expression (9) is satisfied.
0.4 <f1 / f <1.8 (9)
However,
f1 is the focal length of the first lens,
f is the focal length of the entire imaging optical system,
It is. The imaging optical system according to any one of claims 1 to 10, wherein the following conditional expression (10) is satisfied.
−1.5 <f5 / f <−0.3 (10)
However,
f5 is the focal length of the fifth lens,
f is the focal length of the entire imaging optical system,
It is.   The imaging optical system according to any one of claims 1 to 11, wherein the first lens is a biconvex lens.   The imaging optical system according to any one of claims 1 to 12, wherein the second lens is a meniscus lens having a convex surface directed toward the object side. The fourth lens is a meniscus lens having a concave surface facing the object side,
The imaging optical system according to any one of claims 1 to 13, wherein the shape of the object side surface is a concave shape from the center to the periphery.   An imaging apparatus comprising: the imaging optical system according to any one of claims 1 to 14; and an imaging element.   The imaging apparatus according to claim 15, wherein the imaging optical system and the imaging element are integrated.   The image pickup apparatus according to claim 15 or 16, wherein the image pickup optical system is integrated with an autofocus mechanism.

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