JP2012189894A - Imaging optical system and imaging apparatus using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that when it is intended that the F number is to be made smaller and the size is to be reduced in a conventional optical system, the influence of various aberrations, in particular, the influence of a coma aberration results in increasing.SOLUTION: The imaging 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 in a side that is the closest to the object, and satisfies the following conditional formula (1): -11.2<r3/f1<-0.9. In the formula, r3 represents a paraxial curvature radius of the image side surface of the first lens, and f1 represents a focal length of the first lens.

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 is an optical system having a relatively small F number, but the overall length of the optical system is shortened, the lens diameter is kept small, and various aberrations, particularly spherical aberration and coma aberration, are reduced. It is an object of the present invention to provide an imaging optical system that is well corrected and an imaging apparatus using the imaging optical system.

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 refraction. A third lens having a positive power, a fourth lens having a positive refractive power, and a fifth lens having a negative refractive power, the stop is disposed closest to the object side, the first lens is a glass lens, and the following conditions are satisfied The expression (1) is satisfied.
−11.2 <r3 / f1 <−0.9 (1)
However,
r3 is the radius of curvature of the image side surface of the first lens,
f1 is the focal length of the first lens,
It is.

The imaging optical system according to 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, 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).
−11.2 <r3 / f1 <−0.9 (1)
However,
r3 is the paraxial radius of curvature of the image side surface of the first lens,
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 (2).
1.54 <nd1 (2)
However,
nd1 is the refractive index of the first lens with respect to the d-line,
It is.

Moreover, according to the preferable aspect of this invention, it is desirable to satisfy the following conditional expressions (3).
0.7 <r2 / f1 <1.2 (3)
However,
r2 is the paraxial radius of curvature of the object side surface of the first lens,
f1 is the focal length of the first lens,
It is.

Moreover, according to a preferable aspect of the present invention, it is desirable that the following conditional expression (4) is satisfied.
0.2 <f3 / f4 <5 (4)
However,
f3 is the focal length of the third lens,
f4 is the focal length of the fourth lens,
It is.

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

Moreover, according to the preferable aspect of this invention, it is desirable to satisfy the following conditional expressions (5).
0.2 <r6 / f <4.2 (5)
However,
r6 is the paraxial radius of curvature of the object side surface of the third 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 (6).
-6.4 <(r6 + r7) / (r6-r7) <1 (6)
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.

  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 directed toward the object side.

Moreover, according to a preferable aspect of the present invention, it is desirable that the following conditional expression (7) is satisfied.
−0.6 <(r10 + r11) / (r10−r11) <2.5 (7)
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.

  According to a preferred aspect of the present invention, it is desirable that the second lens, the third lens, the fourth lens, and the fifth lens are formed of resin.

  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, an imaging optical system in which the overall length of the optical system is short, the lens diameter is kept small, and various aberrations, in particular, spherical aberration and coma aberration are favorably corrected, although the optical system has a relatively small F number. And an imaging device using the same 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 of 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 first lens having a positive refractive power. It consists of four lenses and a fifth lens having a negative refractive power, and a stop is arranged closest to the object side, and satisfies the following conditional expression (1).
−11.2 <r3 / f1 <−0.9 (1)
However,
r3 is the paraxial radius of curvature of the image side surface of the first lens,
f1 is the focal length of the first 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.

  Further, the fourth lens has a positive refracting power, and the optical system is configured by a total of five lenses, whereby 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, it is possible to avoid the shortening of the entire length of the optical system and the decrease in sensitivity at the periphery of the image sensor 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 condition for satisfactorily correcting spherical aberration and coma. By satisfying conditional expression (1), spherical aberration and coma can be corrected well.

  If the upper limit value of conditional expression (1) is exceeded, the paraxial radius of curvature of the image side surface of the first lens becomes small, and it becomes difficult to correct spherical aberration. If the lower limit value of conditional expression (1) is not reached, the paraxial radius of curvature of the image side surface of the first lens becomes too large, and the incident angle of the off-axis light beam on the image side surface of the first lens becomes steep. As a result, coma correction becomes difficult.

Here, it is preferable to satisfy the following conditional expression (1 ′) instead of conditional expression (1).
−8.5 <r3 / f1 <−2.1 (1 ′)
Further, it is more preferable that the following conditional expression (1 ″) is satisfied instead of conditional expression (1).
-5.4 <r3 / f1 <-2.3 (1 ")

In the imaging optical system of the present embodiment, it is preferable that the first lens is a glass lens.
By using a high refractive glass for the first lens, the paraxial radius of curvature of the object side surface and the image side surface can be increased while maintaining the refractive power of the first lens, so that various aberrations can be corrected well.

Moreover, it is preferable that the imaging optical system of this embodiment satisfies the following conditional expression (2).
1.54 <nd1 (2)
However,
nd1 is the refractive index of the first lens with respect to the d-line,
It is.

  Conditional expression (2) is a preferable condition for properly correcting aberrations such as spherical aberration and reducing fluctuations in curvature of field due to manufacturing errors when shortening the total length of the optical system.

  If the lower limit of conditional expression (2) is not reached, it will be difficult to maintain the refractive power of the first lens while keeping the paraxial curvature of the image side surface and object side surface of the first lens small. For this reason, when the total length of the optical system is shortened, aberrations such as spherical aberration are significantly generated. In addition, it becomes difficult to suppress fluctuations in field curvature due to manufacturing errors.

Here, it is preferable to satisfy the following conditional expression (2 ′) instead of conditional expression (2).
1.58 <nd1 (2 ')
It is more preferable to satisfy the following conditional expression (2 ″) instead of conditional expression (2).
1.65 <nd1 (2 ")

Moreover, it is preferable that the imaging optical system of this embodiment satisfies the following conditional expression (3).
0.7 <r2 / f1 <1.2 (3)
However,
r2 is the paraxial radius of curvature of the object side surface of the first lens,
f1 is the focal length of the first lens,
It is.

  Conditional expression (3) is a preferable condition for satisfactorily correcting the coma generated when the total length of the optical system is shortened and reducing the variation in field curvature with respect to manufacturing errors. By satisfying conditional expression (3), it is possible to suppress the occurrence of coma aberration and the variation in field curvature.

  If the upper limit value of conditional expression (3) is exceeded, the paraxial radius of curvature of the object side surface of the first lens will increase, making it difficult to position the principal point on the object side. Therefore, it becomes difficult to shorten the overall length of the optical system. If the lower limit value of conditional expression (3) is not reached, the paraxial radius of curvature of the object side surface of the first lens becomes small, making it difficult to correct coma.

Here, it is preferable to satisfy the following conditional expression (3 ′) instead of conditional expression (3).
0.8 <r2 / f1 <1.15 (3 ′)
It is more preferable that the following conditional expression (3 ″) is satisfied instead of conditional expression (3).
0.85 <r2 / f1 <1.1 (3 ")

Moreover, it is preferable that the imaging optical system of this embodiment satisfies the following conditional expression (4).
0.2 <f3 / f4 <5 (4)
However,
f3 is the focal length of the third lens,
f4 is the focal length of the fourth lens,
It is.

  Conditional expression (4) is a preferable conditional expression for appropriately distributing the refractive power distribution of the third lens and the fourth lens. By satisfying conditional expression (4), it is possible to appropriately distribute the refractive powers of the third lens and the fourth lens. As a result, it is possible to satisfactorily correct the aberration of the off-axis light beam and to mitigate the deterioration of the eccentricity sensitivity due to the shortening of the optical length.

  If the upper limit value of conditional expression (4) 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 (4) is not reached, the refractive power of the third lens becomes large, so that 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 to satisfy the following conditional expression (4 ′) instead of conditional expression (4).
0.8 <f3 / f <3.8 (4 ′)
Further, it is more preferable that the following conditional expression (4 ″) is satisfied instead of conditional expression (4).
1.4 <f3 / f4 <2.6 (4 ")

  In the imaging optical system of the present embodiment, it is preferable that the object side surface of the third lens is a convex surface on the object side.

  By making the object side surface of the third lens convex to the object side, it is possible to maintain an appropriate distance between the second lens and the third lens even in the periphery of the lens. Therefore, the peripheral part of the second lens and the peripheral part of the third lens do not come into contact with each other. Further, since the distance between the second lens and the third lens on the optical axis can be reduced, the overall length of the optical system can be shortened while satisfactorily correcting various aberrations, mainly coma.

Moreover, it is preferable that the imaging optical system of this embodiment satisfies the following conditional expression (5).
0.2 <r6 / f <4.2 (5)
However,
r6 is the paraxial radius of curvature of the object side surface of the third lens,
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), 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 (5) is exceeded, the paraxial radius of curvature of the object side surface of the third lens will increase. When the image side surface of the second lens is a concave surface on the image side, when the paraxial radius of curvature of the object side surface of the third lens is increased, the distance between the second lens and the third lens in the peripheral portion is reduced. 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, 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 coma. When the lower limit value of conditional expression (5) 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 (5 ′) instead of conditional expression (5).
0.4 <r6 / f <3 (5 ′)
Further, it is more preferable that the following conditional expression (5 ″) is satisfied instead of conditional expression (5).
0.6 <r6 / f <1.8 (5 ")

Moreover, it is preferable that the imaging optical system of this embodiment satisfies the following conditional expression (6).
-6.4 <(r6 + r7) / (r6-r7) <1 (6)
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.

  Conditional expression (6) is a preferable conditional expression for correcting the aberration of the off-axis light beam. By satisfying conditional expression (6), it is possible to satisfactorily correct the aberration of the off-axis light beam.

  If the object side surface of the third lens is convex and the upper limit value of conditional expression (6) is exceeded, the paraxial radius of curvature of the image side surface of the third lens becomes small, so the refractive power of the third lens becomes too strong. End up. As a result, the difference in the beam height of the off-axis light beam between the third lens and the fourth lens becomes small, and it becomes difficult to correct coma and higher-order field curvature. If the lower limit value of conditional expression (6) is not reached, the negative refractive power on the image side surface of the third lens will increase. 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 to satisfy the following conditional expression (6 ′) instead of conditional expression (6).
−4.2 <(r6 + r7) / (r6-r7) <0.6 (6 ′)
Further, it is more preferable that the following conditional expression (6 ″) is satisfied instead of conditional expression (6).
-2 <(r6 + r7) / (r6-r7) <0.2 (6 ")

  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, the fourth lens is preferably a meniscus lens having a concave surface directed toward the object side. 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 optical system of this embodiment satisfies the following conditional expression (7).
−0.6 <(r10 + r11) / (r10−r11) <2.5 (7)
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 (7) 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 (7) is satisfied, the distance between the fifth lens and the image plane at 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 (7) is exceeded, the paraxial radius of curvature of the image side surface of the fifth lens will be small. 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. If the lower limit value of conditional expression (7) is not reached, the position of the principal point of the fifth lens moves closer to the object side, and the back focus length becomes shorter. As a result, it becomes difficult to reduce the effective diameter of the fifth lens while maintaining the telecentricity of the optical system.

Here, it is preferable to satisfy the following conditional expression (7 ′) instead of conditional expression (7).
−0.1 <(r10 + r11) / (r10−r11) <2.2 (7 ′)
Further, it is more preferable that the following conditional expression (7 ″) is satisfied instead of conditional expression (7).
0.8 <(r10 + r11) / (r10−r11) <1.5 (7 ″)

  In the imaging optical system of the present embodiment, it is preferable that the second lens, the third lens, the fourth lens, and the fifth lens are formed of resin. An inexpensive imaging optical system can be provided by using a resin for the second lens, the third lens, the fourth lens, and the fifth lens.

  Moreover, it is preferable that the imaging apparatus of this embodiment is provided with said imaging optical system and an image pick-up element. Realizes an imaging device using an imaging optical system that has a relatively small F-number optical system, has a short overall length, keeps the lens diameter small, and corrects various aberrations, especially field curvature and chromatic aberration. it can.

  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 is a biconvex positive lens. The fourth lens L4 is a positive meniscus lens having a convex surface facing the image side. The fifth lens L5 is a biconcave negative lens.

  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 is a biconvex positive lens. The fourth lens L4 is a positive meniscus lens having a convex surface facing the image side. The fifth lens L5 is a biconcave negative lens.

  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 biconcave negative lens. The third lens is a biconvex positive lens. The fourth lens L4 is a positive meniscus lens having a convex surface facing the image side. The fifth lens L5 is a biconcave negative lens.

  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 biconcave negative lens. The third lens 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 biconcave negative lens. The third lens is a biconvex positive lens. 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, 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. fb indicates back focus.

Numerical example 1
Unit: mm

Surface data surface number rd nd νd
Object ∞ ∞
1 (Aperture) ∞ -0.24
2 * 2.202 0.66 1.70904 53.00
3 * -7.303 0.04
4 * 9.255 0.29 1.61417 25.64
5 * 1.447 0.36
6 * 7.188 0.67 1.53463 56.22
7 * -5.339 0.49
8 * -1.489 0.41 1.53463 56.22
9 * -0.929 0.26
10 * -18.014 0.52 1.53463 56.22
11 * 1.609 0.50
12 ∞ 0.30 1.51633 64.14
13 ∞ 0.48
Image plane ∞

Aspheric data 2nd surface
k = -1.082
A4 = 1.07486e-02, A6 = -6.78068e-03, A8 = 6.16980e-03
Third side
k = -212.704
A4 = 4.11002e-02, A6 = -1.25773e-02, A8 = 8.42077e-03
4th page
k = -0.168
A4 = -5.44036e-03, A6 = 7.22382e-02, A8 = -6.70269e-02, A10 = 1.88383e-02
5th page
k = -0.570
A4 = -1.36668e-01, A6 = 2.02153e-01, A8 = -1.50848e-01, A10 = 3.78136e-02
6th page
k = -92.007
A4 = 2.17740e-02, A6 = -2.05403e-02, A8 = 4.98953e-02, A10 = -1.85936e-02
7th page
k = -74.224
A4 = -6.50176e-02, A6 = 5.00292e-02, A8 = -4.20018e-02, A10 = 1.61884e-02
8th page
k = 0.000
A4 = 1.72886e-02, A6 = 8.90787e-02, A8 = -4.88479e-02, A10 = 1.60684e-02,
A12 = -1.86802e-03
9th page
k = -2.143
A4 = -1.34593e-02, A6 = 3.45396e-03, A8 = 2.40948e-02, A10 = -5.95315e-03,
A12 = -2.47719e-04
10th page
k = 0.000
A4 = -3.44973e-02, A6 = -6.29865e-03, A8 = 1.88036e-03, A10 = 7.39659e-04,
A12 = -1.48776e-04
11th page
k = -11.896
A4 = -5.47053e-02, A6 = 1.29918e-02, A8 = -3.58227e-03, A10 = 5.19652e-04,
A12 = -3.30892e-05

fb (in air) 1.17
Total length (in air) 4.89

Focal length 4.05

Numerical example 2
Unit: mm

Surface data surface number rd nd νd
Object ∞ ∞
1 (Aperture) ∞ -0.23
2 * 2.140 0.69 1.68980 52.80
3 * -6.316 0.03
4 * 36.306 0.30 1.61417 25.64
5 * 1.663 0.35
6 * 5.402 0.61 1.53463 56.22
7 * -18.466 0.40
8 * -1.879 0.47 1.53463 56.22
9 * -0.957 0.37
10 * -21.513 0.35 1.53463 56.22
11 * 1.510 0.50
12 ∞ 0.30 1.51633 64.14
13 ∞ 0.49
Image plane ∞

Aspheric data 2nd surface
k = -1.054
A4 = 1.24910e-02, A6 = -1.33402e-02, A8 = 6.42383e-03
Third side
k = -134.946
A4 = 3.42981e-02, A6 = -2.42552e-02, A8 = 5.53847e-03
4th page
k = 0.015
A4 = -1.95617e-03, A6 = 7.95303e-02, A8 = -7.52991e-02, A10 = 2.00956e-02
5th page
k = -0.395
A4 = -1.35215e-01, A6 = 2.03549e-01, A8 = -1.32067e-01, A10 = 3.06563e-02
6th page
k = -80.110
A4 = 4.68053e-03, A6 = -4.07049e-02, A8 = 6.09961e-02, A10 = -1.72455e-02
7th page
k = -892.691
A4 = -5.51183e-02, A6 = 3.54713e-02, A8 = -5.80090e-02, A10 = 2.23414e-02
8th page
k = -0.122
A4 = 6.09431e-03, A6 = 7.19867e-02, A8 = -5.81382e-02, A10 = 9.93699e-03,
A12 = -1.28641e-03
9th page
k = -2.396
A4 = -2.39128e-03, A6 = 4.75343e-03, A8 = 2.03433e-02, A10 = -8.27335e-03,
A12 = 8.37512e-04
10th page
k = -957.535
A4 = -3.53017e-02, A6 = -8.82204e-03, A8 = 2.90692e-03, A10 = 3.99611e-04,
A12 = -1.02948e-04
11th page
k = -10.239
A4 = -5.98281e-02, A6 = 1.50777e-02, A8 = -4.20626e-03, A10 = 6.45659e-04,
A12 = -4.26072e-05

fb (in air) 1.19
Total length (in air) 4.75

Focal length 3.92

Numerical Example 3
Unit: mm

Surface data surface number rd nd νd
Object ∞ ∞
1 (Aperture) ∞ -0.18
2 * 2.439 0.81 1.74617 45.30
3 * -5.621 0.04
4 * -12.530 0.30 1.61417 25.64
5 * 1.767 0.23
6 * 3.735 0.64 1.53463 56.22
7 * -13.818 0.47
8 * -2.040 0.50 1.53463 56.22
9 * -0.967 0.37
10 * -14.358 0.37 1.53463 56.22
11 * 1.457 0.50
12 ∞ 0.30 1.51633 64.14
13 ∞ 0.35
Image plane ∞

Aspheric data 2nd surface
k = -1.237
A4 = 1.05484e-02, A6 = -2.17607e-02, A8 = 1.62041e-02, A10 = 4.95316e-05,
A12 = -4.72862e-03
Third side
k = -98.818
A4 = 3.37599e-02, A6 = -2.30946e-02, A8 = 6.82769e-03, A10 = 4.000313e-04,
A12 = -5.60391e-03
4th page
k = -568.257
A4 = 4.74259e-03, A6 = 8.16027e-02, A8 = -8.12718e-02, A10 = 1.06371e-02
5th page
k = -0.237
A4 = -1.31665e-01, A6 = 2.01478e-01, A8 = -1.51153e-01, A10 = 3.63871e-02
6th page
k = -27.435
A4 = 1.73857e-02, A6 = -3.86212e-02, A8 = 5.89868e-02, A10 = -1.92251e-02
7th page
k = -977.799
A4 = -3.68218e-02, A6 = 2.84357e-02, A8 = -6.29095e-02, A10 = 2.72274e-02
8th page
k = -0.361
A4 = 5.50020e-03, A6 = 6.83472e-02, A8 = -5.88042e-02, A10 = 1.02686e-02,
A12 = -9.37373e-04
9th page
k = -2.465
A4 = -8.02901e-03, A6 = 5.67621e-03, A8 = 2.12475e-02, A10 = -8.44724e-03,
A12 = 6.87828e-04
10th page
k = -631.392
A4 = -4.27937e-02, A6 = -3.35402e-03, A8 = 3.61575e-03, A10 = -2.62999e-04,
A12 = -2.38278e-05
11th page
k = -9.130
A4 = -5.81541e-02, A6 = 1.60587e-02, A8 = -4.15231e-03, A10 = 5.66259e-04,
A12 = -3.23690e-05

fb (in air) 1.05
Total length (in air) 4.78

Focal length 3.76

Numerical Example 4
Unit: mm

Surface data surface number rd nd νd
Object ∞ ∞
1 (Aperture) ∞ -0.20
2 * 2.233 0.72 1.74698 45.30
3 * -14.006 0.06
4 * -10.599 0.29 1.61417 25.64
5 * 1.940 0.15
6 * 2.413 0.50 1.53463 56.22
7 * 7.536 0.55
8 * -3.079 0.56 1.53463 56.22
9 * -1.124 0.24
10 * 7.470 0.54 1.53463 56.22
11 * 1.318 0.54
12 ∞ 0.30 1.51633 64.14
13 ∞ 0.40
Image plane ∞

Aspheric data 2nd surface
k = -1.743
A4 = 9.38680e-03, A6 = 9.23833e-03, A8 = -1.27825e-02
Third side
k = -51.318
A4 = 2.75357e-03, A6 = 2.08714e-01, A8 = -4.26376e-01, A10 = 2.05397e-01
4th page
k = 0.063
A4 = -2.03215e-03, A6 = 3.87175e-01, A8 = -7.37658e-01, A10 = 3.61778e-01
5th page
k = -13.047
A4 = 7.52922e-02, A6 = 1.14096e-01, A8 = -1.97136e-01, A10 = 8.45512e-02
6th page
k = -18.544
A4 = -1.12895e-04, A6 = -1.65941e-02, A8 = 3.93484e-02, A10 = -1.23599e-02
7th page
k = -13.380
A4 = -2.61631e-02, A6 = -2.93083e-03, A8 = -4.03526e-02, A10 = 2.95277e-02
8th page
k = -1.959
A4 = -5.73444e-03, A6 = 3.96452e-02, A8 = -3.17418e-02, A10 = 3.29663e-03,
A12 = -1.33596e-03
9th page
k = -2.206
A4 = 1.24292e-02, A6 = -1.32829e-02, A8 = 4.38576e-02, A10 = -2.07563e-02,
A12 = 2.65970e-03
10th page
k = -392.292
A4 = -6.05452e-02, A6 = 2.58122e-02, A8 = -4.27893e-03, A10 = 3.23916e-04,
A12 = -1.06413e-05
11th page
k = -7.670
A4 = -6.01023e-02, A6 = 1.93515e-02, A8 = -4.59885e-03, A10 = 5.99111e-04,
A12 = -3.18357e-05

fb (in air) 1.14
Total length (in air) 4.76

Focal length 3.74

Numerical Example 5
Unit: mm

Surface data surface number rd nd νd
Object ∞ ∞
1 (Aperture) ∞ -0.17
2 * 2.602 0.62 1.80460 40.80
3 * -5.640 0.06
4 * -7.062 0.30 1.61417 25.64
5 * 1.689 0.19
6 * 2.846 0.53 1.53463 56.22
7 * -15.854 0.73
8 * -1.892 0.43 1.53463 56.22
9 * -0.964 0.32
10 * 650.706 0.38 1.53463 56.22
11 * 1.400 0.50
12 ∞ 0.30 1.51633 64.14
13 ∞ 0.44
Image plane ∞

Aspheric data 2nd surface
k = -1.882
A4 = 6.28826e-03, A6 = -2.40901e-02, A8 = 1.09121e-02, A10 = 4.58124e-03,
A12 = -6.29482e-03
Third side
k = -126.062
A4 = 2.75842e-02, A6 = -2.54884e-02, A8 = 1.57680e-02, A10 = 2.33328e-03,
A12 = -3.52620e-03
4th page
k = -228.390
A4 = 1.56330e-02, A6 = 8.49436e-02, A8 = -9.45747e-02, A10 = 4.03276e-02
5th page
k = -0.400
A4 = -1.37836e-01, A6 = 1.94898e-01, A8 = -1.52101e-01, A10 = 4.06153e-02
6th page
k = -18.832
A4 = 3.06159e-02, A6 = -3.46724e-02, A8 = 5.47133e-02, A10 = -1.57718e-02
7th page
k = -721.654
A4 = -2.56718e-02, A6 = 3.05657e-02, A8 = -6.17831e-02, A10 = 4.12146e-02
8th page
k = -0.432
A4 = 6.13716e-03, A6 = 6.92639e-02, A8 = -5.35503e-02, A10 = 1.37123e-02,
A12 = -1.35198e-03
9th page
k = -2.528
A4 = -2.89909e-03, A6 = 8.15395e-03, A8 = 2.11701e-02, A10 = -8.82825e-03,
A12 = 6.50951e-04
10th page
k = -14.156
A4 = -4.16290e-02, A6 = -2.82176e-03, A8 = 3.39262e-03, A10 = -3.42604e-04,
A12 = -7.65700e-06
11th page
k = -9.431
A4 = -6.09143e-02, A6 = 1.59904e-02, A8 = -4.10604e-03, A10 = 5.37262e-04,
A12 = -2.98458e-05

fb (in air) 1.14
Total length (in air) 4.70

Focal length 3.84

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

Formula no Example 1 Example 2 Example 3 Example 4 Example 5
1 r3 / f1 -2.98 -2.64 -2.37 -5.36 -2.47
2 nd1 1.71 1.69 1.75 1.75 1.81
3 r2 / f1 0.899 0.896 1.028 0.854 1.142
4 f3 / f4 1.59 2.55 1.89 2.13 1.44
5 r6 / f 1.78 1.38 0.99 0.64 0.74
6 (r6 + r7) / (r6-r7) 0.15 -0.55 -0.57 -1.94 -0.70
7 (r10 + r11) / (r10-r11) 0.84 0.87 0.82 1.43 1.00

  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 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 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 spherical aberration and 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 (15)

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 fifth lens having a negative refractive power. Become
The iris is placed on the most object side,
The first lens is a glass lens,
An imaging optical system that satisfies the following conditional expression (1):
−11.2 <r3 / f1 <−0.9 (1)
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. 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 fifth lens having a negative refractive power. Become
The iris is placed on the most object side,
An imaging optical system that satisfies the following conditional expression (1):
−11.2 <r3 / f1 <−0.9 (1)
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 (2) is satisfied.
1.54 <nd1 (2)
However,
nd1 is the refractive index of the first lens with respect to the d-line,
It is. The imaging optical system according to any one of claims 1 to 3, wherein the following conditional expression (3) is satisfied.
0.7 <r2 / f1 <1.2 (3)
However,
r2 is a paraxial radius of curvature of the side surface of the first lens object;
f1 is the focal length of the first lens,
It is. The imaging optical system according to any one of claims 1 to 4, wherein the following condition (4) is satisfied.
0.2 <f3 / f4 <5 (4)
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 5, wherein an object side surface of the third lens is a convex surface toward the object side. The imaging optical system according to claim 6, wherein the following condition (5) is satisfied.
0.2 <r6 / f <4.2 (5)
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 claim 6 or 7, wherein the following conditional expression (6) is satisfied.
-6.4 <(r6 + r7) / (r6-r7) <1 (6)
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 any one of claims 1 to 8, wherein the second 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 9, wherein the fourth lens is a meniscus lens having a concave surface directed toward the object side. The imaging optical system according to any one of claims 1 to 10, wherein the following conditional expression (7) is satisfied.
−0.6 <(r10 + r11) / (r10−r11) <2.5 (7)
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 11, wherein the second lens, the third lens, the fourth lens, and the fifth lens are formed of resin.   An imaging apparatus comprising: the imaging optical system according to any one of claims 1 to 12; and an imaging element.   The imaging apparatus according to claim 13, wherein the imaging optical system and the imaging element are integrated.   15. The imaging apparatus according to claim 13, wherein the imaging optical system is integrated with an autofocus mechanism.

Images