JP5424815B2 - Imaging optical system and imaging apparatus having the same - Google Patents

Description

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

  In recent years, with the thinning of cellular phones, portable terminals, notebook personal computers, and the like, there has been a demand for camera modules in which the length of the optical system in the high-axis direction is extremely thinned. In order to meet this requirement, many short-focus optical systems composed of about two to three aspheric lenses have been proposed.

  In recent years, a camera module having a high pixel size, a wide angle, and a low price has been demanded in spite of a small size, due to the technological progress of the image sensor and the increasing needs of the market. For example, the following Patent Documents 1, 2, and 3 propose an optical system with four lenses as an optical system that improves the imaging performance while reducing the total length of the optical system.

JP 2002-365529 A JP 2008-158413 A JP 2008-268946 A

  Although the lenses described in Patent Documents 1 to 3 described above are small, they correct chromatic aberration favorably in order to increase the resolution for increasing the number of pixels. However, these lenses have a half angle of view of 33 ° or less, and it is difficult to say that the angle of view is wide. Further, when the angle is further increased, the influence of various aberrations, particularly the influence of coma aberration, becomes large, so that high resolution cannot be satisfied despite being small.

  The present invention has been made in view of the above, and an object of the present invention is to provide a compact imaging optical system having a wide angle of view and an imaging apparatus having the same, in which various aberrations are favorably corrected.

In order to solve the above-described problems and achieve the object, the imaging optical system according to the present invention has a plurality of lenses, and the plurality of lenses are arranged in order from the object side, with a positive refractive power of a biconvex shape. 1 lens, a biconcave second lens having negative refractive power, a meniscus third lens having positive refractive power with the concave surface facing the object side, and a fourth lens having negative refractive power,
The iris is placed on the most object side,
The following conditional expression is satisfied.
-0.07 <(r2 + r3) / (r2-r3) <0.62 (1)
0.53 <(r4 + r5) / (r4-r5) <0.85 (2)
1.56 <r6 / r7 <2.74 (4)
here,
r2 is a radius of curvature of the first lens on the object side,
r3 is the radius of curvature of the first lens on the image side ,
r4 is a radius of curvature on the object side of the second lens,
r5 is the radius of curvature of the second lens on the image side,
r6 is a radius of curvature of the third lens on the object side,
r7 is the radius of curvature of the third lens on the image side,
It is.

Moreover, according to the preferable aspect of this invention, it is desirable to satisfy the following conditional expressions.
1.56 <f / f1 <3.48 (3)
here,
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.
0.12 <d5 / f <0.36 (5)
here,
f is the focal length of the entire imaging optical system,
d5 is the air spacing on the optical axis between the second lens and the third lens,
It is.

Moreover, according to the preferable aspect of this invention, it is desirable to satisfy the following conditional expressions.
0 <| (SAG3AS-SAG3AA) / 3AR | <0.08 (6)
0 <| (SAG3BS-SAG3BA) / 3BR | <0.62 (7)
here,
SAG3AS is the amount of sag at a position of 60% effective diameter when the object side surface of the third lens is a spherical surface.
SAG3AA is the amount of sag at the position of 60% effective diameter of the object side surface of the third lens,
SAG3BS is the amount of sag at a position of 60% effective diameter when the imaging surface side surface of the third lens is a spherical surface,
SAG3BA is the amount of sag at the position of the effective diameter of 60% of the surface on the imaging surface side of the third lens,
3AR is the radius of curvature of the object side surface of the third lens,
3BR is a radius of curvature of the surface on the imaging surface side of the third lens,
It is.

  According to a preferred aspect of the present invention, in the imaging optical system, it is desirable that the first lens, the second lens, the third lens, and the fourth lens are formed of a resin. .

According to the imaging device of the present invention, the above-described imaging optical system;
An imaging device comprising an electronic imaging device having an imaging surface,
The following conditional expression is satisfied.
15 ° <αi <30 ° (8)
Here, αi is the incident angle of the principal ray on the imaging surface at the maximum image height.

  Moreover, according to a preferable aspect of the present invention, it is desirable that the imaging apparatus includes an autofocus mechanism integrated with the imaging optical system.

  Moreover, according to a preferable aspect of the present invention, it is desirable that the imaging apparatus integrates the imaging optical system and the electronic imaging element.

  Advantageous Effects of Invention According to the present invention, there is an effect that it is possible to provide a small imaging optical system having a wide field angle in which various aberrations are favorably corrected and an imaging apparatus having the imaging optical system.

It is sectional drawing which follows the optical axis which shows the optical structure at the time of infinity object point focusing of Example 1 of the imaging optical system of this invention. FIG. 6 is a diagram illustrating spherical aberration, astigmatism, distortion, and lateral chromatic aberration when the imaging optical system according to the example 1 is focused on an object point at infinity. It is sectional drawing which follows the optical axis which shows the optical structure at the time of infinity object point focusing of Example 2 of the imaging optical system of this invention. FIG. 6 is a diagram illustrating spherical aberration, astigmatism, distortion, and lateral chromatic aberration when an imaging optical system according to Example 2 is focused on an object point at infinity. It is sectional drawing which follows the optical axis which shows the optical structure at the time of infinity object point focusing of Example 3 of the imaging optical system of this invention. It is a figure which shows the spherical aberration, the astigmatism, the distortion aberration, and the magnification chromatic aberration at the time of focusing on an object point at infinity of the imaging optical system according to the third example. It is sectional drawing which follows the optical axis which shows the optical structure at the time of infinity object point focusing of Example 4 of the imaging optical system of this invention. FIG. 10 is a diagram illustrating spherical aberration, astigmatism, distortion, and chromatic aberration of magnification when the imaging optical system according to Example 4 is focused on an object point at infinity. It is sectional drawing which follows the optical axis which shows the optical structure at the time of infinity object point focusing of Example 5 of the imaging optical system of this invention. FIG. 10 is a diagram illustrating spherical aberration, astigmatism, distortion, and lateral chromatic aberration when an imaging optical system according to Example 5 is focused on an object point at infinity. It is sectional drawing which follows the optical axis which shows the optical structure at the time of infinity object point focusing of Example 6 of the imaging optical system of this invention. FIG. 10 is a diagram illustrating spherical aberration, astigmatism, distortion, and lateral chromatic aberration when an imaging optical system according to Example 6 is focused on an object point at infinity. It is sectional drawing which follows the optical axis which shows the optical structure at the time of infinity object point focusing of Example 7 of the imaging optical system of this invention. FIG. 10 is a diagram illustrating spherical aberration, astigmatism, distortion, and chromatic aberration of magnification when an imaging optical system according to Example 7 is focused on an object point at infinity. It is sectional drawing which follows the optical axis which shows the optical structure at the time of infinity object point focusing of Example 8 of the imaging optical system of this invention. FIG. 10 is a diagram illustrating spherical aberration, astigmatism, distortion, and lateral chromatic aberration when an imaging optical system according to Example 8 is focused on an object point at infinity. It is sectional drawing which follows the optical axis which shows the optical structure at the time of infinity object point focusing of Example 9 of the imaging optical system of this invention. FIG. 10 is a diagram illustrating spherical aberration, astigmatism, distortion, and chromatic aberration of magnification when the imaging optical system according to Example 9 is focused on an object point at infinity. 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 imaging optical system of the present invention is built 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 as an example of an information processing apparatus in which an imaging optical system of the present invention is built in as a photographic optical system, where FIG. 1A is a front view of the mobile phone 400, FIG. FIG. 4 is a sectional view of the photographing optical system 405. It is a figure explaining the amount of sag.

  First, prior to the description of the examples, the function and effect of the imaging optical system of the present embodiment will be described.

The imaging optical system according to the present embodiment includes four lenses, and in order from the object side, a biconvex first lens having a positive refractive power, a biconcave second lens having a negative refractive power, and an object side. A meniscus third lens having a positive refractive power and a fourth lens having a negative refractive power.
The iris is placed on the most object side,
The following conditional expression is satisfied.
-0.07 <(r2 + r3) / (r2-r3) <0.62 (1)
0.53 <(r4 + r5) / (r4-r5) <0.85 (2)
here,
r2 is the radius of curvature of the first lens on the object side,
r3 is a radius of curvature of the first lens on the object side and the image side,
r4 is the radius of curvature of the second lens on the object side,
r5 is the radius of curvature of the second lens on the image side,
It is.

  With this configuration, the position of the principal point can be arranged on the object side of the optical system. As a result, the total length of the optical system can be made sufficiently small with respect to the focal length. For this reason, the overall length can be shortened. Further, the exit pupil can be separated from the image plane by disposing the stop closest to the object side. Thereby, the angle of the light beam incident on the periphery of the image sensor is reduced. For this reason, it is possible to avoid a decrease in the amount of light at the periphery of the image sensor.

Conditional expression (1) defines the shape of the first lens. If the lower limit of conditional expression (1) is not reached, the radius of curvature of the first lens on the object side becomes small. As a result, the light incident angle on the object-side surface of the first lens becomes steep (large), and it becomes difficult to correct coma. In particular, when the angle of view of the imaging optical system is within the range of the following formula (A), the above problem becomes significant.
If the upper limit of conditional expression (1) is exceeded, the radius of curvature on the object side of the first lens will increase. As a result, the curvature on the image side becomes stronger, making it difficult to bring the principal point to the object side in the entire optical system. As a result, it becomes difficult to shorten the entire optical system.

Conditional expression (2) defines the shape of the second lens.
Below the lower limit of conditional expression (2), the radius of curvature of the image side surface of the second lens becomes large. For this reason, it becomes impossible to increase the emission angle of the light beam from the second lens. As a result, it becomes difficult to shorten the optical system. In particular, when the angle of view of the imaging optical system is within the range of the following formula (A), the above problem becomes significant when a glass material that satisfies the following formula (B) is used for the imaging optical system.
If the upper limit of conditional expression (2) is exceeded, the radius of curvature of the object-side surface of the second lens will increase. This makes it difficult to correct longitudinal chromatic aberration by the second lens having negative refractive power.

Moreover, it is desirable that the imaging optical system of the present embodiment satisfies the following conditional expression (A).
30 ° <ω <60 ° (A)
Here, ω is a half angle of view.
Conditional expression (A) is an expression representing the half angle of view of the imaging optical system.

Moreover, it is desirable that the imaging optical system of the present embodiment satisfies the following conditional expression (B).
0.01 <1 / ν2-1 / ν1 <0.03 (B)
here,
ν1 is the Abbe number (nd1−1) / (nF1−nC1) of the first lens,
ν2 is the Abbe number of the second lens (nd2−1) / (nF2−nC2),
nd1, nC1, nF1, and ng1 are the refractive indexes of the d-line, C-line, F-line, and g-line of the first lens,
nd2, nC2, nF2, and ng2 are the refractive indices of the d-line, C-line, F-line, and g-line of the second lens,
It is.
Conditional expression (B) is a relational expression regarding the Abbe number of the first lens and the second lens. By satisfying conditional expression (B), chromatic aberration can be corrected satisfactorily.

Further, the imaging optical system of the present embodiment may satisfy the following conditional expression (1 ′) instead of conditional expression (1).
0.02 <(r2 + r3) / (r2-r3) <0.46 (1 ′)
Furthermore, it is better to satisfy the following conditional expression (1 ″) instead of conditional expression (1).
0.10 <(r2 + r3) / (r2-r3) <0.32 (1 ")
Moreover, it is preferable to satisfy the following conditional expression (2 ′) instead of conditional expression (2).
0.56 <(r4 + r5) / (r4-r5) <0.84 (2 ′)
Furthermore, it is better to satisfy the following conditional expression (2 ″) instead of conditional expression (2).
0.59 <(r4 + r5) / (r4-r5) <0.82 (2 ")

Moreover, it is desirable that the imaging optical system of the present embodiment satisfies the following conditional expression (3).
1.56 <f / f1 <3.48 (3)
here,
f1 is the focal length of the first lens,
f is the focal length of the entire imaging optical system,
It is.

Conditional expression (3) defines the conditions for shortening the overall length of the optical system and performing good aberration correction.
If the upper limit of conditional expression (3) is exceeded, the refractive power of the first lens will become strong. As a result, various aberrations, particularly high angle of view, deteriorate spherical aberration and increase coma, making it difficult to correct aberrations. Further, the entire refractive power is concentrated on the first lens. For this reason, the manufacturing error sensitivity of the first lens is undesirably increased.
If the lower limit of conditional expression (3) is not reached, the refractive power of the first lens will be weak. This makes it difficult to position the principal point on the object side of the optical system. For this reason, it becomes difficult to shorten the overall length of the optical system.

Moreover, it is preferable to satisfy the following conditional expression (3 ′) instead of conditional expression (3).
1.59 <f / f1 <2.61 (3 ′)
Furthermore, it is better to satisfy the following conditional expression (3 ″) instead of conditional expression (3).
1.61 <f / f1 <1.75 (3 ″)

Moreover, it is desirable that the imaging optical system of the present embodiment satisfies the following conditional expression (4).
1.56 <r6 / r7 <2.74 (4)
r6 is the radius of curvature of the third lens on the object side
r7 is the radius of curvature of the third lens on the image side,
It is.

Conditional expression (4) defines the ratio between the curvature radius on the object side and the curvature radius on the image side of the third lens. This prescribes the distribution ratio of the refractive power of each surface, and is a preferable condition for shortening the overall length and favorably correcting the field curvature.
If the lower limit value of conditional expression (4) is not reached, the refractive power of the object side surface of the third lens becomes too strong. This makes it difficult to correct curvature of field.
If the upper limit of conditional expression (4) is exceeded, the refractive power of the object side surface of the third lens will be too weak. This makes it difficult to shorten the overall length of the optical system.

Moreover, it is preferable to satisfy the following conditional expression (4 ′) instead of conditional expression (4).
1.69 <r6 / r7 <2.59 (4 ′)
Furthermore, it is better to satisfy the following conditional expression (4 ″) instead of conditional expression (4).
1.82 <r6 / r7 <2.44 (4 ")

In addition, it is desirable that the imaging optical system of the present embodiment satisfies the following conditional expression.
0.12 <d5 / f <0.36 (5)
here,
f is the focal length of the entire imaging optical system,
d5 is the air spacing on the optical axis between the second lens and the third lens,
It is.

Conditional expression (5) defines an appropriate ratio between the air distance between the second lens and the third lens and the focal length.
If the lower limit of conditional expression (5) is not reached, the difference in the beam height of the off-axis light beam between the second lens and the third lens becomes small. This reduces the effect of the third lens that is responsible for correcting higher-order field curvature and distortion, and makes correction difficult.
On the other hand, if the upper limit of conditional expression (5) is exceeded, the total length becomes long instead of ensuring the spread of the off-axis light beam incident on the third lens.

Moreover, it is preferable to satisfy the following conditional expression (5 ′) instead of conditional expression (5).
0.13 <d5 / f <0.27 (5 ′)
Furthermore, it is better to satisfy the following conditional expression (5 ″) instead of conditional expression (5).
0.15 <d5 / f <0.19 (5 ")

In addition, it is desirable that the imaging optical system of the present embodiment satisfies the following conditional expression.
0 <| (SAG3AS-SAG3AA) / 3AR | <0.08 (6)
0 <| (SAG3BS-SAG3BA) / 3BR | <0.62 (7)
here,
SAG3AS is the amount of sag at the position of 60% effective diameter when the object side surface of the third lens is a spherical surface,
SAG3AA is the amount of sag at the position of 60% effective diameter of the object side surface of the third lens,
SAG3BS is the amount of sag at the position of 60% effective diameter when the imaging surface side surface of the third lens is a spherical surface,
SAG3BA is the amount of sag at the position of the effective diameter of 60% of the surface on the imaging surface side of the third lens,
3AR is the radius of curvature of the object side surface of the third lens,
3BR is the radius of curvature of the imaging surface side surface of the third lens,
It is.

Here, the sag amount will be described with reference to FIG. “The amount of sag at an effective diameter of 60% when the lens surface is a spherical surface” is indicated by a dotted line in a direction along the direction parallel to the optical axis at an effective diameter of 60% (height). This is the distance SAGs between the reference spherical surface and the plane P passing through the top V.
“The amount of sag at the position where the effective diameter of the lens surface is 60%” means that the lens surface and surface indicated by the solid line in the direction along the direction parallel to the optical axis at the position (height) where the effective diameter is 60%. This is the distance SAGa to the plane P passing through the apex V.

Conditional expressions (6) and (7) define preferable conditions for suppressing image plane fluctuations due to fluctuations in the object distance.
Exceeding the upper limit values of conditional expressions (6) and (7) is not preferable because a large difference occurs in the refractive power between the on-axis and off-axis, and the image plane variation becomes remarkable due to the variation of the object distance.

Moreover, it is preferable to satisfy the following conditional expressions (6 ′) and (7 ′) instead of the conditional expressions (6) and (7).
0.01 <| (SAG3AS-SAG3AA) / 3AR | <0.06 (6 ′)
0.08 <| (SAG3BS-SAG3BA) / 3BR | <0.45 (7 ′)
Furthermore, it is better to satisfy the following conditional expressions (6 ″) and (7 ″) instead of the conditional expressions (6) and (7).
0.02 <| (SAG3AS-SAG3AA) / 3AR | <0.04 (6 ")
0.17 <| (SAG3BS-SAG3BA) / 3BR | <0.31 (7 ")

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

Further, the imaging apparatus of the present embodiment includes the above-described imaging optical system,
An imaging device comprising an electronic imaging device having an imaging surface,
The following conditional expression is satisfied.
15 ° <αi <30 ° (8)
Here, αi is the incident angle of the principal ray on the imaging surface at the maximum image height.

  When a CCD or the like is used for the solid-state imaging device, if the off-axis light beam emitted from the optical system is incident on the imaging surface at a large angle, the brightness of the image changes between the central portion and the peripheral portion of the image. In addition, when the incident angle on the imaging surface is small, this problem is solved, but the total length of the optical system becomes long. Therefore, it is desirable to satisfy conditional expression (8).

In addition, it is desirable that the imaging apparatus of the present embodiment includes an autofocus mechanism integrated with the imaging optical system.
By mounting an autofocus mechanism, it is possible to focus at any subject distance.

In the imaging apparatus of this embodiment, it is desirable that the imaging optical system and the electronic imaging element are integrated.
By integrating the electronic image pickup device, an optical image obtained by the image pickup optical system can be converted into an electric signal. In addition, a small and high-performance imaging device can be provided by selecting an electronic imaging device that can reduce the change in brightness of the image at the central portion and the peripheral portion due to αi.

  Hereinafter, examples of the imaging optical system and the electronic imaging apparatus of the present embodiment will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

  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 the 3rd lens L3 and the 4th lens L4 of negative refractive power. In all the following examples, in the lens cross-sectional views, CG represents a cover glass, and I represents an image pickup surface of an electronic image pickup element.

  The first lens L1 is a biconvex positive lens. The second lens L2 is a biconcave negative lens. The third lens L3 is a positive meniscus lens having a concave surface facing the object side. The fourth lens L4 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 fourth lens L4.

  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 the 3rd lens L3 and the 4th lens L4 of negative refractive power.

  The first lens L1 is a biconvex positive lens. The second lens L2 is a biconcave negative lens. The third lens L3 is a positive meniscus lens having a concave surface facing the object side. The fourth lens L4 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 fourth lens L4.

  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 the 3rd lens L3 and the 4th lens L4 of negative refractive power.

  The first lens L1 is a biconvex positive lens. The second lens L2 is a biconcave negative lens. The third lens L3 is a positive meniscus lens having a concave surface facing the object side. The fourth lens L4 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 fourth lens L4.

  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 the 3rd lens L3 and the 4th lens L4 of negative refractive power.

  The first lens L1 is a biconvex positive lens. The second lens L2 is a biconcave negative lens. The third lens L3 is a positive meniscus lens having a concave surface facing the object side. The fourth lens L4 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 fourth lens L4.

  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 the 3rd lens L3 and the 4th lens L4 of negative refractive power.

  The first lens L1 is a biconvex positive lens. The second lens L2 is a biconcave negative lens. The third lens L3 is a positive meniscus lens having a concave surface facing the object side. The fourth lens L4 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 fourth lens L4.

  Next, an imaging optical system according to Example 6 will be described. FIG. 11 is a cross-sectional view along the optical axis showing the optical configuration of the imaging optical system according to the sixth example when focusing on an object point at infinity.

  FIG. 12 is a diagram illustrating spherical aberration (SA), astigmatism (AS), distortion (DT), and lateral chromatic aberration (CC) when the imaging optical system according to Example 6 is focused on an object point at infinity.

  As shown in FIG. 11, the imaging optical system according to the sixth embodiment includes, in order from the object side, 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. It has the 3rd lens L3 and the 4th lens L4 of negative refractive power.

  The first lens L1 is a biconvex positive lens. The second lens L2 is a biconcave negative lens. The third lens L3 is a positive meniscus lens having a concave surface facing the object side. The fourth lens L4 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 fourth lens L4.

  Next, an imaging optical system according to Example 7 will be described. FIG. 13 is a cross-sectional view along the optical axis showing the optical configuration of the imaging optical system according to the seventh example when focusing on an object point at infinity.

  FIG. 14 is a diagram showing spherical aberration (SA), astigmatism (AS), distortion (DT), and lateral chromatic aberration (CC) when the imaging optical system according to the example 7 is focused on an object point at infinity.

  As shown in FIG. 13, the imaging optical system according to the seventh 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 the 3rd lens L3 and the 4th lens L4 of negative refractive power.

  The first lens L1 is a biconvex positive lens. The second lens L2 is a biconcave negative lens. The third lens L3 is a positive meniscus lens having a concave surface facing the object side. The fourth lens L4 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 fourth lens L4.

  Next, an imaging optical system according to Example 8 will be described. FIG. 15 is a cross-sectional view along the optical axis showing the optical configuration of the imaging optical system according to the eighth embodiment when focusing on an object point at infinity.

  FIG. 16 is a diagram illustrating spherical aberration (SA), astigmatism (AS), distortion (DT), and lateral chromatic aberration (CC) when the imaging optical system according to the eighth example is focused on an object point at infinity.

  As shown in FIG. 15, the imaging optical system according to the eighth 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 the 3rd lens L3 and the 4th lens L4 of negative refractive power.

  The first lens L1 is a biconvex positive lens. The second lens L2 is a biconcave negative lens. The third lens L3 is a positive meniscus lens having a concave surface facing the object side. The fourth lens L4 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 fourth lens L4.

  Next, an image pickup optical system according to Example 9 will be described. FIG. 17 is a cross-sectional view along the optical axis showing the optical configuration of the imaging optical system according to the ninth example when focusing on an object point at infinity.

  FIG. 18 is a diagram illustrating spherical aberration (SA), astigmatism (AS), distortion (DT), and lateral chromatic aberration (CC) when the imaging optical system according to the ninth example is focused on an object point at infinity.

  As shown in FIG. 17, the imaging optical system according to the ninth 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 the 3rd lens L3 and the 4th lens L4 of negative refractive power.

  The first lens L1 is a biconvex positive lens. The second lens L2 is a biconcave negative lens. The third lens L3 is a positive meniscus lens having a concave surface facing the object side. The fourth lens L4 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 fourth lens L4.

  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

Surface data Surface number rd nd νd
1 (Aperture) ∞ 0.00
2 * 3.047 1.12 1.53071 55.71
3 * -2.456 0.05
4 * -10.686 0.43 1.58393 30.22
5 * 2.660 0.76
6 * -2.405 0.92 1.53071 55.71
7 * -1.233 0.12
8 * 3.852 0.88 1.53071 55.71
9 * 1.371 1.00
10 ∞ 0.30 1.51633 64.14
11 ∞ 0.74
Image plane ∞

Aspheric coefficient

Second side
K = -1.654, A4 = -1.00506e-02, A6 = -1.14778e-02, A8 = -1.49068e-04, A10 = -5.14718e-03

Third side
K = -0.329, A4 = -1.93924e-02, A6 = -6.39151e-03, A8 = 2.00408e-02, A10 = -1.28099e-02

4th page
K = -185.540, A4 = -8.23617e-02, A6 = 2.64477e-02, A8 = 1.97935e-02, A10 = -9.21123e-03

5th page
K = -3.805, A4 = -1.22715e-02, A6 = 8.26191e-03, A8 = 1.53602e-03, A10 = -3.08284e-04

6th page
K = -6.631, A4 = -4.14180e-04, A6 = 2.52203e-03, A8 = 7.55909e-04, A10 = -8.42628e-04

7th page
K = -2.808, A4 = -3.20002e-02, A6 = 4.51422e-03, A8 = 1.25490e-03, A10 = 5.28786e-05

8th page
K = -5.431, A4 = -3.93128e-02, A6 = 3.57408e-03, A8 = -6.60600e-05, A10 = 4.26897e-06,
A12 = 9.33515e-08

9th page
K = -5.595, A4 = -2.29629e-02, A6 = 2.05663e-03, A8 = -2.26330e-04, A10 = 9.44899e-06,
A12 = -1.06711e-08


fb (in air) 1.93
Total length (in air) 6.20

Total focal length
4.72

Numerical example 2

Surface data Surface number rd nd νd
1 (Aperture) ∞ -0.11
2 * 3.051 1.13 1.53367 55.84
3 * -2.458 0.05
4 * -10.738 0.41 1.58364 30.31
5 * 2.655 0.76
6 * -2.321 0.89 1.53367 55.84
7 * -1.195 0.07
8 * 4.093 0.86 1.53367 55.84
9 * 1.383 1.00
10 ∞ 0.30 1.51633 64.14
11 ∞ 0.84
Image plane ∞

Aspheric coefficient

Second side
K = -1.664, A4 = -1.00762e-02, A6 = -1.15507e-02, A8 = -3.34048e-04, A10 = -5.54457e-03

Third side
K = -0.330, A4 = -1.93812e-02, A6 = -6.39504e-03, A8 = 2.00290e-02, A10 = -1.28031e-02

4th page
K = -185.263, A4 = -8.23663e-02, A6 = 2.64500e-02, A8 = 1.97894e-02, A10 = -9.23148e-03

5th page
K = -3.804, A4 = -1.22688e-02, A6 = 8.26985e-03, A8 = 1.55508e-03, A10 = -2.82684e-04

6th page
K = -6.653, A4 = -1.61081e-04, A6 = 2.92428e-03, A8 = 7.62211e-04, A10 = -9.21999e-04,
A12 = -1.43021e-05

7th page
K = -2.845, A4 = -3.17002e-02, A6 = 4.11484e-03, A8 = 1.11841e-03, A10 = 1.34060e-04,
A12 = 1.94577e-06

8th page
K = -7.043, A4 = -4.14103e-02, A6 = 3.08790e-03, A8 = -1.43528e-04, A10 = -1.39196e-05,
A12 = 7.37909e-06

9th page
K = -6.306, A4 = -2.58678e-02, A6 = 2.23660e-03, A8 = -2.76715e-04, A10 = 1.07861e-05,
A12 = -2.54429e-08

fb (in air) 2.04
Total length (in air) 6.21

Total focal length
4.77

Numerical Example 3

Surface data Surface number rd nd νd
1 (Aperture) ∞ -0.11
2 * 3.051 1.13 1.53367 55.84
3 * -2.458 0.05
4 * -10.738 0.41 1.58364 30.31
5 * 2.655 0.76
6 * -2.270 0.86 1.53367 55.84
7 * -1.183 0.07
8 * 4.060 0.87 1.53367 55.84
9 * 1.370 1.00
10 ∞ 0.30 1.51633 64.14
11 ∞ 0.82
Image plane ∞

Aspheric coefficient

Second side
K = -1.664, A4 = -1.00762e-02, A6 = -1.15507e-02, A8 = -3.34048e-04, A10 = -5.54457e-03

Third side
K = -0.330, A4 = -1.93812e-02, A6 = -6.39504e-03, A8 = 2.00290e-02, A10 = -1.28031e-02

4th page
K = -185.263, A4 = -8.23663e-02, A6 = 2.64500e-02, A8 = 1.97894e-02, A10 = -9.23148e-03

5th page
K = -3.804, A4 = -1.22688e-02, A6 = 8.26985e-03, A8 = 1.55508e-03, A10 = -2.82684e-04

6th page
K = -6.679, A4 = 3.72833e-05, A6 = 3.18381e-03, A8 = 7.80962e-04, A10 = -9.29996e-04,
A12 = 2.26831e-05

7th page
K = -2.843, A4 = -3.17067e-02, A6 = 4.41220e-03, A8 = 1.18511e-03, A10 = 1.47930e-04,
A12 = 6.55551e-06

8th page
K = -6.929, A4 = -4.13555e-02, A6 = 3.09557e-03, A8 = -1.16770e-04, A10 = -1.40995e-05,
A12 = 7.32933e-06

9th page
K = -6.280, A4 = -2.66552e-02, A6 = 2.49543e-03, A8 = -3.06598e-04, A10 = 1.01663e-05,
A12 = 2.54653e-07

fb (in air) 2.03
Total length (in air) 6.18

Total focal length
4.75

Numerical Example 4

Surface data Surface number rd nd νd
1 (Aperture) ∞ 0.00
2 * 4.065 0.95 1.53071 55.71
3 * -2.131 0.11
4 * -22.214 0.41 1.58393 30.22
5 * 2.287 0.80
6 * -2.185 0.81 1.53071 55.71
7 * -1.194 0.11
8 * 2.059 0.62 1.53071 55.71
9 * 1.097 1.00
10 ∞ 0.30 1.51633 64.14
11 ∞ 1.05
Image plane ∞

Aspheric coefficient

Second side
K = -7.481, A4 = -2.24053e-02, A6 = -3.17843e-02, A8 = -3.31946e-03, A10 = -1.71198e-02

Third side
K = 0.433, A4 = -3.01041e-02, A6 = -1.93713e-02, A8 = 2.19571e-02, A10 = -1.46893e-02

4th page
K = 14.362, A4 = -9.49556e-02, A6 = 2.57209e-02, A8 = 2.21529e-02, A10 = -6.95165e-03

5th page
K = -5.235, A4 = -1.55798e-02, A6 = 8.93182e-03, A8 = 1.53699e-03, A10 = -5.59498e-04

6th page
K = -7.829, A4 = 5.53293e-03, A6 = 1.74790e-03, A8 = 5.48991e-04, A10 = -5.81661e-04

7th page
K = -3.240, A4 = -3.16816e-02, A6 = 6.29949e-03, A8 = 1.81281e-03, A10 = -9.90132e-05

8th page
K = -4.839, A4 = -3.37315e-02, A6 = 3.54489e-03, A8 = -6.82609e-05, A10 = -4.19083e-06

9th page
K = -4.629, A4 = -2.54747e-02, A6 = 2.26243e-03, A8 = -1.70888e-04, A10 = 4.87644e-06

fb (in air) 2.25
Total length (in air) 6.07

Total focal length
4.61

Numerical Example 5

Surface data Surface number rd nd νd
1 (Aperture) ∞ 0.00
2 * 3.636 1.08 1.53071 55.71
3 * -2.268 0.09
4 * -15.497 0.44 1.58393 30.22
5 * 2.349 0.73
6 * -2.222 0.85 1.53071 55.71
7 * -1.166 0.09
8 * 2.240 0.66 1.53071 55.71
9 * 1.133 1.00
10 ∞ 0.30 1.51633 64.14
11 ∞ 0.98
Image plane ∞

Aspheric coefficient

Second side
K = -3.438, A4 = -1.48191e-02, A6 = -1.85166e-02, A8 = 1.96066e-03, A10 = -8.22657e-03

Third side
K = 0.028, A4 = -2.35679e-02, A6 = -8.92280e-03, A8 = 1.77190e-02, A10 = -9.81173e-03

4th page
K = -49.840, A4 = -9.41231e-02, A6 = 2.32456e-02, A8 = 2.36755e-02, A10 = -8.01144e-03

5th page
K = -5.474, A4 = -1.49152e-02, A6 = 7.92132e-03, A8 = 5.28410e-04, A10 = -7.77067e-05

6th page
K = -7.729, A4 = 5.68445e-03, A6 = 2.10085e-03, A8 = 2.43032e-04, A10 = -6.60037e-04

7th page
K = -3.117, A4 = -3.60128e-02, A6 = 5.22224e-03, A8 = 1.81785e-03, A10 = 6.53686e-05

8th page
K = -4.686, A4 = -3.60228e-02, A6 = 3.70835e-03, A8 = -6.27636e-05, A10 = -4.77358e-06

9th page
K = -4.919, A4 = -2.49569e-02, A6 = 2.01934e-03, A8 = -1.60421e-04, A10 = 4.50715e-06

fb (in air) 2.18
Total length (in air) 6.13

Total focal length
4.54

Numerical Example 6

Surface data Surface number rd nd νd
1 (Aperture) ∞ 0.00
2 * 3.399 1.06 1.53071 55.71
3 * -2.447 0.09
4 * -10.856 0.46 1.58393 30.22
5 * 2.701 0.77
6 * -2.736 0.96 1.53071 55.71
7 * -1.127 0.07
8 * 2.946 0.66 1.53071 55.71
9 * 1.078 1.00
10 ∞ 0.30 1.51633 64.14
11 ∞ 0.93
Image plane ∞

Aspheric coefficient

Second side
K = -3.007, A4 = -1.36151e-02, A6 = -1.85411e-02, A8 = 4.64240e-04, A10 = -1.03636e-02

Third side
K = 0.281, A4 = -2.86197e-02, A6 = -2.03521e-02, A8 = 2.58831e-02, A10 = -1.23767e-02

4th page
K = -305.428, A4 = -9.35160e-02, A6 = 2.24905e-02, A8 = 2.24752e-02, A10 = -7.69471e-03

5th page
K = -3.343, A4 = -1.62311e-02, A6 = 7.81925e-03, A8 = 2.19564e-03, A10 = -5.66090e-04

6th page
K = -8.864, A4 = -3.30293e-03, A6 = -3.20850e-03, A8 = 2.38089e-03, A10 = -2.39088e-06,
A12 = -2.39088e-06

7th page
K = -3.729, A4 = -5.36229e-02, A6 = 1.52560e-02, A8 = -2.73114e-03, A10 = 4.79372e-07,
A12 = 4.79372e-07

8th page
K = -5.733, A4 = -4.21558e-02, A6 = 5.42576e-03, A8 = -3.22312e-04, A10 = 1.05532e-05,
A12 = 2.73232e-08

9th page
K = -5.193, A4 = -2.52093e-02, A6 = 2.39054e-03, A8 = -2.24237e-04, A10 = 7.22131e-06,
A12 = 4.40233e-09

fb (in air) 2.12
Total length (in air) 6.20

Total focal length
4.70

Numerical Example 7

Surface data Surface number rd nd νd
1 (Aperture) ∞ 0.00
2 * 3.885 1.05 1.53071 55.71
3 * -2.208 0.09
4 * -23.628 0.42 1.58393 30.22
5 * 2.418 0.83
6 * -2.127 0.80 1.53071 55.71
7 * -1.161 0.08
8 * 2.330 0.68 1.53071 55.71
9 * 1.123 1.00
10 ∞ 0.30 1.51633 64.14
11 ∞ 0.91
Image plane ∞

Aspheric coefficient

Second side
K = -5.011, A4 = -1.80504e-02, A6 = -2.34379e-02, A8 = -1.93673e-03, A10 = -9.31981e-03

Third side
K = 0.227, A4 = -2.71303e-02, A6 = -1.27936e-02, A8 = 1.72436e-02, A10 = -9.16355e-03

4th page
K = -96.012, A4 = -9.34359e-02, A6 = 2.36214e-02, A8 = 2.38425e-02, A10 = -7.80620e-03

5th page
K = -6.267, A4 = -1.53019e-02, A6 = 8.35621e-03, A8 = 5.95937e-04, A10 = -1.59568e-04

6th page
K = -7.207, A4 = 2.72388e-03, A6 = 1.79597e-03, A8 = 4.36335e-04, A10 = -7.92929e-04

7th page
K = -3.174, A4 = -3.22068e-02, A6 = 6.14570e-03, A8 = 1.68663e-03, A10 = -6.59220e-06

8th page
K = -4.922, A4 = -3.78151e-02, A6 = 3.64997e-03, A8 = -5.67913e-05, A10 = -3.28580e-06

9th page
K = -4.960, A4 = -2.45954e-02, A6 = 1.94167e-03, A8 = -1.64255e-04, A10 = 3.98451e-06

fb (in air) 2.12
Total length (in air) 6.07

Total focal length
4.58

Numerical Example 8

Surface data Surface number rd nd νd
1 (Aperture) ∞ 0.00
2 * 3.047 1.12 1.53071 55.71
3 * -2.456 0.05
4 * -10.686 0.43 1.58393 30.22
5 * 2.660 0.75
6 * -2.405 0.92 1.53071 55.71
7 * -1.233 0.12
8 * 3.852 0.88 1.53071 55.71
9 * 1.371 1.00
10 ∞ 0.30 1.51633 64.14
11 ∞ 0.73
Image plane ∞

Aspheric coefficient

Second side
K = -1.654, A4 = -1.00506e-02, A6 = -1.14778e-02, A8 = -1.49068e-04, A10 = -5.14718e-03

Third side
K = -0.329, A4 = -1.93924e-02, A6 = -6.39151e-03, A8 = 2.00408e-02, A10 = -1.28099e-02

4th page
K = -185.540, A4 = -8.23617e-02, A6 = 2.64477e-02, A8 = 1.97935e-02, A10 = -9.21123e-03

5th page
K = -3.805, A4 = -1.22715e-02, A6 = 8.26191e-03, A8 = 1.53602e-03, A10 = -3.08284e-04

6th page
K = -6.631, A4 = -4.14180e-04, A6 = 2.52203e-03, A8 = 7.55909e-04, A10 = -8.42628e-04

7th page
K = -2.808, A4 = -3.20002e-02, A6 = 4.51422e-03, A8 = 1.25490e-03, A10 = 5.28786e-05

8th page
K = -5.431, A4 = -3.93128e-02, A6 = 3.57408e-03, A8 = -6.60600e-05, A10 = 4.26897e-06,
A12 = 9.33515e-08

9th page
K = -5.595, A4 = -2.29629e-02, A6 = 2.05663e-03, A8 = -2.26330e-04, A10 = 9.44899e-06,
A12 = -1.06711e-08

fb (in air) 1.93
Total length (in air) 6.20

Total focal length
4.72

Numerical Example 9

Surface data Surface number rd nd νd
1 (Aperture) ∞ -0.08
2 * 3.051 1.13 1.53367 55.84
3 * -2.457 0.05
4 * -10.738 0.41 1.58364 30.31
5 * 2.655 0.76
6 * -2.477 0.90 1.53367 55.84
7 * -1.054 0.07
8 * 8.094 0.82 1.53367 55.84
9 * 1.346 1.00
10 ∞ 0.30 1.51633 64.14
11 ∞ 0.82
Image plane ∞

Aspheric coefficient

Second side
K = -1.664, A4 = -1.00762e-02, A6 = -1.15507e-02, A8 = -3.34048e-04, A10 = -5.54457e-03

Third side
K = -0.330, A4 = -1.93812e-02, A6 = -6.39504e-03, A8 = 2.00290e-02, A10 = -1.28031e-02

4th page
K = -185.263, A4 = -8.23663e-02, A6 = 2.64500e-02, A8 = 1.97894e-02, A10 = -9.23148e-03

5th page
K = -3.804, A4 = -1.22688e-02, A6 = 8.26985e-03, A8 = 1.55508e-03, A10 = -2.82684e-04

6th page
K = -3.789, A4 = -1.12476e-02, A6 = 1.79553e-02, A8 = 7.65914e-04, A10 = -4.93486e-03,
A12 = 1.34691e-03

7th page
K = -2.761, A4 = -5.03592e-02, A6 = 1.24386e-02, A8 = 1.34300e-03, A10 = 4.54088e-05,
A12 = 1.55075e-05

8th page
K = 6.992, A4 = -3.60963e-02, A6 = 7.98204e-04, A8 = 6.96044e-04, A10 = -7.33146e-05,
A12 = 2.36561e-06

9th page
K = -6.933, A4 = -3.12268e-02, A6 = 4.82151e-03, A8 = -7.47086e-04, A10 = 6.27719e-05,
A12 = -2.15219e-06

fb (in air) 2.02
Total length (in air) 6.17

Total focal length
4.75

The values corresponding to conditional expressions are listed below.
Formula (1) -0.07 <(r2 + r3) / (r2-r3) <0.62
Formula (2) 0.53 <(r4 + r5) / (r4-r5) <0.85
Formula (3) 1.56 <f / f1 <3.48
Formula (4) 1.56 <r6 / r7 <2.74
Formula (5) 0.12 <d5 / f <0.36
Formula (6) 0 <| (SAG3AS-SAG3AA) / 3AR | <0.08
Formula (7) 0 <| (SAG3BS-SAG3BA) / 3BR | <0.62
Formula (8) 15 ° <αi <30 °
Formula (A) 30 ° <ω <60 °
Formula (B) 0.01 <1 / ν2-1 / ν1 <0.03

Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 Example 9
Formula (1) 0.11 0.11 0.11 0.31 0.23 0.16 0.28 0.11 0.11
Formula (2) 0.60 0.60 0.60 0.81 0.74 0.60 0.81 0.60 0.60
Formula (3) 1.72 1.74 1.74 1.66 1.62 1.65 1.63 1.72 1.74
Formula (4) 1.95 1.94 1.92 1.83 1.90 2.43 1.83 1.95 2.35
Formula (5) 0.16 0.16 0.16 0.17 0.16 0.16 0.18 0.16 0.16
Formula (6) 0.03 0.03 0.03 0.04 0.04 0.02 0.04 0.03 0.02
Equation (7) 0.17 0.18 0.18 0.21 0.21 0.31 0.24 0.17 0.28
Equation (8) 26.43 26.37 26.49 26.15 25.15 26.15 26.11 26.44 27.92
Formula (A) 37.02 36.86 37.00 37.92 37.92 37.33 37.92 37.02 36.75
Formula (B) 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02

  The imaging optical system of the present invention as described above is an imaging device that captures an image of an object with an electronic imaging device such as a CCD or CMOS, a personal computer, a telephone, a portable terminal as an example of an information processing device, especially for carrying around. It can be used for convenient mobile phones. The embodiment is illustrated below.

  Next, a personal computer which is an example of an information processing apparatus in which the imaging optical system of the present invention is built as an objective optical system is shown in FIGS. 19 is a front perspective view of the personal computer 300 with the cover open, FIG. 20 is a sectional view of the photographing optical system 303 of the personal computer 300, and FIG. 21 is a side view of FIG. As shown in FIGS. 19 to 21, 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. 19 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 device, 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-sized and high-performance personal computer (imaging device) by selecting an electronic image sensor that can reduce the change in brightness of the image at the central portion and the peripheral portion due to αi.

  Next, FIG. 22 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. 22A is a front view of the mobile phone 400, FIG. 22B is a side view, and FIG. 22C is a cross-sectional view of the photographing optical system 405. As shown in FIGS. 22A to 22C, 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.

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 device, 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 the change in brightness of the image at the central portion and the peripheral portion due to αi.

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

  As described above, the present invention is useful for a compact and high-performance imaging optical system.

L1 1st lens L2 2nd lens L3 3rd lens L4 4th lens CG Cover glass I Imaging surface S Aperture stop 300 PC 301 Keyboard 302 Monitor 303 Shooting optical system 304 Shooting 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 (8)

Having a plurality of lenses,
The plurality of lenses are, in order from the object side, a biconvex first lens having a positive refractive power, a biconcave second lens having a negative refractive power, and a meniscus-shaped positive lens having a concave surface facing the object side. A third lens having a refractive power of 4 and a fourth lens having a negative refractive power,
The iris is placed on the most object side,
An imaging optical system characterized by satisfying the following conditional expression:
-0.07 <(r2 + r3) / (r2-r3) <0.62 (1)
0.53 <(r4 + r5) / (r4-r5) <0.85 (2)
1.56 <r6 / r7 <2.74 (4)
here,
r2 is a radius of curvature of the first lens on the object side,
r3 is the radius of curvature of the first lens on the image side ,
r4 is a radius of curvature on the object side of the second lens,
r5 is the radius of curvature of the second lens on the image side,
r6 is a radius of curvature of the third lens on the object side,
r7 is the radius of curvature of the third lens on the image side,
It is. The imaging optical system according to claim 1, wherein the following conditional expression is satisfied.
1.56 <f / f1 <3.48 (3)
here,
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 claim 1, wherein the following conditional expression is satisfied.
  0.12 <d5 / f <0.36 (5)
  here,
  f is the focal length of the entire imaging optical system,
  d5 is the air spacing on the optical axis between the second lens and the third lens,
It is.   The imaging optical system according to claim 1, wherein the following conditional expression is satisfied.
  0 <| (SAG3AS-SAG3AA) / 3AR | <0.08 (6)
  0 <| (SAG3BS-SAG3BA) / 3BR | <0.62 (7)
  here,
  SAG3AS is the amount of sag at a position of 60% effective diameter when the object side surface of the third lens is a spherical surface.
  SAG3AA is the amount of sag at the position of 60% effective diameter of the object side surface of the third lens,
  SAG3BS has an effective diameter of 60% when the imaging surface side surface of the third lens is a spherical surface.
Amount of sag at
  SAG3BA is the amount of sag at the position of the effective diameter of 60% of the surface on the imaging surface side of the third lens,
  3AR is the radius of curvature of the object side surface of the third lens,
  3BR is a radius of curvature of the surface on the imaging surface side of the third lens,
It is.   5. The imaging optical system according to claim 1, wherein the first lens, the second lens, the third lens, and the fourth lens are made of resin. The imaging optical system according to one item.   The imaging optical system according to any one of claims 1 to 5,
  An imaging device comprising an electronic imaging device having an imaging surface,
  An image pickup apparatus satisfying the following conditional expression:
    15 ° <αi <30 ° (8)
  Here, αi is the incident angle of the principal ray on the imaging surface at the maximum image height.   The image pickup apparatus according to claim 6, further comprising an autofocus mechanism integrated with the image pickup optical system.   The imaging apparatus according to claim 6 or 7, wherein the imaging optical system and the electronic imaging element are integrated.

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