Imaging optical system

1. An imaging optical system wherein the number of lenses is three to seven, an aperture stop is located within the imaging optical system, one to four lenses each of which is an aspheric lens in which radius of curvature of each of both surfaces is infinity in the paraxial region and which has a power of the third-order aberration region in the peripheral area are provided, the first lens from the object side is a negative lens or an aspheric lens in which radius of curvature of each of both surfaces is infinity in the paraxial region and which has a negative power of the third-order aberration region in the peripheral area, the lens adjacent to the aperture stop on the image side is a positive lens, the relationship

0.18

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i

=

1

i

=

n

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1

f

i

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·

f

n

<

0.9

is satisfied where i represents a natural number, fi represents focal length of the i-th lens from the object side, f represents focal length of the whole system and n represents the number of the lenses, a bundle of rays that enters the imaging optical system and reaches the maximum value of image height and a bundle of rays that enters the imaging optical system and has the principal ray parallel to the optical axis do not intersect with each other within the first lens from the object side, and the relationship

40°<HFOV<80°

is satisfied where HFOV represents angle that the principal ray of bundle of rays that enters the imaging optical system and reaches the maximum value of image height forms with the optical axis.

2. The imaging optical system according to 1 wherein the number offenses is four to seven, the aperture stop is located between the second lens and the fourth lens from the object side, at least one aspheric lens in which radius of curvature of each of both surfaces is infinity in the paraxial region and which has a power of the third-order aberration region in the peripheral area is provided respectively on the object side and on the image side of the aperture stop, each of the first lens and/or the second lens from the object side and the lens closest to the image is an aspheric lens in which radius of curvature of each of both surfaces is infinity in the paraxial region and which has a power of the third-order aberration region in the peripheral area, the relationship

0.18

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i

=

1

i

=

n

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1

f

i

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·

f

n

<

0.82

is satisfied, and the bundle of rays that enters the imaging optical system and reaches the maximum value of image height and the bundle of rays that enters the imaging optical system and has the principal ray parallel to the optical axis do not intersect with each other within the lens closest to the image.

3. The imaging optical system according to 2 wherein the number of lenses is four, the aperture stop is located between the second lens and the third lens from the object side, and each of the first lens and the fourth lens from the object side is an aspheric lens in which radius of curvature of each of both surfaces is infinity in the paraxial region and which has a power of the third-order aberration region in the peripheral area.

4. The imaging optical system according to 2 wherein the number of lenses is five, the aperture stop is located between the second lens and the fourth lens from the object side, each of the first lens or the second lens from the object side and the fifth lens from the object side is an aspheric lens in which radius of curvature of each of both surfaces is infinity in the paraxial region and which has a power of the third-order aberration region in the peripheral area, and the relationship

0.18

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(

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i

=

1

i

=

n

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"\[LeftBracketingBar]"

1

f

i

❘

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)

·

f

n

<

0.65

is satisfied.

5. The imaging optical system according to 2 wherein the number of lenses is five, the aperture stop is located between the second lens and the third lens from the object side, each of the first lens, the second lens and the fifth lens from the object side or each of the second lens, the fourth lens and the fifth from the object is an aspheric lens in which radius of curvature of each of both surfaces is infinity in the paraxial region and which has a power of the third-order aberration region in the peripheral area, and the relationship

0.25

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i

=

1

i

=

n

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1

f

i

❘

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)

·

f

n

<

0.82

is satisfied.

6. The imaging optical system according to 2 wherein the number of lenses is six, the aperture stop is located between the second lens and the fourth lens from the object side, each of the first lens or the second lens from the object side and the sixth lens from the object side is an aspheric lens in which radius of curvature of each of both surfaces is infinity in the paraxial region and which has a power of the third-order aberration region in the peripheral area, and the relationship

0.18

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i

=

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i

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n

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1

f

i

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·

f

n

<

0.6

is satisfied.

7. The imaging optical system according to 2 wherein the number of lenses is six, the aperture stop is located between the second lens and the third lens from the object side, and each of the second lens, the fourth lens, the fifth lens and the sixth lens from the object side is an aspheric lens in which radius of curvature of each of both surfaces is infinity in the paraxial region and which has a power of the third-order aberration region in the peripheral area.

8. The imaging optical system according to 2 wherein the number of lenses is seven, the aperture stop is located between the second lens and the third lens from the object side, and each of the second lens, the fifth lens and the seventh lens from the object side is an aspheric lens in which radius of curvature of each of both surfaces is infinity in the paraxial region and which has a power of the third-order aberration region in the peripheral area.

9. The imaging optical system according to 1 wherein the number of lenses is three to five, and any one of the lenses is an aspheric lens in which radius of curvature of each of both surfaces is infinity in the paraxial region and which has a power of the third-order aberration region in the peripheral area.

10. The imaging optical system according to claim 9 wherein the first lens from the object side is an aspheric lens in which radius of curvature of each of both surfaces is infinity in the paraxial region and which has a power of the third-order aberration region in the peripheral area.

11. The imaging optical system according to claim 9 wherein the lens closest to the image is an aspheric lens in which radius of curvature of each of both surfaces is infinity in the paraxial region and which has a power of the third-order aberration region in the peripheral area, and the bundle of rays that enters the imaging optical system and reaches the maximum value of image height and the bundle of rays that enters the imaging optical system and has the principal ray parallel to the optical axis do not intersect with each other within the lens closest to the image.

12. The imaging optical system according to claim 9 wherein the number of lenses is three, and any one of the lenses is an aspheric lens in which radius of curvature of each of both surfaces is infinity in the paraxial region and which has a negative power of the third-order aberration region in the peripheral area.

13. The imaging optical system according to claim 2 wherein the number of lenses is five, each of the first lens, the second lens and the fifth lens from the object side is an aspheric lens in which radius of curvature of each of both surfaces is infinity in the paraxial region and which has a power of the third-order aberration region in the peripheral area, and the second lens is an aspheric lens in which radius of curvature of each of both surfaces is infinity in the paraxial region and which has a positive power of the third-order aberration region in the peripheral area.