초록 ▼

A fisheye lens with a field angle of at least one hundred sixty degrees is formed of two lens groups, arranged in order from the object side, as follows: a first lens group having negative refractive power and a second lens group having positive refractive power. The first lens group includes, arran

A fisheye lens with a field angle of at least one hundred sixty degrees is formed of two lens groups, arranged in order from the object side, as follows: a first lens group having negative refractive power and a second lens group having positive refractive power. The first lens group includes, arranged in order from the object side, two lens elements, each having negative refractive power and a meniscus shape with the convex surface on the object side, a lens element having negative refractive power with a concave surface on the image side, and two lens elements of opposite refractive powers. The second lens group includes, arranged in order from the object side, two lens elements of opposite refractive powers, a stop, and two lens elements of opposite refractive powers. The fisheye lens preferably satisfies specified conditions related to spacings of lens surfaces and to distortion characteristics of the fisheye lens.

대표청구항 ▼

What is claimed is: 1. A fisheye lens comprising two lens groups, arranged in order from the object side, as follows: a first lens group having negative refractive power; and a second lens group having positive refractive power; wherein the fisheye lens has a field angle of at least one hundred si

What is claimed is: 1. A fisheye lens comprising two lens groups, arranged in order from the object side, as follows: a first lens group having negative refractive power; and a second lens group having positive refractive power; wherein the fisheye lens has a field angle of at least one hundred sixty degrees; said first lens group includes, arranged in order from the object side, two lens elements, each having negative refractive power and a meniscus shape with the convex surface on the object side, a lens element having negative refractive power with a concave surface on the image side, and two lens elements, one having positive refractive power and one having negative refractive power; said second lens group includes, arranged in order from the object side, two lens elements, one having positive refractive power and one having negative refractive power, a stop, and two lens elements, one having positive refractive power and one having negative refractive power; and the on-axis distance between the image-side surface of said first lens group and the object-side surface of said second lens group is greater than the on-axis distance between any other adjacent surfaces of any of the lens elements of the fisheye lens. 2. The fisheye lens of claim 1, wherein the following condition is satisfied: description="In-line Formulae" end="lead"0.12< Dm/Ds<0.25description="In-line Formulae" end="tail" where Dm is the on-axis distance between the image-side surface of said first lens group and the object-side surface of said second lens group; and Ds is the on-axis distance from the object-side surface of the object-side lens element of the fisheye lens to the image-side surface of the image-side lens element of the fisheye lens. 3. The fisheye lens of claim 2, wherein the following condition is satisfied: description="In-line Formulae" end="lead"-0.15< (Ym-Ymo)/Ymo<0.15description="In-line Formulae" end="tail" where Ym is the image height at the maximum field angle; and Ymo is the ideal image height at the maximum field angle, which is equal to f쨌θm where f is the focal length of the fisheye lens and θm is the maximum half-field angle, in radians. 4. The fisheye lens of claim 3, wherein all of the lens elements of the fisheye lens are included in one of either said first lens group or said second lens group. 5. The fisheye lens of claim 4, wherein said first lens group includes only five lens elements and said second lens group includes only six lens elements and a stop. 6. The fisheye lens of claim 2, wherein the following conditions are satisfied: description="In-line Formulae" end="lead"-0.03< (Ym-Ymo)/Ymo<0.03description="In-line Formulae" end="tail" description="In-line Formulae" end="lead"0.70< |(dYm/dθ)/f|<1.2description="In-line Formulae" end="tail" where Ym is the image height at the maximum field angle, Ymo is the ideal image height at the maximum field angle, which is equal to f쨌θm where f is the focal length of the fisheye lens and θm is the maximum half-field angle, in radians, and dYm/dθ is the derivative of Ym with respect to the light beam half-field angle θ, in radians. 7. The fisheye lens of claim 2, wherein all of the lens elements of the fisheye lens are included in one of either said first lens group or said second lens group. 8. The fisheye lens of claim 7, wherein said first lens group includes only five lens elements. 9. The fisheye lens of claim 8, wherein said second lens group includes only six lens elements and a stop. 10. An imaging device comprising: the fisheye lens of claim 9; and an image pickup device; wherein said image pickup device detects a real image formed by said fisheye lens. 11. The fisheye lens of claim 1, wherein the following condition is satisfied: description="In-line Formulae" end="lead"-0.15< (Ym-Ymo)/Ymo<0.15description="In-line Formulae" end="tail" where Ym is the image height at the maximum field angle; and Ymo is the ideal image height at the maximum field angle, which is equal to f쨌θm where f is the focal length of the fisheye lens and θm is the maximum half-field angle, in radians. 12. The fisheye lens of claim 11, wherein all of the lens elements of the fisheye lens are included in one of either said first lens group or said second lens group. 13. The fisheye lens of claim 12, wherein said first lens group includes only five lens elements and said second lens group includes only six lens elements and a stop. 14. An imaging device comprising: the fisheye lens of claim 13; and an image pickup device; wherein said image pickup device detects a real image formed by said fisheye lens. 15. The fisheye lens of claim 1, wherein the following conditions are satisfied: description="In-line Formulae" end="lead"-0.03< (Ym-Ymo)/Ymo<0.03description="In-line Formulae" end="tail" description="In-line Formulae" end="lead"0.70< |(dYm/dθ)/f|<1.2description="In-line Formulae" end="tail" where Ym is the image height at the maximum field angle, Ymo is the ideal image height at the maximum field angle, which is equal to f쨌θm where f is the focal length of the fisheye lens and θm is the maximum half-field angle, in radians, and dYm/dθ is the derivative of Ym with respect to the light beam half-field angle θ, in radians. 16. An imaging device comprising: the fisheye lens of claim 1; and an image pickup device; wherein said image pickup device detects a real image formed by said fisheye lens. 17. The fisheye lens of claim 1, wherein all of the lens elements of the fisheye lens are included in one of either said first lens group or said second lens group. 18. The fisheye lens of claim 17, wherein said first lens group includes only five lens elements. 19. The fisheye lens of claim 18, wherein said second lens group includes only six lens elements and a stop. 20. An imaging device comprising: the fisheye lens of claim 19; and an image pickup device; wherein said image pickup device detects a real image formed by said fisheye lens.