Fisheye lens having a short distance compensating function

• US 5,434,713 A
• Filed: 03/19/1993
• Issued: 07/18/1995
• Est. Priority Date: 03/26/1992
• Status: Expired due to Term

• Current Assignee: Nikon Corporation
• Original Assignee: Nikon Corporation
• Inventors: Sato, Haruo
• Primary Examiner(s): Sugarman, Scott J.
• Application Number:
  US08/034,416
• Time in Patent Office: 851 Days
• Field of Search: 359/725, 359/749-753, 359/755, 359/762, 359/770
• US Class Current: 359/725
• CPC Class Codes: G02B 13/06 Panoramic objectives; So-called "sky lenses" including panoramic objectives having reflecting surfaces

Abstract

A fisheye lens comprises sequentially from an object, a first lens group including a negative meniscus lens and a second lens group having positive refracting power. The first and second lens groups move on the optical axis toward the object. The fisheye lens incorporates a short distance compensating function for focusing from an infinity object point onto a short distance object point by expanding n air space between the first and second lens groups and further satisfies various conditions.

Claims

1. A fisheye lens incorporating a short distance compensating function, comprising:

a first lens group including at least one negative meniscus lens, positioned closest to an object, with its convex surface toward the object and at least one positive lens;

a second lens group including a cemented positive lens consisting of a positive lens and a negative lens and disposed closer to an image than said first lens group to have positive refractive power on the whole,

wherein when focusing from an infinity object point onto a short distance object point, at least said first lens group moves on the optical axis toward the object to expand an air space between said first and second lens groups, and moving quantities thereof are set to satisfy the following condition;

space="preserve" listing-type="equation">0≦

X.sub.2 /X.sub.1 ≦

0.9

where X₁ is the moving quantity of said first lens group G₁ during focusing, and X₂ is the moving quantity of said second lens group G₂ during focusing.

2. The fisheye lens according to claim 1, wherein said first lens group is constructed so that a conversion inclination is set to satisfy the following condition:

space="preserve" listing-type="equation">-1.5≦

α

1

where α

is the conversion inclination obtained by multiplying an angle between the paraxial marginal ray emerging from an on-axis infinity object point that is incident on the closest-to-object lens surface of said second lens group and the optical axis by a refractive index of a medium just before said surface.

3. The fisheye lens according to claim 1, wherein said second lens group is constructed to further satisfy the following condition:

space="preserve" listing-type="equation">1≦

f.sub.2 /f≦

5

where f is the focal length of the whole lens system, and f₂ is the focal length of said second lens group.

4. The fisheye lens group according to claim 1, wherein said first lens group is constructed to satisfy the following condition:

space="preserve" listing-type="equation">52 ≦

ν

d.sub.1

where ν

d₁ is the Abbe number of said negative meniscus lens positioned closest to the object in said first lens group.

5. The fisheye lens according to claim 1, wherein said second lens group includes a cemented positive lens positioned closest to the image and consisting of a positive lens and a negative lens, and said cemented positive lens is constructed to satisfy the following condition:

space="preserve" listing-type="equation">0.15≦

n.sub.P -n.sub.n

where

n_P ;

the refractive index, with respect to the d-line, of said positive lens constituting a part of said closest-to-image cemented lens of said second lens group, and

n_n ;

the refractive index, with respect to the d-line, of said negative lens constituting a part of said closest-to-image cemented lens of said second lens group.

6. The fisheye lens according to claim 1, wherein said first and second lens groups are so constructed as to be relatively movable to further satisfy the following condition:

space="preserve" listing-type="equation">0≦

X.sub.2 /X.sub.1 ≦

0.8

where

X₁ ;

the moving quantity of said first lens group during focusing, and

X₂ ;

the moving quantity of said second lens group during focusing.

7. The fisheye lens according to claim 1, wherein said first lens group is constructed of, sequentially from the object, a first negative meniscus lens with its convex surface toward the object, a second negative meniscus lens with its convex surface toward the object and a cemented positive lens consisting of a biconvex positive lens and a negative meniscus lens, said second lens group is constructed of, sequentially from, a cemented lens consisting of a negative lens and a biconvex positive lens and a cemented lens consisting of a biconvex positive lens and a negative meniscus lens, an aperture stop is disposed between said first and second lens groups, and a filter is disposed closer to the image than said second lens group.

8. The fisheye lens according to claim 1, wherein said first lens group is constructed of, sequentially from the object, a first meniscus lens with its convex surface toward the object, a second negative meniscus lens with its convex surface toward the object, a cemented positive lens consisting of a biconvex positive lens and a negative meniscus lens, an aperture stop and a cemented positive lens consisting of a negative lens and a biconvex positive lens, said second lens group is constructed of a cemented positive lens consisting of a biconvex positive lens and a negative meniscus lens, and a filter is disposed closer to the image than said second lens group.

9. The fisheye lens according to claim 1, wherein said first lens group is constructed of, sequentially from the object, a first negative meniscus lens with its convex surface toward the object, a positive meniscus lens with its convex surface toward the object, a second negative meniscus lens with its convex surface toward the object and a biconvex positive lens, said second lens group is constructed of, sequentially from the object, a filter, a positive meniscus lens with its convex surface toward the object, a positive meniscus lens with its convex surface toward the image and a cemented positive lens consisting of a biconvex positive lens and a negative meniscus lens, and an aperture stop is disposed between said first lens group and said filter of said second lens group.

10. The fisheye lens according to claim 1, wherein said first lens group is constructed of, sequentially from the object, a first negative meniscus lens with its convex surface toward the object, a positive meniscus lens with its convex surface toward the object and a second negative meniscus lens with its convex surface toward the object, and second lens group is constructed of, sequentially from the object, a biconvex positive lens, an aperture stop, a filter, a positive meniscus lens with its convex surface toward the object, a positive meniscus lens with its convex surface toward the image and a cemented lens consisting of a biconvex positive lens and a negative meniscus lens.

11. The fisheye lens according to claim 1, wherein said first lens group is constructed of, sequentially from the object, a first negative meniscus lens with its convex surface toward the object, a positive meniscus lens with its convex surface toward the object, a second negative meniscus lens with its convex surface toward the object, a biconvex positive lens, an aperture stop, a filter, a positive meniscus lens with its convex surface toward the object and a positive meniscus lens with its convex surface toward the image, and said second lens group is constructed of only a cemented positive lens consisting of a biconvex positive lens and a negative meniscus lens.

12. The fisheye lens according to claim 1, wherein said first lens group is constructed of, sequentially from the object, a first negative meniscus lens with its convex surface toward the object, a second negative meniscus lens with its convex surface similarly toward the object, a biconvex positive lens and a negative lens with its closer-to-object concave surface toward the object, said second lens group is constructed of a positive lens with its convex surface having a larger curvature toward the image and a cemented positive lens consisting of a biconvex positive lens and a negative meniscus lens, and an aperture stop is disposed between said first and second lens groups.

13. The fisheye lens according to claim 1, wherein said lens is constructed in accordance with the following data:

space="preserve" listing-type="tabular">______________________________________ f = 15.7 2ω

= 180°

F.sub.NO =2.9 r d ν

n ______________________________________ 1 69.258 1.70 60.0 1.64000 2 15.165 10.25 3 130.505 1.70 60.1 1.62041 4 14.794 4.00 5 32.412 8.00 35.7 1.62588 6 -15.298 9.00 45.4 1.79668 7 -38.750 (d7) 8 -81.004 1.20 40.8 1.58144 9 24.002 5.00 58.9 1.51823 10 -20.609 0.10 11 46.733 5.50 70.0 1.51860 12 -19.219 1.30 26.1 1.78470 13 -40.706 0.88 14 0.000 1.20 64.1 1.51680 15 0.000 (Bf) ______________________________________

(Variable space during infinity focusing and short distance focusing when β

=1/30)

space="preserve" listing-type="tabular">______________________________________ f 15.6686 D0 ∞

d7 10.9883 Bf 38.5974 β

-0.0333 D0 457.2746 d7 11.3033 Bf 39.0700 ______________________________________

Note that the condition corresponding values in the embodiments discussed above are shown as below;

space="preserve" listing-type="equation">X.sub.2 /X.sub.1 =0.6 (1)

space="preserve" listing-type="equation">α

=-0.3898 (2)

space="preserve" listing-type="equation">f.sub.2 /f=1.96 (3)

space="preserve" listing-type="equation">n.sub.n -n.sub.P =0.266 (4)

space="preserve" listing-type="equation">ν

d.sub.1 =60.0 (5)

where in the Table given above, f is the focal length, F_NO is the F-number, and 2ω

is the field angle, the numerals at the left end then represent the order from the object side, r is the radius of curvature of the lens surface, d is the space between the lens surfaces, the refractive index n and the Abbe number ν

are values with respect to the d-line (λ

=587.6 nm), d0 is the distance from the object to the top of the closest-to-object lens, Bf is the back focus, β

is the magnification, α

is the conversion inclination obtained by multiplying an angle between the paraxial marginal ray emerging from an on-axis infinity object point that is incident on the closest-to-object lens surface of said second lens group and the optical axis by the refractive index of a medium just before said surface, f₂ is the synthetic focal length of said second lens group, n_P is the refractive index, with resect to the d-line, of said positive lens constituting a part of said closest-to-image cemented lens of said second lens group, n_n is the refractive index, with respect to the d-line, of said negative lens constituting a part of said closest-to-image cemented lens of said second lens group, and ν

d₁ is the Abbe number of said negative meniscus lens positioned closest to the object.

14. The fisheye lens according to claim 1, wherein said lens is constructed in accordance with the following data:

space="preserve" listing-type="tabular">______________________________________ f = 15.7 2ω

= 180°

F.sub.NO = 2.9 r d ν

n ______________________________________ 1 69.258 1.70 60.0 1.64000 2 15.165 10.25 3 130.505 1.70 60.1 1.62041 4 14.794 4.00 5 32.412 8.00 35.7 1.62588 6 -15.298 9.00 45.4 1.79668 7 -38.750 10.98 8 -81.004 1.20 40.8 1.58144 9 24.002 5.00 58.9 1.51823 10 -20.608 (d10) 11 46.733 5.50 70.0 1.51860 12 -19.219 1.30 26.1 1.78470 13 -40.706 0.85 14 0.000 1.20 64.1 1.51680 15 0.000 (Bf) ______________________________________

(Variable space during infinity focusing and short distance focusing when β

=1/30)

space="preserve" listing-type="tabular">______________________________________ f 15.6686 d10 0.0890 Bf 38.6304 β

-0.0333 D0 461.5288 d10 1.0964 Bf 39.0621 ______________________________________

Note that the condition corresponding values in the embodiments discussed above are shown as below;

space="preserve" listing-type="equation">X.sub.2 /X.sub.1 =0.3 (1)

space="preserve" listing-type="equation">α

=0.3033 (2)

space="preserve" listing-type="equation">f.sub.2 /f=3.91 (3)

space="preserve" listing-type="equation">n.sub.n -n.sub.P =0.266 (4)

space="preserve" listing-type="equation">ν

d.sub.1 =60.0 (5)

where in the Table given above, f is the focal length, F_NO is the F-number, and 2ω

is the field angle, the numerals at the left end then represent the order from the object side, r is the radius of curvature of the lens surface, d is the space between the lens surfaces, the refractive index n and the Abbe number ν

are values with respect to the d-line (λ

=587.6 nm), d0 is the distance from the object to the top of the closest-to-object lens, Bf is the back focus, β

is the magnification, α

is the conversion inclination obtained by multiplying an angle between the paraxial marginal ray emerging from an on-axis infinity object point that is incident on the closest-to-object lens surface of said second lens group and the optical axis by the refractive index of a medium just before said surface, f₂ is the synthetic focal length of said second lens group, n_P is the refractive index, with resect to the d-line, of said positive lens constituting a part of said closest-to-image cemented lens of said second lens group, n_n is the refractive index, with respect to the d-line, of said negative lens constituting a part of said closes-to-image cemented lens of said second lens group, and ν

d₁ is the Abbe number of said negative meniscus lens positioned closest to the object.

15. The fisheye lens according to claim 1, wherein said lens is constructed in accordance with the following data:

space="preserve" listing-type="tabular">______________________________________ f = 15.4 2ω

= 180°

F.sub.NO = 2.84 r d ν

n ______________________________________ 1 66.028 1.96 57.5 1.67025 2 12.061 8.00 3 59.825 2.95 25.5 1.73038 4 300.320 0.98 5 223.777 1.96 60.0 1.64000 6 17.224 4.90 7 62.981 9.80 28.3 1.72825 8 -171.272 (d8) 9 0.000 1.80 64.2 1.51680 10 0.000 0.78 11 20.191 3.90 65.7 1.46450 12 21.788 1.65 13 -76.172 2.80 65.7 1.46450 14 -17.891 0.05 15 42.043 7.36 70.4 1.48749 16 -13.281 1.00 23.0 1.86074 17 -21.946 (Bf) ______________________________________

(Variable space during infinity focusing and short distance focusing when β

=1/30)

space="preserve" listing-type="tabular">______________________________________ f 15.4091 D0 ∞

d8 2.9400 Bf 38.0000 β

-0.0333 D0 449.7175 d8 3.1813 Bf 38.3615 ______________________________________

Note that the condition corresponding values in the embodiments discussed above are shown as below;

space="preserve" listing-type="equation">X.sub.2 /X.sub.1 =0.6 (1)

space="preserve" listing-type="equation">α

=-0.7854 (2)

space="preserve" listing-type="equation">f.sub.2 /f=1.58 (3)

space="preserve" listing-type="equation">n.sub.n -n.sub.P =0.373 (4)

space="preserve" listing-type="equation">ν

d.sub.1 =57.5 (5)

where in the Table given above, f is the focal length, F_NO is the F-number, and 2ω

is the field angle, the numerals at the left end then represent the order from the object side, r is the radius of curvature of the lens surface, d is the space between the lens surfaces, the refractive index n and the Abbe number ν

are values with respect to the d-line (λ

=587.6 nm), d0 is the distance from the object to the top of the closest-to-object lens, Bf is the back focus, β

is the magnification, α

is the conversion inclination obtained by multiplying an angle between the paraxial marginal ray emerging from an on-axis infinity object point that is incident on the closest-to-object lens surface of said second lens group and the optical axis by the refractive index of a medium just before said surface, f₂ is the synthetic focal length of said second lens group, n_P is the refractive index, with resect to the d-line, of said positive lens constituting a part of said closest-to-image cemented lens of said second lens group, n_n is the refractive index, with respect to the d-line, of said negative lens constituting a part of said closes-to-image cemented lens of said second lens group, and ν

d₁ is the Abbe number of said negative meniscus lens positioned closest to the object.

16. The fisheye lens according to claim 1, wherein said lens is constructed in accordance with the following data:

space="preserve" listing-type="tabular">______________________________________ f = 15.4 2ω

= 180°

F.sub.NO = 2.87 r d ν

n ______________________________________ 1 69.933 1.96 57.5 1.67025 2 12.013 8.00 3 58.325 2.95 25.5 1.73038 4 312.507 0.96 5 216.905 1.96 60.0 1.64000 6 17.063 (d6) 7 63.606 9.71 28.3 1.72825 8 -166.033 2.94 9 0.000 1.80 64.2 1.51680 10 0.000 0.78 11 20.159 3.90 65.8 1.46450 12 21.871 1.65 13 -75.031 2.80 65.8 1.46450 14 -17.884 0.05 15 41.834 7.36 70.5 1.48749 16 -13.257 1.00 23.0 1.86074 17 -22.051 (Bf) ______________________________________

(Variable space during infinity focusing and short distance focusing when β

=1/30)

space="preserve" listing-type="tabular">______________________________________ f 15.4091 D0 ∞

d6 5.0214 Bf 38.0008 β

-0.0333 D0 444.7335 d6 5.3444 Bf 38.0008 ______________________________________

Note that the condition corresponding values in the embodiments discussed above are shown as below.

space="preserve" listing-type="equation">X.sub.2 /X.sub.1 =0 (1)

space="preserve" listing-type="equation">α

=-1.2610 (2)

space="preserve" listing-type="equation">f.sub.2 /f=1.41 (3)

space="preserve" listing-type="equation">n.sub.n -n.sub.P =0.373 (4)

space="preserve" listing-type="equation">ν

d.sub.1 =57.5

where in the Table given above, f is the focal length, F_NO is the F-number, and 2ω

is the field angle, the numerals at the left end then represent the order from the object side, r is the radius of curvature of the lens surface, d is the space between the lens surfaces, the refractive index n and the Abbe number ν

are values with respect to the d-line (λ

=587.6 nm), d0 is the distance from the object to the top of the closest-to-object lens, Bf is the back focus, β

is the magnification, α

is the conversion inclination obtained by multiplying an angle between the paraxial marginal ray emerging from an on-axis infinity object point that is incident on the closest-to-object lens surface of said second lens group and the optical axis by the refractive index of a medium just before said surface, f₂ is the synthetic focal length of said second lens group, n_P is the refractive index, with respect to the d-line, of said positive lens constituting a part of said closest-to-image cemented lens of said second lens group, n_n is the refractive index, with respect to the d-line, of said negative lens constituting a part of said closest-to-image cemented lens of said second lens group, and ν

d₁ is the Abbe number of said negative meniscus lens positioned closest to the object.

17. The fisheye lens according to claim 1, wherein said lens is constructed in accordance with the following data:

space="preserve" listing-type="tabular">______________________________________ f = 15.4 2ω

= 180°

F.sub.NO = 2.86 r d ν

n ______________________________________ 1 66.028 1.96 57.5 1.67025 2 12.061 8.00 3 59.825 2.95 25.5 1.73038 4 223.777 0.98 5 223.777 1.96 60.0 1.64000 6 17.224 4.90 7 62.981 9.80 28.3 1.72825 8 -171.273 2.94 9 0.000 1.80 64.2 1.51680 10 0.000 0.78 11 20.191 3.90 65.8 1.46450 12 21.788 1.65 13 -76.172 2.80 65.8 1.46450 14 -17.891 (d14) 15 42.043 7.36 70.4 1.48749 16 -13.281 1.00 23.0 1.86074 17 -21.946 (Bf) ______________________________________

(Variable space during infinity focusing and short distance focusing when β

=1/30)

space="preserve" listing-type="tabular">______________________________________ f 15.4091 D0 ∞

d14 0.0500 Bf 37.9996 β

-0.0333 D0 453.6264 d14 0.3253 Bf 38.5108 ______________________________________

Note that the condition corresponding values in the embodiments discussed above are shown as below;

space="preserve" listing-type="equation">X.sub.2 /X.sub.1 =0.65 (1)

space="preserve" listing-type="equation">α

=0.0999 (2)

space="preserve" listing-type="equation">f.sub.2 /f=2.9 (3)

space="preserve" listing-type="equation">n.sub.n -n.sub.P =0.373 (4)

space="preserve" listing-type="equation">ν

d.sub.1 =57.5 (5)

where in the Table given above, f is the focal length, F_NO is the F-number, and 2ω

is the field angle, the numerals at the left end then represent the order from the object side, r is the radius of curvature of the lens surface, d is the space between the lens surfaces, the refractive index n and the Abbe number ν

are values with respect to the d-line (λ

=587.6 nm), d0 is the distance from the object to the top of the closest-to-object lens, Bf is the back focus, β

is the magnification, α

is the conversion inclination obtained by multiplying an angle between the paraxial marginal ray emerging from an on-axis infinity object point that is incident on the closest-to-object lens surface of said second lens group and the optical axis by the refractive index of a medium just before said surface, f₂ is the synthetic focal length of said second lens group, n_P is the refractive index, with resect to the d-line, of said positive lens constituting a part of said closest-to-image cemented lens of said second lens group, n_n is the refractive index, with respect to the d-line, of said negative lens constituting a part of said closest-to-image cemented lens of said second lens group, and ν

d₁ is the Abbe number of said negative meniscus lens positioned closest to the object.

18. The fisheye lens according to claim 1, wherein said lens is constructed in accordance with the following data:

space="preserve" listing-type="tabular">______________________________________ f = 15.3 2ω

= 180°

F.sub.NO = 2.83 r d ν

n ______________________________________ 1 73.110 2.47 55.5 1.69680 2 15.370 14.83 3 40.310 2.47 43.9 1.78590 4 13.520 5.27 5 24.210 3.51 26.6 1.76182 6 -44.260 1.00 7 -31.100 12.14 33.4 1.80610 8 1200.000 (d8) 9 174.000 6.42 70.4 1.48749 10 -17.950 0.10 11 53.680 5.05 70.4 1.48749 12 -14.000 1.00 25.5 1.80518 13 -30.720 (Bf) ______________________________________

(Variable space during infinity focusing and short distance focusing when β

=1/30)

space="preserve" listing-type="tabular">______________________________________ f 15.3008 D0 ∞

d8 3.2700 Bf 38.9928 β

-0.0333 D0 443.8347 d8 3.5129 Bf 39.3571 ______________________________________

Note that the condition corresponding values in the embodiments discussed above are shown as below;

space="preserve" listing-type="equation">X.sub.2 /X.sub.1 =0.6

     91)

space="preserve" listing-type="equation">α

=-0.7671 (2)

space="preserve" listing-type="equation">f.sub.2 /f=1.58 (3)

space="preserve" listing-type="equation">n.sub.n -n.sub.P =0.318 (4)

space="preserve" listing-type="equation">ν

d.sub.1 =55.5 (5)

where in the Table given above, f is the focal length, F_NO is the F-number, and 2ω

is the field angle, the numerals at the left end then represent the order from the object side, r is the radius of curvature of the lens surface, d is the space between the lens surfaces, the refractive index n and the Abbe number ν

are values with respect to the d-line (λ

=587.6 nm), d0 is the distance from the object to the top of the closest-to-object lens, Bf is the back focus, β

is the magnification, α

is the conversion inclination obtained by multiplying an angle between the paraxial marginal ray emerging from an on-axis infinity object point that is incident on the closest-to-object lens surface of said second lens group and the optical axis by the refractive index of a medium just before said surface, f₂ is the synthetic focal length of said second lens group, n_P is the refractive index, with respect to the d-line, of said positive lens constituting a part of said closest-to-image cemented lens of said second lens group, n_n is the refractive index, with respect to the d-line, of said negative lens constituting a part of said closest-to-image cemented lens of said second lens group, and ν

d₁ is the Abbe number of said negative meniscus lens positioned closest to the object.

19. A fisheye lens incorporating a short distance compensating function, comprising:

a first lens group including at least one negative meniscus lens, positioned closest to an object, with its convex surface toward the object and at least one positive lens;

a second lens group including a cemented positive lens consisting of a positive lens and a negative lens and disposed closer to an image than said first lens group to have positive refractive power on the whole,

wherein when focusing from an infinity object point onto a short distance object point, said first and second lens groups are so constructed as to be relatively movable on the optical axis toward the object to expand an air space between said first and second lens groups.

20. The fisheye lens according to claim 19, wherein said first and second lens groups are constructed to satisfy the following condition:

space="preserve" listing-type="equation">0≦

X.sub.2 /X.sub.1 ≦

0.9

where X₁ is the moving quantity of said first lens group G₁ during focusing, and X₂ is the moving quantity of said second lens group G₂ during focusing.

21. The fisheye lens according to claim 19, wherein said first lens group is constructed so that a conversion inclination is set to satisfy the following condition:

space="preserve" listing-type="equation">-1.5≦

α

≦

1

where α

is the conversion inclination obtained by multiplying an angle between the paraxial marginal ray emerging from an on-axis infinity object point that is incident on the closest-to-object lens surface of said second lens group and the optical axis by a refractive index of a medium just before said surface.

22. The fisheye lens according to claim 19, wherein said second lens group is constructed to further satisfy the following condition:

space="preserve" listing-type="equation">1≦

f.sub.2 /f≦

5

where

f;

the focal length of the whole lens system, and

f₂ ;

the focal length of said second lens group.

23. The fisheye lens group according to claim 19, wherein said first lens group is constructed to satisfy the following condition:

space="preserve" listing-type="equation">52≦

ν

d.sub.1

where ν

d₁ is the Abbe number of said negative meniscus lens positioned closest to the object in said first lens group.

24. The fisheye lens according to claim 19, wherein said second lens group includes a cemented positive lens positioned closest to the image and consisting of a positive lens and a negative lens, and said cemented positive lens is constructed to satisfy the following condition:

space="preserve" listing-type="equation">0.15≦

n.sub.P -n.sub.n

where

n_P ;

the refractive index, with respect to the d-line, of said positive lens constituting a part of said closest-to-image cemented lens of said second lens group, and

n_n ;

the refractive index, with respect to the d-line, of said negative lens constituting a part of said closest-to-image cemented lens of said second lens group.

25. The fisheye lens according to claim 19, wherein said first and second lens groups are so constructed as to be relatively movable to further satisfy the following condition:

space="preserve" listing-type="equation">0≦

X.sub.2 /X.sub.1 ≦

0.8

where

X₁ ;

the moving quantity of said first lens group during focusing, and

X₂ ;

the moving quantity of said second lens group during focusing.

26. The fisheye lens according to claim 19, wherein said first lens group is constructed of, sequentially from the object, a first negative meniscus lens with its convex surface toward the object, a second negative meniscus lens with its convex surface toward the object and a cemented positive lens consisting of a biconvex positive lens and a negative meniscus lens, said second lens group is constructed of, sequentially from, a cemented lens consisting of a negative lens and a biconvex positive lens and a cemented lens consisting of a biconvex positive lens and a negative meniscus lens, an aperture stop is disposed between said first and second lens groups, and a filter is disposed closer to the image than said second lens group.

27. The fisheye lens according to claim 19, wherein said first lens group is constructed of, sequentially from the object, a first meniscus lens with its convex surface toward the object, a second negative meniscus lens with its convex surface toward the object, a cemented positive lens consisting of a biconvex positive lens and a negative meniscus lens, an aperture stop and a cemented positive lens consisting of a negative lens and a biconvex positive lens, said second lens group is constructed of a cemented positive lens consisting of a biconvex positive lens and a negative meniscus lens, and a filter is disposed closer to the image than said second lens group.

28. The fisheye lens according to claim 19, wherein said first lens group is constructed of, sequentially from the object, a first negative meniscus lens with its convex surface toward the object, a positive meniscus lens with its convex surface toward the object, a second negative meniscus lens with its convex surface toward the object and a biconvex positive lens, said second lens group is constructed of, sequentially from the object, a filter, a positive meniscus lens with its convex surface toward the object, a positive meniscus lens with its convex surface toward the image and a cemented positive lens consisting of a biconvex positive lens and a negative meniscus lens, and an aperture stop is disposed between said first lens group and said filter of said second lens group.

29. The fisheye lens according to claim 19, wherein said first lens group is constructed of, sequentially from the object, a first negative meniscus lens with its convex surface toward the object, a positive meniscus lens with its convex surface toward the object and a second negative meniscus lens with its convex surface toward the object, and second lens group is constructed of, sequentially from the object, a biconvex positive lens, an aperture stop, a filter, a positive meniscus lens with its convex surface toward the object, a positive meniscus lens with its convex surface toward the image and a cemented lens consisting of a biconvex positive lens and a negative meniscus lens.

30. The fisheye lens according to claim 19, wherein said first lens group is constructed of, sequentially from the object, a first negative meniscus lens with its convex surface toward the object, a positive meniscus lens with its convex surface toward the object, a second negative meniscus lens with its convex surface toward the object, a biconvex positive lens, an aperture stop, a filter, a positive meniscus lens with its convex surface toward the object and a positive meniscus lens with its convex surface toward the image, and said second lens group is constructed of only a cemented positive lens consisting of a biconvex positive lens and a negative meniscus lens.

31. The fisheye lens according to claim 19, wherein said first lens group is constructed of, sequentially from the object, a first negative meniscus lens with its convex surface toward the object, a second negative meniscus lens with its convex surface similarly toward the object, a biconvex positive lens and a negative lens with its closest-to-object concave surface toward the object, said second lens group is constructed of a positive lens with its convex surface having a larger curvature toward the image and a cemented positive lens consisting of a biconvex positive lens and a negative meniscus lens, and an aperture stop is disposed between said first and second lens groups.