Compact wide-angle lens
View Patent ↗An object of the present invention is to create a wide-angle lens that is compact, having a lower front diameter to image circle ratio. Such a lens can be used in space constrained applications such as endoscopy or other applications requiring a wide field of view and a compact design. The lens design includes three lens groups and are scalable. The designs are further characterized by a set of parametric equations defining relationships between ratios of focal lengths for the lens groups and lens elements within the groups. This design can be scaled to a smaller absolute size for space constrained applications, or enlarged to cover an even large image circle.
1 . A wide-angle lens assembly having a field of view of at least 90 degrees, an effective focal length of f0, and, the wide-angle lens assembly comprising from object to image:
a. a first group having a negative refractive power and an effective focal length of f1, the first group comprising two lens elements: a first negative powered lens element having a convex object surface, a concave image surface and a clear aperture of the object side of D1, and a second lens element that has a meniscus shape with a concave object surface, a convex image surface and at least one of the two surfaces is aspherical, and,
b. a second positive powered group having an effective focal length of f2 and comprising a first positive powered lens element and a positively powered cemented doublet with an effective focal length of fd, and,
c. a third group having a focal length of f3, and, comprising an aspherical lens element with negative power.
2 . The wide-angle lens assembly of claim 1 where a negative element of the cemented doublet faces the object side and where a positive element of the doublet faces the image side.
3 . The wide-angle lens assembly of claim 1 the wide angle lens assembly forming an image circle having a diameter IC and the ratio D1/IC<1.5.
4 . The wide-angle lens assembly of claim 1 where the positive elements in the second group have negative dn/dT values, where n is the refractive index of the lens material at d-line and T is the temperature.
5 . The wide-angle lens assembly of claim 1 where the aspherical lens element of Group 3 is an aspherical lens element with inflection points.
6 . The wide-angle lens assembly of claim 1 where the following conditions are satisfied:
a
.
f
1
/
f
0
=
<
-
1.5
(
1
)
b
.
1.2
=
<
f
2
/
f
0
=
<
1.8
(
2
)
c
.
f
3
/
f
0
=
<
-
3.
(
3
)
d
.
1.5
=
<
fd
/
f
2
=
<
3.5
(
4
)
e
.
2.2
=
<
fd
/
f
0
=
<
5.5
.
(
5
)
7 . The wide-angle lens assembly of claim 2 where the following conditions are satisfied:
a
.
f
1
/
f
0
=
<
-
1.5
(
1
)
b
.
1.2
=
<
f
2
/
f
0
=
<
1.8
(
2
)
c
.
f
3
/
f
0
=
<
-
3.
(
3
)
d
.
1.5
=
<
fd
/
f
2
=
<
3.5
(
4
)
e
.
2.2
=
<
fd
/
f
0
=
<
5.5
.
(
5
)
8 . The wide-angle lens assembly of claim 1 where the following conditions are satisfied:
a
.
f
1
/
f
0
<
-
2.
.
(
1
)
9 . The wide-angle lens assembly of claim 1 where the following conditions are satisfied:
a
.
1.5
<
f
2
/
f
0
<
1.8
.
(
2
)
10 . The wide-angle lens assembly of claim 1 where the following conditions are satisfied:
a
.
f
3
/
f
0
<
-
7.
.
(
3
)
11 . The wide-angle lens assembly of claim 1 where the following conditions are satisfied:
a
.
1.5
<
fd
/
f
2
<
2.
.
(
4
)
12 . The wide-angle lens assembly of claim 1 where the following conditions are satisfied:
a
.
3.5
<
fd
/
f
0
<
4.
.
(
5
)
13 . The wide-angle lens assembly of claim 1 where the following conditions are satisfied:
a
.
f
1
/
f
0
<
-
2.
(
1
)
b
.
1.5
<
f
2
/
f
0
<
1.8
(
2
)
c
.
f
3
/
f
0
<
-
7.
(
3
)
d
.
1.8
<
fd
/
f
2
<
2.2
(
4
)
e
.
3.
<
fd
/
f
0
<
4.
(
5
)
f
.
1.2
<
D
1
/
I
C
<
1.5
.
(
6
)