Compact super wide-angle imaging system
A super wide-angle imaging system has a short total track length. The lens system is a retrofocus type lens system that uses only a few lenses with no cemented lens elements. Acceptable performance is achieved by taking advantage of subsequent digital image processing. The compact lens system is designed to create optical images that can be restored by subsequent digital processing that compensates for otherwise unacceptable aberrations introduced by the lens system.
1. An imaging system comprising:
an image-forming lens system consisting of, in order from object to image:
a first negatively powered lens group consisting of two negatively powered non-cemented lenses L 1 and L 2 ; and
a second positively powered lens group consisting of three positively powered non-cemented lenses L 3 , L 4 and L 5 , wherein the lenses are positioned in the order L 1 , L 2 , L 3 , L 4 , L 5 from the object to the image;
the first and second lens groups acting in concert to image a field of view of at least 180 degrees onto an image plane; and
a sensor array located at a focal plane of the lens system, the sensor array operating in three color bands wherein, at a central wavelength of each color band and for every field angle within the field of view, a modulation transfer function of the lens system does not fall below approximately 10% of the diffraction limited modulation transfer function for spatial frequencies below a pixel sampling rate for the color band.
2. The imaging system of claim 1 wherein the image plane has an image height h m and the lens system has a total track length of not more than 10h m .
3. The imaging system of claim 1 wherein lens L 5 is an aspheric lens.
4. The imaging system of claim 3 wherein lenses L 1 -L 4 are spherical lenses.
5. The imaging system of claim 3 wherein either lens L 3 or L 4 is an aspheric lens.
6. The imaging system of claim 1 wherein a ratio of a focal length f 1 of the lens L 1 to a focal length f 2 of the lens L 2 falls in the range:
1.2
≤
f
1
f
2
≤
3.8
.
7. The imaging system of claim 1 wherein a ratio of a focal length f G1 of the first lens group to the maximum image height h m falls in the range:
0.9
≤
f
G
1
h
m
≤
1.9
.
8. The imaging system of claim 1 wherein a ratio of a focal length f G1 of the first lens group to an effective focal length f of the lens system falls in the range:
2.0
≤
f
G
1
f
≤
4.0
.
9. The imaging system of claim 1 wherein a ratio of a focal length f 3 of the lens L 3 to an effective focal length f 45 of the lenses L 4 and L 5 together falls in the range:
4.0
≤
f
3
f
45
≤
50.
10. The imaging system of claim 1 wherein a ratio of a focal length f 4 of the lens L 4 to a focal length f 5 of the lens L 5 falls in the range:
1.6
≤
f
4
f
5
≤
40.
11. The imaging system of claim 1 wherein a ratio of a total lens length Σd of the lens system to an effective focal length f of the lens system falls in the range
10
≤
Σ
d
f
≤
22.
12. The imaging system of claim 1 further comprising:
digital processing communicatively coupled to the sensor array, for digitally filtering the images captured by the sensor array.
13. An image-forming lens system consisting of, in order from object to image:
a first negatively powered lens group consisting of two negatively powered non-cemented lenses L 1 and L 2 , wherein a ratio of a focal length f 1 of the lens L 1 to a focal length f 2 of the lens L 2 falls in the range
1.5
≤
f
1
f
2
≤
2.2
;
and
a second positively powered lens group consisting of three positively powered non-cemented lenses L 3 , L 4 and L 5 , wherein the lenses are positioned in the order L 1 , L 2 , L 3 , L 4 , L 5 from the object to the image;
the first and second lens groups acting in concert to image a field of view of at least 180 degrees onto an image plane.
14. An imaging system comprising:
an image-forming lens system consisting of, in order from object to image:
a first negatively powered lens group consisting of two negatively powered non-cemented lenses L 1 and L 2 ; and
a second positively powered lens group consisting of three positively powered non-cemented lenses L 3 , L 4 and L 5 , wherein the lenses are positioned in the order L 1 , L 2 , L 3 , L 4 , L 5 from the object to the image;
the first and second lens groups acting in concert to image a field of view of at least 180 degrees onto an image plane; and
a sensor array located at a focal plane of the lens system, the sensor array operating in three color bands wherein, for each color band, for all wavelengths in that color band and for every field angle within the field of view, a modulation transfer function of the optical system does not cross zero at any spatial frequency below a pixel sampling rate for the color band.
15. An imaging system comprising:
an image-forming lens system consisting of, in order from object to image:
a first negatively powered lens group consisting of two negatively powered lenses L 1 and L 2 ; and
a second positively powered lens group consisting of two positively powered lenses L 3 and L 4 , wherein the lenses are positioned in the order L 1 , L 2 , L 3 , L 4 from the object to the image; and
a sensor array located at a focal plane of the lens system, the sensor array operating in three color bands wherein, at a central wavelength of each color band and for every field angle within the field of view, a modulation transfer function of the lens system does not fall below approximately 10% of the diffraction limited modulation transfer function for spatial frequencies below a pixel sampling rate for the color band.
16. The imaging system of claim 15 wherein lens L 4 is an aspheric lens.
17. The imaging system of claim 15 wherein lenses L 1 -L 3 are spherical lenses.
18. The imaging system of claim 15 wherein lens L 3 is an aspheric lens.
19. The imaging system of claim 15 wherein a ratio of a focal length f 3 of the lens L 3 to a focal length f 4 of the lens L 4 falls in the range:
0.55
≤
f
3
f
4
≤
2.7
.
20. The imaging system of claim 15 wherein a ratio of a total lens length Σd of the lens system to an effective focal length f of the lens system falls in the range
8.0
≤
Σ
d
f
≤
20.
21. The imaging system of claim 15 further comprising:
digital processing communicatively coupled to the sensor array, for digitally filtering the images captured by the sensor array.
22. An image-forming lens system consisting of, in order from object to image:
a first negatively powered lens group consisting of two negatively powered lenses L 1 and L 2 , wherein a ratio of a focal length f 1 of the lens L 1 to a focal length f 2 of the lens L 2 falls in the range
1.5
≤
f
1
f
2
≤
4.0
;
and
a second positively powered lens group consisting of two positively powered lenses L 3 and L 4 , wherein the lenses are positioned in the order L 1 , L 2 , L 3 , L 4 from the object to the image.
23. An image-forming lens system consisting of, in order from object to image:
a first negatively powered lens group consisting of two negatively powered lenses L 1 and L 2 , wherein a ratio of a focal length f 1 of the lens L 1 to a focal lengthf 2 of the lens L 2 falls in the range
1.5
≤
f
1
f
2
≤
2.2
;
and
a second positively powered lens group consisting of two positively powered lenses L 3 and L 4 , wherein the lenses are positioned in the order L 1 , L 2 , L 3 , L 4 from the object to the image.
24. An imaging system comprising:
an image-forming lens system consisting of, in order from object to image:
a first negatively powered lens group consisting of two negatively powered lenses L 1 and L 2 ; and
a second positively powered lens group consisting of two positively powered lenses L 3 and L 4 , wherein the lenses are positioned in the order L 1 , L 2 , L 3 , L 4 from the object to the image; and
a sensor array located at a focal plane of the lens system, the sensor array operating in three color bands wherein, for each color band, for all wavelengths in that color band and for every field angle within the field of view, a modulation transfer function of the optical system does not cross zero at any spatial frequency below a pixel sampling rate for the color band.