Optical: systems and elements – Lens – With variable magnification
Reexamination Certificate
2002-09-18
2004-01-06
Epps, Georgia (Department: 2873)
Optical: systems and elements
Lens
With variable magnification
C359S684000
Reexamination Certificate
active
06674581
ABSTRACT:
BACKGROUND OF THE INVENTION
In general, the back flange length of a mount in a television camera varies among individual cameras even though they satisfy the same standard. Therefore, after a lens is mounted in a television camera, the back focus is adjusted so that the image pick-up plane of the television camera coincides with the image plane of the lens. Back focus adjustment is performed by moving one or more lens elements of a lens group in order to adjust the image plane position.
PRIOR ART EXAMPLE 1
A prior art zoom lens used in a broadcast television camera that employs a tricolor separation prism is shown in FIG.
17
. This zoom lens includes an afocal part and a lens group having a complex structure that is moved for adjusting the axial position of the image plane. Therefore, aberrations are sufficiently corrected and lens performance is sufficiently maintained after the lens is moved in order to make the position of the image plane coincide with the image pick-up plane of the television camera.
As shown in
FIG. 17
, wherein X is the optical axis, the zoom lens of Prior Art Example 1 is formed of, in order from the object side, a first lens group I having a first lens L
1
through a fifth lens L
5
, a second lens group II having a sixth lens L
6
through a ninth lens L
9
, a third lens group III having a tenth lens L
10
and an eleventh lens L
11
, and a fourth lens group IV having a front subgroup IVa and a rear subgroup IVb. The front subgroup IVa is formed of a twelfth lens L
12
through a fifteenth lens L
15
and the rear subgroup IVb is formed of a sixteenth lens L16 through a twenty-first lens L
21
. A diaphragm stop
1
is positioned on the object side of front subgroup IVa of the fourth lens group. A tricolor separation prism
4
and a filter
2
are positioned between the rear subgroup IVb of the fourth lens group and the image plane R
42
. An image sensor
3
, in this instance a CCD, is provided at the image plane. The image sensor
3
, tricolor separation prism
4
, and filter
2
are provided in the television camera body.
Table 1 below shows the surface # in order from the object side, the radius of curvature R (in mm) of each surface, the on-axis spacing D (in mm) between surfaces, as well as the refractive index N
e
and Abbe number &ngr;
e
(both at the e-line) of the lens elements of the zoom lens of Prior Art Example 1.
TABLE 1
#
R
D
N
e
&ngr;
e
1
−167.933
2.506
1.81264
25.2
2
205.525
5.917
3
∞
8.182
1.43496
94.6
4
−123.571
0.116
5
284.452
7.902
1.43496
94.6
6
−212.171
7.497
7
124.045
9.502
1.57098
70.9
8
−302.956
0.116
9
64.461
6.206
1.82016
46.4
10
130.958
D10
11
54.496
0.771
1.83932
36.9
12
14.181
6.852
13
−61.901
0.771
1.83945
42.5
14
40.862
1.368
15
25.631
4.732
1.85501
23.7
16
−49.180
0.665
17
−32.185
0.771
1.77620
49.3
18
79.600
D18
19
−27.304
0.771
1.75843
52.1
20
41.637
2.390
1.85501
23.7
21
∞
D21
22
∞ (stop)
1.706
23
213.835
4.828
1.52033
58.7
24
−34.837
0.116
25
153.522
3.267
1.59143
61.0
26
−2088.371
0.116
27
51.765
7.016
1.52033
58.7
28
−36.176
1.205
1.80810
46.3
29
−518.539
32.938
30
49.070
4.655
1.51825
63.9
31
−82.602
0.116
32
34.236
6.180
1.48914
70.2
33
−41.312
1.253
1.83945
42.5
34
21.220
3.442
35
31.261
8.163
1.51825
63.9
36
−22.118
1.205
1.83945
42.5
37
−94.916
0.116
38
84.626
6.426
1.48914
70.2
39
−26.108
10.665
40
∞
33.000
1.58565
46.2
41
∞
13.200
1.51825
63.9
42
∞ (image)
Table 2 below shows at both the wide-angle end (WIDE) and telephoto end (TELE) for Prior Art Example 1: the focal length f (in mm); the F-number F
NO
with the diaphragm stop fully open; and the on-axis spacings D10, D18 and D21 (in mm) between the lens groups. Also listed, for the wide-angle end (WIDE) of Prior Art Example 1 are: the back focus Bf (in mm) of the zoom lens; the back focus Bf
4b
of the rear subgroup of the fourth lens group that is moveable in order to adjust the back focus; the ratio Bf
4b
/Bf; the maximum ray height Ha on the image-side surface immediately before the movable component(s) of the fourth lens group (in this case, the surface of radius of curvature R
29
) at the wide-angle end when the diaphragm stop is fully open; the maximum ray height Hb on the lens surface of the movable component(s) of the fourth lens group nearest the object side (in this case, the surface of radius of curvature R
30
) at the wide-angle end when the diaphragm stop is fully open; the absolute value of Ha minus Hb; the value 0.02 Bf/F
N
; and the amount of axial shift (in mm) in focal point position when the rear subgroup IVb is moved (from the position given in Table 1) 1 mm toward the image so as to adjust the back focus. In the bottom portion of the table are listed the image sensor diameter (hereinafter termed the “screen size”, in mm) for which the zoom lens of Prior Art Example 1 is designed, as well as the diameter of the diaphragm stop (in mm) when fully open.
TABLE 2
WIDE
TELE
f
8
160
F
NO
1.65
2.56
D10
0.944
54.595
D18
55.218
7.177
D21
6.514
0.905
Bf
40.171
Bf
4b
40.036
Bf
4b
/Bf
0.997
Ha
15.649
Hb
15.409
Ha − Hb
0.24
0.02 Bf/F
N
0.487
Focal point shift
1
Screen size: &PHgr; = 11.0
Diaphragm stop diameter when fully open = 27.858
FIGS.
19
(
a
) and
19
(
b
) show the spherical aberration and the astigmatism, respectively, at the wide-angle end of the zoom lens of Prior Art Example 1 with the image plane position as designed (i.e., as given in Table 1 above). FIGS.
19
(
c
) and
19
(
d
) show the spherical aberration and astigmatism, respectively, at the wide-angle end of the zoom lens of Prior Art Example 1 after the rear subgroup IVb has been moved (from the position indicated in Table 1 above) 1 mm toward the image so as to adjust the back focus. In FIGS.
19
(
b
) and
19
(
d
) the astigmatism is shown for both the sagittal (S) and tangential (T) image planes. As is apparent from FIGS.
19
(
a
)-
19
(
d
), the zoom lens of Prior Art Example 1 does not show significant differences in spherical aberration and astigmatism after the rear subgroup IVb has been moved (from its position indicated in Table 1) 1 mm toward the image so as to adjust the back focus. In fact, the lens performance changes very little when the rear subgroup IVb is moved 1 mm toward the image from its design position.
PRIOR ART EXAMPLE 2
Unlike the zoom lens of Prior Art Example 1 described above, a zoom lens used in a simple television camera such as a CCTV (hereinafter termed Prior Art Example 2) is formed of a simple and compact lens group that is moved for adjusting the back focus. Therefore, the lens performance will inevitably change in association with the back focus adjustment. The basic lens element configuration of the zoom lens of Prior Art Example 2 is shown in FIG.
18
.
As is shown in
FIG. 18
, the zoom lens of Prior Art Example 2 is formed of, in order from the object side, a first lens group I having a first lens L
1
through a third lens L
3
, a second lens group II having a fourth lens L
4
through a sixth lens L
6
, a third lens group III having a seventh lens L
7
, and a fourth lens group IV having an eighth lens L
8
through a fourteenth lens L
14
. The fourth lens group IV further is organized as a front subgroup IVa formed of an eighth lens L
8
through an eleventh lens L
11
, and a rear subgroup IVb formed of a twelfth lens L
12
through a fourteenth lens L
14
.
A diaphragm stop
1
is positioned between L
8
and L
9
. A filter
2
is positioned between the rear subgroup IVb and an image sensor
3
such as a CCD. The image sensor
3
and filter
2
are provided in the television camera body. X is the optical axis in FIG.
18
.
Table 3 below shows the surface # in order from the object side, the radius of curvature R (in mm) of each surface, the on-axis spacing D (in mm) between surfaces, as well as the refractive index N
e
and Abbe number &ngr;
e
(both at the e-line) of the lens elements of the zoom lens of Prior Art Example 2.
TABLE 3
#
R
D
N
e
&ngr;
e
1
101.143
1.739
1.7
Arnold Bruce Y.
Arnold International
Collins Darryl J.
Epps Georgia
Fuji Photo Optical Co., Ltd.
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