Television – Camera – system and detail – Optics
Reexamination Certificate
1997-12-24
2002-08-13
Garber, Wendy R. (Department: 2612)
Television
Camera, system and detail
Optics
C348S352000, C348S096000
Reexamination Certificate
active
06433824
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image pickup apparatus suitable for use in a video camera which has a mode for photographing a subject located at a predetermined distance and is equipped with an adapter for holding a film original at the predetermined distance so that the film original is photographed, and, more specifically, to lens control in the image pickup apparatus.
2. Description of Related Art
With rapid technical improvements in personal computers and peripherals, it has been becoming easier for photographers to store, for example, photographs taken with cameras using silver-halide film in memories of personal computers and edit the stored photographs to create their original picture postcards or posters, and the demand for the field of such art has been becoming greater in markets year after year.
To input a photograph to a personal computer, it is necessary to convert image information of a photograph into an electrical signal by using a video camera, so that a device for fixing the position of a subject such as a photograph becomes necessary. Since photographs are printed on printing paper in variously different sizes, an awkward operation is needed to set a field angle and correct lighting for each photograph. It is also necessary to prepare a large-sized dedicated image pickup apparatus having a fixing base for a video camera.
FIG. 1
shows a manner in which a negative film
901
held in a film holder
902
is photographed by using a VTR-integrated type camera
904
with a film adapter
903
attached thereto. The negative film;
901
is illuminated from its rear side by a backlight (not shown) provided in the film adapter
903
, and a transmitted image is photographed by the VTR-integrated type camera
904
. If the VTR-integrated type camera
904
has the function of converting a negative image into a positive image (a negative/positive conversion function), the electrical signal outputted from the VTR-integrated type camera
904
is a video signal indicative of a positive image even during the photography of the negative film
901
. If this video signal is inputted to a personal computer
905
, the positive image can be stored in a memory provided in the personal computer
905
. In the method shown in
FIG. 1
, since the size of each frame of the negative film
901
is uniform and only the backlight can be used as a light source, a photographic image can be stored in the personal computer
905
far more readily than when an image of a photograph printed on printing paper is picked up.
FIG. 2
shows a lens system called an inner focus type lens system, which includes a fixed first lens group
102
, a variator lens
103
, an iris
104
, a fixed third lens group
105
and a focusing/compensating lens
106
. Reference numeral
107
denotes an image pickup element such as a CCD, the image pickup surface of which is shown in FIG.
2
.
FIG. 3
shows the image pickup surface in-focus position of the focusing/compensating lens
106
with respect to the subject distance for leach focal length. In
FIG. 3
, the horizontal axis represents the position of the variator lens
103
, while the vertical axis represents the position of the focusing/compensating lens
106
. As can be seen from
FIG. 3
, in the lens system shown in
FIG. 2
, if the focusing/compensating lens
106
is moved to focus an image on the image pickup element
107
, the position of the focusing/compensating lens
106
with respect to the subject distance varies for each local length. It is known that when the variator lens
103
is on a shortest focal length side, if the focusing/compensating lens
106
is moved to the vicinity of its closest-distance end, a minimum subject distance which can be focused by the focusing/compensating lens
106
is reduced to an immediately close distance from the first lens group
102
. In
FIG. 3
, a curve
601
represents an in-focus curve relative to an extremely short subject distance which is several centimeters to the first lens group
102
, and it can be seen from
FIG. 3
that the lens-focusable focal length area of the variator lens
103
with respect to this subject distance is a limited area
602
which extends from the wide-angle end to a point A on a short focal length side. Accordingly, if an in-focus image is to be obtained on the image pickup element
107
when a film lying at an extremely close distance from the fixed first lens group
102
is being photographed by using the film adapter
903
shown in
FIG. 1
, the combination of the positions of the variator lens
103
and the focusing/compensating lens
106
must be contained in a portion
604
defined by three areas
601
,
602
and
603
in FIG.
3
.
A method of maintaining an in-focus state during zooming in the inner focus type lens system will be described below. In
FIG. 3
, the position of the focusing/compensating lens
106
for focusing an image on the image pickup element
107
is continuously plotted with respect to different subject distances for each focal length. During zooming, a cam locus is selected from among the loci of
FIG. 3
according to the subject distance, and if the focusing/compensating lens
106
is moved along the selected cam locus, zooming free of defocusing can be effected.
FIG. 4
is a view aiding in describing one example of a locus tracing method which has previously been proposed. In
FIG. 4
, Z
0
, Z
1
, Z
2
, . . . , Z
6
indicate the position of a variator lens, a
0
, a
1
, a
2
, . . . , a
6
and b
0
, b
1
, b
2
, . . . , b
6
respectively indicate representative loci stored in a lens control microcomputer, and p
0
, p
1
, p
2
, . . . , p
6
indicate a locus calculated on the basis of the two loci. An equation for calculating this locus is shown below:
p
(
n+
1)=(|
p
(
n
)−
a
(
n
)|/|
b
(
n
)−
a
(
n
)|)×|
b
(
n+
1)−
a
(
n+
1)|+
a
(
n+
1). (1)
According to Equation (1), for example, if a focusing/compensating lens is located at the point p
0
in
FIG. 4
, the ratio in which the point p
0
internally divides a line segment b
0
−a
0
is obtained, and a point which internally divides a line segment b
1
−a
1
in accordance with that ratio is determined as p
1
. The moving speed of the focusing/compensating lens required to keep an in-focus state can be found from the p
1
−p
0
positional difference and the time required for the variator lens to move from Z
0
to Z
1
.
A case in which the stop position of the variator lens is not limited only to boundaries having stored representative locus data will be described below with reference to FIG.
5
.
FIG. 5
is a view aiding in describing a method for interpolating the position of the variator lens.
FIG. 5
is an extracted portion of FIG.
4
and shows a case in which the variator lens can be stopped at an arbitrary stop position.
In
FIG. 5
, the vertical and horizontal axes respectively represent the position of the focusing/compensating lens and the position of the variator lens. Letting Z
0
, Z
1
, . . . , Zk−1, Zk, . . . Zn represent the position of the variator lens, the corresponding positions of the focusing/compensating lens for different subject distances, i.e., the representative locus positions (the position of the focusing/compensating lens relative to the position of the variator lens) stored in the lens control microcomputer are as follows:
a
0
,
a
1
, . . . ,
ak
−1,
ak, . . . an,
b
0
,
b
1
, . . . ,
bk
−1,
bk, . . . bn.
If it is now assumed that the position of the variator lens is Zx which is not a zoom boundary position and that the position of the focusing/compensating lens is px, positions ax and bx are obtained as follows:
ax=ak−
(
Zk−Zx
)×(
ak−ak
−1)/(
Zk−Zk
−1), (2)
bx=bk−
(
Zk−Zx
)×(
bk−bk
−1)/(
Zk−Zk
−1). (3)
Specifically, in accordance with an internal ratio which is obtained
Tanaka Taeko
Yasuda Hitoshi
Canon Kabushiki Kaisha
Garber Wendy R.
Robin Blecker & Daley
Tillery Rashawn N.
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