Television – Camera – system and detail – Optics
Reexamination Certificate
1997-06-12
2004-05-04
Vu, Ngoc-Yen (Department: 2612)
Television
Camera, system and detail
Optics
C348S240100, C348S354000
Reexamination Certificate
active
06731339
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a lens device and an image pickup apparatus adapted for use in lens-interchangeable type video cameras or the like.
2. Description of Related Art
The resent advancement of video apparatuses such as video cameras or the like has been conspicuous. These apparatuses are being arranged to have high performance capabilities and diverse functions. In the case of the video cameras, for example, they have come to be arranged to permit use of interchangeable lenses for the purpose of diversifying their functions and obtaining a higher image quality.
FIG. 1
shows, in a block diagram, the conventional arrangement of a lens-interchangeable type electronic camera adapted for a video camera.
Referring to
FIG. 1
, a lens unit
816
is arranged to have a variable magnification. A camera body
817
is arranged to permit the lens unit
816
to be mounted thereon. In the lens unit
816
, a variator lens
802
and a compensator lens
803
are mechanically connected by a cam. When a magnification varying action is performed either manually or by means of a motor, the variator lens
802
and the compensator lens
803
move together. The variator lens
802
and the compensator lens
803
jointly form a zooming lens. In the lens system of the lens unit
816
, a front lens is arranged to be a focusing lens
801
. The focus of the lens system is adjusted by moving the focusing lens
801
along the optical axis. Light passing through these lenses is imaged on an image pickup plane of an image sensor
804
which is composed of a CCD or the like and is disposed within the camera body
817
. The image thus formed is photo-electrically converted into an electrical signal and is outputted as a video signal. The video signal is supplied to a CDS/AGC (correlated double sampling/automatic gain control) circuit
805
to be sampled and held and amplified to a predetermined level. The amplified video signal is converted into digital video data by an A/D converter
806
. The digital video data is supplied to a camera signal processing circuit
819
to be converted into a standard television signal. The digital video signal is supplied also to a band-pass filter (hereinafter referred to as BPF)
807
.
At the BPF
807
, a high frequency component of the video signal is extracted from the video signal. The output of the BPF
807
is supplied to a gate circuit
808
to extract therefrom only a signal part corresponding to a focus detecting area set within an image plane. The signal extracted is supplied to a peak hold circuit
809
to be peak-held at intervals synchronous with a period which is an integer times as much as the period of a vertical synchronizing signal. An AF (automatic focusing) evaluation value is obtained by this peak holding action. The AF evaluation value is taken in a microcomputer
810
which is disposed within the camera body
817
. If the operated state of an AF/MF (automatic focusing/manual focusing) selection switch
823
indicates an AF mode, the camera-body microcomputer
810
decides a focusing speed corresponding to the degree of focusing and a motor driving direction for increasing the AF evaluation value. Information on the driving speed and the driving direction of a focus motor
813
is then sent from the camera-body microcomputer
810
to a microcomputer
811
which is disposed within the lens unit
816
. In the event of the MF mode, the camera-body microcomputer
810
sends an instruction to the lens microcomputer
811
to stop the focus motor
813
. In accordance with the instruction of the camera-body microcomputer
810
, the lens microcomputer
811
makes focus adjustment by causing a motor driver
812
to drive the focus motor
813
in such a way as to move the focusing lens
801
along the optical axis.
Further, according to the operated state of a zoom switch
818
, the camera-body microcomputer
810
decides the driving direction and the driving speed of the zooming lens (
802
and
803
) and sends information on the driving direction and speed to the lens microcomputer
811
to cause the zooming lens (
802
and
803
) to be driven accordingly by a zoom motor
815
through a zoom motor driver
814
disposed within the lens unit
816
. The camera body
817
is arranged to permit the lens unit
816
to be detached therefrom and replaced with another lens unit, so that a photographable range of the video camera can be broadened.
For the purpose of attaining reduction in size and also making it possible to take a shot of an object located immediately in front of the camera, some of lens-integrated cameras designed for general consumers has come to be arranged to store the movement loci of a compensator lens beforehand in a microcomputer as lens cam data, instead of the above-stated arrangement of mechanically interconnecting the compensator lens
803
and the variator lens
802
, to drive the compensator lens according to the lens cam data and to adjust focus also by means of the compensator lens. That arrangement is called an inner-focus type lens arrangement and has become popular. The advantages of the inner-focus type lens lie in that it is not expensive and permits system simplification and reduction in size and weight of the lens barrel.
FIG. 2
schematically shows the arrangement of the conventional inner-focus type lens system mentioned above. Referring to
FIG. 2
, a first lens group
901
is fixed. A second lens group
902
is arranged to be used for varying the magnification of the lens system. Reference numeral
903
denotes an iris. A third lens group
904
is fixed. A fourth lens group
905
is a focusing lens which is arranged to have a focus adjusting function and another function of compensating for a shift of a focal plane caused by a magnification varying action. Reference numeral
906
denotes an image pickup plane. In the lens system illustrated, the focusing lens
905
is arranged, as well known, to perform both the compensating function and the focus adjusting function. Therefore, even when the lens system remains at one and the same focal length, the focusing position of the focusing lens
905
relative to the image pickup plane
906
varies with the object distance, i.e., a distance to a shooting object. When the object distance changes at each focal length, the positions of the focusing lens
905
at which an in-focus state is obtainable on the image pickup plane
906
become as continuously plotted on a graph in FIG.
3
. While a magnification varying action is in process, one of the loci of the focusing positions of the focusing lens
905
as shown in
FIG. 3
is selected according to the object distance. A zooming action can be accomplished without blurring an image, by moving the focusing lens
905
according to the locus thus selected.
In the case of the front-lens focus type lens system shown in
FIG. 1
, the compensator lens is arranged independently of the variator lens, and the variator lens and the compensator lens are interconnected by means of a mechanical cam ring. Therefore, with the focal length of the lens system arranged to be manually variable by a manual zooming knob provided on the cam ring, the cam ring can be caused to rotate following the manual zooming knob to let the variator lens and the compensator lens move along the cam groove of the cam ring, at whatever fast speeds the knob may be moved. Therefore, the focal length can be varied as desired without causing any blur as long as the focusing lens of the lens system is in focus.
In controlling the inner-focus type lens system which is arranged as shown in
FIG. 2
, on the other hand, information on a plurality of lens-position loci which are as shown in
FIG. 3
is stored in any suitable form, i.e., in the form of the loci or in the form of functions with the lens positions used as variables. Then, a suitable locus is selected according to the position of the focusing lens and that of the variator lens, and a zooming action is carried out by tracing the selected locus in general.
Further, in readin
Robin Blecker & Daley
Vu Ngoc-Yen
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