Television – Camera – system and detail – Optics
Reexamination Certificate
1996-08-26
2004-01-27
Vu, Ngoc-Yen (Department: 2612)
Television
Camera, system and detail
Optics
C348S348000, C348S354000, C348S360000, C348S364000
Reexamination Certificate
active
06683652
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a video camera system whose lens assemblies are interchangeable.
Conventionally, a so-called hill-climbing method is known as the method of an automatic focusing (AF) device used in video apparatuses such as video cameras. The method performs focusing by extracting a high-frequency component from a video signal obtained by an image sensing device such as a CCD and driving a taking lens such that the mountain-like characteristic curve of this high-frequency component is a maximum.
This automatic focusing method requires no special focusing optical members and has an advantage in that an object can be accurately focused regardless of whether the distance to the object is long or short. An example in which an automatic focusing method of the above sort is applied to an interchangeable lens video camera will be described below with reference to FIG.
24
.
Referring to
FIG. 24
, in a lens assembly
816
, a variable power lens
802
and a compensating lens
803
are connected by a mechanical cam (not shown). When a zooming operation is manually or electrically performed, the variable power lens
802
and the compensating lens
803
integrally move.
These variable power lens
802
and compensating lens
803
are called zoom lenses.
In this lens system, a front lens
801
which is closest to an object when the image is taken is a focus lens. The focus lens
801
moves in the direction of an optical axis to perform focusing.
An image of light transmitting through these lenses is formed on the image sensing surface of an image sensing device
804
of a camera
817
, photoelectrically converted into an electrical signal, and output as a video signal.
This video signal is sampled-and-held by a CDS/AGC circuit
805
constituted by a correlated double sampling circuit and an auto gain control circuit, amplified to a predetermined level, and converted into digital video data by an analog/digital (A/D) converter
806
. The digital video data is input to the process circuit (not shown) of the camera
817
and converted into a standard TV signal. The data is also input to a bandpass filter (to be referred to as a BPF hereinafter)
807
.
The BPF
807
extracts a high-frequency component which changes in accordance with the focus state from the video signal. A gate circuit
808
extracts only a video signal corresponding to a portion which is set as a focus detection area in a picture frame. A peak hold circuit
809
holds a peak of the video signal at an interval synchronizing with an integral multiple of a vertical sync signal, thereby generating a focus state evaluation value (to be referred to as an AF evaluation value hereinafter) representing the in-focus degree in the automatic focusing operation.
The AF evaluation value is fetched by an AF control microcomputer (to be referred to as a main body AF microcomputer hereinafter)
810
on the camera main body
817
side. The main body AF microcomputer
810
determines the focusing speed, i.e., a focus motor speed in accordance with the in-focus degree and the driving direction of the focus motor along which the AF evaluation value increases. The main body AF microcomputer
810
sends the speed and direction of the focus motor to a lens control microcomputer of the lens assembly
816
.
A lens microcomputer
811
controls a focus motor
813
through a motor driver
812
in accordance with an instruction from the main body AF microcomputer
810
to drive the focus lens
801
along the optical axis, thereby performing the focusing operation.
The main body AF microcomputer
810
also determines the driving directions and the driving speeds of the variable power lens
802
and the compensating lens
803
, which constitute zoom lenses, in accordance with the operation state of a zoom switch
818
. The main body AF microcomputer
810
transmits these driving directions and driving speeds to a zoom motor driver
814
of the lens assembly
816
. The lens assembly side calculates the driving information of a zoom motor
815
in accordance with the zoom speed and direction information sent from the camera main body side and drives the zoom motor
815
through the motor driver
814
, thereby driving the variable power lens
802
and the compensating lens
803
.
The camera main body
817
can be detached from the lens assembly
816
and connected to another lens assembly. This widens the sensing range.
In recent popular cameras integrated with video recorders for consumers having the above structure, the front lens is fixed while the focus lens is arranged behind the variable power lens, and the cam for mechanically connecting the compensating lens to the variable power lens is no longer used in order to miniaturize a camera and enable sensing at a close distance such as when an object is just in front of the lens. In these cameras, the locus of movement of the compensating lens is previously stored as lens cam data in a microcomputer, and the compensating lens is driven in accordance with this lens cam data. Also, a focusing operation is performed by using this compensating lens. Lenses of this type, i.e., so-called inner focus type (rear focus type) lenses have become most popular.
A zooming operation by such an inner focus type lens will be described below.
FIG. 25
is a view schematically showing the arrangement of a general inner focus type lens system.
Referring to
FIG. 25
, reference numeral
901
denotes a fixed first lens group;
902
, a second lens group for performing a zooming operation;
903
, an iris stop;
904
, a fixed third lens group;
905
, a fourth lens group (to be referred to as a focus lens hereinafter) having both a focusing function and a so-called compensator function of compensating for the movement of a focal plane caused by zooming; and
906
, an image sensing device.
As is well known, in the lens system as illustrated in
FIG. 25
, the focus lens
905
has both the compensating function and the focusing function. Accordingly, the position of the focus lens
905
for focusing an image on the image sensing surface of the image sensing device
906
changes in accordance with the object distance even at the same focal length.
FIG. 26
shows the result of continuous plotting of the position of the focus lens
905
for focusing an image on the image sensing surface while the distance between the focus lens
905
and the object is changed at different focal lengths.
During the zooming operation, one of the loci shown in
FIG. 26
is selected in accordance with the object distance, and the focus lens
905
is moved to trace that focus. This allows a zooming operation free from a blur.
In a conventional front lens focus type lens system, compensating lens is provided independently of a variable power lens, and the variable power lens and the compensating lens are coupled by a mechanical cam ring. A manual zoom knob, for example, is formed on this cam, and the focal length is manually changed. Even if the knob is moved as fast as possible, the cam rotates to trace the movement of the knob, and the variable power lens and the compensating lens move along a cam groove for holding the cam. Therefore, no blur is caused by the above operation as long as the focus lens is focused on an object.
In controlling the inner focus type lens system, however, a plurality of pieces of locus information shown in
FIG. 26
are stored in some format (the locus itself or a function of a lens position as a variable). In general, one of the loci is selected in accordance with the positions of the focus lens and the variable power lens, and a zooming operation is performed while tracing the selected locus.
FIG. 28
is a graph for explaining one invented locus tracing method. In
FIG. 28
, reference symbols Z
0
, Z
1
, Z
2
, . . . , Z
6
denote the positions of the variable power lens; and a
0
, a
1
, a
2
, . . . , a
6
and b
0
, b
1
, b
2
, . . . , b
6
, representative loci stored in the microcomputer.
Also, p
0
, p
1
, p
2
, . . . , p
6
denote loci calculated on the basis of the above two loci. T
Ohkawara Hiroto
Suda Hirofumi
Canon Kabushiki Kaisha
Morgan & Finnegan
Vu Ngoc-Yen
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