U.S. patent application number 08/667881 was filed with the patent office on 2001-11-08 for interchangeable lens video camera system.
Invention is credited to OHKAWARA, HIROTO, SUDA, HIROFUMI.
Application Number | 20010038418 08/667881 |
Document ID | / |
Family ID | 27473393 |
Filed Date | 2001-11-08 |
United States Patent
Application |
20010038418 |
Kind Code |
A1 |
SUDA, HIROFUMI ; et
al. |
November 8, 2001 |
INTERCHANGEABLE LENS VIDEO CAMERA SYSTEM
Abstract
In an interchangeable lens assembly video camera system
including an interchangeable lens assembly and a camera, a filter
of an AF signal processing circuit (113) of the camera extracts a
focus evaluation value signal from an image sensing signal
corresponding to one or a plurality of focus detection areas in an
image sensing surface, and on the basis of the transmitted focus
evaluation value signal from the camera and data stored in a ROM
(120), the microcomputer (116) performs a zooming operation of a
zoom lens (102) while maintaining an in-focus state of a focus lens
(105).
Inventors: |
SUDA, HIROFUMI;
(YOKOHAMA-SHI, JP) ; OHKAWARA, HIROTO;
(TORIDE-SHI, JP) |
Correspondence
Address: |
MORGAN AND FINNEGAN
345 PARK AVENUE
NEW YORK
NY
10154
|
Family ID: |
27473393 |
Appl. No.: |
08/667881 |
Filed: |
June 20, 1996 |
Current U.S.
Class: |
348/347 ;
348/240.3; 348/335; 348/E5.044; 348/E5.045 |
Current CPC
Class: |
H04N 5/232123 20180801;
H04N 5/23209 20130101 |
Class at
Publication: |
348/347 ;
348/335; 348/358 |
International
Class: |
H04N 005/232 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 22, 1995 |
JP |
7-156138 |
Jun 22, 1995 |
JP |
7-156142 |
Jun 23, 1995 |
JP |
7-157775 |
Jun 23, 1995 |
JP |
7-157776 |
Claims
What is claimed is:
1. An interchangeable lens assembly video camera system comprising
a camera and an interchangeable lens assembly, wherein said camera
comprises extracting means for extracting a focus signal from an
image sensing signal corresponding to an interior of one or a
plurality of focus detection areas in an image sensing surface of
said camera, and transmitting means for transmitting the focus
signal to said lens assembly; said lens assembly comprises
receiving means for receiving the focus signal from said camera,
control means for determining a driving direction and a driving
velocity of a focus lens of said lens assembly, on the basis of the
received focus signal, in order to drive said focus lens to an
in-focus point, and driving means for driving said focus lens in
accordance with the driving direction and the driving velocity; and
said lens assembly controls an operation of said focus lens.
2. The system according to claim 1, wherein said extracting means
comprises a plurality of filter means for extracting a signal of a
predetermined frequency component as the focus signal from the
image sensing signal.
3. The system according to claim 2, wherein said extracting means
further comprises peak value detecting means for detecting a peak
value of a luminance component in the image sensing signal.
4. The system according to claim 2, wherein said extracting means
further comprises contrast component detecting means for detecting
a contrast component in the image sensing signal.
5. The system according to claim 4, wherein said extracting means
further comprises peak holding means for detecting the contrast
component by holding a peak value of a difference between a maximum
value and a minimum value of the luminance component.
6. A lens assembly which can be detachably attached to a camera
including focus detecting means, comprising: receiving means for
receiving a focus signal transmitted from said camera; control
means for checking an in-focus state on the basis of the focus
signal and determining a driving direction and a driving velocity
of a focus lens of said lens assembly; and driving means for
driving said focus lens in accordance with the driving direction
and the driving velocity.
7. A camera to which a lens assembly can be detachably attached,
comprising: extracting means for extracting a focus signal from an
image sensing signal corresponding to an interior of one or a
plurality of focus detection areas in an image sensing surface of
said camera; and transmitting means for transmitting the focus
signal to said lens assembly.
8. The camera according to claim 7, wherein said extracting means
comprises a plurality of filter means for extracting a signal of a
predetermined frequency component as the focus signal from the
image sensing signal.
9. The camera according to claim 8, wherein said extracting means
further comprises peak value detecting means for detecting a peak
value of a luminance component in the image sensing signal.
10. The camera according to claim 8, wherein said extracting means
further comprises contrast component detecting means for detecting
a contrast component in the image sensing signal.
11. The camera according to claim 10, wherein said extracting means
further comprises peak holding means for detecting the contrast
component by holding a peak value of a difference between a maximum
value and a minimum value of the luminance component.
12. An interchangeable lens assembly video camera system comprising
a camera and an interchangeable lens assembly, wherein said camera
comprises extracting means for extracting a focus signal from an
image sensing signal corresponding to an interior of one or a
plurality of focus detection areas in an image sensing surface of
said camera, a switch for manipulating a zooming operation, and
transmitting means for transmitting the focus signal and a state of
said switch to said lens assembly; said lens assembly comprises
receiving means for receiving the focus signal and the state of
said switch from said camera, a zoom lens for performing a zooming
operation; a focus lens for maintaining an in-focus state during
the zooming operation, memory means for storing data representing a
positional relationship between said zoom lens and said focus lens,
zoom lens driving means for driving said zoom lens in accordance
with the state of said switch, control means for checking the
in-focus state on the basis of the focus signal and determining a
driving direction and a driving velocity of said focus lens while
compensating for a movement of a focal plane caused by the zooming
operation of said zoom lens on the basis of the data, and focus
lens driving means for driving said focus lens in accordance with
the driving direction and the driving velocity; and said lens
assembly controls operations of said focus lens and said zoom
lens.
13. The system according to claim 12, wherein said extracting means
comprises a plurality of filter means for extracting a signal of a
predetermined frequency component as the focus signal from the
image sensing signal.
14. The system according to claim 13, wherein said extracting means
further comprises peak value detecting means for detecting a peak
value of a luminance component in the image sensing signal.
15. The system according to claim 13, wherein said extracting means
further comprises contrast component detecting means for detecting
a contrast component in the image sensing signal.
16. The system according to claim 15, wherein said extracting means
further comprises peak holding means for detecting the contrast
component by holding a peak value of a difference between a maximum
value and a minimum value of the luminance component.
17. A lens assembly which can be detachably attached to a camera
including focus detecting means, comprising: receiving means for
receiving a focus signal and a state of a switch for manipulating a
zooming operation, both of which are transmitted from said camera;
a zoom lens for performing a zooming operation; a focus lens for
maintaining an in-focus state during the zooming operation; memory
means for storing data representing a positional relationship
between said zoom lens and said focus lens; zoom lens driving means
for driving said zoom lens in accordance with the state of said
switch; control means for checking the in-focus state on the basis
of the focus signal and determining a driving direction and a
driving velocity of said focus lens while compensating for a
movement of a focal plane caused by the zooming operation of said
zoom lens on the basis of the data; and focus lens driving means
for driving said focus lens in accordance with the driving
direction and the driving velocity.
18. A camera to which a lens assembly can be detachably attached,
comprising: extracting means for extracting a focus signal from an
image sensing signal corresponding to an interior of one or a
plurality of focus detection areas in an image sensing surface of
said camera; a switch for manipulating a zooming operation of a
zoom lens of said lens assembly; and transmitting means for
transmitting the focus signal and a state of said switch to said
lens assembly.
19. The camera according to claim 18, wherein said extracting means
comprises a plurality of filter means for extracting a signal of a
predetermined frequency component as the focus signal from the
image sensing signal.
20. The camera according to claim 19, wherein said extracting means
further comprises peak value detecting means for detecting a peak
value of a luminance component in the image sensing signal.
21. The camera according to claim 19, wherein said extracting means
further comprises contrast component detecting means for detecting
a contrast component in the image sensing signal.
22. The camera according to claim 21, wherein said extracting means
further comprises peak holding means for detecting the contrast
component by holding a peak value of a difference between a maximum
value and a minimum value of the luminance component.
23. An interchangeable lens assembly video camera system comprising
a camera and an interchangeable lens assembly, wherein said camera
comprises extracting means for extracting a focus signal from an
image sensing signal corresponding to an interior of one or a
plurality of focus detection areas in an image plane of said
camera, a switch for permitting an automatic focusing operation;
and transmitting means for transmitting the focus signal and a
state of said switch to said lens assembly; said lens assembly
comprises receiving means for receiving the focus signal and the
state of said switch from said camera, control means for
determining a driving direction and a driving velocity of a focus
lens of said lens assembly on the basis of the received focus
signal, when said switch permits the automatic focusing operation,
in order to drive said focus lens to an in-focus point, and driving
means for driving said focus lens in accordance with the driving
direction and the driving velocity; and said lens assembly controls
an operation of said focus lens.
24. The system according to claim 23, wherein said extracting means
comprises a plurality of filter means for extracting a signal of a
predetermined frequency component as the focus signal from the
image sensing signal.
25. The system according to claim 24, wherein said extracting means
further comprises peak value detecting means for detecting a peak
value of a luminance component in the image sensing signal.
26. The system according to claim 24, wherein said extracting means
further comprises contrast component detecting means for detecting
a contrast component in the image sensing signal.
27. The system according to claim 26, wherein said extracting means
further comprises peak holding means for detecting the contrast
component by holding a peak value of a difference between a maximum
value and a minimum value of the luminance component.
28. An interchangeable lens assembly video camera system comprising
a camera and an interchangeable lens assembly, wherein said camera
comprises extracting means for extracting a focus signal from an
image sensing signal corresponding to an interior of one or a
plurality of focus detection areas in an image sensing surface of
said camera, normalizing means for normalizing an output from said
extracting means, and transmitting means for transmitting the focus
signal normalized by said normalizing means to said lens assembly;
said lens assembly comprises receiving means for receiving the
normalized focus signal from said camera, control means for
determining a driving direction and a driving velocity of a focus
lens of said lens assembly on the basis of the received focus
signal, in order to drive said focus lens to a focus point, and
driving means for driving said focus lens in accordance with the
driving direction and the driving velocity; and said lens assembly
controls an operation of said focus lens.
29. The system according to claim 28, wherein said extracting means
comprises a plurality of filter means for extracting a signal of a
predetermined frequency component as the focus signal from the
image sensing signal and, when an image of a specific object is
taken, said normalizing means so performs normalization that the
predetermined frequency component has substantially the same
characteristics.
30. The system according to claim 29, wherein said extracting means
further comprises peak value detecting means for detecting a peak
value of a luminance component in the image sensing signal and,
when an image of a specific object is taken, said normalizing means
so performs normalization that the peak value has substantially the
same value.
31. The system according to claim 29, wherein said extracting means
further comprises contrast component detecting means for detecting
a contrast component in the image sensing signal and, when an image
of a specific object is taken, said normalizing means so performs
normalization that the contrast component has substantially the
same value.
32. The system according to claim 31, wherein said extracting means
further comprises peak holding means for detecting the contrast
component by holding a peak value of a difference between a maximum
value and a minimum value of the luminance component.
33. A camera to which a lens assembly can be detachably attached,
comprising: extracting means for extracting a focus signal from an
image sensing signal corresponding to an interior of one or a
plurality of focus detection areas in an image sensing surface of
said camera; normalizing means for normalizing an output from said
extracting means; and transmitting means for transmitting the focus
signal normalized by said normalizing means to said lens
assembly.
34. The camera according to claim 33, wherein said extracting means
comprises a plurality of filter means for extracting a signal of a
predetermined frequency component as the focus signal from the
image sensing signal and, when an image of a specific object is
taken, said normalizing means so performs normalization that the
predetermined frequency component has substantially the same
characteristics.
35. The camera according to claim 34, wherein said extracting means
further comprises peak value detecting means for detecting a peak
value of a luminance component in the image sensing signal and,
when an image of a specific object is taken, said normalizing means
so performs normalization that the peak value has substantially the
same value.
36. The camera according to claim 34, wherein said extracting means
further comprises contrast component detecting means for detecting
a contrast component in the image sensing signal and, when an image
of a specific object is taken, said normalizing means so performs
normalization that the contrast component has substantially the
same value.
37. The camera according to claim 36, wherein said extracting means
further comprises peak holding means for detecting the contrast
component by holding a peak value of a difference between a maximum
value and a minimum value of the luminance component.
38. An interchangeable lens assembly video camera system comprising
a camera and an interchangeable lens assembly, wherein said camera
comprises extracting means for extracting a focus signal from an
image sensing signal corresponding to an interior of one or a
plurality of focus detection areas in an image sensing surface of
said camera, and transmitting means for transmitting the focus
signal and data representing a type of the focus signal to said
lens assembly; said lens assembly comprises receiving means for
receiving the focus signal and the data representing the type of
the focus signal from said camera, control means for determining a
driving direction and a driving velocity of a focus lens of said
lens assembly on the basis of the received focus signal and data
representing the type of the focus signal, in order to drive said
focus lens to an in-focus point, and driving means for driving said
focus lens in accordance with the driving direction and the driving
velocity; and said lens assembly controls an operation of said
focus lens.
39. The system according to claim 38, wherein said control means
changes the control of the focusing operation in accordance with
the data representing the type information of the focus signal.
40. A lens assembly which can be detachably attached to a camera
including focus detecting means, comprising: receiving means for
receiving a focus signal and data representing a type of the focus
signal transmitted from said camera; control means for checking an
in-focus state on the basis of the focus signal and the data
representing the type of the focus signal and determining a driving
direction and a driving velocity of a focus lens of said lens
assembly; and driving means for driving said focus lens in
accordance with the driving direction. and the driving
velocity.
41. The lens assembly according to claim 40, wherein said control
means changes the method of controlling the focusing operation in
accordance with the type information of the focus signal.
42. A camera to which a lens assembly can be detachably attached,
comprising: extracting means for extracting a focus signal from an
image sensing signal corresponding to an interior of one or a
plurality of focus detection areas in an image sensing surface of
said camera; and transmitting means for transmitting the focus
signal and data representing a type of the focus signal to said
lens assembly.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a video camera system whose
lens assemblies are interchangeable.
[0002] Conventionally, a so-called hill-climbing method is known as
the method of an automatic focusing device used in video
apparatuses such as video cameras. The method performs focusing by
extracting a high-frequency component from an image sensing 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.
[0003] This automatic focusing method requires neither
emission/reception of infrared rays nor special focusing optical
members for detecting the movement of an image which changes in
accordance with the state of a focus. The method also has an
advantage in that an object can be accurately focused regardless of
whether the distance to the object is long or short.
[0004] An example in which an automatic focusing method of he above
sort is applied to an interchangeable lens video camera will be
described below with reference to FIG. 15.
[0005] FIG. 15 is a block diagram showing an interchangeable lens
video camera system as one prior art.
[0006] In FIG. 15, an automatic focusing system comprises a lens
assembly 500 and a camera main body 550. Focusing is performed by
driving a focus lens 501 in the direction of an optical axis by a
lens driving motor 511. An image of light transmitting through this
lens is formed on the image sensing surface of an image sensing
device 502 and changed into an electrical signal by photoelectric
conversion. This electrical signal is output as a video signal. The
video signal is sampled-and-held and amplified to a predetermined
level by a CDS/AGC (Correlated Double Sampling/Auto Gain Control)
circuit 503, and converted into digital video data by an A/D
(Analog/Digital) converter 504. The data is input to a process
circuit (not shown) of the camera and converted into a standard
television signal. The data is also input to a bandpass filter (to
be referred to as BPF hereinafter) 505.
[0007] The BPF 505 extracts a high-frequency component from the
video signal. A gate circuit 506 extracts only a signal
corresponding to a portion set in an in-focus designated area in an
image sensing surface. A peak hold circuit 507 holds peak values at
intervals synchronized with integral multiples of a vertical sync
signal, generating an AF (AutoFocus) evaluation value.
[0008] An AF microcomputer 508 of the camera main body 550 fetches
this AF evaluation value and determines the driving velocity of a
focus motor 511 in accordance with an in-focus degree and the
driving direction of the motor along which the AF evaluation value
increases. The AF microcomputer 508 transmits the driving velocity
and the driving direction of the focus motor 511 to a microcomputer
509 of the lens assembly 500.
[0009] In accordance with the designations from the AF
microcomputer 508 of the camera main body 550, the microcomputer
509 operates the focus motor 511 via a motor driver 510 to drive
the focus lens 501 in the optical axis direction, thereby
performing focusing.
[0010] In the above prior art, however, the camera main body has
the function of controlling automatic focusing in order to allow an
interchange of lenses. Therefore, if, for example, the response
characteristics of automatic focusing are so determined as to be
optimum for a specific lens, the characteristics may not be optimum
for other lenses, resulting in a low versatility.
[0011] A problem arising when an interchangeable lens is a zoom
lens will be described below with reference to FIG. 16.
[0012] FIG. 16 is a block diagram of an interchangeable zoom lens
video camera system as another prior art.
[0013] In a conventional variable power lens assembly, a variable
power lens 21 and a compensating lens 22 are mechanically connected
by a cam. When a zooming operation is manually or electrically
performed, the variable power lens 21 and the compensating lens 22
integrally move.
[0014] These variable power lens 21 and compensating lens 22 are
called zoom lenses. In this lens system, a lens (front lens) 1
which is closest to an object when the image is taken is a focus
lens. The focus lens 1 moves in the direction of an optical axis to
perform focusing.
[0015] An image of light transmitting through these lenses is
formed on the image sensing surface of an image sensing device 3,
photoelectrically converted into an electrical signal, and output
as a video signal. This video signal is sampled-and-held
(correlated double sampling) by a CDS/AGC circuit 4, amplified to a
predetermined level by AGC (Auto Gain Control), and converted into
digital video data by an A/D converter 5. The digital video data is
input to a subsequent camera process circuit (not shown) and
converted into a standard television signal. The data is also input
to an AF signal processing circuit 6.
[0016] The AF signal processing circuit 6 extracts a high-frequency
component which changes in accordance with the focus state from the
video signal. A microcomputer 7 for controlling the system fetches
this high-frequency component as an AF evaluation value.
[0017] The microcomputer 7 determines the driving velocity of a
focus motor in accordance with the in-focus degree and the driving
direction of the motor along which the AF evaluation value
increases. The microcomputer 7 sends the velocity and the direction
of the focus motor to a focus motor driver 9 of a lens assembly 12
and drives the focus lens 1 via a focus motor 10.
[0018] The microcomputer 7 also reads the state of a zoom switch 8
and, in accordance with the operation state of the zoom switch 8,
determines the driving directions and the driving velocities of the
zoom lenses 21 and 22. The microcomputer 7 transmits these driving
directions and driving velocities to a zoom motor driver 11 of the
lens assembly 12 and drives the zoom lenses 21 and 22 via a zoom
motor 12.
[0019] A camera main body 13 can be separated from the lens
assembly 12 and connected to another lens assembly. This widens the
range of shooting.
[0020] In recent integrated cameras for consumers having the above
structure, the cam for mechanically connecting the compensating
lens with the variable power lens is no longer used in order to
miniaturize a camera and enable shooting at a close distance such
as when an object is almost at the front surface 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.
[0021] According to the technical concept of the above prior art,
however, all control operations are done in the camera main body,
and the lens assembly is driven in accordance with control signals
supplied from the camera main body. Therefore, to use an inner
focus type lens as an interchangeable lens assembly, the camera
main body must have the data of the locus of movement of the focus
lens, i.e., the lens cam data, for maintaining the in-focus state
by compensating for a change in the focal plane caused by a zooming
operation.
[0022] This, however, imposes on the camera main body the serious
burden of having the lens cam data which differs from one lens
assembly to another. Accordingly, the method becomes unrealistic as
the number of interchangeable lenses increases.
SUMMARY OF THE INVENTION
[0023] The present invention has been made in consideration of the
above situation, and has as its object to provide an
interchangeable lens (assembly) video camera system capable of
performing optimum automatic focusing with not only a front focus
type lens assembly but also an inner focus type lens assembly.
[0024] A video camera system of the present invention and a camera
and a lens assembly constituting the system have the following
characteristic features.
[0025] There is provided a lens assembly which can be detachably
attached to a camera including focus detecting means, comprising
receiving means for receiving a focus signal transmitted from the
camera, control means for checking an in-focus state on the basis
of the focus signal and determining a driving direction and a
driving velocity of a focus lens of the lens assembly, and driving
means for driving the focus lens in accordance with the driving
direction and the driving velocity.
[0026] There is also provided a camera to which a lens assembly can
be detachably attached, comprising extracting means for extracting
a focus signal from an image sensing signal corresponding to an
interior of one or a plurality of focus detection areas in an image
sensing surface of the camera, and transmitting means for
transmitting the focus signal to the lens assembly.
[0027] There is further provided a video camera system constituted
by the above lens assembly and camera.
[0028] There is further provided a lens assembly which can be
detachably attached to a camera including focus detecting means,
comprising receiving means for receiving a focus signal and a state
of a switch for manipulating a zooming operation, both of which are
transmitted from the camera, a zoom lens for performing a zooming
operation, a focus lens for maintaining an in-focus state during
the zooming operation, memory means for storing data representing a
positional relationship between the zoom lens and the focus lens,
zoom lens driving means for driving the zoom lens in accordance
with the state of the switch, control means for checking the
in-focus state on the basis of the focus signal and determining a
driving direction and a driving velocity of the focus lens while
compensating for a movement of a focal plane caused by the zooming
operation of the zoom lens on the basis of the data, and focus lens
driving means for driving the focus lens in accordance with the
driving direction and the driving velocity.
[0029] There is further provided a camera to which a lens assembly
can be detachably attached, comprising extracting means for
extracting a focus signal from an image sensing signal
corresponding to an interior of one or a plurality of focus
detection areas in an image sensing surface of the camera, a switch
for manipulating a zooming operation of a zoom lens of the lens
assembly, and transmitting means for transmitting the focus signal
and a state of the switch to the lens assembly.
[0030] There is further provided a video camera system constituted
by the above lens assembly and camera, wherein the lens assembly
controls the operation of the focus lens.
[0031] In any of the above constructions, the extracting means
comprises a plurality of filter means for extracting a signal of a
predetermined frequency component as the focus signal from the
image sensing signal.
[0032] The extracting means further comprises peak value detecting
means for detecting a peak value of a luminance component in the
image sensing signal.
[0033] The extracting means further comprises contrast component
detecting means for detecting a contrast component in the image
sensing signal.
[0034] The extracting means further comprises peak holding means
for detecting the contrast component by holding a peak value of a
difference between a maximum value and a minimum value of the
luminance component.
[0035] The camera may further comprise a switch for permitting an
automatic focusing operation, and the lens assembly may control the
focus lens when the switch permits the automatic focusing
operation.
[0036] The camera may further comprise normalizing means for
normalizing the output from the extracting means and, when an image
of a specific object is taken, substantially the same focus signal
may be output to the lens assembly under the same taking conditions
even if the characteristics of cameras vary.
[0037] Data representing the type of the focus signal may be
transmitted between the camera and the lens assembly, and the
control of the focus lens may be changed in accordance with the
type signal.
[0038] Other features and advantages of the present invention will
be apparent from the following description taken in conjunction
with the accompanying drawings, in which like reference characters
designate the same or similar parts throughout the figures
thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
[0039] The accompanying drawings, which are incorporated in and
constitute a part of the specification, illustrate embodiments of
the invention and, together with the description, serve to explain
the principles of the invention.
[0040] FIG. 1 is a block diagram of an interchangeable lens video
camera system according to an embodiment of the present
invention;
[0041] FIG. 2 is a block diagram showing an internal configuration
of an AF signal processing circuit of the camera according to the
embodiment of the present invention;
[0042] FIG. 3 is a view for explaining the operations and timings
of extraction of various focus evaluation values according to the
embodiment of the present invention;
[0043] FIG. 4 is a flow chart of AF processing in the embodiment of
the present invention;
[0044] FIG. 5 is a timing chart showing the timings of
communications of the AF evaluation values to a lens assembly in
the embodiment of the present invention;
[0045] FIG. 6 is an illustration showing the locus of movement
(lens cam data) of a focus lens used to maintain an in-focus state
by compensating for the position of a focal plane which changes
with a zooming operation of a zoom lens in the embodiment of the
present invention;
[0046] FIG. 7 is an illustration for explaining a method of
calculating a locus not stored in the lens cam data from the
information of a plurality of loci stored in the lens cam data in
the embodiment of the present invention;
[0047] FIG. 8 is an illustration for explaining a method of
calculating a locus not stored in the lens cam data from the
information of a plurality of loci stored in the lens cam data in
the embodiment of the present invention;
[0048] FIGS. 9A and 9B are illustrations for explaining an
algorithm for allowing the focus lens to trace the locus stored in
the lens cam data in the embodiment of the present invention;
[0049] FIGS. 10A and 10B are views showing details of the
evaluation values and version information exchanged between the
camera and the lens according to the first modification of the
embodiment of the present invention;
[0050] FIG. 11 is a flow chart for explaining the processing
performed by a microcomputer of a lens assembly according to the
first modification of the embodiment of the present invention;
[0051] FIG. 12 is a flow chart for explaining a method of matching
the versions of communications between the camera and the lens
assembly according to the first modification of the embodiment of
the present invention;
[0052] FIG. 13 is a block diagram of an interchangeable lens video
camera system according to the second modification of the
embodiment of the present invention;
[0053] FIGS. 14A to 14D are illustrations for explaining the
processing done by an evaluation value normalizing circuit 132
which constitutes a normalizing means in the embodiment of the
present invention;
[0054] FIG. 15 is a block diagram showing the configuration of an
interchangeable lens video camera system as one prior art; and
[0055] FIG. 16 is a block diagram showing the configuration of an
interchangeable lens video camera system as another prior art.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0056] A preferred embodiment of the present invention will be
described in detail in accordance with the accompanying drawings.
FIG. 1 is a block diagram of an interchangeable lens video camera
system according to an embodiment of the present invention.
[0057] Referring to FIG. 1, a lens assembly 127 is detachably
attached to a main body 128 of the camera to constitute a so-called
interchangeable lens system.
[0058] An image of light from an object is formed by image sensing
devices 106 to 108, e.g., CCDs, in the camera main body through a
fixed first lens group 101, a second lens group 102 for performing
a zooming operation, an iris stop 103, a fixed third lens group
104, and a fourth lens group 105 (to be referred to as a focus lens
hereinafter) in the lens assembly 127. The fourth lens 105 has both
a focusing function and a function of compensating for the movement
of a focal plane caused by zooming.
[0059] The image pick devices 106, 107, and 108 in the camera main
body 128 are provided for three primary colors, red (R), green (G),
and blue (B), respectively, constituting a so-called three-sensor
image sensing system.
[0060] Images of the three primary colors, red, green, and blue,
are formed on the image sensing devices 106, 107, and 108,
respectively.
[0061] The images formed on the image sensing devices 106, 107, and
108 are photoelectrically converted and amplified to their
respective optimum levels by amplifiers 109, 110, and 111,
respectively. These images are then input to a camera signal
processing circuit 112 and converted into a standard television
signal. This signal is output to, e.g., a video recorder (not
shown) and also input to an autofocus (AF) signal processing
circuit 113.
[0062] An AF evaluation value generated by the AF signal processing
circuit 113 is read out at a period which is an integral multiple
of a vertical sync signal by a data read circuit 115 of a
microcomputer 114 in the camera main body 128. The readout AF
evaluation value is transferred to a microcomputer 116 of the lens
assembly 127 via communication interfaces 135 and 136.
[0063] In the camera signal processing circuit 112, the levels of
luminance signals of the output image sensing signals from the
image sensing devices are detected and transferred from the
microcomputer 114 to the microcomputer 116 of the lens assembly 127
via the communication interfaces 135 and 136. On the basis of this
luminance signal information, an iris driver 124 is controlled, an
IG (Iris Galvano) meter 123 is driven, and the iris stop 103 is
controlled.
[0064] The aperture value of the iris stop 103 is detected by an
encoder 129, supplied to the microcomputer 116, and used as
depth-of-field information.
[0065] The microcomputer 114 of the camera 128 transmits the states
of a zoom switch 130 and an AF switch 131 (when ON, an AF operation
is performed; when OFF, a manual focus mode is set) to the
microcomputer 116 of the lens via the communication interfaces 135
and 136.
[0066] In the microcomputer 116 of the lens, an AF arithmetic
circuit 117 receives the state of the AF switch 131 and the AF
evaluation value from the microcomputer 114 of the camera 128. When
the AF switch 131 is ON, the AF arithmetic circuit 117 operates a
motor control circuit 118 on the basis of the AF evaluation value,
driving a focus motor 125 by a focus motor driver 126 and moving
the focus lens 105 in the optical axis direction to perform
focusing.
[0067] The microcomputer 116 also receives the manipulated state of
the zoom switch 130. In accordance with this manipulated state, the
microcomputer 116 controls a motor driver 122 to drive a zoom motor
121, driving the zoom lens 102 to perform a zooming operation.
[0068] The lens assembly is of an inner focus type, so the focal
plane moves when the zoom lens 102 is driven. Therefore, the focus
lens 105 is driven in accordance with predetermined characteristics
as the zoom lens 102 is driven, thereby simultaneously performing
an operation of preventing a blur (out of focus) caused by the
displacement of the focal plane.
[0069] To perform this operation, lens cam data, i.e., a locus
indicating a change in in-focus position of the focus lens with a
change in the position of the zoom lens is stored in a ROM 120 of
the microcomputer 116 advance in accordance with the distance to an
object.
[0070] Also, a zoom control circuit 119 reads out the locus (lens
cam data) to be traced by the focus lens 105 during a zooming
operation from the ROM 120 and thereby controls driving of the
focus lens 104.
[0071] When the information from the microcomputer 114 of the
camera main body indicates that the AF switch 131 is OFF (manual
focus mode) and the zoom switch 130 is depressed, the zoom control
circuit 119 specifies the in-focus locus along which the focus lens
105 is to trace during a zooming operation and the trace direction,
in accordance with the information of the zoom direction operated
by the zoom switch 130 and with the position information obtained
by detecting the positions of the zoom lens 102 and the focus lens
105 from the respective motor driving amounts or by using the
encoder. The zoom control circuit 119 reads out the specified locus
and trace direction from the ROM 120 and calculates the
compensating velocity and direction of the focus lens corresponding
to the zooming operation.
[0072] The information of the compensating velocity and direction
is supplied to the focus motor driver 126 to drive the focus motor
125. Consequently, the focus lens is driven to prevent a blur which
occurs when the focal point shifts during the zooming
operation.
[0073] When the AF switch 131 is ON and the zoom switch 130 is
depressed, it is necessary to hold the in-focus state even if the
object moves. Accordingly, the zoom control circuit 119 not only
performs control on the basis of the lens cam data stored in the
ROM 120 of the microcomputer 116 as described above but also
simultaneously refers to the AF evaluation value signal sent from
the microcomputer 114 of the camera, thereby performing a zooming
operation while holding the position at which the AF evaluation
value is a maximum.
[0074] That is, the driving velocity and the driving direction of
the focus lens 105 are calculated by adding the information of the
compensating velocity and direction of the focus lens obtained by
the zoom control circuit 119 in accordance with the zooming
operation to the information of the driving velocity and direction
of the focus lens based on the output focus movement information,
obtained by AF processing, from the AF circuit 117. The driving
velocity and direction thus calculated are supplied to the focus
motor driver 126.
[0075] When the AF switch 131 is ON and the zoom switch 130 is not
depressed, the AF circuit 117 in the microcomputer 116 receives the
AF evaluation value transmitted from the microcomputer 114 of the
camera 128. On the basis of this AF evaluation value, the motor
control circuit 118 is operated, the focus motor 125 is driven by
the focus motor driver 126, and focusing is performed by moving the
focus lens 105 in the optical axis direction so that the AF
evaluation value is maximum.
[0076] The aperture value of the iris stop 103 is detected by the
encoder 129, supplied to the microcomputer 116, and used as the
depth-of-field information to compensate for, e.g., the velocity of
the focus lens 105.
Autofocus Operation
[0077] The AF signal processing circuit 113 in the camera signal
processing circuit 112 will be described below with reference to
FIG. 2. FIG. 2 is a block diagram showing the internal
configuration of the AF signal processing circuit of the camera
according to the embodiment of the present invention. Referring to
FIG. 2, the image sensing device outputs of red (R), green (G), and
blue (B) are amplified to their respective optimum levels by
amplifiers 109, 110, and 111 and supplied to the AF signal
processing circuit 113. The output signals are converted into
digital signals by A/D converters 206, 207, and 208 and supplied to
the camera signal processing circuit 112. At the same time, these
digital signals are amplified to their respective optimum levels by
amplifiers 209, 210, and 211 and added by an adder 208, generating
an automatic focusing luminance signal S5.
[0078] The luminance signal S5 is input to a gamma circuit 213 and
gamma-converted in accordance with a preset gamma curve, forming a
signal S6 whose low-luminance component is increased and
high-luminance component is decreased. The gamma-converted signal
S6 is applied to a low-pass filter (to be referred to as an LPF
hereinafter) with a high cut-off frequency, i.e., a TE-LPF 214, and
to an FE-LPF 215 which is an LPF with a low cut-off frequency. The
TE-LPF 214 and the FE-LPF 215 extract low-frequency components on
the basis of the respective filter characteristics determined by
the microcomputer 114 via a microcomputer interface 253.
Consequently, the TE-LPF 214 generates an output signal S7, and the
FE-LPF 215 generates an output signal S8.
[0079] A line E/O signal is generated by the microcomputer 114 to
identify whether the horizontal line is an even-numbered line or an
odd-numbered line. On the basis of this signal, the signals S7 and
S8 are switched by a switch 216 and applied to a high-pass filter
(to be referred to as an HPF hereinafter) 217.
[0080] That is, the signal S7 is supplied to the HPF 217 when the
horizontal line is an even-numbered line, and the signal S8 is
supplied to the HPF 217 when the horizontal line is an odd-numbered
line.
[0081] The HPF 217 extracts only a high-frequency component in
accordance with filter characteristics determined for even- and
odd-numbered lines by the microcomputer 114 via the microcomputer
interface 253. An absolute value circuit 218 obtains an absolute
value of the extracted signal to generate a positive signal S9.
That is, the signal S9 alternately indicates the levels of
high-frequency components extracted by the filter having different
filter characteristics for even-and odd-numbered lines.
Consequently, different frequency components can be obtained by
scanning one picture frame.
[0082] In accordance with an instruction supplied by the
microcomputer 114 via the microcomputer interface 253, a frame
generating circuit 254 generates gate signals L, C, and R for
forming focus control gate frames L, C, and R, respectively, at
positions in the image sensing surface as shown in FIG. 3.
[0083] Timings at which various kinds of information are fetched in
the AF signal processing circuit 113 will be described below with
reference to FIG. 3 which shows the layout of focus detection areas
in the image sensing surface.
[0084] FIG. 3 is a view for explaining the operations and timings
of extraction of various focus evaluation values in the embodiment
of the present invention. Referring to FIG. 3, the outside frame is
an effective image sensing surface of the outputs from the image
sensing devices 106, 107, and 108.
[0085] Three divided inside frames are focus detection gate frames.
A left frame L, a central frame C, and a right frame R are formed
in accordance with the frame L generating gate signal, the frame C
generating gate signal, and the frame R generating gate signal,
respectively, from the frame generating circuit 254.
[0086] At the start positions of these frames L, C, and R, reset
signals are output for the frames L, C, and R to generate
initialization (reset) signals LR1, CR1, and RR1, respectively,
thereby resetting integrating circuits 232 to 237 and peak hold
circuits 219 to 221, 225 to 227, and 247 to 249.
[0087] Also, when the focus detection area consisting of the frames
L, C, and R is completely scanned, a data transfer signal IR1 is
generated to transfer the integral values of the integrating
circuits and the peak hold values of the peak hold circuits to
their respective buffers.
[0088] Referring to FIG. 3, the scan of an even-numbered field is
indicated by the solid lines, and the scan of an odd-numbered field
is indicated by the dotted lines. In both the even- and
odd-numbered fields, the TE-LPF output is selected on an
even-numbered line, and the FE-LPF output is selected on an
odd-numbered line.
[0089] Automatic focusing performed by the microcomputer by using a
TE/FE peak evaluation value, a TE line peak integral evaluation
value, an FE line peak integral evaluation value, a Y signal peak
evaluation value, and a Max-Min evaluation value in each frame.
Note that these evaluations values are transmitted to the
microcomputer 116 in the lens assembly and the microcomputer 116
performs actual control.
[0090] The signal S9 is supplied to the peak hold circuits 225,
226, and 227 for detecting signal peak values in the left, central,
and right frames, i.e., the frames L, C, and R, in the image
sensing surface. These peak hold circuits detect the peak values of
high-frequency components in their respective frames. The signal S9
is also supplied to the line peak hold circuit 231 to detect the
peak value of each horizontal line.
[0091] The peak hold circuit 225 receives the output gate signal L
for forming the frame L from the frame generating circuit 254, the
signal S9, and the Line E/O signal. As shown in FIG. 3, the peak
hold circuit 225 is initialized in the upper left corner, LR1,
which is the start position of the focusing frame L. The peak hold
circuit 225 holds a peak value of the signal S9 in the frame L of
either an even- or odd-numbered line designated by the
microcomputer 114 via the microcomputer interface 253. In the lower
right corner IR1, i.e., when the entire focusing area is completely
scanned, the peak hold value in the frame L is transferred to the
area buffer 228 to generate a TE/FE peak evaluation value.
[0092] Likewise, the peak hold circuit 226 receives the output
frame C signal from the frame generating circuit 254, the Line E/O
signal, and the signal S9. As in FIG. 3, the peak hold circuit 226
is initialized in the upper left corner, CR1, which is the start
position of the focusing frame C. The peak hold circuit 226 holds a
peak value of the signal S9 in the frame C of either an even- or
odd-numbered line designated by the microcomputer 114 via the
microcomputer interface 253. In IR1, i.e., when the overall
focusing area is completely scanned, the peak hold value in the
frame C is transferred to the area buffer 229 to generate a TE/FE
peak evaluation value.
[0093] Similarly, the peak hold circuit 227 receives the output
frame R signal from the frame generating circuit 254, the Line E/O
signal, and the signal S9. As in FIG. 3, the peak hold circuit 227
is initialized in the upper left corner, RR1, which is the start
position of the focusing frame R. The peak hold circuit 227 holds a
peak value of the signal S9 in the frame R of either an even- or
odd-numbered line designated by the microcomputer 114 via the
microcomputer interface 253. In IR1, i.e., when the overall
focusing area is completely scanned, the peak hold value in the
frame R is transferred to the area buffer 230 to generate a TE/FE
peak evaluation value.
[0094] The line peak hold circuit 231 receives the signal S9 and
the output gate signals for generating the frames L, C, and R from
the frame generating circuit 254. The line peak hold circuit 231 is
initialized at the start point in the horizontal direction of each
frame and holds a peak value of each line in the horizontal line of
the signal S9 in each frame.
[0095] The integrating circuits 232, 233, 234, 235, 236, and 237
receive the output from the line peak hold circuit 231 and the Line
E/O signal which identifies whether the horizontal line is an even-
or odd-numbered line. The integrating circuits 232 and 235 receive
the frame L generating gate signal supplied from the frame
generating circuit 254. The integrating circuits 233 and 236
receive the frame C generating gate signal supplied from the frame
generating circuit 254. The integrating circuits 234 and 237
receive the frame R generating gate signal supplied from the frame
generating circuit 254.
[0096] The integrating circuit 232 is initialized in the upper left
corner, LR1, which is the start position of the focusing frame L.
The integrating circuit 232 adds the output from the line peak hold
circuit 231 to an internal register immediately before the end of
an even-numbered line in each frame. In IR1, the integrating
circuit 232 transfers the peak hold value to the area buffer 238 to
generate a TE line peak integral evaluation value.
[0097] The integrating circuit 233 is initialized in the upper left
corner, CR1, which is the start position of the focusing frame C.
The integrating circuit 233 adds the output from the line peak hold
circuit 231 to an internal register immediately before the end of
an even-numbered line in each frame. In IR1, the integrating
circuit 233 transfers the peak hold value to the area buffer 239 to
generate a TE line peak integral evaluation value.
[0098] The integrating circuit 234 is initialized in the upper left
corner, RR1, which is the start position of the focusing frame R.
The integrating circuit 234 adds the output from the line peak hold
circuit 231 to an internal register immediately before the end of
an even-numbered line in each frame. In IR1, the integrating
circuit 234 transfers the peak hold value to the area buffer 240 to
generate a TE line peak integral evaluation value.
[0099] The integrating circuits 235, 236, and 237 perform the same
operations as the integrating circuits 232, 233, and 234,
respectively, except that the integrating circuits 235, 236, and
237 perform addition of odd-numbered line data, instead of
performing addition of even-numbered line data such as done by the
integrating circuits 232, 233, and 234. The integrating circuits
235, 236, and 237 transfer the results to the area buffers 241,
242, and 243, respectively, generating FE line peak integral
evaluation values.
[0100] The signal S7 is input to the peak hold circuits 219, 220,
and 221, a line maximum value hold circuit 244, and a line minimum
value hold circuit 245.
[0101] The peak hold circuit 219 receives the frame L generating
gate signal supplied from the frame generating circuit 254. The
peak hold circuit 219 is initialized in the upper left corner, LR1,
which is the start position of the frame L, and holds a peak value
of the signal S7 in each frame. In IR1, the peak hold circuit 219
transfers the peak hold result to the buffer 222 to generate a peak
evaluation value of a luminance level (to be referred to as a Y
signal hereinafter).
[0102] Analogously, the peak hold circuit 220 receives the frame C
generating gate signal supplied from the frame generating circuit
254. The peak hold circuit 220 is initialized in the upper left
corner, CR1, which is the start position of the frame C, and holds
a peak value of the signal S7 in each frame. In IR1, the peak hold
circuit 220 transfers the peak hold result to the buffer 223 to
generate a Y signal peak evaluation value.
[0103] Likewise, the peak hold circuit 221 receives the frame R
generating gate signal from the frame generating circuit 254. The
peak hold circuit 221 is initialized in the upper left corner, RR1,
which is the start position of the frame R, and holds the peak
value of the signal S7 in each frame. In IR1, the peak hold circuit
221 transfers the peak hold result to the buffer 224 to generate a
Y signal peak evaluation value.
[0104] The line maximum value hold circuit 244 and the line minimum
value hold circuit 245 receive the frame L, C, and R generating
gate signals supplied from the frame generating circuit 254. The
line maximum value hold circuit 244 and the line minimum value hold
circuit 245 are initialized at the start point in the horizontal
direction in each frame and hold the maximum value and the minimum
value, respectively, of the Y signal on one horizontal line of the
signal S7 in each frame.
[0105] The maximum and the minimum values of the Y signal held by
the line maximum value hold circuit 244 and the line minimum value
hold circuit 245 are input to a subtracter 246. The subtracter 246
calculates a (maximum value-minimum value) signal, i.e., a signal
S10 which indicates the contrast, and inputs the signal to the peak
hold circuits 247, 248, and 249.
[0106] The peak hold circuit 247 is applied with the frame L
generating gate signal from the frame generating circuit 254. The
peak hold circuit 247 is initialized in the upper left corner, LR1,
which is the start position of the frame L, and holds a peak value
of the signal S10 in each frame. In IR1, the peak hold circuit 247
transfers the peak hold result to the buffer 250 to generate a
Max-Min evaluation value.
[0107] Similarly, the peak hold circuit 248 receives the frame C
generating gate signal from the frame generating circuit 254. The
peak hold circuit 248 is initialized in the upper left corner, CR1,
which is the start position of the frame C, and holds a peak value
of the signal S10 in each frame. In IR1, the peak hold circuit 248
transfers the peak hold result to the buffer 251 to generate a
Max-Min evaluation value.
[0108] Analogously, the peak hold circuit 249 is applied with the
frame R generating gate signal from the frame generating circuit
254. The peak hold circuit 249 is initialized in the upper left
corner, RR1, which is the start position of the frame R, and holds
a peak value of the signal S10 in each frame. In IR1, the peak hold
circuit 249 transfers the peak hold result to the buffer 252 to
generate a Max-Min evaluation value.
[0109] In IR1, i.e., when the entire focusing area consisting of
the frames L, C, and R is completely scanned, the data in these
frames are transferred to the buffers 222, 223, 224, 228, 229, 230,
238, 239, 240, 241, 242, 243, 250, 251, and 252. Simultaneously,
the frame generating circuit 254 sends an interrupt signal to the
microcomputer 114 and transfers the data, which are transferred to
these buffers, to the microcomputer 114.
[0110] That is, upon receiving the interrupt signal, the
microcomputer 114 reads out the data (focus evaluation values) from
the buffers 222, 223, 224, 228, 229, 230, 238, 239, 240, 241, 242,
243, 250, 251, and 252 via the microcomputer interface 253 before
the succeeding scan of the frames L, C, and R is completed and the
data are transferred to these buffers. As will be described later,
the microcomputer 114 transfers the data to the microcomputer 116
in synchronism with a vertical sync signal.
[0111] The microcomputer 116 of the lens assembly 127 detects the
focus state by performing calculations by using these transferred
focus evaluation values. The microcomputer 116 then calculates,
e.g., the driving velocity and the driving direction of the focus
motor 125 and controls driving of the focus motor 125, thereby
driving the focusing lens 105.
[0112] The characteristics and applications of the above evaluation
values will be described below.
[0113] The TE/FE peak evaluation value represents an in-focus
degree and is a peak hold value. Therefore, this evaluation value
is less influenced by a camera shake and comparatively less depends
upon the state of an object. For these reasons, this evaluation
value is optimum for in-focus degree determination and reactivation
determination.
[0114] The TE line peak integral evaluation value and the FE line
peak integral evaluation value also represent an in-focus degree.
However, these evaluation values are optimum for direction
determination since they have little noise and are stable as a
result of integration. of the above peak evaluation values and line
peak integral evaluation values, each TE evaluation value is formed
by extracting higher frequencies and hence is optimum as an
evaluation value near the in-focus point. In contrast, each FE
evaluation value is optimum when an image is largely blurred in a
position very far from the in-focus point. Accordingly, by adding
these signals or selectively switching the signals in accordance
with the TE level, it is possible to perform AF over a wide dynamic
range from the state in which an image is largely blurred to the
vicinity of the in-focus point.
[0115] The Y signal peak evaluation value and the Max-Min
evaluation value do not depend much upon the in-focus degree but
upon the state of an object. Therefore, these evaluation values are
optimum to check the change or movement of an object in order to
reliably perform in-focus degree determination, reactivation
determination, and direction determination. These values are also
used in normalization for removing the influence of a change in
brightness.
[0116] More specifically, the Y signal peak evaluation value is
used to check whether the object is a high-luminance object or a
low-luminance object. The Max-Min evaluation value is used to check
whether the contrast is high or low. Furthermore, optimum AF
control can be performed by predicting and compensating for the
peak values, i.e., the magnitudes of peaks, on the characteristic
curves of the TE/FE peak evaluation value, the TE line peak
integral evaluation value, and the FE line peak integral evaluation
value.
[0117] These evaluation values are transferred from the camera main
body 128 to the lens assembly 127 and supplied to the microcomputer
116 of the lens assembly 127, and the automatic focusing operation
is performed.
[0118] The algorithm of an automatic focusing operation performed
by the microcomputer 116 of the lens assembly 127 will be described
below with reference to FIG. 4.
[0119] FIG. 4 is a flow chart of AF processing in this embodiment
of the present invention.
[0120] When the processing is started, the microcomputer 116
activates the AF operation in step S1, and the flow advances to
step S2. In step S2, the microcomputer 116 checks the distance from
the in-focus point by comparing the level of the TE or FE peak with
a predetermined threshold, and performs velocity control.
[0121] If the TE level is low, i.e., if the current focus point is
far from the in-focus point and therefore the image is predicted to
be largely blurred, the microcomputer 116 performs hill-climbing
control for the focus lens by controlling the direction of the lens
by primarily using the FE line peak integral evaluation value. When
the TE level rises to a certain degree near the peak of the
characteristic curve, the microcomputer 116 performs hill-climbing
control for the focus lens by using the TE line peak integral
evaluation value. In this way, the microcomputer 116 so performs
control that the in-focus point can be accurately detected.
[0122] If the lens comes close to the focus point, the flow
advances to step S3 and the microcomputer 116 determines the peak
of the characteristic curve by using the absolute value of the TE
or FE peak evaluation value or a change in the TE line peak
integral evaluation value. If the microcomputer 116 determines that
the level of the evaluation value is highest at the peak, i.e., the
in-focus point, the microcomputer 116 stops the focus lens in step
S4 and advances to reactivation standby in step S5.
[0123] In the reactivation standby, if the microcomputer 116
detects that the level of the TE or FE peak evaluation value
decreases by a predetermined level or more from the peak value
obtained when the in-focus point is detected, the microcomputer 116
reactivates the operation in step S6.
[0124] In the loop of the automatic focusing operation as described
above, the velocity of the focus lens is controlled by using the
TE/FE peak. The level of the absolute value for determining the
peak of the characteristic curve and the change in the TE line peak
integral evaluation value are determined by predicting the height
of the hill by checking the object by using the Y peak evaluation
value or the Max-Min evaluation value. The AF operation can always
be performed by repeating the above processing.
[0125] FIG. 5 is a timing chart for explaining the timing at which
the microcomputer 114 of the camera main body 128 transmits various
data such as the AF evaluation value to the microcomputer 116 of
the lens assembly 127. As described previously, the timing of
communication between the camera main body 128 and the lens
assembly 127 is such that the AF evaluation value read out by the
microcomputer 114 is transferred to the microcomputer 116
immediately after the next vertical sync signal in synchronism with
the vertical sync signal (V synchronization).
[0126] As a consequence, the AF operation can be controlled in
synchronism with the vertical sync signal.
Zooming Operation
[0127] The relationship between the movements of the zoom lens 102
and the focus compensating lens 105 and a method of referring to
the AF evaluation value signal during a zooming operation from wide
to telephoto will be described below.
[0128] In the lens system as illustrated in FIG. 1, the focus lens
105 has both the compensating function and the focusing function.
Accordingly, the position of the focus lens 105 for focusing an
image on the image sensing devices 106, 107, and 108 change in
accordance with the object distance even at the same focal
length.
[0129] FIG. 6 shows the result of continuous plotting of the
position of the focus lens 105 for focusing an image on the imaging
plane of each image sensing device while the object distance is
changed at different focal lengths. In FIG. 6, the abscissa
indicates the position (focal length) of the zoom lens, and the
ordinate indicates the position of the focus lens. Each locus
information represents the contents of the lens cam data of the ROM
120 of the microcomputer 116.
[0130] During the zooming operation, one of the loci shown in FIG.
6 is selected in accordance with the object distance, and the focus
lens 105 is moved to trace that locus. This allows a zooming
operation free from a blur.
[0131] In a lens system by which focusing is performed by using a
lens (front lens) closest to an object, a 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.
[0132] A manual zoom knob, for example, is formed on this cam ring,
and the focal length is manually changed. Even if the knob is moved
as fast as possible, the cam ring rotates to trace the movement of
the knob, and the variable power lens and the compensating lens
move along a cam groove of the cam ring. Therefore, no blur is
caused by the above operation as long as the focus lens is focused
on an object.
[0133] In controlling the inner focus type lens system of this
embodiment having the characteristics as described above, however,
when a zooming operation is performed while the in-focus state is
held, it is necessary to store the locus information (FIG. 6) as
the lens cam data in the ROM 120 of the microcomputer 116, read out
the locus information from the ROM 120 in accordance with the
position or the moving velocity of the zoom lens 102, and move the
focus lens 105 on the basis of the readout information.
[0134] FIG. 7 is a graph for explaining one invented locus tracing
method. In FIG. 7, reference symbols Z0, Z1, Z2, . . . , Z6 denote
the positions of the zoom lens; and a0, a1, a2, . . . , a6 and b0,
b1, b2, . . . , b6, representative loci stored as the lens cam data
in the ROM 120 of the microcomputer 116.
[0135] Also, p0, p1, p2, . . . , p6 denote loci calculated on the
basis of the above two loci. This locus calculation is done by the
following equation:
p(n+1)=.vertline.p(n)-a(n).vertline./.vertline.b(n)-a(n).vertline.*.vertli-
ne.b(n+1)-a(n+1).vertline.+a(n+1) (1)
[0136] In equation (1), if, for example, the focus lens is at p0 in
FIG. 7, the ratio at which p0 internally divides a line segment
b0-a0 is calculated, and the point at which a line segment b1-a1 is
internally divided by this ratio is given as p1.
[0137] The focus lens moving velocity for holding the in-focus
state can be known from this positional difference, p1-p0, and the
time required for the zoom lens to move from Z0 to Z1.
[0138] An operation when there is no such limitation that the stop
position of the zoom lens 102 must be on a boundary having the
previously stored representative locus data will be described
below.
[0139] FIG. 8 is a graph for explaining a method of calculating a
locus not stored on the basis of a plurality of pieces of stored
locus information. FIG. 8 extracts a part of FIG. 7, and the zoom
lens can take any arbitrary position.
[0140] In FIGS. 7 and 8, the ordinate indicates the focus lens
position, and the abscissa indicates the zoom lens position. The
representative locus positions (the focus lens positions with
respect to the zoom lens positions) stored as the lens cam data in
the ROM 120 of the microcomputer 116 are represented as follows for
various object distances with respect to zoom lens positions Z0,
Z1, . . . , Zk-1, Zk, . . . , Zn:
[0141] a0, a1, . . . , ak-1, ak, . . . , an
[0142] b0, b1, . . . , bk-1, bk, . . . , bn
[0143] If the zoom lens position is Zx not on a zoom boundary and
the focus lens position is Px, ax and bx are calculated as
follows:
ax=ak-(Zk-Zx)*(ak-ak-1)/(Zk-Zk-1) (2)
bx=bk-(Zk-Zx)*(bk-bk-1)/(Zk-Zk-1) (3)
[0144] That is, ax and bx can be calculated by internally dividing
data having the same object distance of the four stored
representative locus data (ak, ak-1, bk, and bk-1 in FIG. 8) by the
internal ratio obtained from the current zoom lens position and the
two zoom boundary positions (e.g., Zk and zk-1 in FIG. 8) on the
two sides of the current zoom lens position.
[0145] In this case, pk and pk-1 can be calculated, as shown in
equation (1), by internally dividing data having the same focal
length of the four stored representative data (ak, ak-1, bk, and
bk-1 in FIG. 8) by the internal ratio obtained from ax, px, and
bx.
[0146] When zooming is performed from wide to telephoto, the focus
lens moving velocity for holding the in-focus state can be known
from the positional difference between the focus position pk to be
traced and the current focus position px and the time required for
the zoom lens to move from Zx to Zk.
[0147] When zooming is performed from telephoto to wide, the focus
lens moving velocity for holding the focused state can be known
from the positional difference between the focus position pk-1 to
be traced and the current focus position px and the time required
for the zoom lens to move firm Zx to Zk-1. The locus tracing method
as described above is invented.
[0148] When the AF switch 131 is ON, it is necessary to trace the
locus while maintaining the in-focus state. When the zoom lens
moves in a direction from telephoto to wide, the diverged loci
converge as can be seen from FIG. 6. Therefore, the in-focus state
can be maintained by the above locus tracing method.
[0149] In a direction from wide to telephoto, however, a locus
which the focus lens in the point of convergence is to trace is
unknown. Consequently, the in-focus state cannot be maintained by
the locus tracing method as above.
[0150] FIGS. 9A and 9B are graphs for explaining one locus tracing
method invented to solve the above problem. In each of FIGS. 9A and
9B, the abscissa indicates the position of a zoom lens. In FIG. 9A,
the ordinate indicates the level of a high-frequency component
(sharpness signal) of a video signal as an AF evaluation signal. In
FIG. 9B, the ordinate indicates the position of a focus lens.
[0151] Assume that in FIG. 9B, a focusing locus is a locus 604 when
a zooming operation is performed for a certain object.
[0152] Assume also that a tracing velocity with respect to a locus
indicated by lens cam data closer to a wide side than a zoom
position 606 (z14) is positive (the focus lens is moved to the
closest focusing distance), and that a tracing velocity with
respect to a locus indicated by lens cam data when the focus lens
is moved in the direction of infinity on a telephoto side from the
position 606 is negative.
[0153] When the focus lens traces the locus 604 while being kept in
the in-focus state, the magnitude of the sharpness signal is as
indicated by 601 in FIG. 9A. It is generally known that a zoom lens
kept in the in-focus state has an almost fixed sharpness signal
level.
[0154] Assume that in FIG. 9B, a focus lens moving velocity for
tracking the focusing locus 604 during a zooming operation is Vf0.
When an actual focus lens moving velocity is vf and a zooming
operation is performed by increasing or decreasing Vf with respect
to Vf0 for tracing the locus 604, the resulting locus is zigzagged
as indicated by reference numeral 605.
[0155] Consequently, the sharpness signal level so changes as to
form peaks and valleys as indicated by reference numeral 603. The
magnitude of the level 603 is a maximum at positions where the loci
604 and 605 intersect (at even-numbered points of Z0, Z1, . . . ,
Z16) and is a minimum at odd-numbered points where the moving
direction vectors of the locus 605 are switched.
[0156] Reference numeral 602 denotes a minimum value of the level
603. When a level TH1 of the value 602 is set and the moving
direction vectors of the locus 605 are switched every time the
magnitude of the level 603 equals the level TH1, the focus lens
moving direction after the switching can be set in a direction in
which the movement approaches the in-focus locus 604.
[0157] That is, each time an image is blurred by the difference
between the sharpness signal levels 601 and 602 (TH1), the moving
direction and velocity of the focus lens are so controlled as to
decrease the blur. Consequently, a zooming operation by which a
degree (amount) of blur is suppressed can be performed.
[0158] The use of the above method is effective even in a zooming
operation from wide to telephoto, as shown in FIG. 6, in which
converged loci diverge. That is, even if the in-focus velocity Vf0
is unknown, the switching operation is repeated as indicated by 605
(in accordance with a change in the sharpness signal level) while
the focus lens moving velocity Vf is controlled with respect to the
tracing velocity (calculated by using p(n+1) obtained from equation
(1)) explained in FIG. 6. As a consequence, it is possible to
select an in-focus locus by which the sharpness signal level is not
decreased below the level 602 (TH1), i.e., a predetermined amount
or more of blur is not produced.
[0159] Assuming a positive compensating velocity is Vf+ and a
negative compensating velocity is Vf-, the focus lens moving
velocity Vf is determined by
Vf=Vf0+Vf+ (4)
Vf0+Vf- (5)
[0160] In order that no deviation is produced when the tracing
locus is selected by the above method of zooming operation, the
compensating velocities Vf+ and Vf- are so determined that the
internal angle of the two vectors of Vf obtained by equations (4)
and (5) is divided into two equal parts.
[0161] Another method is proposed in which the
increasing/decreasing period of the sharpness signal is changed by
changing the compensating amount by using the compensating velocity
in accordance with the object, the focal length, or the depth of
field, thereby improving the accuracy of the selection of the
tracing locus.
[0162] In the embodiment as described above, the lens assembly
includes the focus lens locus information and the AF circuit, and a
plurality of evaluation values are transmitted from the camera main
body to the lens assembly. Accordingly, the lens assembly can be
informed of the operation state of the focus lens, and this makes
it possible to realize complicated control of the focus lens by
using the lens assembly capable of a zooming operation.
Consequently, a video camera system with which various lens
assemblies can be used is realized without complicating the
construction of the camera main body.
First Modification of Embodiment
[0163] In this modification, evaluation values and version
information indicating the type and the contents of each evaluation
value are transferred from the camera 128 to the lens assembly 127
and supplied to the microcomputer 116 to perform an automatic
focusing operation. The rest of the configuration is identical with
that of the above embodiment and so a detailed description thereof
will be omitted.
[0164] The version information of the evaluation value will be
described below. This version information allows the selection of
an optimum signal as an AF evaluation value in accordance with the
function and performance of a camera main body. For example, when
the sensitivity or the number of pixels of the image sensing
devices 106, 107, and 108 is greatly increased compared to that of
conventional devices and consequently the frequency characteristics
or the dynamic range of a video signal is improved, it is predicted
that the frequency component of a signal indicating an in-focus
degree shifts to higher frequencies and a change in the evaluation
value when the lens is defocused by a minimum diameter of a circle
of confusion becomes larger.
[0165] Accordingly, it is necessary to change the filter
characteristics of the TE-LPF 214 and the FE-LPF 215 from the
conventional settings, and the obtained AF evaluation value becomes
different from the conventional evaluation value.
[0166] Assuming the former version of an evaluation value is Ver.1
and the latter version is Ver.2, FIGS. 10A and 10B illustrate the
detailed contents of the versions and the evaluation values
transmitted from the camera main body to the lens assembly.
[0167] In this modification, it is assumed, for the sake of
simplicity, that the type of evaluation value remains unchanged
even when its version changes. However, the present invention is
not limited to this modification, provided that the lens assembly
as the reception side can control the number of words to be
transmitted and the type or contents of an evaluation value of each
word.
[0168] As described above, the characteristic of an evaluation
value changes in accordance with the version. Therefore, AF with
higher performance can be realized by making the AF control
algorithm meet the characteristic.
[0169] FIG. 10A shows the AF evaluation values of the two versions
transmitted from the camera main body to the lens assembly. FIG.
10B shows the contents transmitted from the lens assembly to the
camera main body.
[0170] The algorithm of an automatic focusing operation performed
by the microcomputer 116 of the lens assembly will be described
below with reference to FIG. 11.
[0171] In this modification, the microcomputer 116 corresponds to
AF control of Ver.2. The camera main body corresponds to both Ver.1
and Ver.2.
[0172] FIG. 11 is a flow chart showing a focusing operation
performed by the lens assembly in the first modification of the
embodiment of the present invention.
[0173] The microcomputer 116 activates the system in step S101 and
checks the version of an evaluation value in step S102. If the
version is Ver.1, the microcomputer 116 executes hill-climbing
control 1 in step S103. If the version is Ver.2, the microcomputer
116 executes hill-climbing control 2 in step S104. If the level of
the TE or FE peak is low, the microcomputer 116 determines that the
focus lens is far from the in-focus point and drives the focus lens
at a high velocity (velocity control). The microcomputer 116
controls the search for the in-focus point by performing direction
control by primarily using the TE line peak integral evaluation
value near the in-focus point and the FE line peak evaluation value
if the lens is far from the in-focus point.
[0174] Assuming, as described above, that an evaluation value of
Ver.2 corresponds to a video signal obtained from a
high-resolution, high-sensitivity image sensing device, in the
vicinity of the in-focus point, the image is blurred more by an
evaluation value of Ver.2 than that of Ver.1 when the focus lens is
moved the same amount.
[0175] Accordingly, the lens moving velocity near the in-focus
point in step 104 is set to be lower than that in step S103 (S103:
velocity .alpha., S104: velocity .beta.=a/2).
[0176] In step S105, the microcomputer 116 determines the peak of
the characteristic curve (the in-focus point) from the absolute
value of the TE or FE peak evaluation value and a change in the TE
line peak integral evaluation value. The microcomputer 116 stops
the lens at a point at which the level is highest, and stores these
evaluation values in the memory.
[0177] In step S106, the microcomputer 116 performs the same
processing as in step S102. If the version of an evaluation value
is Ver.1, the flow advances to reactivation standby 1 in step S107.
If the version is Ver.2, the flow advances to reactivation standby
2 in step S108.
[0178] In the reactivation standby, the microcomputer 116 detects
whether the level of the TE or FE peak evaluation value decreases
from the level stored in the memory in step S105. If the decrease
is detected, the flow advances to step S109 to perform
reactivation.
[0179] If an evaluation value of Ver.2 corresponds to a
high-resolution, high-sensitivity image sensing signal, the level
of an evaluation value of Ver.2 tends to change more than that of
Ver.1 for visually the same blur. Therefore, the evaluation value
variation threshold for determining reactivation in reactivation
standby 2 in step S108 is set to be larger than that in step S107
(in this modification, reactivation is performed when the level
changes 20% or more from the stored level in step S107 and when the
level changes 40% or more from the stored level in step S108).
[0180] In the loop of the automatic focusing operation as described
above, the velocity control of the focus lens is performed by using
the TE/FE peak. A characteristic curve is predicted by checking the
object by using the Y peak evaluation value or the Max-Min
evaluation value, and the absolute value for determining the peak
of the characteristic curve and the change in the TE line peak
integral evaluation value are determined on the basis of the
characteristic curve.
[0181] In the above explanation, it is assumed that the version of
the lens assembly is Ver.2. If the lens assembly is Ver.1, it is
only necessary to perform the processing in the order of steps
S101, S103, S105, S106, S107, and S109 in FIG. 11.
[0182] The communication timings between the camera main body and
the lens will be described below with reference to FIG. 5. As
described above, the AF evaluation values read out by the
microcomputer of the main body are transferred to the microcomputer
of the lens immediately after the next vertical sync signal in
synchronism with the vertical sync signal (V synchronization).
[0183] FIG. 12 is a flow chart for explaining the method of
matching the versions of communications between the camera main
body and the lens. This flow chart shows the processing performed
by the microcomputer 114 of the camera main body. In FIG. 12, it is
assumed that the camera main body corresponds to the evaluation
values of Ver.2 in FIG. 10A and the lens assembly corresponds to
both the AF control versions Ver.1 and Ver.2 in FIG. 10B.
[0184] In step S111, the microcomputer 114 activates the system. In
step S112, the microcomputer 114 performs initialization, i.e.,
performs settings for generating AF evaluation values corresponding
to the latest version (in this case Ver.2) of the microcomputer of
the main body (in the case explained in FIG. 11, the microcomputer
114 sets the filter characteristics of the TE-LPF 214 and the
FE-LPF 215 so that higher frequencies than that in conventional
methods can be extracted).
[0185] To communicate with the microcomputer 116 at the
communication timings shown in FIG. 5, the microcomputer 114 waits
in step S113 until the vertical sync signal comes. In step S114,
the microcomputer 114 performs mutual communication, i.e.,
exchanges data as illustrated in FIGS. 4A and 4B.
[0186] In step S115, the microcomputer 114 checks whether the
version of the transmitted evaluation value agrees with the control
version by which the microcomputer of the lens can perform AF
control.
[0187] If the versions agree, the flow advances to step S118, and
the microcomputer 114 executes usual control of the camera, which
includes AE (Automatic Exposure) control, AWB (Automatic White
Balance) control, and the other processing to sense an image. The
microcomputer 114 then waits in step S113 until the next vertical
sync signal comes.
[0188] If the versions disagree in step S115, the flow advances to
step S116, and the microcomputer 114 performs settings for
generating AF evaluation values corresponding to the AF control
version of the lens assembly. The microcomputer 114 changes the
version of the evaluation value in step S117, and the flow returns
to step S113.
[0189] In this modification as described above, upgrading is
realized by transferring the type information of a focus signal.
For example, a focus signal newly required in accordance with the
progress of technologies such as a high-pixel CCD can be added to
the conventional focus signal, or the contents or type of the
signal can be changed. It is also possible to provide a highly
expandable video system by optimizing AF control in accordance with
the version of the transferred focus signal.
Second Modification of Embodiment
[0190] The second modification of the embodiment of the present
invention will be described below. FIG. 13 is a block diagram
showing the configuration of an interchangeable lens video camera
system of this modification. FIG. 13 differs from the video system
in FIG. 1 in that a microcomputer 114A incorporates an evaluation
value normalizing circuit 132. The rest of the configuration
including the microcomputer 114A is identical with the above
embodiment (the same reference numerals as in FIG. 1 denote parts
having the same functions in FIG. 13) and a detailed description
thereof will be omitted.
[0191] In this modification, an AF evaluation value generated by
the AF signal processing circuit 113 is read out at a period which
is an integral multiple of a vertical sync signal by the data read
circuit 115 of the microcomputer 114A of the camera main body. The
readout evaluation value is normalized by the evaluation value
normalizing circuit 132 and transferred to the microcomputer 116 of
the lens assembly.
[0192] The evaluation value normalizing circuit 132 will be
described below with reference to FIGS. 14A to 14D. FIGS. 14A to
14D are graphs showing changes in the TE peak evaluation value when
the lens is searched from the closest focusing distance to infinity
while a certain object is imaged.
[0193] FIGS. 14A and 14C show the values read out by the data read
circuits 115 of different cameras (image sensing means) when an
image of the same object is taken by the same lens.
[0194] These output levels are different although an image of the
same object is taken by the same lens. The evaluation value
normalizing circuit 132 determines levels such that the signal
levels at two points P1 and P2 have predetermined values and, in
accordance with the levels thus determined, shifts, compresses, or
expands the whole signal level.
[0195] The output from the evaluation value normalizing circuit 132
in FIG. 14A is shown in FIG. 14B, and the output from the
evaluation value normalizing circuit 132 in FIG. 14C is shown in
FIG. 14D. Although the input levels to the evaluation value
normalizing circuits 132 shown in FIGS. 14A and 14C are different,
the output levels in FIGS. 14B and 14D are almost the same. The
evaluation value normalizing circuit 132 performs similar
normalization for other evaluation values.
[0196] That is, the evaluation value normalizing circuit 132
receives the TE peak values in the frames L, C, and R output from
the buffers 228 to 230, the TE peak integral values and the FE peak
integral values in the frames L, C, and R output from the buffers
238 to 243, and the contrast peak values in the frames L, C, and R
output from the buffers 250 to 252. The evaluation value
normalizing circuit 132 performs maximum value level shift
processing and minimum value level shift processing for these input
values. In the maximum value level shift processing, the peak value
of each input signal level is compressed or expanded and forcibly
matched with the level of P1 in FIGS. 14B and 14D. In the minimum
value level shift processing, the minimum value of each input
signal level is compressed or expanded and forcibly matched with
the level of P2 in FIGS. 14B and 14D. Although FIGS. 14A to 14D
illustrate the TE peak, other evaluation values described
previously are similarly normalized and transmitted to the
microcomputer 116 of the lens assembly 127.
[0197] Consequently, even if variations are present in the image
sensing devices 106 to 108 or the AF signal processing circuit 113
of the camera main body, each focus evaluation value has a
normalized predetermined characteristic. Accordingly, even when a
plurality of camera main bodies having different image sensing
means are combined with different lens assemblies, a common output
can be transferred to these lens assemblies by normalizing the
focus signal. Additionally, since the respective optimum response
characteristics can be determined in the individual lens
assemblies, objects to be imaged can be focused more stably in a
taking area under various taking conditions.
[0198] As many apparently widely different embodiments of the
present invention can be made without departing from the spirit and
scope thereof, it is to be understood that the invention is not
limited to the specific embodiments thereof except as defined in
the appended claims.
* * * * *