Camera system

In a camera system for use in a camera of the type having a lens, a lens shutter, and automatic focusing utilizing the light transmitted through the lens, a light-blocking device is provided ahead of the image plane to be photographed and moveable between blocking and non-blocking positions, and a control device is operable upon manual actuation of the camera to open the shutter and provide for automatic focus adjustment utilizing the light transmitted through the lens, the control device further being operable to move the light-blocking device to its blocking position when the shutter is opened to provide for automatic focus adjustment and to subsequently move the light-blocking device to its non-blocking position to provide for exposure operation of the shutter to expose the film in the camera.

FIELD OF THE INVENTION 
The present invention relates to a control system for use in an autofocus 
camera equipped with a lens shutter. 
BACKGROUND OF THE INVENTION 
A popular autofocus camera having a lens shutter performs automatic focus 
detection which generally relies on the principles of triangulation near 
the viewfinder in a path differing from the photographical path. In 
practice, the camera lens is set at a given position according to the 
results of the detection. 
Meanwhile, a single lens reflex (SLR) camera equipped with a focal-plane 
shutter automatically adjusts the focus with high accuracy, because the 
error associated with the lens-driving portion is accommodated, which 
arises from the fact that the lens is brought into focus by focusing the 
light rays which pass through the lens. 
On the other hand, a camera having a lens shutter is more advantageous than 
SLR cameras in flash photography. Further, the former camera is excellent 
in portability. Therefore, cameras having a lens shutter have enjoyed wide 
acceptance. 
In recent years, multifocal cameras and cameras having a zoom lens have 
gained popularity. With these cameras, a method adopted to bring the 
camera lens into focus involves measuring the distance externally when the 
lens is used at a longer focal point. The camera lens is focused according 
to the obtained value. In this method, errors arising during setting and 
errors intrinsically present in the lens system cannot be neglected. 
Hence, each step of the manufacturing process requires that adjustments be 
made with excessively high accuracy. 
In view of the foregoing, the invention seeks to provide a camera which has 
a lens shutter but provides automatic focus adjustment equivalent to the 
adjustment in an SLR camera, thereby accurately adjusting the focus. 
In a camera equipped with a lens shutter, the optical path of the camera 
lens is closed before operation. Therefore, it is impossible to know 
whether the light rays transmitted through the optical path are focused. 
Accordingly, the provision of a separate means which shields the image 
plane to be photographed may be contemplated to enable the lens shutter to 
open. However, to achieve complete shielding, large shielding members such 
as a pair of focal-plane shutters are required, thus rendering the 
structure complex. 
The present invention enables adjustment of the focus by focusing the light 
rays which pass through the camera lens. The invention also provides that 
the image plane to be photographed is completely shielded by a simple 
method. 
SUMMARY OF THE INVENTION 
The above object is achieved in accordance with the teachings of the 
invention by a camera system whose focus is automatically adjusted and 
which has a lens shutter in the optical path of a camera lens, the lens 
being brought into focus by focusing the transmitted light. The camera 
system comprises a light-blocking member disposed ahead of the image plane 
to be photographed, a driving means which operates the lens when the 
camera is manually operated, and a sequential shutter control means. 
Usually, the shutter is closed to attenuate passing light. When the camera 
is manually operated, the shutter is opened, and the focus is 
automatically adjusted according to the light transmitted through the 
lens. When the shutter is subsequently closed, the light-blocking member 
is withdrawn, and the shutter performs its exposure operation.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
One example of the invention will now be described in detail by referring 
to the accompanying drawings. Referring to FIG. 1, the body of a camera is 
indicated by numeral 1. The body 1 has a lens barrel 3 in which a camera 
lens 2 is mounted. An image of the subject is passed through the lens 2 
and focused onto a photosensitive material F (hereinafter referred to as 
the film). The film F is located behind a region defined by the field of 
view 4. 
A viewfinder 5 that indicates the limits of the field of view and a strobe 
6 are mounted in the upper portion of the camera body. A shutter release 7 
for setting the camera into operation is mounted on the top of the camera 
body. 
FIG. 2 is a cross-sectional view of the main components of the camera. A 
lens shutter 8 which opens and closes the lens opening is mounted behind 
the lens 2. The shutter 8 has a shutter blade 8a that normally closes the 
lens opening. 
A stepper motor 9 is disposed inside the lens barrel 3 and drives a known 
activating means D to bring the lens into a focal point and to open and 
close the blade 8a. 
The activating means D that drives the lens 2 causes a helicoid mount to 
move the lens 2 toward the optical axis. The helicoid mount is driven by a 
ring R that rotates around the lens opening. 
An electronic circuit 10 which controls the stepper motor 9 comprises a 
known motor-driving circuit, a sequential control circuit for controlling 
the timing at which the shutter is driven, and an illuminance-measuring 
circuit. Since all of these circuits are known, none of them are shown. 
The illuminance-measuring circuit includes a light-receiving device 11 
which measures the illuminance on the subject. This structure is known and 
described in detail, for example, in Japanese Patent Laid-Open No. 
200,339/1987. 
A mirror M is inclined and held to a frame 12 on the optical axis P behind 
the lens 2. The mirror is rotatably held by a shaft 12a mounted below the 
viewfinder 5. The shaft 12a is held to a light-tight cylinder 13 which 
extends toward the film surface from the rear of the shutter 8. The whole 
outer surface of the cylinder 13 is made light-tight. An operation lever 
12b and a pin 12c are mounted on the shaft. 
The image from an object is reflected toward the viewfinder 5 by the mirror 
M. A sensor 14 is rigidly fixed to the frame 12 to detect the focus point 
equivalent to the film surface. The sensor 14 detects that the lens 2 is 
focused. 
The sensor 14 is connected with a known automatic focusing detection 
circuit (not shown). An electromagnet 20 and the stepper motor 9 are 
actuated according to the output from the focusing detection circuit. 
A light-blocking member 16 is disposed between the light-tight cylinder 13 
and a flange 15 defining the field of view. That is, the member 16 is 
located behind the cylinder 13. The flange 15 is positioned ahead of the 
film surface F. As shown in FIG. 3, the blocking member 16 comprises 
sectors 16b - 16g and an actuating lever 16j. The sectors 16b - 16g 
revolve about a pin 16a. The lever 16j turns around a shaft 16h. The 
sectors 16b - 16g have their respective grooves in which a pin 16i is 
fitted. A second actuating lever 16k is firmly fixed to the shaft 16h and 
has a pin 16l. 
FIG. 4 shows main portions of the activating means D that is driven by the 
stepper motor 9. For simplicity, the members rotating around the lens 
opening are shown to be expanded onto a plane. 
The shutter blade 8a which opens and closes the lens opening is engaged so 
as to be actuated by an opening lever 17. In FIG. 4, only one of a set of 
blades is shown. The lever 17 is biased to the left by a spring (not 
shown). An activating pin 17a is mounted at the right end of the lever 17. 
The activating means D has grooves D.sub.0 so as to be slidably held. The 
activating means D comprises teeth D.sub.1, a cam portion D.sub.2 for 
activating the activating pin 17a, a pressing portion D.sub.3 at the left 
end, a first inclined surface D.sub.4 engageable with the pin 12c on the 
lever 12b, and a second inclined surface D.sub.5 engageable with the pin 
16l on the actuating lever 16k. The teeth D.sub.1 are driven by the 
stepper motor 9 via gears 9a and 9b. 
A distance-setting member 18 has a groove 18a and is held so as to be 
slidable from side to side. The distance-setting member 18 comprises a pin 
18b engaging with the ring R, an arm 18c engaging with the pressing 
portion D.sub.3, a distance-setting step portion 18d, and a raised step 
portion 18e. The setting member 18 is biased to the right by a spring (not 
shown). 
An armature lever 19 consists of an attracted member 19a and a retaining 
portion 19b. The member 19a is controlled and attracted to the 
electromagnet 20. The retaining portion 19b engages with the 
distance-determining member 18. The lever 19 is biased to the right by a 
spring 19c. 
FIG. 5 is an enlarged view of the cam portion D.sub.2 of the activating 
means D. The cam portion is shown to be comprised of cams D.sub.21, 
D.sub.22, D.sub.23, D.sub.24, D.sub.25 and D.sub.26. The cam D.sub.21 
locks the activating pin 17a against the action of a spring (not shown) to 
bring the shutter blade 8a into its closed position before the camera is 
operated. The cam D.sub.22 moves the blade 8a into its open position when 
the operation of the camera is started. The cam D.sub.23 maintains the 
blade 8a in its open state while automatic focusing adjustment is being 
made. The cam D.sub.24 acts to return the blade 8a to its closed position. 
When the mirror M and the light-blocking member 16 are being withdrawn, 
the cam D.sub.25 keeps the blade 8a in its closed position. The cam 
D.sub.26 opens and closes the blade 8a for exposure operation. 
The method of operating the camera is next described. Under the condition 
shown in FIG. 4, if the shutter release 7 is depressed to take a picture, 
the electronic circuit 10 is set into operation. The electromagnet 20 is 
energized to attract the attracted member 19a and thereafter the stepper 
motor 9 is rotated. This moves the activating means D to the right. The 
cam D.sub.22 activates the lever 17 to move the shutter blade 8a from the 
illustrated first position to a second position where the lens opening is 
opened. Then, the optical path to the sensor 14 is open. As a result, the 
automatic focusing detection (AF) circuit is set into operation. 
The sensor 14 receives the image of the subject transmitted through the 
camera lens 2. When the camera lens arrives at the optimum focus point, 
the AF circuit (not shown) stops the output from the sensor and 
deenergizes the electromagnet 20 by a known method. 
More specifically, when the stepper motor 9 is driven, the activating means 
D shifts to the right. The arm 18c of the distance-determining member 18 
follows the pressing portion D.sub.3, and is moved to the right by a 
spring (not shown). The retaining portion 19b of the armature lever 19 is 
pushed by the raising step portion 18e and pressed against the 
electromagnet 20. Thus, the lever 19 is atracted and retained to the 
electromagnet 20. When the electromagnet 20 is deenergized at the focus 
point as described above, the armature lever 19 is rotated to the right by 
the spring 19c. The retaining portion 19b of the lever 19 engages the 
setting step portion 18d corresponding to the focus point of the lens 2. 
The ring R is thereby driven to set the lens 2 at the focus point. 
In the sequence diagram of FIG. 6, the operation is started after time 
t.sub.1 elapses. The AF circuit begins to operate at instant t.sub.2. The 
camera lens 2 is stopped. The illustrated condition is just prior to 
instant t.sub.3. 
The stepper motor 9 rotates further to move the activating means D to the 
right. The cam D.sub.24 rotates the lever 17 to the right. The shutter 
blade 8a moves into the first position where the opening is closed. The 
first inclined surface D.sub.4 activates the pin 12c of the operation 
lever 12b to rotate the mirror M about the shaft 12a. The mirror is moved 
out of the optical path of the lens 2 and the flange 15. 
The pin 16l of the second activating lever 16k of the light-blocking member 
16 is activated by the second inclined surface D.sub.5. The activating 
lever 16j is rotated to the right about the shaft 16h. Thus, the pin 16l 
rotates the sectors 16b - 16g about the shaft 16a, thereby providing an 
opening at the flange 15. That is, the operation is complete at time 
t.sub.5 as shown in FIG. 6. 
Subsequently, the stepper motor 9 turns to move the activating means D 
further to the right. The cam D.sub.26 activates the lever 17 to cause the 
shutter blade 8a to open the lens opening. Since the sectors 16b - 16g are 
withdrawn from the field of view at the flange 15, the film F is exposed 
to light. If a desired exposure amount is obtained by a known method, the 
motor 9 is reversed by the sequential control circuit. Then the exposure 
operation is completed. That is, the operation is complete at time t.sub.6 
as shown in FIG. 6. 
If the stepper motor 9 further rotates counterclockwise, the sectors 16b - 
16g return to their original positions where they cover the field of view 
at the flange 15 while the shutter blade 8a is closed. The mirror M goes 
back into the optical path. The blade 8a is driven by the cams D.sub.24, 
D.sub.23, D.sub.22, D.sub.21 and returns to the position in which it 
closes the opening. In this way, preparations for photography are 
complete. 
In the above example, the opening lever 17 may be retained by a separate 
engaging means to permit the lever 17 to reach the cam D.sub.21 while the 
shutter blade 8a is kept closed by the cam D.sub.25 when the motor 9 is 
reversed. Another means may be provided to release the lever when the 
activating means D returns to its initial position. 
Also in the above example, the exposure operation is performed by the lens 
shutter comprising the shutter blade 8a. It is also possible to fabricate 
the light-blocking member 16 from a focal-plane shutter. In this case, the 
cams D.sub.24, D.sub.25, and D.sub.26 of the activating means D are 
unnecessary. The second inclined surface D.sub.5 may start the focal-plane 
shutter with further delay. 
In this case, if the ability of the focal-plane shutter to block light is 
relatively inferior, the function can be performed sufficiently because of 
the subject matter of the present invention. Therefore, the shutter can be 
made simple in structure. 
The second inclined surface D.sub.5 and the first inclined surface D.sub.4 
are provided to activate the light-blocking member 16 and the mirror M. 
They may be activated by other power means such as a motor or spring. In 
this case, the activating means D may be designed to be used only to start 
them. 
Withdrawing the mirror M is independent of the subject matter of the 
invention. A known half mirror may be fixed. Further, the mirror M may 
perform the function of the light-blocking member 16. It may be moved out 
of the optical path during photography. The stepper motor 9 can take other 
forms such as an ultrasonic motor, as long as it can be rotated either 
forwardly or rearwardly. 
In the above example, the lens opening is closed by the shutter blade 8a 
prior to operation. It is not necessary that the opening be totally 
closed. If the opening opens slightly, no problems occur, provided that 
light does not leak to the film F through the light-blocking member 16. 
Also, a separate shutter blade performing the same function or other means 
such as a liquid crystal which attenuates light may be provided. 
Where the sensor 14 cannot perform the automatic focus adjusting function, 
weak light from the strobe 6 may be projected to continue the operation. 
As can be understood from the description made thus far, in accordance with 
the present invention, the light passing through the optical path of the 
camera lens is usually attenuated. The field of view 4 is shielded by the 
light-blocking member 16. During photography, the optical path is opened 
and the light transmitted through the lens is used to carry out an 
automatic focus adjusting operation. Errors intrinsic to individual 
cameras are accommodated. Consequently, focus control operation can be 
performed automatically with high precision. The field of view 4 is 
shielded by the sectors 16b - 16g only substantially immediately prior to 
the exposure operation and so the sectors 16b - 16g can be made simple in 
structure and small. The sectors can be fabricated from an inexpensive 
light-blocking member.