Electronic camera having a built-in strobe

An electronic camera having a built-in strobe, in which upon a normal photographing mode a return light of a light emitted from the strobe on an object to be photographed is detected to thereby control a light emission amount of the strobe and a controller is provided for controlling the light emission amount of the strobe and an opening degree of an iris to be fixed to constant values, respectively, upon a macroscopic photographing mode where a distance between the camera and the object is shorter than that upon the normal photographing mode.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to electronic cameras and, more particularly, 
to an electronic camera having a built-in strobe suitable for use in an 
electronic still camera or the like. 
2. Description of the Prior Art 
Various types of recording apparatus, have previously been developed in the 
art, including so-called electronic still cameras, each for recording a 
still picture in the form of an electric image signal on a magnetic disk. 
In order to perform the photographing operation by using the electronic 
still camera, its exposure condition is required to be controlled in the 
same manner as a general still camera using a metal halide film. As the 
exposure control methods when photographing an object by using a strobe in 
the night and so forth there are two approaches, one being to control the 
exposure by controlling an amount of emission light of the strobe and the 
other being to control the exposure by controlling an opening degree of an 
iris and a shutter speed while making an amount of the light emission of 
the strobe constant. 
The former method of controlling the exposure by controlling an amount of 
the light emission of the strobe is called an auto-strobe control method, 
wherein the amount of the light emission of the strobe is controlled by 
detecting incident radiation or an amount of light which is reflected from 
an object to which light is emitted from the strobe. This auto-strobe 
control method can be realized with relatively simplified constructions 
and so the method has been applied broadly to various types of cameras 
with strobes. 
The latter method of controlling the exposure by controlling an opening 
degree of an iris and a shutter speed while making an amount of the light 
emission of the strobe constant is called a "flashmatic method", wherein 
the opening degree of an iris and a shutter speed are controlled in 
accordance with a distance between the camera and an object. Thus, this 
method requires an accurate control of the opening degree of an iris and a 
shutter speed in accordance with information of the distance in order to 
suitably control the exposure, so that this method has not been used 
generally. In particular, in an electronic still camera, an exposure 
latitude capable of performing proper photographing is narrower when 
compared with that of a still camera using a silver film and so it is 
required to control the exposure value more strictly when compared with a 
still camera using a silver film. Thus, it has been difficult to apply the 
flashmatic method to an electronic still camera and so the auto-strobe 
method has been applied thereto generally. 
Now, there is known a type of camera that is capable of photographing an 
object positioned in a range of distance shorter than the normal range of 
distance which can be focused by rotating a normal focus ring, that is, a 
camera capable of performing macroscopic photographing. In this type of 
camera, the distance between the camera and an object capable of 
performing the macroscopic photographing is around 50 cm, for example. 
When performing the macroscopic photographing by using this type of 
camera, a field angle of a photographing lens or the photographing lenses 
sometimes does not coincide with an incident angle of a photo receptor 
element which detects an amount of light reflected from an object to which 
a light beam is emitted from a strobe due to the distance between the 
camera and an object. In this case, the auto-strobe control can not be 
performed satisfactorily, so that the exposure may not performed suitably. 
This phenomenon will be explained with reference to FIG. 2 illustrating 
major portions of a typical example of conventional electronic still 
cameras. In FIG. 2, an object image is focused on an image plane of a 
solid state image-pickup element 2 such as a charge-coupled device (CCD) 
through a photographing lens 1, or a plurality of lenses. The solid state 
image-pickup element 2 converts the focused image into an electric image 
signal and applies it to an image signal processing circuit 3 which in 
turn converts the image signal into a predetermined video signal. The 
video signal is applied to a recording portion (not shown) through an 
output terminal 4. In this case, an aperture is determined by controlling 
an opening degree of an iris 5 disposed in the vicinity of the 
photographing lens 1 and a shutter speed is determined in accordance with 
a time period during which the light is received on the image plane of the 
solid state image-pickup element 2. 
A strobe or a stroboscopic lamp 6 is mounted on the camera at a position 
apart from the photographing lens 1. The light emission of the strobe 6 is 
controlled by a light emission control circuit 7 in an interlocked 
relation with the photographing operation. Further, a photo receptor 
element 8 used in the auto-strobe control for detecting an amount of light 
reflected from an object to which a light is emitted from the strobe 6 is 
mounted in the vicinity of the photographing lens 1. The photo receptor 
element 8 delivers information representing the detected amount of the 
reflected light from an object to the light emission control circuit 7 
when the strobe 6 emits light. The light emission control circuit 7 then 
controls suitably an amount of emitted light, i.e. a time period during 
which the strobe 6 emits light, in accordance with the information of the 
detected amount of the reflected light to thereby perform the auto-strobe 
operation. 
In a normal photographing operation for photographing an object in a normal 
range where the distance between the photographing lens 1 and an object ml 
is more than 80 cm, for example, the field angle of the photographing lens 
1 coincides with the incident angle of the photo receptor element 8, while 
in the macroscopic photographing operation where the distance between the 
photographing lens 1 and an object m2 is about 50 cm, for example, the 
incident angle of the photo receptor element 8 can not cover all of the 
field angle of the photographing lens 1 due to a difference of mounted 
position between the photographing lens 1 and the photo receptor element 
8. Thus, in the macroscopic photographing mode, the return light from the 
object m2 can not be detected satisfactorily on the basis of the light 
incident on the photo receptor element 8 so that the auto-strobe operation 
can not be performed satisfactorily and hence the exposure can not be 
performed suitably. 
In order to overcome this drawback in the macroscopic photographing mode, 
it is proposed to control the exposure by the flashmatic method. However 
as described above, use of the flashmatic method requires an accurate 
measurement of the distance between the camera and an object and so forth 
in order to suitably control the exposure, resulting in complex 
constructions of the camera. 
OBJECTS AND SUMMARY OF THE INVENTION 
Accordingly, it is a general object of the present invention to provide an 
improved electronic camera in which the aforementioned shortcomings and 
disadvantages of the prior art can be eliminated. 
More specifically, it is an object of the present invention to provide an 
improved electronic camera which is capable of performing the macroscopic 
photographing using a strobe built therein satisfactorily with simplified 
constructions thereof. 
According to an aspect of the present invention, an electronic camera 
having a built-in strobe is provided, in which, when in a normal 
photographing mode, a return light of a light emitted from the strobe is 
detected to thereby control a light emission amount of the strobe. This 
electronic camera is composed of a device for controlling the light 
emission amount of the strobe and an opening degree of an iris to be fixed 
to constant values respectively, when in a macroscopic photographing mode 
where a distance between the camera and an object is shorter than that of 
the normal photographing mode. 
The above and other objects, features, and advantages of the present 
invention will become apparent from the following detailed description of 
an illustrative embodiment thereof to be read in conjunction with the 
accompanying drawing.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Preferred embodiment of the present invention will now be described by way 
of example and with reference to the accompanying drawing. 
FIG. 1 is a block diagram illustrating a strobe and a control unit thereof 
of an electronic camera according to the present invention. Other 
constructions of the camera of the embodiment are the same as the 
conventional ones and so the constructions thereof are omitted in FIG. 1 
and in the following descriptions. 
In FIG. 1, an amount of emitted light, i.e. a time period of light emission 
from a strobe or a stroboscopic lamp 11 is controlled by a light emission 
control circuit 12. The electronic camera is so constructed that the 
strobe 11 is supplied with power from a power supply source or circuit 13 
to thereby emit light under a pregiven condition in an interlocking 
relation with a photographing operation when a shutter button or switch 
(not shown) provided on a body of the camera is pushed down. 
A photo receptor element 14, which is used in an auto-strobe control mode, 
detects light reflected from an object to which the light is emitted from 
the strobe 11 and generates a current signal representing an amount of the 
detected light which is a function of an incident radiation as information 
of an amount of received (detected) light to apply the current signal to a 
first stationary contact 21 of a change-over switch 20. A constant current 
source 15 supplies a current signal with a constant current value to a 
second stationary contact 22 of the change-over switch 20. The constant 
current source 15 starts supplying the current signal at the moment when 
the strobe 11 emits the light. The change-over switch 20 applies one of 
the current signals applied to a moving contact 23 thereof to an 
integration circuit 16. The change-over operation of the change-over 
switch 20 is interlocked with the change-over operation of the 
photographing mode of the camera to which the strobe control unit of FIG. 
1 is mounted. Namely, the moving contact 23 is connected to the first 
stationary contact 21 in a normal photographing mode for photographing an 
object which is away from the camera by a distance more than 80 cm, for 
example, to thereby apply the current signal from the photo receptor 
element 14 to the integration circuit 16, while the moving contact 23 is 
connected to the second stationary contact 22 in a macroscopic 
photographing mode for photographing an object which is away from the 
camera by a distance less than 80 cm, for example, to thereby apply the 
current signal from the constant current source 15 to the integration 
circuit 16. 
The integration circuit 16 integrates the current signal applied thereto to 
thereby obtain an integrated voltage value, thereby applying the 
integrated voltage value to an inverted input terminal of a comparator 17. 
A non-inverted input of the comparator 17 is applied with a constant 
voltage from a constant voltage source 18. The comparator 17 therefore 
compares the integrated voltage value with the constant voltage value and 
delivers a result of the comparison to the light emission control circuit 
12. 
Now, in this embodiment, if the macroscopic photographing mode is selected 
by connecting the moving contact 23 of the change-over switch 20 to its 
second stationary contact 22, the opening degree of an iris (not shown) 
located at a position to face a photographing lens or photographing lenses 
(not shown) fixed at a constant value. 
Next, the explanation will be made of the operations of the electronic 
camera having the built-in strobe of this embodiment when photographing an 
object. In the normal photographing mode where the distance between the 
camera and the object is more than 80 cm, the moving contact 23 of the 
change-over switch 20 is connected to the first stationary contact 21, 
thereby performing an auto-strobe control as described below. In this 
state, if the photographing operation is performed by using the strobe 11, 
the photo receptor element 14 detects the reflected light from an object 
to thereby apply the current signal representing the information of an 
amount of the received light to the integration circuit 16 through the 
switch 20. The light emission control circuit 12 controls the light 
emission of the strobe 11 in response to the output of the comparator 17 
in a manner that the light emission of the strobe 11 is continued by 
applying the power from the power supply circuit 13 to the strobe 11 until 
the output voltage of the integration circuit 16 representing the 
integrated value of the received light exceeds the constant voltage value 
from the constant voltage source 18. If the output voltage of the 
integration circuit 16 exceeds the constant voltage value from the 
constant voltage source 18, the light emission control circuit 12 stops 
the application of the power from the power supply circuit 13 to the 
strobe 11 to thereby stop the light emission of the strobe 11. 
On the other hand, in a macroscopic photographing mode where the distance 
between the camera and an object is less than 80 cm, the moving contact 23 
of the switch 20 is connected to the second stationary contact 22, so that 
the application of the current signal from the photo receptor element 14 
to the integration circuit 16 is terminated, thereby terminating the 
auto-strobe control mode. The integration circuit 16 therefore receives 
the current signal of the constant current value from the constant current 
source 15 instead of the information of an amount of received light from 
the photo receptor element 14. Thus, the integrated value of the 
integration circuit 16 increases at a constant rate with the lapse of time 
in proportion to the luminance time period of the strobe 11 and, when a 
predetermined time period lapses after the initiation of the light 
emission from the strobe 11, the integrated value exceeds the constant 
voltage value from the constant voltage source 18, so that the light 
emission of the strobe 11 is terminated. 
Thus, in the macroscopic photographing mode, the light emission period of 
the strobe 11 is controlled to the predetermined time period. Further, in 
the macroscopic photographing mode, the opening degree of the iris is 
fixed to the constant value, so that the photographing operation using the 
strobe in the macroscopic photographing mode can be performed under a 
predetermined exposure condition. 
Accordingly, the macroscopic photographing can be performed under the 
predetermined exposure condition. 
Now, since in the macroscopic photographing mode, the distance between the 
camera and an object is less than 80 cm, the point-blank range less than 
80 cm can be assumed. Therefore, if exposure conditions such as the light 
emission time period of the strobe and the opening degree of the iris 
suitable for the macroscopic photographing in the point-blank range less 
than 80 cm are set, the photographing operation can be made 
satisfactorily. 
Thus, according to the electronic camera having the built-in strobe of this 
embodiment, the photographing operation in the normal photographing mode 
can be performed satisfactorily by the auto-strobe control and also the 
photographing operation in the macroscopic photographing mode can be 
performed satisfactorily under the predetermined exposure conditions, so 
that the photographing operation can be performed satisfactorily under 
suitable exposure states over all ranges of the distance between the 
camera and an object. Further, since the macroscopic photographing can be 
performed without requiring the measurement of the distance between the 
camera and an object, the constructions of the electronic camera can be 
simplified. 
Now, the explanation has been made about a case where the present invention 
is applied to an electronic still camera but the present invention may 
also be applied to a normal still camera using a silver film. 
Accordingly, the present invention can perform even the macroscopic 
photographing satisfactorily by using the strobe with the simplified 
constructions. 
Having described a preferred embodiment of the invention with reference to 
the accompanying drawing, it is to be understood that the invention is not 
limited to the precise embodiment and that various changes and 
modifications could be effected by one skilled in the art without 
departing from the spirit or scope of the novel concepts of the invention 
as defined in the appended claims.