Camera with minimum subject-distance alarm display device

A camera with a too-close-subject-distance alarm display device, further comprising a flash device for flashing the light to a subject to be photographed; a selection device for selecting at least the flash exposure mode in which the flash device is permitted to flash or the flash inhibit mode in which the flash device is inhibited to flash; a subject-distance measuring instrument for measuring a subject distance; a decision device for detecting whether the subject distance measured by said distance measuring instrument is less than a predetermined distance or not; an alarm device for alarming when said subject distance measured by said subject-distance measuring instrument is detected to be shorter than said predetermined subject distance by said decision device; and a setting device for setting said predetermined distance to a first predetermined distance when said selection device has selected the flash exposure mode and for setting said predetermined distance to a second predetermined distance longer than the first predetermined distance when the selection device has selected the flash inhibit mode.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a camera with a minimum subject-distance 
alarm display device. 
2. Related Background Art 
In a conventional camera with a flash apparatus and a minimum 
subject-distance (that is, the distance from the camera to a subject or 
object) alarm display device which can inhibit the flash operation of the 
flash apparatus by the operation from the exterior of the camera, a range 
at which an alarm signal representative of the minimum subject distance is 
generated is equal to not only a range at which a flash exposure is 
permitted (the flash mode) but also a range at which a flash exposure is 
inhibited (the flash exposure inhibit mode). 
There has been also devised and demonstrated a camera of the type in which, 
in order to maintain a predetermined depth of focus when the subject 
distance is close so as to avoid a too deep depth of focus, in case of an 
exposure at a short subject distance, an aperture limit device is provided 
so that only when an selected aperture is opened wider than the limited 
aperture, the aperture is narrowed and a flash exposure is carried out by 
activating a flash apparatus. 
However, in the conventional cameras, "the flash mode" distance is equal to 
"the flash inhibit mode" distance even though the above-mentioned two 
distances must be different from each other. As a result, distance at 
which the minimum subject distance is determined becomes erroneous. 
In general, the narrower the aperture, the depth of focus is increased and 
the degree of resolution of camera lens becomes sharper. 
When the quantity of flash light is maintained constant and when it is 
desired to obtain a most optimum exposure, a flash exposure with a 
narrower depth of focus than a deep depth of focus must be made when a 
subject distance is closer. That is, a sharply focused exposure can be 
attained at a relatively closer subject distance when the flash apparatus 
is flashed. In the "exposure mode", a flash exposure is possible even when 
the aperture limit is further made narrower by the flash light and the 
deep depth of focus can be maintained, but in the case of the "flash 
inhibit mode" when a subject distance is shorter, the aperture can be 
widened than the limited aperture and the exposure control can carried out 
so that the depth of focus becomes shallow. Therefore, a distance at which 
an exposure is made at a closer subject distance is different. 
Furthermore, when the "the flash inhibit mode" is selected, there is a fear 
that an exposure is carried out against the will of a photographer in the 
case of a camera whose flash apparatus flashes when an aperture is opened 
wider than the limited aperture. 
SUMMARY OF THE INVENTION 
In view of the above, the primary object of the present invention is to 
provide a camera with a limited-subject-distance alarm display device 
which lets a photographer select whether or not an exposure is made by 
correctly giving him/her alarm information whether the flash exposure mode 
or the flash inhibit mode is selected because a subject distance is closer 
and which even when the flash exposure mode is inhibited, an exposure can 
be carried out according to the will of the photographer. 
In order to attain the above and other objects, in the case of a camera of 
the type comprising a flash apparatus (B4) for flashing light to the field 
of view, a selection device (SBS) for selecting at least one of the flash 
mode in which said flash apparatus can flash and the flash inhibit mode in 
which said flash apparatus is inhibited to flash, a distance meter (B4) 
for detecting a distance from a camera to a subject, a sensor (B1) for 
detecting whether the subject distance detected by said distance meter is 
closer or longer than a predetermined distance (from said camera) and an 
alarm device (LED) for generating the close subject distance alarm signal 
when said distance detected by said sensor is less than a predetermined 
value, according to the present invention, said camera is characterized by 
further comprising a setting device for setting said predetermined value 
in such way that when the flash mode is selected by said selection device, 
said predetermined value is changed to a first predetermined value, but 
when said flash inhibit mode is selected by said selection device, said 
predetermined value is changed to a second predetermined value greater 
than said first predetermined value. 
In the case of the flash mode in which the flashing of said flash apparatus 
(B4) is permitted and in the case of the flash inhibit mode in which the 
flashing by said flash apparatus is inhibited, a 
too-close-subject-distance alarm signal is displayed in response to a 
correct close-subject-distance at which a too-close-subject-distance alarm 
is generated depending upon the depth of focus in the case of the flash 
mode or the flash inhibit mode. 
In the flash mode, when a subject distance is short, the flash apparatus 
(B4) flashes, it becomes possible to obtain an exposure of a subject at a 
shorter subject distance and the closer-subject-distance alarm signal is 
displayed at a relatively close subject distance. 
In the flash inhibit mode, the flash apparatus (B4) cannot flash so that a 
distance at which a too-close-subject-distance alarm is displayed is 
selected at a relatively longer subject distance.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
Referring first to FIG. 1 illustrating the major components of the 
preferred embodiment of the present invention, B1 denotes a central 
processing unit (CPU); and B2, a distance meter for delivering a signal 
representative of a subject distance to a CPU(B1). B3 represents a light 
meter for delivering a signal representative of the degree of brightness 
of a subject to be photographed to CPU(B1); and B4, a flash apparatus for 
flashing in response to the output signal from CPU(B1) when a shutter (not 
shown) is released when a subject distance is shorter and/or the 
brightness of a subject is lower than a predetermined value. S1 indicates 
a double-stroke switch; and S2, a release switch. The double-stroke switch 
(S1) and the release switch (S2) constitute a double-stage switch. When 
the double-stage switch is pushed a half stroke, the double-stroke switch 
(S1) is turned on and when the double-stage switch is pushed to the end of 
its stroke, the release switch (S2) is turned on. Such states of the 
switches (S1) and (S2) are detected by CPU(B1). SBS is a switch for 
selecting the automatic flash mode or the flash inhibit mode. In this 
embodiment, it is assumed that when the switch (SBS) is turned on, the 
flash inhibit mode is selected, but when the switch (SBS) is turned off, 
the automatic flash mode is selected. LED is a light-emitting diode which 
flashes for alarming a photographer that a subject to be photographed is 
too short from the camera. R represents a resistor for controlling the 
quantity of light emitted from the LED so as to control the brightness. TR 
denotes a switching transistor which is controlled by CPU(B1). In response 
to ON-OFF operation of the switching transistor TR the light-emitting 
diode (LED) is turned on and off. In this embodiment, the light-emitting 
diode (LED) has been described as being used as an alarm device, but it is 
understood that a buzzer or the like may be equally used in the present 
invention. 
FIG. 2 is a flowchart illustrating the mode of operation of the preferred 
embodiment with the above-mentioned construction. 
The control process of the preferred embodiment of the present invention is 
started "START" shown in FIG. 2. In the step S101, it is detected whether 
or not the double-step switch (S1) is depressed and when it is depressed, 
the procedure proceeds to the step S102, but when it is not depressed, the 
step S101 is repeated. In the step S102, the distance meter (B2) measures 
a subject distance. In the step S103, the light meter (B3) measures the 
brightness of a subject. In the step S104, whether the switch (SBS) is 
depressed or not is detected. When the switch (SBS) is turned on, the 
camera is in the flash exposure inhibit mode, the control process proceeds 
to the step S105, but when the switch (SBS) is turned off, the control 
process proceeds to the step S106. In the step S105, in the case of the 
flash inhibit mode, the value of L2 of the close subject distance alarm is 
substituted into a variable L. The value of L2 is determined depending 
upon the characteristics of a photographic lens (and is, for instance, one 
meter). In the step S106, the value of L1 of the close subject distance 
alarm is substituted into the variable L. The value of L1 is also 
dependent upon the characteristics of a photographic lens (and is for 
instance, 0.5 meters). In the step S107, the value of L is compared with 
the distance obtained in the step S102 and the subject distance measured 
in the step S102 is shorter than the variable L, the control process 
proceeds to the step S108, but when the measured subject distance is 
longer, the control process proceeds to the step S109. In the step S108, 
the light-emitting diode (LED) blinks to inform to a photographer that the 
subject is within an exposure range. In the step S111, whether the 
double-stroke switch (S1) is turned on or off is detected and when the 
switch is turned on, the control process proceeds to the step S111, but 
when it is turned off, the process proceeds to the step S114. In the step 
S111, whether the release switch (S2) is turned on or off is detected and 
when it is turned on, the control process proceeds to the step S112, but 
when it is turned off, the process proceeds to the step S110. That is, 
when the two-stage switches (S1, S2) are turned off in the steps S110 and 
S111, the control process proceeds to the step S114, but when they are 
depressed full stroke, the control process proceeds to the step S112. When 
the two-stroke switches (S1, S2) are depressed half stroke, an exposure is 
not made and the alarm signal is given to a photographer. In the step 
S112, in response to the data obtained in the steps S102 and S103, an 
optimum exposure and an optimum subject distance are set and thereafter 
the shutter is released for an exposure of the subject. In the case of 
setting an optimum exposure, an aperture limit control is carried out. 
Whether the flash apparatus is flashed or not is detected while the 
aperture is being controlled. It follows therefore that in the case of a 
camera capable of informing a photographer whether a flash exposure is 
made or not, before the step S110, the above-mentioned aperture control 
must be made. 
In the step S113, whether the double-stroke switch (S1) is turned on or off 
is detected and when it is detected to be turned off, the control 
procedure proceeds to the step S114, but when the switch is detected to be 
turned on, the control procedure repeats the step S113. In the step S114, 
the light-emitting diode (LED) which has been flashing is turned off. Thus 
the control procedure terminates. 
According to the present invention, in both of the flash mode in which the 
flash apparatus (B4) can flash and the flash inhibit mode in which the 
operation of the flash apparatus (B4) is inhibited, the close 
subject-distance alarm is displayed depending upon a correct closer 
subject-distance at which a close subject-distance alarm is generated 
depending upon the respective depth of focus so that a photographer or 
camera person can obtain the information of the limit of the subject 
distance and consequently the subject distance is not shortened. 
When the too-close-subject-distance alarm is displayed, a photographer can 
release the flash inhibition mode of the flash apparatus (B4) and then 
releases the shutter button or forcibly release the shutter button even 
when the subject is out of focus or refrains from the shutter release 
according to the will of the photographer.