Distance indication arrangement for automatic focus control camera

An improved distance indication arrangement for use in an automatic focus control camera in which a distance signal produced by a distance measuring device is utilized for giving warning so as to prevent under-exposure in the case of flash light photographing.

BACKGROUND OF THE INVENTION 
The present invention generally relates to a photographic camera and more 
particularly, to a distance indication arrangement for a photographic 
camera equipped with automatic focus control means or an automatic focus 
control camera. 
Generally, in a photographic camera which employs, among automatic distance 
measuring devices conventionally proposed, an automatic distance measuring 
device of a type capable of measuring distance without utilization of 
surrounding light such as natural light or the like, there has been such a 
disadvantage that an improper or incorrect exposure takes place in 
photographing, if the distance indicated by the distance signal produced 
from the automatic distance measuring device exceeds the photographic 
associated distance of flash means such as an electronic flash employed 
therefor. On the assumption that the guide number GN of the electronic 
flash employed is 12 and the maximum f-number F of the photographing lens 
of the camera is 2.8, the maximum distance up to an object to be 
photographed in which the correct exposure is available in the above 
photographing by the electronic flash is approximately 4.3 m, and any 
objects located farther than the above distance are undesirably subjected 
to under-exposure due to an insufficient amount of light. 
SUMMARY OF THE INVENTION 
Accordingly, an essential object of the present invention is to provide a 
distance indication arrangement for an automatic focus control camera 
which is capable of warning a photographer in advance so as to prevent 
underexposure in the case of flash light photographing, through 
utilization of a distance signal obtained by a distance measuring device. 
Another important object of the present invention is to provide a distance 
indication arrangement of the above described type which indicates the 
distance signal produced by the distance measuring device in such a manner 
that, when the distance represented by the distance signal exceeds a 
photographing associated distance of the electronic flash employed, an 
out-of-association warning indication is given by a distance indication 
device together with the distance indication so as to prevent 
photographing which may result in under-exposure. 
A further object of the present invention is to provide a distance 
indication arrangement of the above described type which is simple in 
construction and accurate in functioning with high reliability, and can be 
readily incorporated into automatic focus control cameras at low cost. 
In accomplishing these and other objects, according to one preferred 
embodiment of the present invention, there is provided a distance 
indication arrangement for use in a photographic camera having distance 
measuring means for producing a distance signal corresponding to a 
distance up to an object to be measured for distance, and lens adjusting 
and setting means for adjusting and setting a photographing lens of the 
photographic camera to a position corresponding to the distance signal 
produced from the distance measuring means. The distance indication 
arrangement includes a distance indication device for effecting a zone 
indication of the distance corresponding to the distance signal, a flash 
photographing assocation distance signal generation circuit for producing 
a signal corresponding to the photographing association distance of the 
flash means employed, an out-of-association detection circuit for 
producing an out-of-association signal when the distance corresponding to 
the zone indication exceeds the photographing association distance of the 
flash means, and a warning indication signal generation circuit for 
producing a signal of warning indication in response to the 
out-of-association signal. 
By the arrangement according to the present invention as described above, 
an improved distance indication arrangement capable of giving a warning 
when an object to be photographed is out of photographing association 
distance in the flash photographing, has been advantageously presented, 
with substantial elimination of the disadvantages inherent in the 
conventional distance indication arrangements of this kind.

Before the description of the present invention proceeds, it is to be noted 
that like parts are designated by like reference numerals throughout 
several views of the accompanying drawings. 
DETAILED DESCRIPTION OF THE INVENTION 
Referring now to the drawings, there is shown in FIG. 1 the construction of 
a distance indication arrangement for an automatic focus control camera 
according to one preferred embodiment of the present invention. In FIG. 1, 
a known distance measuring device 1 of light beam projection type, based 
on the principle of trigonometric distance measurement, includes a light 
source 2, for example, of an infrared light emitting diode type which is 
arranged to be energized at a first stage of depression of a shutter 
release button (not shown). The light from the light source 2 is condensed 
by a condenser lens 3 into a beam configuration so as to be projected 
toward an object to be measured for distance, while the image of the 
object to be measured for distance is formed on an image forming surface 
through another lens 4 disposed in a position side by side with and at a 
predetermined distance from the lens 3. On the image forming surface of 
the lens 4, there are arranged a plurality of photodiodes 5a, 5b, 5c, 5d 
and 5e for receiving light rays reflected from points P1, P2, P3, P4 and 
P5 which are respectively at distances of 0.8 m, 1 m, 1.5 m, 2.7 m and 13 
m from the lens 3. Output signals from the photodiodes 5a, 5b, 5c, 5d and 
5e are applied to a signal treating circuit 6 which detects particular 
photodiodes 5a to 5e upon which the reflected light is incident, and 
produces, for example, ten kinds of distance signals including distance 
information equivalent to infinity based on presence or absence of light 
incident upon the respective photodiodes 5a to 5e and the combination 
thereof. The above distance signals are applied to a register 7, coupled 
to the signal treating circuit 6, so that the distance signals are stored 
therein as the distance information, and simultaneously, when any one of 
output terminals 7a, 7b, 7c, 7d, 7e, 7f, 7g, 7h, 7i and 7j becomes "high", 
the "high" signal is applied to a lens adjusting and setting mechanism 8 
which is connected to the register 7. Upon depression of the shutter 
release button to a second stage, the lens adjusting and setting mechanism 
8 adjusts and sets a photographing lens (not shown) to a position 
corresponding to the distance signal stored in the register 7. 
Meanwhile, the distance indication device 10 which indicates the distance 
up to the object to be photographed includes a plurality of light emitting 
diodes 11a, 11b, 11c, 11d, 11e, 11f, 11g, 11h, 11i and 11j whose anodes 
are connected to the corresponding output terminals 7a to 7j of the 
register 7 and which are arranged in one row together with numerals 
representing distances, for example, at an upper portion of a camera 
view-finder as shown in FIG. 2. 
The electronic flash photographing association distance signal and warning 
signal generating circuit 15 comprises a switch 16 which is to be closed 
in association with turning ON of the power supply for an electronic flash 
(not shown) incorporated in the camera, a pulse generation circuit 17 
which is actuated upon closing of the switch 16 for producing pulses 
having a period, for example, of 0.5 sec., an inverter 18, and NOR 
circuits 19 and 20. As described later, the output pulses from the above 
pulse generating circuit 17 are arranged to be applied, for example, to 
the light emitting diodes 11h, 11i and 11j of the distance indication 
device 10 which indicate the distance determined by the guide number of 
the electronic flash and, the maximum f-number of the photographing lens, 
and also distances further than said distance. The circuit 15 as described 
above further includes a change-over switch 21 to be actuated in 
association with the setting of film sensitivity and having a stationary 
contact 21a connected to one input terminal of each of the inverter 18 and 
NOR circuits 19 and 20, and another stationary contact 21b connected to 
the other input terminals of said NOR circuits 19 and 20. Accordingly, by 
the changing over of the switch 21, the output pulses from the pulse 
generation circuit 17 are applied either to the light emitting diodes 11h, 
11i and 11j or to the light emitting diodes 11and 11j, so as to allow the 
above electronic flash photographing association distance indication to be 
altered. 
On the other hand, the electronic flash photographing out-of-association 
detection circuit 23 includes AND circuits 24, 25 and 26 inserted between 
the output terminals 7h, 7i and 7j of the register 7 and the light 
emitting diodes 11h, 11i and 11j so as to be applied with outputs from the 
inverter 18 and NOR circuits 19 and 20. 
By the above arrangement, it is assumed that a photographing lens having 
minimum f-number or fully open aperture value of F2.8 and an electronic 
flash having the guide number of GN12 with respect to film sensitivity of 
ASA100 are incorporated in the camera body (not shown), with the lens 
aperture being set to a desired f-number through adjustment by a known 
flash-matic mechanism. Note that, since the film sensitivity is ASA100 in 
the above case, the change-over switch 21 of the electronic flash 
photographing association distance signal and warning signal generation 
circuit 15 has been changed over to the side of the contact 21a in the 
similar manner as in the case of ASA50, and that, in the case of film 
sensitivities of ASA200 and ASA400, the switch 21 is to be changed over to 
the side of contact 21b. 
Firstly, in the state where the above electronic flash is not used, the 
light source 2 is energized at the first stage of depression of the 
shutter release button, and the distance measuring is effected by the 
distance measuring device 1, with the distance signal stored in the 
register 7, and thus, a "high" signal is assumed to be produced, for 
example, from the output terminal 7h. In the above state, since the 
electronic flash is not used and the switch 16 is in the OFF state, with 
the pulse generation circuit 17 being in non-functioning state, the input 
signal to the inverter 18 is of "low", while the output signal therefrom 
is of "high", and the AND circuit 24 is functioning. Therefore, the "high" 
signal from the output terminal 7h of the register 7 is applied to the 
light emitting diode 11h through the AND circuit 24 for continuously 
lighting said diode 11h, and thus, it is indicated that the distance from 
the lens 3 to the object to be photographed is in the region before or 
after 4.5 m as a central point. 
Subsequently, at the second stage of depression of the shutter release 
button, the photographing lens (not shown) is adjusted to be set for 
standing-by at the position corresponding to the distance signal stored in 
the register 7 by the lens adjusting and setting mechanism 8. 
In the above state, upon turning ON of the switch 16 for electronic flash 
photographing, the pulse generation circuit 17 is actuated to produce 
output pulses which are applied to the AND circuits 24, 25 and 26 through 
the contact 21a, inverter 18, and NOR circuits 19 and 20. Since the 
photographing lens having fully open aperture value of F2.8 and the 
electronic flash having the guide member of GN12 are employed as stated 
earlier, the photographing association distance for the electronic flash 
is 4.3 m. Accordingly, the output pulses from the pulse generation circuit 
17 are applied to the light emitting diode 11h through the AND circuit 24 
to which the "high" signal is applied from the output terminal 7h of the 
register 7, and thus, the diode 11h continuously flickers at a 
predetermined period, by which it is judged for indication that the 
distance up to the object to be photographed as measured by the distance 
measuring device 1 is out of the photographing association range of the 
electronic flash. 
Meanwhile, in the case where the film sensitivity is ASA200 or ASA400, the 
change-over switch 21 has been changed over to the side of the contact 21b 
as described earlier, and the photographing association distance for the 
electronic flash has been altered, for example, to 8 m, while the output 
pulses from the pulse generation circuit 17 are being applied to the AND 
circuits 25 and 26 through the contact 21b and NOR circuits 19 and 20. 
Therefore, if the distance up to the object to be measured for distance is 
4.5 m or thereabout as described earlier, the light emitting diode 11h is 
continuously lit to effect the indication that the distance is within the 
photographing association range of the electronic flash. Similarly, when 
the distance up to the object to be measured for distance is 13 m or 
thereabout, the output pulses are applied through the AND circuit 25 in 
the similar manner to cause the light emitting diode 11i to continuously 
flicker for indication that the distance is out of the photographing 
association range of the electronic flash. 
As described in the foregoing, even a person unskilled in the electronic 
flash photographing can readily avoid failure due to under-exposure based 
on the contents of the indications by the respective light emitting diodes 
11. 
It is to be noted here that, in the foregoing embodiment, although the 
description has been mainly given with respect to the arrangement in which 
the photographing lens has the fully open aperture value of F2.8, with the 
guide number GN of the electronic flash being 12, the arrangement should 
of course be correspondingly modified, in the case where the fully open 
aperture value, guide number, number of the distance zones to be 
indicated, and width of each zone, etc. are different from the above. 
Meanwhile, it is necessary that the distance measuring device 1 as 
described above is capable of measuring distance with respect even to such 
an object to be photographed as will not give the correct exposure unless 
an auxiliary light source is employed, and is provided with means for 
storing the measured distance value, and therefore, the distance measuring 
device 1 may be one which measures distance by utilizing the propagation 
time of sound waves or one utilizing contrast of dark and light portions 
of the object to be photographed through employment of auxiliary light 
depending on the state of the surrounding light. 
On the other hand, the warning indication described as effected by causing 
the light emitting diode 11 indicating the distance up to the object, the 
flicker in the foregoing embodiment, may be so modified that when films 
having predetermined sensitivities, for example, of ASA50 and 100 are 
employed, the light emitting diode 11h flickers, while if films with 
sensitivities of ASA200 and 400 are employed, the light emitting diode 11i 
flickers, or that a particular light emitting diode, for example, the 
diode 11j is exclusively caused to flicker irrespective of the film 
sensitivities. Moreover, it is also possible to arrange in such a manner 
that a particular light emitting diode and the light emitting diode 
effecting the distance indication are alternately caused to flicker, with 
simultaneous warning by sound. 
Furthermore, as shown in FIG. 3, it may be so arranged that the distance 
indication is effected by applying the outputs from the respective output 
terminals of the register 7 to a segment display member 31 through a 
decoder 30, while the outputs from the inverter 18, and NOR circuits 19 
and 20 are applied, through an OR circuit 32, to the base of a switching 
transistor 33 inserted between the segment display member 31 and the 
ground for causing the segment display member 31 to continuously flicker. 
As is clear from the foregoing description, according to the arrangement of 
the present invention, it is arranged that in a camera equipped with the 
automatic focus adjusting means and distance indication device, warning is 
given in the distance indication device when the object to be photographed 
is out of the photographing association distance range in the electronic 
flash photographing, and therefore, even a person not accustomed to 
electronic flash photographing can readily avoid failures which may result 
in under-exposure, and operate the camera without uneasiness. 
Although the present invention has been fully described by way of example 
with reference to the attached drawings, it is to be noted that various 
changes and modifications will be apparent to those skilled in the art. 
Therefore, unless otherwise such changes and modifications depart from the 
scope of the present invention, they should be construed as included 
therein.