Two zone infrared ranging system

An economical dual zone active rangefinding system for a photographic camera operates upon the principle of triangulation without lateral displacement of either the radiation source or detector to provide an output signal indicative of whether the subject in the scene to be photographed is located in a select distance range from the photographic camera.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates generally to a two zone ranging system for a 
photographic camera apparatus and, more particularly, to a two zone active 
infrared ranging system for a photographic camera apparatus utilizing a 
low output, low cost infrared emitting diode. 
2. Description of the Prior Art 
Infrared ranging systems for photographic cameras are now well known in the 
art. One such infrared ranging system by Canon operates on the well-known 
principle of triangulation by beaming an infrared signal at the subject to 
be photographed and establishing the subject distance from the manner in 
which the infrared signal is reflected. This rangefinding system consists 
of an infrared emitting diode that is shifted sidewards during the 
measuring cycle and a fixed receiving cell. The traveling infrared 
emitting diode moves through a path of about ten millimeters and during 
this time emits a continuous signal in a specific wavelength band chosen 
to avoid interference from natural infrared sources such as sunlight. 
Also, during this time a sensing cell monitors the intensity of the 
infrared radiation reflected from the subject and converts this to an 
output voltage which is measured. When the output voltage reaches a peak 
and starts to decline, a control circuit stops the movement of the 
traveling infrared emitting diode and this movement is coupled with the 
movement of the objective lens which moves from a near to a far focusing 
limit such that the peak voltage signal can be utilized to determine the 
optimal focal position of the lens. This ranging system allows the 
objective lens to be set to an infinite number of focal positions 
corresponding to any camera to photographic subject distance determined by 
the detection of the peak voltage as the infrared emitting diode is 
shifted sidewards. Ranging systems of the above-described type are 
referred to as active systems in that they require both a source of 
radiance preferably in the infrared frequency range and a radiation sensor 
for sensing the reflected radiance from the photographic subject. In 
addition, either the source or the receptor must be displaced laterally in 
order to achieve the rangefinding function by the principle of 
triangulation. 
Simple rangefinding systems which do not require the mechanical complexity 
required to provide for the lateral displacement of either the radiation 
source or the radiation detector are also well known in the art as taught 
in U.S. Pat. No. 4,357,083, entitled "Method and Apparatus Using Weighted 
Range Signal for Controlling Photographic Functions", by Bruce K. Johnson 
et al., issued Nov. 2, 1982, in common assignment herewith. The 
rangefinding system of the aforementioned Johnson et al. patent operates 
by directing a preliminary pulse of radiation from a selectively 
energizeable light source toward a subject and thereafter evaluating the 
amplitude of the reflected pulse of radiation from the subject so as to 
determine a weighted range signal as a function of the amplitude of 
generally non-visible or infrared radiation frequencies. This rangefinding 
system thus also provides an output ranging signal indicative of the 
actual position of the photographic subject within the field of view of 
the camera. 
Such precision, however, in the determination of the camera-to-subject 
range may not always be necessary particularly for the design of a low 
cost camera in which it may be only necessary to provide two focal 
settings for the objective lens corresponding to a near camera-to-subject 
distance range and a far camera-to-subject distance range. 
Therefore, it is a primary object of this invention to provide a low cost 
active rangefinding system which operates to provide an output signal 
indicative of whether the photographic subject is located in either a near 
distance zone from the photographic camera or a far distance zone from the 
photographic camera. 
It is a further object of this invention to provide a low cost two zone 
rangefinding system which operates on the well-known principle of 
triangulation without requiring lateral movement of either the radiation 
source or the radiation detector. 
It is an even further object of this invention to provide a low cost two 
zone active infrared rangefinding system which can utilize a low cost, low 
output infrared emitting diode for a source of radiation. 
Other objects of the invention will be in part obvious and will in part 
appear hereinafter. The invention accordingly comprises a mechanism and 
system possessing the construction, combination of elements and 
arrangement of parts which are exemplified in the following detailed 
disclosure. 
SUMMARY OF THE INVENTION 
A dual zone ranging system for use with a photographic camera apparatus 
comprises means for transmitting radiation toward a scene to be 
photographed as well as means for detecting the radiation from the scene 
to be photographed. The means for detecting the radiation from the scene 
to be photographed operates to detect both ambient radiation as well as 
radiation emitted from the radiation emitting means and subsequently 
reflected from a subject in the scene to be photographed if the subject is 
located within a selected distance range from the photographic camera 
apparatus. The radiation detecting means also provides an output 
responsive to the detected radiation. Means are also provided for 
integrating the output from the detecting means for a first select period 
during which the radiation emitting means are rendered inoperative and for 
a second select period during which the radiation emitting means are 
rendered operative. Integrating means thereafter provide an output signal 
in response to the integration indicative of whether the subject in the 
scene to be photographed is located in the select distance range from the 
photographic camera. 
This dual zone ranging system operates by emitting primarily radiation 
within the infrared frequency range. In addition, the integration during 
one of the selected periods is offset by the integration during the other 
of the selected periods and the output signal indicative of whether the 
subject is located in the select distance range is provided in response to 
this offsetting integration.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to FIG. 1 there is shown in cross section a photographic 
camera apparatus 10 embodying the infrared rangefinding system of this 
invention. The photographic camera apparatus 10 comprises a housing 14 
within the forward wall of which is fixedly disposed an objective lens 12 
having a field of view extending forward of the camera in a well-known 
manner. Immediately adjacent the objective lens 12 there is disposed an 
infrared radiation transmitter as shown generally at 16 comprising an 
infrared emitting diode 18 and a lens 20 which operates to direct the 
infrared radiation from the diode 18 in a relatively narrow beam forward 
of the camera into the field of view of the objective lens 12. Beside the 
infrared radiation transmitter 16, there is provided a photometer 22 
comprising a photoresponsive element 24 such as a silicon diode which 
receives radiation from the scene to be photographed by way of a 
photometer lens 26. 
The photometer lens 26 and photoresponsive element 24 are arranged in 
accordance with the well-known principle of triangulation relative to each 
other and the field of view so as to detect only that infrared radiation 
transmitted by the infrared radiation transmitter 16 which is subsequently 
reflected by a photographic subject located within a select distance range 
from the photographic camera apparatus 10. The selected distance range is 
labeled in FIG. 1 "near zone" and may characteristically extend from a 
near distance of only a few inches from the photographic camera apparatus 
10 to a far distance of five feet. Thus any subject in the scene to be 
photographed located within the near zone of FIG. 1 will reflect infrared 
radiation received from the infrared radiation transmitter 16 back for 
detection by the photometer 22, while conversely any subject in the scene 
to be photographed located beyond five feet from the photographic camera 
apparatus 10 in the far zone as shown in FIG. 1 will not reflect infrared 
radiation from the infrared transmitter 16 back for detection by the 
photometer 22. 
Referring now to FIG. 3 in conjunction with FIG. 1 there is shown a circuit 
diagram for a ranging circuit 28 to be used in conjunction with the 
infrared radiation transmitter 16 and photometer 22 to provide an output 
ranging signal indicative of whether the subject in the scene to be 
photographed is located in the near zone as shown in FIG. 1. The 
photoresponsive element 24 provides an output current to a current mirror 
30 which operates to multiply the output current from the photoresponsive 
element 24 by a factor of two. The current multiplied by the current 
mirror 30 is subsequently directed by way of a line 32 to another current 
mirror 36, which in like manner also operates to multiply the output 
current from the current mirror 30 by a factor of two. The current mirror 
36, in turn, provides the multiplied output current by way of a line 38 to 
still another current mirror 40 which operates to again multiply the 
output current from the current mirror 36 by a factor of two. The 
multiplied output current from the current mirror 36 provided by line 38 
is also simultaneously directed to another current mirror 42 which 
operates to multiply the output current from the current mirror 36 by a 
factor of one. The multiplied current from the current mirror 40 is 
thereafter directed by way of a line 44 to the collector terminal of a PNP 
control transistor 46 and to the input terminal of still another current 
mirror 47 which operates to multiply the output current from the current 
mirror 40 by a factor of one. 
The PNP control transistor 46 receives base current by way of two resistors 
48 and 50 which serially connect to the collector terminal of an NPN 
transistor 52 having a grounded emitter terminal. The base terminal of the 
transistor 52 receives a control current from a timer 58 by way of an 
interconnecting resistor 60. 
The output current from the current mirror 47 is directed by way of a line 
54 to the positive terminal of an integration capacitor 56 which also 
simultaneously connects to the output terminal of the current mirror 42. 
The voltage level at the positive terminal of the integration capacitor 
56, in turn, is directed by way of a line 66 to one input terminal of a 
comparator 68, the other input terminal of which receives an input 
reference voltage by way of a resistor divider network comprising serially 
connected resistors 70 and 72. The output from the comparator 68, in turn, 
is directed to a latch circuit as shown at 74 comprising two NOR gates 76 
and 78 connected in a well-known manner. The other input to the latch 
circuit 74 is received from the timer 58. The timer 58 may be actuated to 
initiate its timing function in the manner of this invention to be 
subsequently described upon the closure of a switch 62 connected to the 
start input terminal of the timer 58 and grounded by way of a resistor 64. 
Referring now to the timing diagram of FIG. 2 in conjunction with the 
circuit diagram of FIG. 3 it can be seen that a rangefinding operation is 
commenced upon the closure of the switch 62 to provide a start signal to 
the timer 58 at T.sub.0 as shown in the timing diagram of FIG. 2. In 
response to the start signal, the timer 58 switches to provide at T.sub.0 
a low (binary logic 0) output signal level as shown by waveform A in FIG. 
2 which signal is directed by way of base resistor 60 to turn off NPN 
transistor 52 and subsequently turn off PNP control transistor 46 so as to 
ultimately turn on current mirror 47. Simultaneous to this, the low 
(binary logic 0) output signal level A from the timer 58 is directed by 
way of a line 79 to one input terminal of an AND gate 80 so as to enable 
the AND gate 80 to provide a low (binary logic 0) output signal level. The 
low (binary logic 0) output signal level from the AND gate 80, in turn, is 
directed to a switch 82 to thereby turn the switch 82 off and insure that 
the infrared emitting diode 18 is also turned off. At time T.sub.0 the 
timer 58 also switches to provide a high (binary logic 1) output signal 
level as shown by waveform B in FIG. 2 to the other input terminal of the 
AND gate 80 as well as to one input terminal of the latch 74. The input 
reference voltage to the comparator 68 provided by the divider resistors 
70 and 72 may be assumed to be substantially zero so that any slight 
increase in charge on the integration capacitor 56 will operate to trigger 
the comparator 68 into providing a high (binary logic 1) output signal 
level. Although the zero input reference voltage level to the comparator 
68 is an idealized representation, it will be readily understood to those 
of ordinary skill in the art that a slight offset to the input reference 
voltage to the comparator 68 must in actuality be provided. 
With the infrared transmitter 16 turned off in the aforementioned manner, 
the photoresponsive element 24 responds only to the detection of ambient 
scene light from the scene to be photographed and provides an output 
current signal that is subsequently multiplied by the current mirrors 30, 
36 and 40 to provide an output current signal along line 44 that is eight 
times the original current signal provided from the photoresponsive 
element 24. The multiplied current signal in the line 44, in turn, is 
directed to the current mirror 47 so as to be multiplied by a factor of 
one and thereafter directed by way of line 54 to charge the integration 
capacitor 56 with an input current signal that is eight times the output 
current signal from the photoresponsive element 24. The output current 
signal from the current mirror 36 which is four times the output current 
signal from the photoresponsive element 24, in turn, is directed by way of 
line 38 to input the current mirror 42 so as to enable the current mirror 
42 to receive a discharge current signal from the integration capacitor 56 
which is equivalent to four times the output current signal from the 
photoresponsive element 24. 
Thus the integration capacitor 56 is charged by an input current signal 
along line 54 from the current mirror 47 which is eight times the output 
current signal from the photoresponsive element 24 while simultaneously 
being discharged through the current mirror 42 by a current signal which 
is four times the output current signal from the photoresponsive element 
24. The net effect is that the integration capacitor 56 is charged 
starting at time T.sub.0 with an input current signal which is four times 
the output current signal from the photoresponsive element 24. This 
charging current signal operates to cause the voltage at the positive 
terminal of the integration capacitor 56 to ramp upwardly in a waveform as 
shown at C in FIG. 2. The upwardly ramping waveform C operates to 
immediately trigger the comparator 68 in a manner as previously described 
to provide a high (binary logic 1) output signal to the latch 74 and 
thereby set the latch 74 to provide a low (binary logic 0) output signal 
level. 
At time T.sub.1, which may be in the order of 1 millisecond subsequent to 
time T.sub.0, the timer 58 again switches to provide a high (binary logic 
1) output signal level as shown by the waveform A in FIG. 2. This high 
(binary logic 1) output signal level is directed by way of the base 
resistor 60 to turn on the NPN transistor 52 which subsequently operates 
to turn on the PNP transistor 46 and thereby turn off the current mirror 
47. Simultaneously to this, the high (binary logic 1) output signal level 
of waveform A is directed along line 79 to switch the output from the AND 
gate 80 to provide a high (binary logic 1) output signal level which, in 
turn, gates the switch 82 to turn on the infrared emitting diode 18. In 
this manner the current mirror 47 is turned off so as to provide no 
further charging current by way of the line 54 to the integration 
capacitor 56 at the same instant that the infrared emitting diode 18 is 
turned on to provide the beam of infrared radiation as shown in FIG. 1. 
As previously discussed, when the photographic subject is located within 
the near distance zone as shown in FIG. 1, infrared radiation from the 
infrared emitting diode 18 will be reflected back for detection by the 
photoresponsive element 24. Thus in this situation the photoresponsive 
element 24 will detect not only the ambient scene radiation previously 
detected during the time interval from T.sub.0 to T.sub.1 but, in 
addition, will detect the reflected infrared radiation from the 
photographic subject. Therefore, when the photographic subject is located 
within the near distance zone, the photoresponsive element 24 provides an 
output current signal in a time interval subsequent to T.sub.1 greater 
than the output current signal provided in the previous time interval from 
T.sub.0 to T.sub.1. The current signal output from the photoresponsive 
element 24 is thereafter multiplied by the current mirrors 30, 36 and 42 
in the aforementioned manner. The output current signal from the current 
mirror 42 which is equivalent to four times the output current signal from 
the photoresponsive element 24, thereafter operates to discharge the 
integration capacitor 56. Since the current mirror 47 is turned off by the 
control transistor 46 as previously discussed, there is no charging 
current signal provided to the integration capacitor 56 subsequent to the 
time T.sub.1, and the voltage at the positive terminal of the integration 
capacitor 56 ramps downwardly as shown by the waveform C of FIG. 2. This 
discharge current effectively provides a reverse integration of the output 
current signal from the photoresponsive element 24 which offsets the 
previous integration which occurred between time T.sub.0 and T.sub.1. 
The timer 58 will subsequently switch at a time immediately prior to 
T.sub.2 to provide a low (binary logic 0) output signal level as shown by 
the waveform B of FIG. 2 so as to disable the AND gate 80 from providing 
its affirmative logic signal to the switch 82 and thereby turn off the 
infrared emitting diode 18. The low (binary logic 0) output signal level 
of waveform B from the timer 58 is also directed to the latch 74. Under 
the aforementioned conditions where the photographic subject is located 
within the near distance zone from the photographic camera apparatus 10 as 
shown in FIG. 1, the integration capacitor 56 will be discharged at a 
greater rate than it was previously charged as illustrated by the waveform 
C so as to switch the comparator 68 to provide a low (binary logic 0) 
output signal level to the latch 74 prior to the time at which the timer 
58 switches to provide its low (binary logic 0) output signal level to the 
latch 74. Thus the switching of the comparator 68 prior to the switching 
of the output waveform B from the timer 58 operates in a well-known manner 
to switch the latch 74 to provide a high (binary logic 1) output signal 
level indicative of the photographic subject in the scene being located 
within the near distance zone from the photographic camera. As is readily 
understood, subsequent switching of the output waveform B from the timer 
58 to a low (binary logic 0) output signal level would not affect the low 
(binary logic 0) output signal level from the latch 74. As is readily 
apparent, the timing intervals from time T.sub.0 to time T.sub.1 are 
substantially equivalent to the time interval from time T.sub.1 to time 
T.sub.2 and may preferably be in the order of 1 millisecond apiece in 
order to enable the ranging circuit 28 not to be influenced by 60 cycle 
light especially from a fluorescent light source. 
Conversely, if the subject is located beyond the near distance zone from 
the photographic camera in FIG. 1, no infrared radiation would be 
reflected back to the photoresponsive element 24 and there would be no 
increase in the current output from the photoresponsive element 24 during 
the time interval from time T.sub.1 to time T.sub.2 ; and, hence, the 
integration capacitor 56 would discharge at substantially the same rate at 
which it was previously charged during the time interval from time T.sub.0 
to time T.sub.1. Since the output waveform B from the timer 58 switches 
from a high (binary logic 1) output signal level to a low (binary logic 0) 
output signal level at a time immediately prior to time T.sub.2, it is 
apparent that the output waveform B from the timer 58 will switch prior to 
the comparator 68 so as to cause the latch 74 to switch to a low (binary 
logic 0) output signal level indicative of a subject located in the far 
distance zone from the photographic camera 10 as shown in FIG. 1. 
In this manner, a two zone ranging output signal can be provided in a 
simple and economical manner without regard to the ambient scene light 
intensity since the two zone ranging system of this invention depends only 
upon the reflection of infrared radiation from the subject. When the 
subject is located within the near distance zone from the photographic 
camera, it is apparent that a low output infrared emitting diode 18 may be 
utilized in order to minimize costs. The two zone output signal may be 
used in any well-known manner to control the focusing of the objective 
lens 12 between a near and far focus zone or, alternatively, to control 
the firing of an electronic flash in a manner that might prohibit the 
camera from operating when the subject to be photographed is located in 
the far distance zone from the photographic camera 10. 
Under certain conditions of minimum ambient scene light intensity, there 
may be insufficient ambient scene light detected by the photoresponsive 
element 24 to sufficiently charge the integration capacitor 56 during the 
time interval from time T.sub.0 to time T.sub.1 to affect the switching of 
the latch 68. Under these conditions, an alternate current signal is 
introduced by an alternative current source 90 to input the current mirror 
40. The alternative current source 90 is controlled from a comparator 84 
which derives an input reference voltage from a resistor divider network 
comprising the resistors 86 and 88 for comparison to an input voltage 
signal corresponding to the output current signal from the current mirror 
30 along line 34. Thus under conditions of low ambient scene light 
intensity where little or no scene light is detected by the 
photoresponsive element 24 resulting in little or no current being 
directed to the current mirror 30, the comparator 84 senses the low 
current signal output from the current mirror 30 along line 34 and 
operates to turn on the alternative current source 90 to provide a 
constant steady state input current signal to the current mirror 40. This, 
in turn, enables the integration capacitor 56 to provide the output 
response as shown by the waveform C and thereby switch the comparator 68 
in the aforementioned manner. 
Other embodiments of the invention including additions, subtractions, 
deletions and other modifications of the preferred disclosed embodiments 
of the invention will be obvious to those skilled in the art and are 
within the scope of the following claims.