Digital indicator device for indicating photographing exposure values in the form of digits

Very precise indications of the Apex indication values in a camera are displayed through the viewfinder. The nominal value is displayed numerically and further indications are provided to display fractional parts of one step of a nominal Apex indication value.

BACKGROUND OF THE INVENTION 
This invention relates to a digital indicator device for displaying the 
Apex indication exposure values. The indicator is adapted to provide an 
indication of every step and fractions of a step. 
The Apex indication values are related to one another by the well known 
Apex indication equation: 
EQU E.sub.v = B.sub.v + S.sub.v = A.sub.v + T.sub.v, (1) 
where; 
B.sub.v is the Apex indication value of brightness; 
S.sub.v is the Apex indication value of film sensitivity; 
A.sub.v is the Apex indication value of aperture opening; 
T.sub.v is the Apex indication value of shutter speed; and 
E.sub.v is the Apex indication exposure value. 
It is quite common for cameras to display the A.sub.v or T.sub.v values by 
means of a meter. Such a display is an analog indication of these values. 
It is less common but also known to display the E.sub.v values by a meter. 
More recently, digital display devices have been used to digitally 
indicate to the camera user, the values A.sub.v, T.sub.v and/or E.sub.v. 
While such displays are very useful, they do have the disadvantage of not 
being capable of indicating values intermediate two nominal values. 
Some such systems use one step for every .+-. 1 E.sub.v, A.sub.v or 
T.sub.v, and therefore are not high precision systems, whereas in other 
systems, in which illuminant members (electric lamps or the like) are 
aligned along the frame of a finder field to read numerical values on a 
character plate fixedly mounted corresponding in position to illuminant 
members, precise indication is not possible because digital readout is not 
provided. 
In the Kisanuki U.S. Pat. No. 3,909,137, a very complex system, using 
analog to digital converters with digital to analog feedback, is described 
for providing a digital indication of the steps of a specific combination 
of Apex indication values plus an indication of fractional parts of one 
step of the specific combination of values. The value specifically 
displayed in the Kisanuki patent is the value B.sub.v -T.sub.v, which the 
patent refers to generally as the exposure value. However, the "exposure 
value" of the Kisanuki patent is not the exposure value E.sub.v which 
equals B.sub.v + S.sub.v and A.sub.v + T.sub.v. 
SUMMARY OF THE INVENTION 
The present invention eliminates the disadvantages noted above with respect 
to prior art and provides a simplified indication system which is capable 
of digitally displaying immediately nominal values heretofore customarily 
used for Apex indication values plus digital indications of fractions of a 
nominal value. The Apex indication values which can be displayed by the 
invention are E.sub.v, B.sub.v, S.sub.v, T.sub.v and A.sub.v. Typically, 
S.sub.v would not be displayed in this manner because it remains constant 
for a given film. Also, it is not generally useful to the camera user to 
display the values B.sub.v. However, the values E.sub.v, T.sub.v and 
A.sub.v are particularly useful to the camera user when trying to obtain 
the optimum exposure characteristics for photographing a given scene. 
It is well known in the art that the Apex exposure value E.sub.v is 
customarily described as B.sub.v when S.sub.v =5. The typical nominal 
values for the aperture or diaphragm are, for example, 1, 2 . . . 16. The 
typical nominal values for the shutter speed are, for example, 1, 1/2, 
1/4, 1/8 . . . 1/1000. The present invention not only displays these 
values, but also displays fractions of these values. For convenience sake, 
the numerical values corresponding to the specific Apex indication values 
E.sub.v, B.sub.v, T.sub.v, S.sub.v and A.sub.v are referred to herein as 
exposure values.

DETAILED DESCRIPTION OF THE INVENTION 
A preferred embodiment according to the invention will now be described. 
FIG. 1 illustrates one example in which the diaphragm value is indicated 
in the form of digits with the precision of 1/3 A.sub.v. In FIG. 1, the 
reference number 1 designates a finder frame, 2 a digital main indication 
member, and 3 and 4 auxiliary indication members. The nominal values are 
indicated by the main indication member, and if the value to be indicated 
is 131/3, "13" is indicated by the main indication member 2 and the 1/3 is 
indicated by illumination of the auxiliary indication member, 3. On the 
other hand, if the exposure value (in this case the diaphrgam value) is 
132/3, "13" is indicated by the main indication member 2, and 2/3 is 
indicated by illumination of the auxiliary indication members 3 and 4. 
FIG. 2 illustrates an embodiment in which the shutter speed indication is 
provided with the precision of 1/3 T.sub.v. The reference number 11 
designates a finder frame, 12 a digital main indication member, and 
auxiliary indication members 13, 14, 15, 16. 
If the value to be indicated is 1/250, "250" is indicated by the digital 
main indication member 12. If the value is one third of the way towards 
the next nominal shutter speed value, (on the EV scale), i.e., 1/500, 
"250" is indicated by member 12 and the auxiliary indication member 13 is 
also illuminated. If the value is towards 1/500 by 2/3 T.sub.v, the 
auxiliary indication members 13 and 14 are illuminated. 
The auxiliary indication members 15 and 16, positioned below the main 
indication member 12, are provided to indicate values which are 1/3 
T.sub.v and 2/3 T.sub.v below the value indicated by the main indication 
member 12. For example, if the value is 1/3 T.sub.v towards 1/125, the 
auxiliary indication member 15 will be illuminated, and if the value is 
2/3 E.sub.v towards 1/125, the auxiliary indication members 15 and 16 are 
illuminated. It is assumed for the example described that the nominal 
value in box 12 is 250. It will be apparent that the same display format 
could be used for any of the exposure values. 
As described above, the device according to the present invention has a 
small number of indication members for providing an indication of high 
precision. This allows a photographer to see the precise exposure values 
in an easy to read manner. 
An embodiment of circuitry which actuates the indication is described 
hereinafter with reference to FIGS. 3 and 4. These figures will be 
described in detail in connection with the display of the Apex indication 
value E.sub.v (remembering that E.sub.v equals B.sub.v + 5 for 
conventional usage). However, as will be pointed out subsequently, the 
same circuitry could be used for displaying A.sub.v or T.sub.v, by simply 
substituting appropriate resistors normally present in any photometric 
camera circuit. 
In FIG. 3, there is shown a photometric circuit 21, the details of which 
may be designed as shown by circuit 101 in FIG. 4(a). A constant current 
source 101a and a capacitor 101c are arranged in series with a power 
source, +Vcc. A node 101d, between the constant current source 101a and 
the capacitor 101c is connected to the inversion input terminal of a 
comparator 101g composed of an operational amplifier. The node between a 
composite photoconductive cell 101e and a resistor 101f, also connected in 
series with the power source, is connected to the non-inversion input 
terminal of comparator 101g. A trigger switch is indicated at 101b. 
A delay circuit 22, shown in FIG. 3 may consist of a circuit 102 as shown 
in FIG. 4(b). In FIG. 4(b), a node between resistors 102b and 102c, 
arranged in series with the power source +Vcc, is connected to an 
inversion input terminal of comparator 102d composed of an operational 
amplifier. A terminal 102a is connected to the ion inversion input 
terminal of comparator 102d. The terminal 102a of the delay circuit is 
also connected to node 101d of the photometric circuit. 
An AND circuit 24 receives an output from photometric circuit 21, delay 
circuit 22 and a pulse source, such as a mult-vibrator 23. The reference 
numeral 25 designates a ternary counter and 26 an OR circuit which 
receives each bit output of the ternary counter 25. The reference numerals 
27 and 28 are auxiliary indicators which receive outputs of the ternary 
counter 25 and the OR circuit 26, respectively. The system also includes a 
decimal counter 29, a decoder 30 for driving a 7-segment indicator 31, a 
binary counter 32, an indicator 33 for indicating the numeral "1", and a 
reset circuit 34 for resetting the ternary counter 25, the decimal counter 
29, and the binary counter 32. 
With the construction as described, the device operates as follows: The 
light receiving element 101e in the photometric circuit 21 is the 
composite photoconductive cell, and the current i.sub.1 through the cell 
101e is proportional to the amount B.sub.v of Apex indication of the 
brightness B of an object, as is well known. Also as is well known, the 
value EV of Apex indication equals the sum of B.sub.v of Apex indication 
and S.sub.v of Apex indication (S.sub.v being film sensitivity). The 
relation between the current i.sub.1 and the amount B.sub.v of Apex 
indication may be given as: 
EQU i.sub.1 = i.sub.o + i.sub.2 (B.sub.v) (2) 
where, i.sub.o is the current through composite photoconductive cell 101e 
at B.sub.v = 0 .ident. B.sub.vo, and i.sub.2 is a proportional constant. 
C.sub.1 represents the capacitance of the capacitor 101c, i.sub.3 the 
current value of the constant current source 101a, and R.sub.1 the 
resistance value of the resistor 101f. The voltage at the negative input 
of the operational amplifier is V.sup.-. The voltage at the positive input 
of the operational amplifier is V.sup.+. Initially, the switch 101b is 
closed. At this time, 
EQU V.sup.- = 0, 
and 
EQU V.sup.+ = i.sub.1 R.sub.1. 
the output at 101h will be positive. 
When switch 101b closes, capacitor 101c begins charging, thereby increasing 
the voltage V.sup.- according to the equation; 
##EQU1## 
When V.sup.- reaches the value of V.sup.+, the output at 101h drops to 
zero. The time, t.sub.1, between the opening of switch 101b and dropping 
of the output 101h to a zero value, is determined by setting V.sup.- equal 
to V.sup.+ and solving for t.sub.1. Thus, i.sub.3 t.sub.1 /c = i.sub.1 
R.sub.1, therefore 
##EQU2## 
In the delay circuit 102, resistor 102c has a value R.sub.1 and resistor 
102b has a value equal to that of photoconductor 101e at B.sub.vo. Thus, 
the voltage at the inversion input node of 102d is R.sub.1 i.sub.o. The 
positive or non-inversion input of 102d is connected to node 101d of the 
photometric circuit. Thus, prior to opening switch 101b, the output at 
102e is low or zero. The output will become positive (equivalent to binary 
1) at a time t.sub.2 following the opening of switch 101b when the voltage 
at node 101d equals R.sub.1 i.sub.o. Thus, the time t.sub.2 is given as 
follows: 
##EQU3## 
The only time that both output lines 101h and 102e are positive (i.e., 
binary 1's) is between t.sub.2, when 102e goes positive, and t.sub.1 when 
101h goes to zero. Inasmuch as both outputs control AND gate 24, the 
latter is gated on to pass pulses from the multi-vibrator 23, for the 
period t.sub.o, where, 
##EQU4## 
Since the value 
##EQU5## 
is a constant, equation (5) may be rewritten as: 
EQU t.sub.o = K.sub.1 (B.sub.v) 
Thus, it is apparent that the time that AND gate 24 is closed to pass 
pulses from pulse source 23 is directly proportional to the B.sub.v value. 
If the period of multi-vibrator 23 is set at 1/3 K.sub.1, then the number 
of pulses, N, passed through AND gate 24 to ternary counter 25 is given by 
the following equation: 
EQU N = 3 .multidot. (B.sub.v) (6) 
Reset circuit 34 is set to reset counters 25, 29 and 32 in synchronism with 
the closing of switch 101b for a new counting period. 
It will now be apparent that counter 25 will receive three pulses for each 
B.sub.v value (stated otherwise, it receives one pulse for each 1/3 
B.sub.v value) and provides an output pulse every third input pulse; 
counter 29 receives one input pulse for each one B.sub.v and provides an 
output pulse for every ten input pulses and counter 32 receives one input 
pulse if the B.sub.v value is above 10. The numbers of pulses applied to 
counters 29 and 32 are defined as N' and N", respectively, in the 
equations below: 
EQU N' = B.sub.v (7) 
EQU N" = B.sub.v /10 (8) 
Indicator 33 displays either a "1" or zero corresponding to the count in 
counter 33. Indicator 31 is a conventional seven segment indicator, e.g., 
seven LED segments or the like, and decoder 30 is a conventional 
decoder/segment driver for decoding the binary values 0 through 9 in 
counter 29 and energizing selected ones of the segments to display the 
value in counter 29 as a decimal digit. Indicators 27 and 28 may be simple 
illuminating devices which are illuminated when energized; 27 being 
illuminated when the binary value in counter 25 is either 10, or 01, and 
28 being illuminated when the binary value in counter 25 is 10 (it will be 
noted that counter 25 does not reach the binary value 11 since it is only 
a ternary counter and counts the three values 00, 01, 10 and then 
recycles). To display the value E.sub.v, rather than B.sub.v, the decimal 
counter can simply be wired to as to start counting from a count of five 
rather than zero. Alternatively, the counter could be simply connected to 
the film sensitivity dial so as to cause a count corresponding to the Apex 
value of film sensitivity to be entered initially into the counter. 
Thus, it is apparent that the indicators display the E.sub.v value to a 
precision of 1/3 of the E.sub.v value, by providing a decimal indication 
of the nominal E.sub.v value and a further indication of additional 1/3 
and 2/3 toward the next nominal E.sub.v value. 
Table 1 
______________________________________ 
E.sub.v 33 31 28 27 
______________________________________ 
0 0 0 
1/3 o 
2/3 o o 
1 0 1 
1 . 1/3 0 1 o 
1 . 2/3 0 1 o o 
2 0 2 
15 1 5 
15 . 1/3 1 5 o 
15 . 2/3 1 5 o o 
16 1 6 
______________________________________ 
o indicates that the auxiliary indicator goes on. 
As seen in Table 1, the E.sub.v values may be indicated by the main 
indicators 33 and 31 and the intermediate 1/3 E.sub.v and 2/3 E.sub.v by 
the auxiliary indicators 28 and 27. 
The value A.sub.v can be displayed by simply replacing the photosensitive 
resistor 101e with a variable resistor that is controlled by the diaphragm 
ring. Resistors whose values respond to alteration of the diaphragm of 
aperture are common in photometric circuits. Alternatively, the values of 
T.sub.v can be displayed by substituting for resistor 101e a variable 
resistor whose value is determined by the shutter speed which is either 
set into the camera by the user or calculated by a photometric circuit. 
Such resistors are common in photometric circuits. 
From the foregoing, it will be appreciated in the present invention that 
the exposure values may not only be indicated with extreme precision in 
the form of digits but also it is possible to visually perceive 
immediately if the required camera settings should be slightly advanced 
from the numerical values indicated on the main indication portion.