View finder device having liquid crystal cell

By providing a liquid crystal cell nearly at the position of the clear vision of the view finder optical system together with a means for masking the display part of the liquid crystal cell the noise appearing on the boundary between the display part and the object view field is eliminated while the invasion of dusts is avoided, whereby further by means of the liquid crystal cell the alarm for the improper exposure, the alarm of the consumption of the power source battery and so on are displayed besides the photographic informations.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a view finder display device having a 
liquid crystal cell for displaying the photographic informations and 
various kinds of alarms. 
2. Description of the Prior Art 
In case of the conventional device for displaying the photographic 
informations such as the measured value of the brightness of the object to 
be photographed or the alarm for the fact that the photographic 
informations are out of the mechanically linked range for obtaining the 
proper exposure, an ampere meter is supplied with a current corresponding 
to the measured light value or the preset exposure value in such a manner 
that the measured light value is displayed at the display part by the 
position of the pointer of the ampere meter. However there are so many 
inconveniences, for example the device is subject to breakage, being 
provided with movable means such as ampere meter, the invasion of dust 
into the focus plate part through the opening for the movable means 
hinders the view field, it is difficult to build the device itself in a 
camera with small space, much noise takes place along the boundary between 
the display part and the object view field or other photographic 
informations than that of the object to be photographed are always seen in 
the object view field. Further, there are such devices in which the 
pointer of the ampere meter is brought out of the display window or 
brought into the alarm zone provided at the upper or the lower end of the 
display part, whereby either it is difficult for the photographer to find 
the pointer or the red alarm zone is always seen in the view field, which 
is troublesome for the photographer. Further, in case of such type of the 
device in which the mechanically linked alarm display plate projects into 
the display part only at the time of alarm, it is mechanically so 
complicated that the manufacturing cost is high and there is much 
possibility for damage. Further in case of the type of device in which LED 
(illuminating diode) illuminates the power consumption is large, which is 
also inconvenient. 
In case of the conventional device by means of which the battery can be 
checked, the display LED (illuminating diode) is connected to the power 
source through a switching circuit in such a manner that the consumption 
of the battery is checked, observing whether the LED illuminates or not. 
However, LED consumes much power, the battery checking itself consumes the 
battery, which is also inconvenient. 
Further in case of the type of the device in which the pointer of the 
ampere meter for displaying the measured light value in the view finder 
serves further to display the battery checking, it is difficult to tell 
the battery checking display from the light measurement display, while the 
display of the consumption of the battery does not sufficiently serve as 
an alarm. 
Further in case some informations are displayed in the view finder whereby 
the display part is in the photographic view field frame, the decision of 
the composition of the picture is hindered, which is troublesome, while in 
case the display part is out of the photographic view field frame the 
display becomes obscure and there is a danger that the photographer should 
fail to observe the alarm display such as for the improper exposure. 
Thus in order that one display can be observed along to different 
directions at the same time it is necessary to prepare each one display 
device or a complicated optical system, for example in order that the 
information display output can be observed both outside of the camera and 
in the view finder it is necessary to provide the display devices at two 
positions, which is not profitable. 
So far various kinds of display devices having a liquid crystal, for 
example, the seven-element display by means of a digital driving circuit, 
the analog display by means of a high voltage, the integral analog display 
by means of the digital driving circuit and so on. 
Recently for those display devices, the liquid crystal of field effective 
type has come to be used, whereby the liquid crystal cell of this type 
consists of polarization plates so that the light is attenuated by the 
polarization plates in such a manner that the sufficient brightness can 
not be obtained for the brightness, whereby when it is used as the 
photographic information display device in the view finder the 
discrimination of the display is difficult even at the place with the 
brightness in the ordinary room. 
SUMMARY OF THE INVENTION 
A purpose of the present invention is to offer a nice display in the view 
finder for the photographer, by means of providing the liquid crystal cell 
nearly at the position of the clear vision of the view finger optical 
system and a means for masking the display part of the liquid crystal 
cell. 
Another purpose of the present invention is to display both the 
photographic informations and the alarm by means of the liquid crystal 
cell provided in the view finder optical path, whereby the liquid crystal 
cell is designed in such a manner that on the one transparent base plate 
of the two plates sandwitching the liquid crystal a transparent electrode 
is provided while on the other transparent base plate a combination of a 
transparent electrode and a transparent resistance body is provided so as 
to display the photographic informations by means of the liquid crystal 
sandwitched between the transparent electrode and the transparent 
resistance body and the alarm by means of the liquid crystal sandwitched 
between the two transparent electrodes. 
Further another purpose of the present invention is to display the measured 
values by means of the liquid cell and the alarm by repeating the 
transparency and the untransparency of almost the whole plane of the 
liquid cell at the visible speed, by periodically altering the voltage 
applied to the resistance layer when the measured values enter into the 
alarm zone. 
Further another purpose of the present invention is to offer a battery 
alarm display device without ampere meter and illuminating element, 
whereby the voltage of the power source battery is stepped up by means of 
a D.C. step up circuit and applied to the liquid crystal cell in such a 
manner that the width of the display line of the liquid crystal cell is 
made thick as alarm display when the power source battery is consumed. 
Further another purpose of the present invention is to offer no troublesome 
display at the time of determining the composition and to offer the alarm 
display covering the whole plane in the view finder only immediately 
before taking a photograph when the set exposure is not proper, by 
providing a liquid cell normally allowing the passage of the light at the 
position at which the cell covers nearly all the light beam in the view 
finder optical path in a camera. 
Further another purpose of the present invention is to offer a liquid 
crystal display device consisting of a pair of windows, a light conducting 
means optically connecting the both windows and a liquid crystal provided 
in the light path, whereby by making use of the transparent display system 
of the liquid cell observation can be made through the pair of the window. 
In case the device is applied to a camera, the information display output 
can be observed by means of one liquid crystal display device outside of 
the camera and in the view finder in a simple way. 
Further another purpose of the present invention is to offer an 
illumination device at the low brightness in case the liquid crystal 
display device is used for the display in the view finder, whereby the 
illumination device is automatically operated when the display of the 
liquid crystal display device becomes dark so as to be difficult for 
recognition. 
Further other purposes will be disclosed out of the detailed explanation to 
be made below in accordance with the accompanying drawings.

DESCRIPTION OF PREFERRED EMBODIMENT 
FIG. 1(a) shows a composition of the liquid crystal cell, whereby 51 is the 
first polarization plate, 52 the first base plate, 53 the resistance layer 
formed on the base plate 52, 54 the space to be filled with a liquid 
crystal of nematic state having a field effect, 56 the second base plate, 
55 the conductive or the resistance layer formed on the base plate 56 and 
57 the second polarization plate. In the drawing, a liquid crystal cell of 
the transparent type is shown, whereby when the liquid crystal cell of the 
reflection type is to be used a dispersion refracting plate is provided 
behind the polarization plate 57. In FIG. 1 (b) shows the plane view of 
the base plate 52, on which plate a resistance layer 53 is formed in such 
a manner that at least two separated zones of the resistance layer 53 very 
conductive electrode parts 53a and 53b are formed as terminal electrodes. 
FIG. 1 (c) shows a plane view of the base plate 56, on which plate the 
conductive or the resistance layer 55 is formed, presenting at least on 
very conductive electrode part (terminal electrode) 55a. The liquid 
crystal cell is composed in such a manner that two equal base plates are 
provided parallel to each other normally with a gap about 4.mu.-50.mu. 
between them, which gap is filled with a liquid crystal of the nematic 
state having a field effect, while the above mentioned terminal electrodes 
are provided so as to be connectable to the external circuit, whereby the 
whole is hermetically sealed (FIG. 1 (d), in which the liquid crystal cell 
is shown schematically, whereby 53 is the resistance layer on the base 
plate 52 and 55 the conductive layer on the base plate 56). 
The arrow on the above mentioned polarization plate 51 shows the 
polarization plane of the polarization plate, the arrow on the resistance 
layer 53 the direction of the orientation of the liquid crystal molecules 
on the resistance layer and the arrow on 55 the direction of the 
orientation of the liquid crystal molecules on the layer 55 opposite to 
the resistance layer 53, whereby the liquid crystal filled between both 
layers assumes a gradually distorted orientation in the angle between the 
two arrows shown in dotted lines. The arrow on the polarization plate 57 
shows the polarization plane of the polarization plate. This polarization 
plate 57 is intended to detect the light coming out of the liquid crystal. 
In FIG. 1 (a) the orientation of the liquid crystal molecules is in a 
state distorted at 90.degree.. The polarization plane of the light Io 
incident from the above follows the polarization plane of the polarization 
plate 51 and is rotated by an angle corresponding to the distorted 
orientation of the liquid crystal molecules when the light passes the 
liquid crystal layer between thelayers 53 and 55 so as to enter into the 
second polarization plate 57. When now the angle of the then polarization 
plane and that of the polarization plate 58 is 90.degree., the incident 
light Io is interrupted here in such a manner that the observer in the 
lower part of the drawing can not recognize but a dark state. When an 
electrical field which is higher than a certain determined intensity is 
applied to the liquid crystal cell the liquid crystal molecules are 
orientated in such a manner that their long axis lies perpendicular to the 
surface of the base plate, when the liquid crystal is isotropic to the 
incident light Io so that no rotation of the polarization plane of the 
incident light takes place. Consequently when the polarization directions 
of the two polarization plates are parallel to each other the light passes 
through when an electrical field is applied in such a manner that contrary 
to the non-applied state a bright state is observed. When the directions 
are made perpendicular to each other, the negative state and the positive 
state are inversed into each other. FIG. 1 (e) shows a diagram for 
explaining the electro-optical characteristics of the liquid crystal cell, 
whereby the abscissa shows the voltage, the ordinate the amount of the 
transmitted light and Vth the threshold level. The diagram shows the 
characteristics when a field effect twisted nematic liquid crystal is 
applied (hereinafter abreviated TN effect), whereby for TN effect Vth is 
sc low as 1-3 volt, while for the deformation of vertically aligned phase 
liquid crystal (hereinafter abreviated DAP effect) Vth is so as 3-6 volt. 
Namely the threshold level for both of the above cases is sufficiently low 
as compared with the threshold level of 8-15 volt for the dynamic 
scattering mood liquid crystal (hereinafter abreviated DSM effect). Beside 
above a variation of the TN effect and the DAP effect belongs to the field 
effect presenting the low threshold level characteristics, whereby they 
take place through the variation of the alignment of the liquid crystal or 
of the display detecting method by means of the polarization plate. 
Further there is a method to directly recognize the color variation due to 
the change of the alignment without using a polarization plate, by adding 
a dichromatic agent to the liquid crystal layer. Although the present 
liquid crystal cell can be applied every liquid crystal display system 
having a low threshold level characteristics, it is especially effective 
for the TN effect having the most low threshold level that is known at 
present as liquid crystal display system. 
The principle driving method of the present liquid crystal cell is that a 
potential distribution as is shown in FIG. 1 (d) is given to the 
resistance layer 53, a voltage is applied in such a manner that a 
potential difference takes place between the resistance layer 53 and the 
conductive or resistance layer 55 and a distribution of the potential 
difference is given by changing the potential difference between the 
resistance layer 53 and the conductive or resistance layer 55, whereby the 
application of the voltage is adjusted in such a manner that the range of 
the potential difference lower than the electrooptical threshold level 
serves as the display part. FIG. 1(f) shows with the straight line AB the 
distribution of the potential difference taking place by means of the 
resistance layer 53 with an even voltage between A and B in FIG. 1 (d). On 
the other hand, when 55 shown in FIG. 1 (d) consists of a conductive layer 
or a low resistance layer having a resistance sufficiently low as compared 
with that of the resistance layer 53, the applied voltage has no variation 
according to the position of l, so that C.sub.1 C.sub.2 can be represented 
by a horizontal straight line. The distribution of the voltage taking 
place in the liquid crystal comes between the straight lines AB and 
C.sub.1 C.sub.2. In the drawing, the distribution is shown with several 
arrows, whereby the voltage distribution is continuous in practice. The 
electrooptical characteristics of the liquid crystal applied to the 
present invention has no polarity (.+-.)(Direction), so that no 
electrooptical modulation takes place in l.sub.1 l.sub.2, a domain in 
which the potential difference lies, whereby a tape shaped domain with 
center at C.sub.1 C.sub.2 and width of 2 Vth is taken into consideration. 
FIG. 1(g) shows such a display state, whereby the non-modulation range (I) 
corresponding to l.sub.1 l.sub.2 in the whole range in a square serves as 
the display part. 
As explained above in accordance with the present invention it is possible 
to produce seemingly a point-shaped or a line-shaped display to arrange 
the domain (II) which surpasses the threshold level of the liquid crystal 
sufficiently larger than the domain (I) which does not surpass the level. 
Namely by means of the liquid crystal display device in accordance with the 
present invention the display can be obtained steplessly at any position 
with any width in the display range by changing the inclination of the 
potential difference between A and B (represently by the inclination of 
the straight line AB) or the change of the potential level at C 
(represented by the upward and the downward translation of the straight 
line C.sub.1 C.sub.2). 
In case of the liquid crystal cell shown in FIG. 1(h), 55 is the resistance 
layer, namely the layers provided on the two base plates 52 and 56 are the 
resistance layers, whereby as is shown in FIG. 1(i) the distribution of 
the potential difference produced between the electrodes is represented by 
the arrows surrounded by the two straight lines. In this way, a 
substantially large distribution of the potential difference can be 
obtained without such a large voltage between A and B or D and E as is 
shown in FIG. 1(f). 
It goes without saying that not only the FE type liquid crystal cell but 
also the DSM type liquid crystal cell and so on can be applied to the 
present invention. 
FIG. 2 shows an embodiment of the view finder device in accordance with the 
present invention, whereby the device is built in a single reflex camera. 
In the drawing, 1 is the eye piece lens, 2 the pentagonal prism, 3 the 
condenser lens, 4 the view finder field frame, 5 the focus plate, 6 the 
reflex mirror, 7 the photographic lens, F the half permeable mirror 
provided slantly to the condenser lens, PC the photoelectric element and 
100 the display element consisting of a liquid crystal cell provided in a 
part of the focus plate. 
FIG. 3(a) and (b) show the disposition of the liquid crystal cell shown in 
FIG. 2 respectively in section and in perspective view. The focus plate 5 
is the formed part consisting of acryl resin, presenting a split prism (or 
microprisms) 5S and the matted focus plane 5P on the upper surface, the 
Fresnel prism 5F on the lower surface and a concave part for mounting the 
display element consisting of a matted plane 5M to be illuminated by the 
light from the object to be photographed, the mounting seat 5A for the 
display element and so on on the one side plane. The display element is 
designed in such a manner that a desired electrical field V is applied to 
the liquid crystal matter 12 surrounded with the plane glass plates 10 and 
11 sandwiched between the polarization plates 8 and 9, so as to carry out 
the display. The view field frame 4 offers the display window 5P, masking 
the joint part of the focus plane 5P with the liquid crystal cell and 
serving as the spacer between the condenser lens and the focus plate so 
that not only the clear display can be obtained but also the invasion of 
dust can be avoided. 
FIG. 4(a) and (b) show the liquid crystal cell in detail respectively in 
plane view and in section. In the drawing, on the back side of the plane 
glass plate 10 a concave part with the inlet 12I of the liquid crystal 
matter 12 is provided by glass etching, whereby the transparent resistance 
body 10R is provided for example by means of metallization. It suffices 
that the resistance body 10R is thin as compared with the depth of the 
concave part 10C while the etched part of the concave part 10C can be 
4-50.mu. so that the leakage of the liquid crystal matter 12 at the time 
of the introduction can be avoided in a comparatively simple way. At both 
ends of the resistance body 10R the electrodes 10P and 10P' for wiring are 
provided for example by means of metallization. On the surface of the 
plane glass plate 9 a transparent electrode 11T is provided for example by 
means of the metallization and at the one end an electrode 11P for wiring 
is provided for example by means of metallization. The both plane glass 
plates having been cemented to each other by means of a sealing agent S, 
the liquid crystal matter 12 is introduced through the inlet 12I under 
pressure, the inlet 12I is closed with the sealing agent S, the wires 10W, 
10W' and 11W are soldered, the polarization plates 8 and 9 are mounted one 
over the other so as to form a liquid crystal cell and the mounting parts 
10A are cemented on the above mentioned mounting seat 5A. 
FIG. 5 (a) and (b) respectively show a view field of the view finder of the 
above mentioned composition, whereby respectively the aperture value and 
the shutter time are displayed. In the drawing, 4P and 4M are the view 
field windows consisting of the view field frames 4. 12F and 12T 
respectively are the display scale with the over-exposure part and the 
under-exposure part, being formed at 5M of the focus plate 5 consisting of 
acryl resin or a photographic film with figures being provided in the 
neighborhood of the focus plane 5P. In the case of this composition the 
untransparent part 12H is displayed when an electrical field is applied to 
the liquid crystal cell whereby the content of the display can be seen 
nearly at the position of the optical clear vision, whereby further the 
view field frame 4 serving as masking means covers the joint part of the 
view field window with the display cell so that the display noise can be 
eliminated. 
FIG. 6 shows a variation of the liquid crystal cell in perspective view, 
while FIG. 7(a), (b) and (c) respectively show the cell shown in FIG. 6 in 
detail, whereby FIG. 7(a) shows the plane view of the plane glass plate 
10, FIG. 7(b) the plane view of the plane glass plate 11 and FIG. 7(c) the 
enlarged section through the important part when the both glass plates are 
cemented with each other. 
In FIGS. 6 and 7 the plane glass plate 11 is provided with three electrodes 
10P, 10P' and 10P" for wiring, whereby the electrodes 10P and 10P' are 
connected to the transparent resistance body 10R on the plane glass plate 
11, while the electrode 11P' is located at the position corresponding to 
the electrode 11P for wiring at the end of the transparent electrode 11T 
on the plane glass plate 10. 
In accordance with the above mentioned wiring system, when the both plane 
glass plates in FIG. 7(a) and (b) are cemented with each other, the 
electrode 11P for wiring on the one plane glass plate is connected to the 
electrode 11P' for wiring on the other plane glass plate automatically as 
is shown in FIG. 7(c), in such a manner that three terminals can be taken 
out of the one of the plane glass plates so that the wiring can be carried 
out in a simple way. Further in order to take three terminals out of the 
one of the plane glass plates it is possible to make use of a terminal as 
is shown with 14 in FIG. 6 in such a manner that as is shown in FIG. 8 the 
liquid crystal cell can easily be built in the focus plate 5 so that the 
wiring can be simplified, which is very profitable. 
Further, it goes without saying that the transparent electrode 11T and the 
electrode 11P for wiring shown in FIG. 7(a) can be formed as one body, 
being cemented by means of the same transparent resistance material. 
FIG. 8(a) shows a section through the important part of another embodiment 
of the liquid crystal cell display part while FIG. 8(b) shows the then 
view finder field mode. This embodiment is suited for the follow pointer 
system exposure setting, whereby between the liquid crystal cell and the 
dial plate a follow pointer 13 movable in functional engagement with the 
aperture ring or with the shutter time setting dial is provided in such a 
manner that the proper exposure can be obtained by means of watching the 
follow pointer with the light measurement display 12H of the liquid 
crystal cell. In accordance with this system the display in the view 
finder can be observed as is shown in FIG. 8(b). In the same way, as the 
afore-mentioned embodiment there is a mask 4 serving as a spacer provided 
so that even when dusts enter from the space in which the follow pointer 
moves, the dust reaches only the liquid crystal display part in such a 
manner that the internal part of the object view field window can be kept 
in the hermetic state. FIG. 8(c) shows a variation of the finder view 
field mode, whereby the follow pointer 13 is provided under the focus 
plate 5 as in case of the conventional camera or between the condenser 
lens 3 and the pentagonal prism 2. 
FIG. 9(a) shows further another embodiment, whereby a liquid crystal cell 
is built in the view finder of the camera mechanically linked with the 
range finder. In the drawing, 18 is the liquid crystal cell presenting the 
polarization plates 8 and 9 and 22 a half permeable mirror. In front of 
the liquid crystal cell 18 a dial plate 23 provided with the aperture 
value, the shutter time and so on is provided in such a manner the 
aperture value display, the shutter time display and so on can be observed 
in the view finder. D.sub.1 is the driving circuit for the liquid crystal 
cell while E.sub.1 is the direct current source and SW.sub.1 the switch. 
FIG. 9(c) shows an example of the composition of the liquid crystal cell 
shown in FIG. 9(a). In the drawing, 10' is the one of a pair of the plane 
glass plates, on the surface of which plane glass plate 10' a transparent 
resistance body 10R and the transparent electrode 11T are cemented as is 
shown in the drawing, when the corresponding parts have been etched in 
advance in such a manner that the liquid crystal matter 12 can be 
introduced there. On the lower surface of the plane glass plate 11' 
opposite to the plane glass plate 10' a transparent electrode 11T' is 
cemented. On an untransparent dial plate 23 serving a mask for the liquid 
crystal display part the view field mark 24, the view field mark 25 for 
correcting the parallax, the light window 24' for double image and the 
display window 4I for letting the light in the scale seal 26 are provided. 
In the drawing, the polarization plates 8 and 9 are omitted. The three 
terminals of the above mentioned driving circuit are connected to the both 
terminals of the transparent resistance body 10R and to the transparent 
electrode 11T. The transparent resistance body 10R is connected to the 
transparent electrode 11T at the one end 11Su (10Su), so that when the 
switch of the driving circuit is closed the view field mark 24 and the 
light measurement display part 4I are driven at the same time in such a 
manner that the sight as is shown in FIG. 9(b) can be obtained. Further on 
the upper surface of the plane glass plate 10' which is etched in such a 
manner that the liquid crystal matter can be introduced at the position of 
the view field mark for correcting the parallax, a transparent electrode 
25T is provided, being insulated from the transparent electrode 11T in 
such a manner that the electrode 25T is driven with other driving circuit 
than the above mentioned driving circuit at the time of the close-up 
photography, whereby the view field mark 25 for correcting the parallax 
can be observed at the time of the close-up photography. 
FIG. 9(d) shows a variation of the liquid crystal display cell, whereby the 
mark 25 for correcting the parallax appears automatically in accordance 
with the photographic resistance. In the drawing, 28 is the distance ring 
having a projection 28A, and SW.sub.2 is the switch to be closed when it 
is pushed by the projection. Consequently, in accordance with this 
composition, when the focus comes in a photographic distance for which the 
correction of the parallax is needed, the switch is automatically closed 
in such a manner that a voltage is applied to the electrode 25T and the 
mark 25 for correcting the parallax is displayed in the view finder. 
FIG. 10 shows a variation of the display system of the liquid crystal cell, 
whereby in this variation the view field frame is displayed in functional 
engagement of the battery. The liquid crystal cell, in which the liquid 
crystal is sandwiched between two glass plates on each of which a 
transparent electrode is cemented, while two dichromatic polarization 
plates are used as the polarization plates 8, 9 is so designed as to have 
the same areas as the whole view finder plane while the area of the parts 
on which the above mentioned transparent electrodes are cemented is 
choosen to be of the same area as the whole range of the view finder 
range, in such a manner that when the switch of the battery is opened the 
whole plane is displayed in color as is shown in FIG. 10(a), while when 
the switch of the battery is closed only the range inside of the view 
field frame 27 serving to mask the display part 4I is display in a 
transparent way, as is shown in FIG. 10(b). This display system not only 
displays the view field frame serving as the mask of the liquid crystal 
display part but also displays whether the battery switch is closed or 
opened. 
Below a concrete embodiment of the driving circuit of the liquid crystal 
cell in case of the light measurement display and the electrical field 
applying system will be explained. FIG. 11 (a) shows an embodiment of the 
driving circuit consisting of a combined cell of photoelectric elements. 
In the drawing, 15 is the power source circuit for giving a proper 
potential difference inclination to the transparent resistance body 10R of 
the liquid crystal. In order to obtain a narrow tape shaped display of a 
liquid crystal cell it is profitable to apply to the transparent 
resistance body 10 as high voltage as possible so that a DC-AC inverter 
(called transistor type inverter) and so on is often used in order to stop 
the DC voltage E2 up to a high AC-voltage. Below the operation principle 
of such step up circuit will be explained briefly. The transistor type 
inverter is in principle that by means of vibrator, whereby by making use 
of the saturation characteristics of the magnetic material of the 
transformer the switching effect of the transistor is maintained in such a 
manner that a rectangular AC voltage with an optional voltage and an 
optional frequency is produced at the secondary side of the transformer 
out of a certain determined DC voltage. This power source circuit is an 
oscillator generally with the frequency from several hundred to several 
thousand Hz, whereby the frequency of the AC applied to a liquid crystal 
becomes higher, the liquid crystal has a tendency to become unable to 
produce a clear tape shaped display due to its physical characteristics. 
In such a case, it becomes necessary to keep the frequency of the AC 
voltage to be applied to the liquid crystal cell under several hundred Hz. 
Even by means of the power source circuit 15 an oscillation below several 
hundred Hz can be obtained, whereby the case of the oscillation 
transformer becomes remarkably large, which is out of practice. 
Consequently as is shown in the drawing a high frequency voltage from the 
secondary side of the transformer of the power source circuit 15 is 
rectified by means of the voltage doubler rectifier 16 into a high DC 
voltage which DC voltage is interrupted by means of a signal from the low 
frequency pulse generator 20 so as to obtain a low frequency AC voltage. 
20 is the low frequency pulse generator consisting of a transistor 
multivibrator and so on, 17 the interrupting circuit, and 21 the 
overcurrent protecter circuit. In this way, the above mentioned low 
frequency AC voltage is applied to the liquid crystal 18 and the light 
measuring circuit. The light measuring circuit 19 is composed by 
connecting a three terminal combined cell consisting of the photoelectric 
elements PC.sub.1 and PC.sub.2, and the variable resistance VR.sub.2 in 
series with the variable resistance VR.sub.1. The dividing point of the 
both above mentioned elements is connected to the transparent electrode 
11T of the liquid crystal cell 18. When a single photoelectric element is 
used instead of the above mentioned three terminal combined cell, the 
electrical potential at the dividing point varies as is shown in FIG. 
11(b) with reference to the logarithm of the amount of the incident light 
whereby the linear range is limited to the middle part while in case of 
the above mentioned three terminal combined cell in which the resistance 
value of the photoelectric element PC.sub.1 is chosen about ten times as 
large as that of the element PC.sub.2 the electrical potential at the 
dividing point varies almost linearly, as is shown in FIG. 11(c) in a wide 
range with reference to the logarithm of the amount of the incident light. 
In this way, the electrical potential of the transparent electrode 11T of 
the liquid crystal 18 varies proportionally to the logarithm of the amount 
of the incident light, whereby the above mentioned display part 12H moves 
at an equal distance in proportion to the logarithm of the amount of the 
incident light. The reason is that in accordance with the variation of the 
electrical potential of the transparent electrode 11T the range 12H in 
which the potential difference between the inclination A-B of the 
electrical potential of the transparent resistance body 10R and the 
electrical potential of the transparent electrode 11T is below the 
potential difference twice as high as the threshold voltage Vth is moves 
in proportion to the amount of the incident light, which means that the 
display part moves at an equal distance in proportion to the logarithm of 
the amount of the incident light. Hereby the variable resistance VR.sub.1 
serves to vary the display position of the liquid crystal optionally while 
the variable resistance VR.sub.2 serves to compensate the deteriorated 
characteristics of the photoelectric element PC.sub.2 when the amount of 
the incident light is very small. 
As another embodiment of the driving circuit it is thought that the power 
source circuit 15 in FIG. 11(a) is directly connected to the liquid 
crystal cell 18 and the light measuring circuit 19, whereby in order to 
keep the frequency of the AC voltage below several hundred Hz it is 
necessary to prepare large space in the transformer, which is problematic 
for the installation in a camera. 
FIG. 11(d) shows further another embodiment of the driving circuit 
applicable to the present invention. In the drawing 15, 16, 17, 18, 20 and 
21 correspond to the elements with same figures in FIG. 11(a). 19a is the 
interrupting circuit for converting the light measuring circuit 19 into 
the interrupted signal, being synchronously controlled by means of the 
signal of the pulse generator 20 for driving the high voltage interrupting 
circuit 17. Consequently at the output of the interrupting circuit a pulse 
voltage with an amplitude variable in accordance with the light 
measurement output of the light measuring circuit 19 is produced. 19b is a 
signal amplifier circuit for amplifying the pulse voltage into such with 
corresponding amplitude so as to apply to the signal step up circuit 19c. 
The circuit consists of a signal transistor allowing the passage of a 
sufficiently low frequency current, whereby the voltage at the secondary 
side of the transistor is stepped up at maximum into a voltage to be 
applied to the resistance body electrode 10R of the liquid crystal cell 18 
so as to be applied to the electrode 11T of the liquid crystal cell 18. 
This circuit has the following merits. Because as is shown in FIG. 11(a) 
the light measuring circuit 19 does not act as the load of the transistor 
inverter 15 serving as the power source of the liquid crystal cell 18, the 
transistor inverter 15 with small capacity will do so that the inverter 15 
can be made very small. Further because the voltage applied to the both 
terminals of the photoelectric element of the light measuring circuit 19, 
a photoelectric element with low withstand voltage can be used. In case 
the above mentioned three terminal correspond cell is used instead of the 
photoelectric element PC.sub.3 of the light measuring 19, the display part 
12H moves at an equal distance in proportion to the logarithm of the 
amount of the incident light as is already explained in accordance with 
the embodiment of the driving circuit shown in FIG. 11(a). 
In case the above mentioned liquid crystal cell for view finder display by 
means of the above mentioned driving circuit, an accurate light 
measurement output in proportion of the logarithm of the amount of the 
incident light can be displayed, whereby in case of the over-exposure or 
the under-exposure the display part 12H moves to one end of the liquid 
crystal cell so as to display the over-exposure or the under-exposure 
alarm display. 
Further all of the liquid crystal cells used in the so far explained 
embodiment are driven by AC voltage so that the adhesion of dust due to 
static electricity never takes place. 
Because as explained above a display in accordance with the electrical 
field to be applied in the liquid crystal matter provided nearly at the 
position of the clear vision is obtained through the eye piece lens while 
a mask measuring for eliminating other display noises the contents of the 
display is provided, the invasion of dusts is avoided, there is no fear of 
the adhesion of dusts due to the static electricity thanks to the AC 
driving, the display can be made in such a manner that either the display 
in the display part can be made black or only the display can be made 
transparent and by arranging the relative polarizaation direction of a 
pair of the polarization plates on resp. under the liquid crystal cell 
either parallel to each other or perpendicular to each other, whereby in 
comparison with a mechanical display device the mounting space can be cut 
small while it can be so designed that when the switch of the display part 
of the liquid crystal cell the display part can be made untransparent so 
that nothing can be seen, whereby the photographer can concentrate his 
attention to the object to be photographed. 
Below a finder display device by means of which a large alarm display is 
obtained when the photographic information value surpasses a certain 
determined critical value in case the information value is displayed in 
analog variation by means of the liquid crystal cell will be explained. 
FIG. 12 shows the liquid crystal cell 100A applied to this embodiment in 
dismantled view. In the drawing, 31a and 31b are the polarization plates 
presenting the polarization planes along the directions of the arrow shown 
on the respective polarization plate. 32a and 32b are the glass base 
plates opposited to each other so as to sandwitch the liquid crystal. 33 
is the transparent electrode provided on the glass base plate 32a. 34a and 
34b are the transparent electrodes provided on the glass base plate 32b, 
whereby a figure is cut out of the electrode so as to give an alarm 
display in case of the improper exposure. 36 is the transparent resistance 
body provided on the glass base plate 32b, being provided at the position 
sandwitched between the transparent electrodes 34a and 34b so as to 
electrically connect the both electrodes 34a and 34b to each other. 35 is 
the space to be filled with a nematic liquid crystal with a field effect. 
It goes without saying that not only the above mentioned FE type liquid 
crystal cell but also the DSM type liquid crystal and so on can only be 
applied to the present invention. 
FIG. 13(a), (b) and (c) respectively show a diagram for explaining the 
operation of the liquid crystal shown in FIG. 12. 
In the electrical circuit shown in FIG. 13(a), the output voltage Vc of the 
light measuring circuit 37 is applied to the transparent electrode 33 
while the voltage VAB of the power source 38 is applied to the external 
terminals B and A of the transparent electrodes 34a and 34b. At this time, 
as is shown in FIG. 13(b) an inclination of the potential shown with the 
folded line LAB is produced between the terminals A and B, while all over 
the surface of the transparent electrode 3 the output voltage Vc of the 
light measuring circuit is kept. The range in which the then potential 
difference surpasses the electrooptical threshold value Vth for operating 
the liquid crystal is optically modulated so as to allow the passage of 
the light while the range X in which the potential difference is below Vth 
is not electrooptically modulated so as to interrupt the passage of the 
light and to display the measured light value. In accordance with the 
variation of the voltage Vc of the measured light output the range X moves 
so as to display the measured light value. When now the brightness of the 
object to be photographed becomes so dark into an under-exposure the 
voltage Vc of the measured light output becomes low in such a manner that 
the part including the transparent electrode 34b is contained in the range 
X as is shown in FIG. 13(c), whereby the figured part in the drawing 
permits the passage of the light while the remaining part interrupts the 
passage of the light so as to give an alarm display. 
FIG. 14(a), (b) and (c) respectively show the display mode in the view 
finder in case the above mentioned liquid crystal cell 100A is provided on 
the focus plane of a single reflex camera in the same way as the 
embodiment shown in FIG. 2. 
In FIG. 14(a) the horizontal tape shaped display X.sub.1 appearing in the 
display window 4I beside the finder view field frame 4P of the mask 4 
displays the photographic informations such as the brightness of the 
object to be photographed, the aperture value, the shutter time and so on 
whereby a proper exposure can be obtained in the mechanically linked 
range. Although omitted in the drawing, it is sufficient to arrange the 
information values as is shown in the embodiment in FIG. 5. In FIG. 14(b), 
the display X.sub.2 displays the over-exposure alarm, while in FIG. 14(c) 
the display X.sub.3 displays the under-exposure alarm. 
FIG. 15 shows a variation 100B of the liquid crystal cell in dismantled 
view. This embodiment is so designed that the alarm display appears as key 
shaped pattern along the contour of the picture plane. In the drawing 71 
is the polarization plate, 72 the glass base plate, 75 the transparent 
electrode, 73 the transparent resistance body, 74 the two transparent 
electrodes connected to the both ends of the transparent resistance body 
73 and 76 the space to be filled with the nematic liquid crystal. 
Being composed as explained above a rectangle shaped liquid crystal cell is 
obtained, whereby for example a display shown in FIG. 16 can be obtained 
by means of the transparent electrode 74. 
In FIG. 17, the liquid crystal cell shown in FIG. 15 is provided in the 
view finder optical path of a single reflex camera in the same way as the 
above mentioned embodiment. In the drawing, 100B is the liquid crystal 
cell shown in FIG. 15, being arranged on the circumference of the object 
light beam on the focus plate 5. 4 is the mask having a view field frame 
4P and the display window 4I, serving to make the finder view field and to 
prevent the invasion of dust into the view field part, being in close 
contact between the liquid crystal cell 100B and the condenser lens 3. 
This embodiment operates in the same way as that of the afore-mentioned 
embodiment, whereby the display mode in the view finder is shown in FIG. 
18(a), (b) and (c). 
In FIG. 18(a), the horizontal line display X.sub.4 in the display window 4P 
displays the photographic informations, while the proper exposure can be 
obtained in the mechanically linked range. In FIG. 18(b), the display 
X.sub.5 in the circumference of the finder view field displays the 
over-exposure alarm. In FIG. 18(c) the display X.sub.6 displays the 
under-exposure alarm. 
FIG. 19 shows further another variation of the liquid crystal cell in 
dismantled view. In this embodiment, the shape of the transparent 
electrode which is connected the both ends of the transparent resistance 
body of the liquid crystal cell is composed simple. In the drawing, 41 is 
the polarization plate, 42 the glass base plate, 43 the transparent 
electrode, 44 the transparent resistance body and 45 the transparent 
electrode arranged in contact with the both ends of the transparent 
resistance body 44, whereby the shape of the transparent electrode 45 is 
simply rectangular. 
The liquid crystal cell 100C operates in the same way as the liquid crystal 
cell 100A, 100B applied to the afore mentioned embodiments. When this 
liquid crystal cell 100C is provided beside the focus plate in the view 
finder optical path of the single reflex camera, the finder view field 
mode becomes as is shown in FIG. 20(a), (b), (c), (d), (e) and (f). In 
this FIG. 20(a), the horizontal line display X.sub.7 in the display window 
4I displays the photographic informations, whereby the proper exposure can 
be obtained in the mechanically linked range. In FIG. 20(b), the display 
X.sub.8 at the upper end of the display window corresponding to the 
transparent electrode 45 displays the over-exposure alarm. This display 
X.sub.8 is wider than the above mentioned display X.sub.7, so that the 
former can be distinguished from the latter. In FIG. 20(c) the display 
X.sub.9 displays the under-exposure alarm in the same way. At this time, 
it is possible to give color to the display part so as to obtain an easy 
observation by providing a color filter in front of the liquid crystal 
cell or color polarization plates combined with the liquid crystal cell. 
In FIG. 20(d), the display window 4I is made a little longer in such a 
manner that the transparent parts 4S remain outside of the display when an 
alarm is displayed so as to be able to distinguish the display X.sub.8 
from the dark part on the mask plane in the view finder. FIG. 20(e) shows 
the mode of the display window when the power source which is opened, 
whereby all the parts corresponding to the transparent resistance body 44 
and the transparent electrode 45 do not allow the passage of the light so 
as to alarm that the power source is switched off. When now the device is 
designed in such a manner that no light transmitting part remains at the 
upper and the lower end of the display window a display mode as is shown 
in FIG. 20(f) is obtained when the power source is switched off whereby 
the display window becomes totally dark so that at the time of taking a 
photograph the photographer can concentrate all of his attention to the 
composition of the picture, being undisturbed with useless displays. 
FIG. 21 shows further another variation of the liquid crystal cell in 
dismantled view. In this embodiment, the liquid crystal display covers 
total light beam in the view finder optical path whereby the large alarm 
display is obtained in the finder view field frame. In the drawing, 61 is 
the polarization plate, 62 the glass base plate, 63 the transparent 
electrode cemented all over the glass base plate, 64 the transparent 
resistance body and 65 the two transparent electrodes arranged in contact 
with the both ends of the transparent resistance body whereby both present 
the figure shaped form for the alarm display. 
FIG. 22(a), (b) and (c) respectively show the display mode when the above 
mentioned liquid crystal cell 100D is arranged in the view finder optical 
path of a single reflex camera, being combined with a mask in the same way 
as in case of the embodiment shown in FIG. 17. In FIG. 22(a), the 
horizontal line display X.sub.11 in the display window displays the 
photographic informations, whereby the proper exposure can be obtained in 
the mechanically linked range. In FIG. 22(b)and (c) the large display 
X.sub.12 or X.sub.13 appears in the view field frame 4P so as to alarm the 
improper exposure. 
Because thus the mask 4 having the display window 4I and the view field 
frame 4P the information values are displayed in the display window when 
the proper exposure can be obtained, while the alarm figures at the time 
of the improper exposure the part excepting the part 65a for wiring of the 
transparent electrode 65 so as to obtain a clear vision. 
Further in case in this embodiment the polarization plates are arranged in 
the upper and the lower position so as to cover the part excepting the 
part 65a for wiring of the figure shaped transparent electrode 65, even if 
the figure part is arranged near the center of the view field, and not in 
contact with the view field frame only the figure part excepting the part 
for wiring can be displayed near the center of the view field at the time 
of the alarm display. 
Below a view finder display device whose display part repeats the 
transparent state and the untransparent state at the time of alarm display 
to make an impressive alarm display will be explained. Hereby the same 
liquid crystal as is shown in FIG. 1 can be applied. FIG. 23 shows the 
circuit diagram for explaining the principle of this alarm system. In the 
drawing, E.sub.3 is the power source battery. SW.sub.4 is the periodically 
interrupting switch serving to periodically produce the potential 
inclination in the transparent resistance layer 78. The transparent 
electrode layer 77 is under the constant voltage, being kept at the earth 
potential in this case. When the switch SW.sub.4 is closed the 
untransparent part as X.sub.21 appears only at the one end of the liquid 
crystal cell, while the switch SW.sub.4 is opened the liquid crystal cell 
does not operate whereby the untransparent part as X.sub.22 appears all 
over the plane. The alarm is display in such a manner that the above 
mentioned two modes appears one after another at the visible speed. 
FIG. 25 shows the electrical circuit diagram of an embodiment of the device 
for carrying out the above mentioned alarm display. This embodiment is 
suited for the automatic exposure controlled camera with priority on 
shutter time or on aperture value whereby the proper aperture value or the 
proper aperture value basing upon the measured value of the brightness of 
the object to be photographed is displayed, while the alarm is also 
displayed when the proper exposure can be obtained with the preset shutter 
time or the preset aperture value or where there is a fear for an unstable 
camera holding by the hand, whereby by changing over the switch the 
voltage of the power source as well as the consumption of the power source 
can be display as alarm. In FIG. 25, 112 is the power source voltage. The 
block 111 the step up circuit consisting of a transistor inverter serving 
to convert the D.C. of the battery into an A.C. to be stepped up. The 
block 113 is the three terminal photoconductive element CdS on which the 
light from the object to be photographed is incident. 114 is the variable 
resistance, at which the ASA sensitivity of the film, the preset shutter 
time or the preset aperture value is put. Consequently the electrical 
potential at the point G1 differs in accordance with the brightness of the 
object to be photographed and the set conditions at the side of the 
camera. SW.sub.12 and SW.sub.13 are the manual switches mechanically 
linked with each other. The block 115 is the voltage level detecting 
circuit with bipolarity, being closed when the input voltage is below the 
low threshold value VL or above the threshold value VH. Namely the coil L1 
is excited when the input voltage is below VL, while the coil L2 is 
excited when the input voltage is above VH. The switches SW14, SW15, SW16 
and SW17 are the relay switches to be opened and closed in functional 
engagement with the above mentioned coils L1 or L2 in such a manner that 
when either the coil 1 or the coil 2 is excited all of the switches SW14, 
SW15 and SW16 are connected to the side of b. The block 116 are the 
rectifying circuit, serving to rectify the half waves of the A.C. from the 
step up circuit 111 into D.C. The block 117 is the low frequency 
oscillation circuit including a multi-vibrator, whereby the transistor 118 
is switched on or off in accordance with the frequency of the 
multi-vibrator so that a low frequency oscillation voltage with nearly 
rectangular wave form is obtained from the half wave rectified current. 
119 is the liquid crystal cell. 
Below the operation of the device composed as mentioned above will be 
explained. In case the display basing upon the measured value of the 
brightness of the object and the alarm are carried out, the switches SW12 
and SW13 are set at the side of a. The A.C. ouptut voltage of the step up 
circuit 111 is divided by means of the photoconductive element 113 and the 
information input resistance 114 and appears at the point G1. In case now 
the brightness of the object to be photographed is in a range in which the 
proper exposure can be obtained, the voltage appearing at the point G2, 
half wave rectified by means of the diode 120 and the condenser 121 in the 
detecting circuit 115 is between the low threshold value VL and the high 
threshold value VH so that no current flows through L1 and L2 in such a 
manner that the switches SW14, SW15, SW16 and SW17 are all connected to 
the side of a. Consequently, the A.C. output voltage of the step up 
circuit 111 are applied to the both ends A and B of the transparent 
resistance layer 78 of the liquid crystal cell 119 so as to establish an 
inclination of the electrical potential, whereby the transparent electrode 
layer 77 assumes the same electrical potential as at the point G1 in such 
a manner that by means of the liquid crystal cell 119 the value 
corresponding to the brightness of the object to be photographed, the 
shutter time value or the aperture value operated out of the brightness of 
the object to be photographed and the preset value so as to obtain the 
proper exposure is displayed. In this way, the photographic informations 
are displayed in an analog way by means of the liquid crystal cell when 
they are in the range in which the proper exposure can be obtained. 
When on the other hand, the brightness of the object to be photographed is 
too high or too low for the preset shutter time or the preset aperture 
value to get the proper exposure, the voltage appearing at the point G2 is 
higher than the high threshold value VH or lower than the low threshold 
value VL so that a current flows through the coil L1 or L2 in such a 
manner that the switches SW14, SW15, SW16 and SW17 are connected to the 
side of b. Consequently, the A.C. output of the step up circuit 111 is 
supplied to the rectifier circuit 116 through the switch SW14 so as to 
actuate the low frequency oscillation circuit 117 whose output voltage is 
applied to the transparent resistance layer 78 of the liquid crystal cell 
119. Because at this time, the transparent electrode layer 77 is at the 
earth potential through the switch SW7, the display plane of the liquid 
crystal cell assumes the transparent state and the untransparent state 
periodically as mentioned above. The period is that of the multi-vibrator 
and the visible speed. 
Because as explained above the constants of the voltage level detecting 
circuit are chosen in such a manner that when the photographic 
informations are in the range in which the proper exposure can be obtained 
the electrical potential at the point G2 is between the low threshold 
value VL and the high threshold value LH of the voltage level detecting 
circuit 115, the above mentioned alarm display is automatically carried 
out when the photographic informations are out of the range in which the 
proper exposure can be obtained. It goes without saying that by properly 
chosing the circuit constants the alarm for the unstable manual holding of 
camera for the long exposure time can be carried out in case of the 
automatic exposure camera with priority on aperture value. 
Below the operation for the check of the power source will be explained. At 
this time, the switches SW12 and SW13 are changed over to the side of b. 
In this state, the voltage of the power source 112 is, instead of the 
electrical potential at the point G1 as the light measurement information, 
applied to the voltage level detecting circuit 116 through the switch SW12 
and the variable resistance 122. The operation after this is as follows. 
When in the same way as in case of the above mentioned photographic 
informations the applied voltage is between the low threshold value VL and 
the high threshold value LH a line shaped display in accordance with the 
power source voltage is carried out by means of the liquid crystal cell 
119 in such a manner when the voltage of the consumed battery is lower 
than the threshold value VL the periodical alarm display is made. 
FIG. 27(a) and (b) respectively show a disoplay mode in the view finder 
when the above mentioned liquid crystal cell is built in the view finder 
optical system in a single reflex camera in the same way as in case of the 
embodiment shown in FIG. 2. In FIG. 27, 4P is the view field frame, 4I the 
display window, 25 the untransparent display and 12F the line of figures 
of the aperture value provided on the upper side of the focus plate. FIG. 
27(a) shows that the proper exposure can be obtained with the preset 
shutter time whereby the proper aperture value is 8. FIG. 27(b) shows the 
state of the alarm display, whereby in the display window 4I the 
transparent state (I) and the untransparent state (II) appears one other 
another. Because the display window 4I of the mask is made a little 
smaller than the liquid crystal cell, at this time the untransparent part 
at the end of the liquid crystal cell in the state (I) can not been seen 
in the display window. 
Below further another embodiment will be explained. In this embodiment the 
over-exposure and the under-exposure can be displayed at the time of the 
exposure alarm display. In case of this embodiment the liquid crystal cell 
100A shown in FIG. 13(a) is applied. FIG. 28 shows the electrical circuit 
diagram. This circuit is so designed that a switch SW18 is added to the 
circuit shown in FIG. 25 and a switch SW19 is provided instead of the 
switch SW17. The switch SW18 is a relay switch mechanically linked with 
the coil L2 in such a manner that the switch SW18 is charged over to the 
side of b when a voltage higher than the high threshold value VH is 
applied to the point G2 of the voltage level detecting circuit 115, so as 
to keep the transparent electrode layer 33 of the liquid crystal cell 100A 
at a high electrical potential. Further the switch SW19 is a relay switch 
mechanically linked with the coil L1 in such a manner that the switch SW19 
is changed over to the side of b when a voltage lower than the low 
threshold value VL is applied to the point G2 of the voltage level 
detecting circuit 115, so as to keep the transparent electrode layer 33 at 
the earth potential. Other parts of this circuit are same as shown in FIG. 
25. 
FIG. 29(a) and (b) respectively show a diagram for explaining the operation 
of the circuit shown in FIG. 28. When the voltage VAB is applied between 
the both ends A B of the electrode of the liquid crystal cell 100A, on the 
side on which the transparent resistance layer 36 and the transparent 
electrode layers 34a and 34b are provided, an inclination of the potential 
difference appears as is shown by the folded line MAB. Because when now a 
voltage higher than the threshold value VH is applied to the point G2 of 
the voltage level detecting circuit 115 a current flows through the coil 
L2, the switches SW14, SW15, SW16 and SW18 are changed over to the side of 
b. Consequently the transparent electrode layer 33 is kept at a high 
electrical potential Vc as is shown in FIG. 29(a), an untransparent 
display as X26 including the part of the transparent electrode 34a appears 
in the liquid crystal cell 100A. Because however, in the same way as in 
case of the embodiment shown in FIG. 25 the low frequency oscillation 
circuit is operating, the display X26 and the display X27 appears one 
after another periodically. When on the other hand, a voltage lower than 
the low threshold value VL is applied to the point G2 of the voltage level 
detecting circuit 115, a current flows through the coil L1 so that the 
switches SW14, SW15, SW16 and SW17 are changed over to the side of b. 
Consequently the transparent electrode layer 33 is kept at a low 
electrical potential Vc as is shown in FIG. 29(b) so that an untransparent 
display as X28 including the part of the transparent electrode 34b appears 
in the liquid crystal cell 100A. The low frequency oscillation circuit is 
operating at this time also, the display X28 and the display X29 are made 
one after another periodically. Further when a voltage between the low 
threshold value VL and the high threshold value LH is applied to the point 
G2 of the voltage level detecting circuit 115, no current flows through 
the coils L1 and L2, so that the switchs SW14, SW15, SW16, SW17 and SW18 
are all changed over to the side of a, in such a manner that in the same 
way as in case of the above mentioned embodiment an analog display is 
carried out by means of the transparent electrode layer 33 and the 
transparent resistance layer 36 of the liquid crystal cell 100A. 
FIG. 30(a) and (b) respectively show a display mode in the view finder when 
the liquid crystal cell is built in a camera in the same way as in case of 
the above mentioned embodiment. At the time of the over-exposure the 
untransparent parts X26 and X27 appears one after another in the display 
window 4I as is shown in FIG. 30(a) so as to give alarm, whereby the 
untransparent part X26 displays the over-exposure alarm. At the time of 
the under-exposure the untransparent parts X28 and X29 appears one after 
another in the display window 4I as is shown in FIG. 30(b), so as to give 
alarm, whereby the untransparent part X28 displays the under-exposure. 
In case of this embodiment the battery can be checked in the same way as in 
case of the above mentioned embodiment, whereby when the battery is 
consumed, the same alarm as is shown in FIG. 30(b) is displayed in the 
view finder. 
Below the battery alarm display device by means of a liquid crystal cell in 
accordance with another principle will be explained. The liquid crystal as 
is shown in FIG. 1 is applied to this principle. FIG. 31 shows the circuit 
diagram of an embodiment of this battery alarm display device. In this 
embodiment the liquid crystal cell for the battery alarm serves for the 
light measurement display for the camera at the same time whereby the 
battery can also be checked at any time by changing over the switch. In 
FIG. 31, 211 is the liquid crystal cell, 212 the power source battery, 213 
the step up circuit and 214 the three terminal light sensing element for 
sensing the light of the object to be photographed. 215 and 216 are the 
fixed resistances, SW20 the power source switch, SW21 the change over 
switch. The above mentioned step up circuit 213 consists of the transistor 
inverter, whose operation principle is as follows. When the power source 
switch SW20 is closed, a current flows through the coil Nc of the 
transformer through the condenser 210, whereby the voltage then induced in 
the coil NB brings the transistor 217 in the switched on state. The 
collector current corresponding to the base current controlled by means of 
the base resistance R13 is limited below a certain determined value so 
that the core looses the magneto-motive force in such a manner that the 
voltage in the coil Nc disappears suddenly. Consequently the transistor 
217 is brought in the switched off state quickly, whereby at the next 
moment by means of the energy stored in the transformer 218 the transistor 
217 is biased again in order. By repeating this operation an A.C. voltage 
VAB corresponding to the turn ratio is produced in the output coil N.sub.o 
of the transistor 218. 
FIG. 32 shows a diagram for explaining the principle for giving a battery 
alarm by means of the device shown in FIG. 31. As is shown in FIG. 32, 
when a voltage V1 is applied to the both end of the transparent resistance 
layer 204 of the liquid crystal cell an inclination of the electrical 
potential represented by a line Q1 takes place on the transparent 
resistance layer 204. When on the other hand, a voltage KV1 (0&lt;K&lt;1) is 
applied to the transparent electrode layer 203 the electrode 203 is kept 
at the voltage KV1 all over the layer.Thus the range Y1 in which the 
potential difference for operating the liquid crystal is higher than the 
electrooptical threshold value Vth is optically modulated as mentioned 
above so as to allow the passage of the light, while the range in which 
the potential difference is lower than Vth is not optically modulated so 
as to interrupt the passage of the light, giving a display as D11. When 
now the voltage applied to the transparent resistance layer 204 lowers 
down to V2 the inclination of the electrical potential on the transparent 
resistance layer 204 becomes dull as is shown by Q2 whereby the electrical 
potential on the transparent electrode layer 203 becomes KV2. At this 
time, consequently, a wide untransparent range W3 as D13 appears so as to 
alarm the consumption of the battery. The ranges W1 and W3 have a common 
central position so that if an index with standard width for the 
unconsumed battery is provided here, the consumed degree of the battery is 
clearly displayed. 
As explained above, when the polarization direction of the upper 
polarization plate is made perpendicular to that of the lower polarization 
plate, the transparent and the untransparent range are exchanged for each 
other so that instead of D11 and D13 the display like D12 and D14 are 
obtained. At this time for example, by means of enlarging the transparent 
range W2 up to W3 the device can be designed in such a manner that the 
alarm mark covered with the untransparent range Y2 can be visually 
recognized. 
Below the operation of the embodiment shown in FIG. 31 and FIG. 32 will be 
explained. When the battery is checked, the switch SW21 is changed over to 
the side of b. When the power source switch SW20 is closed the step up 
circuit 213 operates in such a manner that the A.C. output voltage VAB is 
applied to the transparent resistance layer 204 of the liquid crystal cell 
211. Further the voltage VAB is divided by means of the resistances 215, 
216 in such a manner that KVAB (0&lt;K&lt;1) is applied to the transparent 
electrode layer 203. When at this time, the voltage of the power source 
battery is sufficiently high a high voltage V1 can be obtained from the 
step up circuit accordingly so that a narrow untransparent range W1 is 
displayed as is shown by D11 in FIG. 32. When the power source battery is 
consumed and the output voltage is lowered, only a low voltage V2 can be 
obtained from the step up circuit 213 accordingly so that a side 
untransparent range W3 as is shown by D13 in FIG. 32 is displayed for 
alarm. 
When on the other hand, the device is used as the light measurement 
display, the switch SW21 is changed over to the side of a. At this time 
also the output voltage VAB of the step up circuit 213 is applied to the 
transparent resistance layer 204 of the liquid crystal cell 211. The 
voltage Vc applied to the transparent electrode layer 203 at this time 
varies in proportion to the logarithm of the amount of the light incident 
on the light sensing element 214. The untransparent range displayed by 
mean of the liquid crystal cell 211 corresponds to the amount of the 
incident light. 
As explained above in accordance with the above mentioned embodiment the 
battery alarm and the measured light value are displayed by means of the 
same liquid crystal cell. Further the A.C. voltage from the step up 
circuit is applied to the liquid crystal cell so that the durability of 
the cell itself is improved. 
FIGS. 33(a), (b) and (c) respectively show a display mode in the view 
finder when the above mentioned embodiment is built in the view finder of 
a single reflex camera in the same way as in case of the embodiment shown 
in FIG. 2. In the drawing, 4P is the view field frame, 4I the display 
window, X30, X31 and X32 the untransparent displays of the liquid crystal 
cell and 4Q the index notch provided in the mask 4 for showing the 
standard width for the above mentioned battery alarm, also capable of 
serving as the fixed point for actual diaphragm driving light measurement. 
FIG. 33(a) shows the case of the measured light display, whereby the 
untransparent display X30 moves in the display window 4I so as to make a 
display in accordance with the measured light value. FIG. 33(b) shows the 
mode at the time of the battery check whereby the setting is made in such 
a manner that the untransparent display X31 comes beside the index 4Q in 
accordance with the set value of the above mentioned resistances 215 and 
216. When the width of the display X31 is narrower than that of the index 
4Q, it means that the power source battery can sufficiently be used. When 
the power source battery is consumed the width of the untransparent 
display X32 is wider than that of the index 4Q as is shown in FIG. 33(c) 
so as to give alarm. 
In this way, the untransparent display at the time of the battery check 
always appears beside the index 4Q, whereby further the width of the index 
4Q is set at the width of the untransparent display when the voltage of 
the power source battery is suited for operating the circuit of the camera 
in order in such a manner that the battery checking can be carried out 
clearly while no inferior influence is given to the light measurement of 
the camera or the film because no illuminating element such as LED is 
used. Further when the above mentioned liquid crystal cell carries out the 
light measurement display, the consumption of the power source battery is 
judged by the fact that the width of the untransparent display X30 becomes 
wide in accordance with the same principle as in case of the battery 
checking. 
Below a device by means of which a large alarm is displayed in the finder 
view field independent of the analog display will be explained. FIG. 34 
shows the composition of an embodiment of this device, whereby a large 
alarm is displayed in the view finder when the shutter has been charged. 
In the drawing 304 is the mask, 302 and 308 the polarization plates, and 
303 the glass base plate on which a transparent electrode 305 is provided. 
306 is also a glass base plate on which a transparent electrode 307 with 
the shape for alarm display is provided. 304 is the space to be filled 
with the liquid crystal. E4 is the power source, SW25 the switch to be 
opened when the shutter has not yet been charged and to be closed when the 
shutter has been charged. 
FIGS. 35(a) and (b) respectively show a concrete composition of the above 
mentioned switch SW25. FIG. 35(a) shows the mode when the shutter has been 
charged, while FIG. 35(b) shows the mode when the shutter has not been 
charged. In these drawings, 310 is the release lever, 311 the holding claw 
rotatable around the shaft 314 as center, 312 the shutter disk for driving 
the focal shutter plane not shown in the drawing and 315 the release 
lever. 
Below the operation of the composition shown in FIG. 34 and FIG. 35 will be 
explained. When the shutter has been charged as is shown in FIG. 35(a) the 
switch SW25 is opened so that no voltage is applied to the liquid crystal 
whereby no alarm is displayed in the view finder. When the shutter is 
released and the holding claw 311 is rotated along the counter clockwise 
direction against the force 313, the shutter disk is free so as to finish 
the photographing, while at the same time, the switch SW25 is opened so 
that a voltage is applied to the liquid crystal so as to display an alarm 
in the view finder that the shutter is not wound up. 
Further in case of the composition shown in FIG. 34, the glass base plates 
303 and 306 can serve as the condenser lens and the focus plate at the 
same time. In case of the so far mentioned embodiments, the photographic 
information or the alarm is displayed by the untransparent display in the 
display window or the view field frame, whereby when the direction of the 
polarization plane of the upper polarization plate is made perpendicular 
to that of the lower polarization plate the transparent part and the 
untransparent part can be exchanged for each other. Further the alarm can 
be display in color effectively when a color filter is provided in front 
of the liquid crystal or a color polarization plate is combined with the 
liquid crystal cell. 
It goes without saying that not only the FE type liquid crystal cell as 
mentioned above but also the DSM type liquid crystal cell can be applied 
to the present invention. 
Further by means of the display device in accordance with the present 
invention the photographic information, the alarm and so on can be 
displayed clearly in the view finder of not only the single reflex camera 
but also the range finder camera or the pocket camera without using the 
ampere meter or other complicated link mechanism, whereby the device is 
hard to be damaged and economical for production, being consisting of a 
liquid crystal cell. 
Below the device in which one liquid crystal cell provided in a camera or 
so can be observed along the two directions by making use of the 
transparency of the cell will be explained. 
FIG. 36 shows in embodiment of such a liquid crystal display device in 
section. In the drawing, 451 is the liquid crystal cell connected to a 
control means (not shown in the drawing) so as to display transparent 
letters or figures, 452 the lens, 453 the mirror, 454 the screen, 455 the 
casing serving as the mask means at the same time, 456 the first window 
and 457 the second window. When in this composition, a display control 
signal is applied to the liquid crystal display cell 451 the cell 451 
makes a transparent display so that the second window 457 acts as the 
lighting window in such a manner that the light is guided by means of the 
mirror 453 and the lens 452 so that the display output of the liquid 
crystal cell 451 can be visually recognized through the first window 456. 
On the other hand, the first window 465 acts as the lighting window and 
the display output light of the liquid crystal cell 451 is formed on the 
screen 454 through the lens 452 and the mirror 453 so that the display 
output of the liquid crystal display cell 451 can be visually recognized 
from the second window 457. In this way, the device can easily be designed 
that the display of one display part can be visually recognized from the 
two positions. 
FIG. 37(a) and (b) respectively show the first and the second embodiment of 
such liquid crystal display device applied to a single reflex camera, 
whereby the embodiments are cut in the neighborhood of the pentagonal 
prism. In case of the first embodiment shown in FIG. 37(a), 401 is the 
first information display window, 402 the view finder window serving as 
the second information display window at the same time, 451 the liquid 
crystal display cell for carrying out the transparent display, 403 the 
camera casing, 404 the prism for guiding the display output light of the 
liquid crystal display cell 451, 405 the pentagonal prism, 418 the 
condenser lens having a half permeable mirror, 406 the light sensing 
element for sensing the incident light for measurement from the condenser 
lens, 408 the photographic information setting circuit for producing the 
preset value or the film sensitivity value and 407 the operation circuit 
connected to the photographic information setting circuit 408 and the 
light sensing element 406 for producing the display signal for the above 
mentioned liquid crystal display cell 451. 419 is the focus plate, 410 the 
mirror, 409 the photographic lens and 444 the mask. 
In case of the composition shown in FIG. 37(a) by means of the display 
signal from the operation circuit 407, the liquid crystal display cell 451 
display the photographic informations such as the operated value, the 
preset value, the alarm signal and so on in a transparent way. At this 
time, the first information display window acts as the lighting window 
whereby the display output light of the liquid crystal display cell 451 
can be visually recognized from the view finder window 402 through the 
prism 404, the pentagonal prism 405, and again the prism 404 as is shown 
by the arrow in the drawing. On the other hand, the view finder window 402 
also acts as the lighting window, whereby the light is guided to the 
liquid crystal cell 451 along the inversed optical path so as to be 
visually recognized through the first information display window. 
When hereby the length of the optical path from the display plane of the 
liquid crystal display cell 451 to the view finder window 402 is chosen so 
as to be equal to that of the optical path from the focus plate 419 to the 
view finder window 402, the object to be photographed and the information 
display are seen respectively at the same position in the finder view 
field. 
In the second embodiment shown in FIG. 37(b), the same elements as in case 
of the first embodiment have the same figures, whereby the mirrors 415 and 
417 and the lens 416 compares the light guide part from the liquid crystal 
display cell 451 to the first information display window 401, while 413 is 
the plate for shading the light guide part from the photographic optical 
system. In the second embodiment the liquid crystal display cell 451 is 
provided beside the focus plate so that the information display is made 
beside the object to be photographed, whereby in the same way as in case 
of the above mentioned embodiment a clear finder view field can be 
obtained by means of the mask 444. 
As explained above in detail the pair of the windows of the present 
embodiment respectively act as the window of the light incident on the 
liquid crystal and as the window for the light coming out of the liquid 
crystal alternatively, whereby the most important feature is the double 
direction. 
Below the device for illuminating the liquid crystal cell in a dark place 
when the liquid crystal cell is used as the view finder display in a 
camera will be explained. 
FIG. 38 shows the driving circuit for the liquid crystal cell and the 
illuminating lamp in the present embodiment. In this embodiment an 
illuminating lamp is used as illuminating body. In the drawing, 511 is the 
power source battery, 513 the photoconductive element (hereby CdS is 
used), 512 the dividing resistance and 514 the operation amplifier between 
whose inversing terminal and whose output terminal a no load feed back 
circuit is connected so as to compose a buffer circuit. 515 is the 
illuminating lamp provided behind the liquid crystal so as to illuminate 
the liquid crystal. 516 is the current limiting resistance for controlling 
the current to be supplied to the illuminating lamp, 517 the transistor 
connected in series with the illuminating lamp and 524 the operation 
amplifier forming a non-inversing amplifier with the resistances 519 and 
520. 518 is the transistor connected parallel to the non-inversing input 
terminal of the operation amplifier 524, and 521 the transistor connected 
to the output terminal of the operation amplifier 524. 523 is the DC-AC 
inverter, namely the transistor type two stone inverter. 522 is the liquid 
crystal cell to be driven by A.C. voltage. 
Below the operation of the driving circuit for the above will be explained. 
A voltage corresponding to the amount of the light incident on CdS 513 is 
produced at the output terminal of the operation circuit 514 in such a 
manner that at the output terminal of the operation circuit 540, an output 
voltage amplified by the ratio of the value of the resistance 520 to that 
of the resistance 519. 
On the other hand, at the output terminal of the above mentioned DC-AC 
inverter another trap 524 is provided in such a manner that by means of 
the output voltage from the trap 524 the above mentioned transistor 518 is 
switched on and off. Thus at the output terminal of the transformer 521 an 
A.C. voltage is produced with the same frequency as that of the output 
A.C. voltage of the DC-AC inverter, being synchronized with the output 
A.C. voltage. Thus produced output voltage is applied to the C electrode 
of the liquid crystal cell 522, on which the light measurement information 
is displayed. 
Below the driving principle of the illuminating lamp 515 for illuminating 
the liquid cell will be explained. 
When the brightness of the object to be photographed is lowered while the 
resistance value of CdS 513 is raised, the output voltage of the operation 
amplifier 514 goes up until it surpasses a certain determined level in 
such a manner that the transistor is switched on and the illuminating lamp 
515 is lit up. Hereby the resistance 530 is adjusted in such a manner that 
the above mentioned illuminating lamp 515 is lit up when the visual 
acknowledgement of the display in the view finder becomes difficult. 
As explained above, in accordance with the embodiments in accordance with 
the present invention, a finder liquid crystal display device which is 
bright even in a dark place can be offered, whereby the illuminating body 
illuminates automatically when it is dark, so as to prevent from 
illuminating alway and thus to minimize the power consumption, which 
practical effect is very large.