Photography – Having camera indicator – Having display in viewfinder
Reexamination Certificate
2001-06-19
2003-10-14
Adams, Russell (Department: 2851)
Photography
Having camera indicator
Having display in viewfinder
C396S374000, C348S333010
Reexamination Certificate
active
06633731
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electronic view finder apparatus that is suitably used in, for example, a video camera apparatus. More particularly, the invention concerns an electronic view finder apparatus adapted to observe a video display apparatus, such as an LCD, having the characteristic of Viewing-Angle by magnifying it with the use of an ocular lens unit, which can enhance the contrast of the image depending upon the characteristic of Viewing-Angle by making proper the relative disposition between the video display apparatus and the ocular lens unit.
2. Description of the Prior Art
Conventionally, in an electronic view finder for use in a video camera apparatus, a small-sized CRT (cathode ray tube), LCD, etc. is mainly used as the video display apparatus; and, it is arranged so that the image of the video display apparatus is observed by being magnified through the use of an ocular lens unit. However, because the CRT has a long size in the depth direction, as measured from the image screen surface, it is unsuitable for being used in a small-sized video camera apparatus. Also, the LCD is small in size and light in weight, and, in addition, the number of pixels thereof has in recent years been remarkably enhanced. Therefore, it also becomes sufficiently practical to perform focusing with respect to the image of the finder, so that the LCD has been widely diffused over a high grade of apparatus as well.
By the way, in the video display apparatus using a CRT, even when the image screen surface is looked at from an oblique direction with the direction in which to observe it being more or less shifted from the front, brightness or contrast of the image does not change sensitively. However, in case of an LCD, when looking at the image screen surface from an oblique direction, the brightness or contrast sensitively changes. In addition, when having observed the image screen surface from the front, the best contrast is not always obtained. There is also a case where the contrast becomes the best when observing the image screen surface from a direction that is oblique by a prescribed degree of angle with respect to a prescribed azimuth angle. This characteristic in which the brightness or contrast depends upon the direction in which to observe is referred to as “the characteristic of Viewing-Angle”.
While there are some kinds of liquid crystals for use in an LCD, the liquid crystal that is most widely used is TN (Twisted Nematic) type liquid crystal. The present invention also concerns an electronic view finder apparatus that uses therein an LCD that uses TN type liquid crystal.
Here, an explanation will be given of the operational principle that the characteristic of Viewing-Angle of the TN type liquid crystal is not symmetrical and, when this liquid crystal is looked at from a prescribed direction and at a prescribed angle, it has the best contrast.
FIG. 4
illustrates the arrangement of the liquid crystal molecules when no voltage is applied to the TN type liquid crystal.
Between two sheets of polarizing plates
10
,
11
, whose polarization directions intersect each other at a right angle, liquid crystal cells
12
and
13
are clamped in a way so as to be sandwiched therebetween. Regarding the liquid crystal cells
12
and
13
, the liquid crystal molecules
14
thereof on one liquid crystal cell
12
side are parallel with the polarizing plate
10
on the light incidence side. On the other hand, on the other liquid crystal cell
13
side, they are twisted through an angle of 90° and, in this state, they become parallel with the polarizing plate
11
on the light emission side. Accordingly, the back light that has entered the liquid crystal from the polarizing plate
10
side on the light incidence side is linearly polarized by the polarizing plate
10
. Thereby, as in the case of the liquid crystal molecules
14
, the back light is twisted (rotated) by 90° and goes out of the polarizing plate
11
. Namely, the LCD looks white.
FIG. 5
illustrates the arrangement of the liquid crystal molecules when a voltage has been applied across transparent electrodes (not illustrated) between the liquid crystal cells
12
and
13
.
According to this arrangement, the liquid crystal molecules
14
become vertical with respect to the liquid crystal cells
12
and
13
along the electric field that has been applied as above. As a result of this, the rotatory action does not occur. Accordingly, the back light that has entered from the polarizing plate
10
side on the light incidence side is interrupted by the polarizing plate
11
on the light emission side. Resultantly, the LCD looks black.
By the way, speaking strictly, the liquid crystal molecules
14
illustrated in
FIG. 5
have only their liquid crystal molecules alone that are in contact with the liquid crystal cells
12
and
13
influenced by the inter-molecular attractive force between themselves and high-molecular thin film surfaces coated on the surfaces of the liquid crystal cells. For this reason, those liquid crystal molecules, owing to this influence, don't completely become vertical with respect to the liquid crystal cells
12
and
13
but become slightly rotated. Namely, the LCD doesn't completely look black.
FIG. 6
illustrates the relationship between the voltage (V) applied across the liquid crystal cells and the transmittance (T). This graphic diagram is an example of the V-T characteristic (&thgr;=0°) as measured in the vertical direction of the LCD. As apparent from this graphic diagram, applying a high voltage to the liquid crystal cells results in the transmittance becoming zero. However, for the reason that the liquid crystal molecules become slightly rotated, as stated above, that transmittance doesn't completely become zero. Also, applying a high voltage is not realistic because of the problems with the withstanding voltage of a device constituting the drive circuit, the unnecessary increase in the voltage consumption, etc. Accordingly, in general, the black signal voltage level of the LCD is set to 4 volts.
Also, the white signal voltage of the LCD is set to 1.5 volts, whereby through applying a signal voltage of 4 to 1.5 volts, colors from black to gray to white are displayed.
Here, the degree of excellence of the contrast of the brightness of the LCD is quantitatively defined in terms of the contrast ratio between the transmittance at the time of applying a white signal voltage and the transmittance at the time of applying a black signal voltage. Namely, because the transmittance corresponding to 4 volts is 2%, the contrast ratio in this case is 100/2=50.
FIG. 7
illustrates the V-T characteristic with regard to the oblique direction in addition to the V-T characteristic (&thgr;=0°) with regard to the vertical direction of the LCD of FIG.
6
. Namely, as stated previously, even when a high voltage is applied, the liquid crystal molecules that are in contact with the liquid crystal cells are not completely vertical with respect to the liquid crystal cells. Namely, they are more or less inclined and thereby have a certain low level of rotatability. When the LCD is looked at from that inclined direction, that low level of rotatability is relatively mitigated. As a result, even when applying the same black signal voltage, the LCD looks black.
For example, the V-T characteristic (&thgr;=10°) is such that when the black signal voltage is 4 bolts, the transmittance is approximately 0.1%. Therefore, the contrast ratio becomes 100/0.1=1000. The contrast ratio, therefore, is greatly improved. Conversely, when the LCD is looked at from a side of promoting the rotatory polarization, the V-T characteristic (&thgr;=−10°) is such that when the black signal voltage is 4 volts, the transmittance is approximately 10%. Therefore, the contrast ratio becomes 100/10=10, which indicates that the contrast ratio becomes greatly deteriorated.
SUMMARY OF THE INVENTION
The present invention has been made in
Isogawa Toshiaki
Nanjo Yusuke
Adams Russell
Blackman Rochelle
Kananen, Esq. Ronald P.
Rader & Fishman & Grauer, PLLC
Sony Corporation
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