Optical device

This disclosure relates to an optical device which includes means for forming a pair of images in an optical channel and means for viewing the images. The viewing means includes a liquid crystal display, an eyelens, and an analyzer arranged between the liquid crystal display and the eyelens. In order to provide for selectively viewing one of the images, the image forming means is adapted to orthogonally polarize the images and project the polarized images onto the liquid crystal display. When the display is energized, one of the images can be viewed through the eyelens; and when the display is unenergized, the other image can be viewed through the eyelens.

FIELD OF THE INVENTION 
The present invention relates to an optical device, and more particularly, 
to an optical device which is particularly adapted for use as a viewfinder 
in apparatus such as a camera. 
DESCRIPTION OF THE PRIOR ART 
In many optical devices, it is desirable to display information from two 
separate sources. For example in the viewfinder of a camera, it is 
desirable to see the subject as well as to have information displayed 
concerning camera data, such as shutter speed or light conditions. An 
ideal viewfinder for cameras should provide a clear, unobstructed view of 
the subject and equally clear graphics when indicating camera data. In 
prior art viewfinders, such data is normally displayed around the margin 
of the image in order not to obscure the picture area. 
U.S. Pat. No. 4,140,378, discloses a viewfinder having a liquid crystal 
cell within the viewfinder. Mask means are provided to cover a portion of 
the liquid crystal cell so that only a display part of the cell is shown 
within the viewfinder, and a light source is operable in response to a 
brightness detecting circuit to illuminate the liquid crystal cell. A 
problem with the patented viewfinder is that the liquid crystal cell and 
the mask means for the cell take up a portion of the viewfinder, thereby 
reducing the size of the viewing area. A further disadvantage is that only 
a very limited amount of data can be displayed in a liquid crystal cell of 
the type disclosed in the patent. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to overcome the problems in the 
prior art noted above and to provide an optical device which can 
selectively provide a clear unobstructed view of an image from either of 
two sources. 
In accordance with one aspect of the invention, there is provided an 
optical device comprising: means for forming two images on a liquid 
crystal display; and means for selectively viewing one of the images 
independently of the other. 
In accordance with another aspect of the invention, there is provided a 
viewfinder comprising means for forming an image of a scene, means for 
producing graphic information, means for viewing the image and the 
information, the viewing means including a liquid crystal display 
characterized in that the forming means comprises means for forming an 
image of the information and means for projecting the images onto the 
liquid crystal display, and the viewing means comprises means for viewing 
the images independently of each other. 
In one embodiment of the present invention, a first image, for example 
graphic information, is transmitted along one optical channel to a 
polarizing beam splitter, and a second image, for example a scene, is 
transmitted along a second optical channel to the beam splitter. A 
polarizer is disposed in each optical channel such that the images are 
orthogonally polarized. The orthogonally polarized images are projected 
onto a liquid crystal display. When the liquid crystal display is 
energized, one of the images can be viewed through an analyzer, and when 
the display is not energized, the other image is seen through the 
analyzer. 
The present invention provides an optical device which is particularly 
suitable for selectively viewing images from two different sources. In one 
embodiment of the invention, either one of the images can be viewed over 
the entire viewing area of the device; an advantage of this arrangement is 
that the device can be made smaller than would otherwise be possible, 
inasmuch as a portion of the viewing area is not taken up by a display 
such as a liquid crystal display. It is also possible, by energizing 
different portions of the liquid crystal display, to view two or more 
images adjacent each other.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
With reference to FIG. 1, there is shown an optical device 10 constructed 
in accordance with the present invention. Optical device 10 comprises 
image forming means 15 and image viewing means 17. Image forming means 15 
includes an objective lens 12 which is adapted to form an image of an 
object 11 along a first optical channel 13, a field lens 14, a polarizer 
16, and a polarizing beam splitter 18. A second image originates with a 
graphics-producing device 19 indicated schematically by a bulb 20 and a 
panel 21 having the letter E formed thereon; the second image passes 
through a polarizer 22 and travels along an optical channel 24 to beam 
splitter 18. The direction of polarization of light passing through 
polarizer 16 is at an angle of 90.degree. to the direction of polarization 
of light passing through polarizer 22. 
From polarizing beam splitter 18, both images pass through a relay lens 
group 30 and are transmitted to the image viewing means 17 which includes 
a liquid crystal display 34. From display 34, the images pass through an 
analyzer 36, a field lens 38, and an eyelens 40. 
As shown in FIG. 1, display 34 comprises a liquid crystal 35 which is 
sandwiched between glass supporting plates 37 and 39; electrodes 41 and 43 
are mounted respectively on plates 37 and 39. The construction of liquid 
crystals is well known in the art, and thus, their construction will not 
be explained herein in detail. The liquid crystal 35 can be of the nematic 
type and consist, for example, of p,p'-din-butylazoxy benzene, and it can 
be about 0.015 mm in thickness. Other elements can also be used to perform 
the function described herein for liquid crystal 35. For example, solid 
electro-optic crystals or ceramic crystals can also be used. 
Control of display 34 can be effected by energizing liquid crystal 35 with 
a voltage of about 10 volts AC. The voltage to liquid crystal 35 could be 
turned on and off, for example, by movement of a camera shutter release 
(not shown). The inside surfaces of the supporting plates 37 and 39 are 
provided in a known manner with parallel grooves (not shown), and the 
direction of the grooves in the plate 37 is at a right angle to the 
direction of the grooves in plate 39. If there is no voltage between 
electrodes 41 and 43, the molecules of the liquid crystal 35 will orient 
parallel to the grooves in the layers adjoining plates 37 and 39, since 
the elastic deformation energy in the layer is then at a minimum. 
Consequently, a twisted configuration is formed in the liquid crystal 35, 
the orientation of the molecules changing gradually through the thickness 
of the crystal 35. Such a twisted configuration has the property of 
rotating the direction of polarization of incident linearly polarized 
light. The linear polarization of the light is then maintained when the 
direction of polarization of the incident light is parallel to or at right 
angles to the orientation of the molecules on the side where the light is 
incident. Thus, in display 34, the direction of polarization is rotated 
through 90.degree. in the unenergized condition, and in the energized 
condition, the light is passed without rotation of the direction of 
polarization. Analyzer 36 is, in fact, a polarizer. 
In the operation of device 10, two othogonally polarized images, indicated 
schematically in FIGS. 2 and 3 by superposed letters T and E, are 
presented to display 34. In the energized state of liquid crystal 35, both 
images would pass through display 34 without change, and with analyzer 36 
set to receive horizontally polarized light, the viewer would see the 
letter T. In the unenergized state of liquid crystal 35 the direction of 
polarization would be rotated 90.degree., and the viewer would see the 
vertically polarized image, that is the letter E. In the operation just 
discussed, the position of analyzer 36 does not change in the energized 
and unenergized states. Under some conditions, however, it may be 
desirable to see the images superposed. To obtain this condition, analyzer 
36 must be rotated to a 45.degree. angle to the horizontal and the liquid 
crystal 35 must be in the unenergized state. In the event device 10 is 
used as a viewfinder in a camera (not shown), graphic data, for example 
shutter speed, could be superposed on a view of the subject; in this 
application, the data would appear as an opaque luminous display in front 
of the scene. 
Any area of the liquid crystal 35 can be selectively energized by 
techniques well known in the art. In FIGS. 2 and 3, the electrodes extend 
over essentially the entire viewing area, and thus, with analyzer 36 
fixed, the viewer sees either one image or the other. In FIGS. 4a-4c, 
there are shown a series of diagrams which illustrate another embodiment 
of applicant's invention in which only a portion of the liquid crystal 35 
is energized. In FIG. 4a, the two orthogonally polarized images, indicated 
by the words "test" and "scene" are shown as they are presented to display 
34. In FIG. 4b, the images are shown after they have passed through liquid 
crystal 35 in which a left portion 50 has passed through an energized 
portion of liquid crystal 35 and a right portion 52 has passed through an 
unenergized portion of liquid crystal 35. In FIG. 4c, the images are shown 
after passing through analyzer 36 and as they would be seen by the viewer. 
If such an arrangement was used in a viewfinder of a camera, the viewer 
could have a constant view of the scene and also receive camera 
information in the viewfinder during any desired portion of a 
picture-taking cycle. 
It will be apparent that the present invention could be used to selectively 
view more than two images. For example, two devices 10 could be placed in 
a cascade arrangement to achieve such a result. Also, a movable mirror 
could be located to direct a selected one of a plurality of images along 
one of the channels 13, 24. 
The invention has been described in detail with particular reference to 
certain embodiments thereof, but it will be understood variations and 
modifications can be effected within the spirit and scope of the invention 
.