a) (prior art) shows the image formation of a normal person when a point object is at infinity, and
a) (prior art) shows the image formation of a hyperopic person when a point object is at the hyperopic near point,
a) shows a small screen and a large screen at the normal near point, and
a) shows the image formation of a normal person when a display is placed closer than the normal near point without and
a) shows two screens 28 and 30 at normal near point A, which is 25 cm from an eye 32. The view angles of screens 28 and 30 are α and β, respectively. If small screen 28 is moved toward eye 32 so that view angle is β as shown in
To produce the view angle of small screen 28 β as shown in
However, when an object is located at F (
Reading eyeglasses 36 can also be replaced by goggles, or glasses with a frame extended from a cap or helmet. Portable device 40 can be a portable video player, a cell phone, a digital camera, a video game player, or a pocket TV.
For example, to magnify the display (2.5″ or 6.25 cm in diagonal) of an iPod video player, the video player is held at a distance less than the distance of the normal near point to the eye. If the normal near point is 25 cm from the eye, to magnify the display two times, the video player is held at 12.5 cm from the eye. To magnify the display three times, the video player is held at 8.33 cm from the eye. And so on.
The view angle of a screen in a theater is usually between 260 to 360, and the typical value is 30°. A 2.5″ (6.25 cm) diagonal display has 2″ (5 cm) width and 1.5″ (3.75 cm) height. To get 30° view angle, the display has to be placed at a distance of 9.25 cm from the eye (tan 15°=2.5 cm/9.25 cm). So the viewer will see the screen as if watching a movie in theater. However, since 9.25 cm is less than the distance of a normal near point, a normal person cannot see the display clearly as shown in
To focus the image of an object at 9.25 cm (point F in
To accomplish this, the focal length of the positive lens must satisfy the lens equation given below.
where f is the focal length of lens, o is the object distance from the lens, and i is the image distance from the lens. Assume the lens is very close to the eye, object is +9.25 cm from the lens, and image is −25 cm from the lens. The focal length of lens will be 14.68 cm.
The dioptric power of a lens is defined as follows.
Where D is dioptric power in Diopter and f is focal length in cm. For 14.68 cm focal length, the dioptric power is +6.81 D.
The virtual image formed by the added lens becomes an object at 25 cm (point A in
In one embodiment, the added positive lens forms a virtual image at infinity. This is done so that the virtual image formed by the added lens can be clearly seen by the eye without contraction (
for o=9.25 cm and i=−∞, the focal length will be 9.25 cm. The dioptric power of the positive lens is +10.81 D.
A display placed at 9.25 cm from the eye can be clearly seen by a viewer with normal vision using a positive lens placed in front of the eye. If the focal length of lens is 9.25 cm (+10.81 D), the magnified display can be seen without any eye contraction. If the focal length is 14.68 cm (+6.81 D), the magnified display still can be seen with maximum eye contraction. A viewer with normal vision needs some contraction to see clearly the magnified display using a lens with any focal length between 9.25 and 14.48 cm. Therefore, for a person with normal vision, a 30 view angle can be achieved for an iPod by placing the device at a distance 9.25 cm from the eye and using a magnifying lens having +6.81 D to +10.81 D power.
In one embodiment, the viewer wears a pair of reading eyeglasses, for example with +4 D power. Reading eyeglasses are sold over-the-counter in the dioptric power range of +1 D to +4 D. A prescription is required for eyeglasses over +4 D power. An eyeglass with +4 D power has a 25 cm focal length. Using the same lens equation again
where f=25 cm and i=−25 cm, one obtains o=12.5 cm.
By adding this eyeglass in front of the eye, the display can be moved up to a distance of only 12.5 cm from the eye such that the magnified display can still be clearly seen by a person with normal vision. At this position, the view angle is about 23°. This is equivalent to viewing a 32″ (80 cm) large-screen TV at a distance of about 2.05 m (6.83 feet). Thus the image will be as large as a large-screen TV at home, yet will be in focus.
Accordingly, the reader will see that the small display of a portable device can be magnified by placing the device closer than the normal near point to the eye and using a positive lens placed in front of the eye by a lens mounting means. The viewer can use a pair of non-prescription reading eyeglasses, which usually have the dioptric power range of +1 D to +4 D. The viewer can also use a pair of specially made eyeglasses, which have higher power as compared with over-the-counter reading glasses.
Portable devices with small displays include portable video players such as those sold under the trademarks iPod by Apple Computer Inc. and Zen by Creative Technology Ltd., cell phones, digital cameras, video game players, and pocket TVs.
Since the portable device is held at a distance closer than 25 cm, when the device is viewed in a plane, a train, a bus, or any public places, other people next to the viewer will not be able to see the display. Therefore it will protect the privacy of the viewer.
Although the description above contains many specificities, these should not be construed as limiting the scope of the invention but as merely providing illustrations of some of the presently preferred embodiments of this invention. Other preferred embodiments are possible, including:
All embodiments mentioned above are for viewing a display of a portable device at a distance closer than the near point (<25 cm). In the mentioned embodiments, the magnifying lens is similar to an eyeglasses lens, i.e., it is placed very close to the eye.
Furthermore, one skilled in the art will be aware of a variety of means for mounting the positive lens or magnifying glass on a frame that holds the lens in front of the eye. Thus the scope of the invention should be determined by the appended claims and their legal equivalents, rather than by examples given.