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For a thin lens in air, the focal length is the distance from the center of the lens to the principal foci (or focal points) of the lens.For a converging lens (for example a convex lens), the focal length is positive and is the distance at which a beam of collimated light will be focused to a single spot.
A toric lens is a lens with different optical power and focal length in two orientations perpendicular to each other. One of the lens surfaces is shaped like a "cap" from a torus (see figure at right), and the other one is usually spherical. Such a lens behaves like a combination of a spherical lens and a cylindrical lens.
In a real optical system, the best optical quality is usually achieved where most rays of light are roughly normal (i.e., at a right angle) to the lens surface. In the case of an eyeglass lens, this means that the lens should be roughly shaped like a cup with the hollow side toward the eye, so most eyeglass lenses are menisci in shape.
A similar sort of eyeglass lens is the myodisc, sometimes termed a minus lenticular lens, used for very high negative corrections. More aesthetic aspheric lens designs are sometimes fitted. [ 3 ] A film made of cylindrical lenses molded in a plastic substrate as shown in above picture, can be applied to the inside of standard glasses to correct ...
A man controls Google Glass using the touchpad built into the side of the device.. An optical head-mounted display (OHMD) is a wearable device that has the capability of reflecting projected images as well as allowing the user to see through it.
Red-tinted lenses were considered effective in reducing internecine pecking because they disguise the color of blood. [7] As summed up in a 1953 article in Indiana's National Road Traveler newspaper, "The deep rose-colored plastic lenses make it impossible for the cannibal [chicken] to see blood on the other chickens, although permitting it to see the grain on the ground."
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