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Thus an eye care professional, having determined that a myopic (nearsighted) person requires a basic correction of, say, −2 dioptres to restore normal distance vision, might then make a further prescription of 'add 1' for reading, to make up for lack of accommodation (ability to alter focus). This is the same as saying that −1 dioptre ...
Two of the FVEY information collection mechanisms are the PRISM program and the Upstream collection system. The PRISM program gathers user information from technology firms such as Google , Apple , and Microsoft ; while the Upstream system gathers information directly from civilian communications as they travel through infrastructure like fiber ...
An important development, the Gundlach rotary periscope, incorporated a rotating top with a selectable additional prism which reversed the view. This allowed a tank commander to obtain a 360-degree field of view without moving his seat, including rear vision by engaging the extra prism.
The first records of the spring are from early European explorers and surveyors. In 1839, a group of four trappers from the American Fur Company crossed the Midway Geyser Basin and made note of a "boiling lake", most likely the Grand Prismatic Spring, [5] with a diameter of 300 feet (90 m).
The wedge prism is a prism with a shallow angle between its input and output surfaces. This angle is usually 3 degrees or less. Refraction at the surfaces causes the prism to deflect light by a fixed angle. When viewing a scene through such a prism, objects will appear to be offset by an amount that varies with their distance from the prism.
First-order rotating catadioptric Fresnel lens, dated 1870, displayed at the Musée national de la Marine, Paris.In this case the dioptric prisms (inside the bronze rings) and catadioptric prisms (outside) are arranged to concentrate the light from the central lamp into four revolving beams, seen by sailors as four flashes per revolution.
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