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A Dove prism is a type of reflective prism which is used to invert an image. Dove prisms are shaped from a truncated right-angle prism. The Dove prism is named for its inventor, Heinrich Wilhelm Dove. Although the shape of this prism is similar to the shape described by a Dovetail joint, the etymology of the two is unrelated.
Porro prisms are most often used in pairs, forming a double Porro prism. A second prism rotated 90° with respect to the first, is placed such that light will traverse both prisms. The net effect of the prism system is a beam parallel to but displaced from its original direction, with the image rotated 180°.
The oldest known description of anaglyph images was written in August 1853 by W. Rollmann in Stargard about his "Farbenstereoscope" (color stereoscope). He had the best results viewing a yellow/blue drawing with red/blue glasses.
Time magazine: "The Five Faces of Barack Obama" Family biography of Obama from The Washington Post; The Many Faces of Barack Obama – slideshow by Life magazine; Spaniards to Win Trademark Rights to 'Obama' Belfast Telegraph, April 23, 2009; Obama College Photos To Go On Display by Rachel Weiner, The Huffington Post, May 28, 2009
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.
Glasses are worn for eye protection in some sports, such as squash. Glasses wearers may use a strap to prevent the glasses from falling off. Wearers of glasses that are used only part of the time may have the glasses attached to a cord that goes around their neck to prevent the loss and breaking of the glasses.
A Perger prism or Perger–Porro prism system is a prism, that is used to invert (rotate by 180°) an image. The special feature of this prism is that, like a traditional double Porro prism system, it manages this with only four beam deflections and has neither a roof edge with the accompanying phase correction problems, a mirrored surface or ...
Kesh was such an important symbol of identity that during the persecution of Sikhs under the Mughal Empire, followers were willing to face death rather than shave or cut their hair to disguise themselves. The symbol of long hair for Sikhs was the stamp or insignia of the Guru.