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Photochromism is the reversible change of color upon exposure to light. It is a transformation of a chemical species ( photoswitch ) between two forms by the absorption of electromagnetic radiation ( photoisomerization ), where the two forms have different absorption spectra.
A photochromic eyeglass lens, part of the lens darkened after exposure to sunlight while the other part remained covered. A photochromic lens is an optical lens that darkens on exposure to light of sufficiently high frequency, most commonly ultraviolet (UV) radiation.
One simple yet important implication of this reciprocity principle is that any light directed through a lens in one direction (from object to image plane) is optically equal to its conjugate, i.e. light being directed through the same set-up but in the opposite direction.
The component S1 of the system, situated between the aperture stop and the object O, projects an image of the diaphragm, termed by Abbe the entrance pupil; the exit pupil is the image formed by the component S2, which is placed behind the aperture stop. All rays which issue from O and pass through the aperture stop also pass through the ...
Focal length of lens varies with the color of light Photographic example showing a high quality lens (top) compared to a lower quality one exhibiting transverse chromatic aberration (seen as a blur and a rainbow edge in areas of contrast)
Reversed achromatic lens. Charles Chevalier's Paris optical firm produced lenses for both Niépce and Daguerre for their experiments in photography.In 1829 [3] [citation needed], Chevalier created an achromatic lens (a two-element lens made from crown glass and flint glass) to cut down on chromatic aberration for Daguerre's experiments.
For the same reason sunglasses and filters were used by the American Army, especially for aviation, indeed Polaroid glasses were thought to protect aviator from sunlight but also atomic bomb explosions. [8] Cool-Ray was a division of American Optical for the sunglasses. It was the originator of the polarized sunglass as it is known today.
The glass–liquid transition, or glass transition, is the gradual and reversible transition in amorphous materials (or in amorphous regions within semicrystalline materials) from a hard and relatively brittle "glassy" state into a viscous or rubbery state as the temperature is increased. [2]