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  2. PRISM - Wikipedia

    en.wikipedia.org/wiki/PRISM

    PRISM is a code name for a program under which the United States National Security Agency (NSA) collects internet communications from various U.S. internet companies. [1] [2] [3] The program is also known by the SIGAD US-984XN. [4] [5] PRISM collects stored internet communications based on demands made to internet companies such as Google LLC ...

  3. Binoculars - Wikipedia

    en.wikipedia.org/wiki/Binoculars

    However they have large eye lenses, excellent eye relief, and are comfortable to use at lower powers. Field flattener lens. High-end binoculars often incorporate a field flattener lens in the eyepiece behind their prism configuration, designed to improve image sharpness and reduce image distortion at the outer regions of the field of view.

  4. Crown glass (optics) - Wikipedia

    en.wikipedia.org/wiki/Crown_glass_(optics)

    Crown glass is a type of optical glass used in lenses and other optical components. It has relatively low refractive index (≈1.52) and low dispersion (with Abbe numbers between 50 and 85). Crown glass is produced from alkali-lime silicates containing approximately 10% potassium oxide and is one of the earliest low dispersion glasses.

  5. Glasses - Wikipedia

    en.wikipedia.org/wiki/Glasses

    Glasses, also known as eyeglasses and spectacles, are vision eyewear with clear or tinted lenses mounted in a frame that holds them in front of a person's eyes, typically utilizing a bridge over the nose and hinged arms, known as temples or temple pieces, that rest over the ears. Glasses are typically used for vision correction, such as with ...

  6. Lens - Wikipedia

    en.wikipedia.org/wiki/Lens

    An example is eyeglass lenses that are used to correct astigmatism in someone's eye. Types of simple lenses Types of lenses. Lenses are classified by the curvature of the two optical surfaces. A lens is biconvex (or double convex, or just convex) if both surfaces are convex. If both surfaces have the same radius of curvature, the lens is ...

  7. Four prism dioptre reflex test - Wikipedia

    en.wikipedia.org/wiki/Four_prism_dioptre_reflex_test

    assess alignment of both eyes. The Four Prism Dioptre Reflex Test (also known as the 4 PRT, or 4 Prism Dioptre Base-out Test) is an objective, non-dissociative test used to prove the alignment of both eyes (i.e. the presence of binocular single vision) by assessing motor fusion. [1] Through the use of a 4 dioptre base out prism, diplopia is ...