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  2. Ophthalmic trial frame - Wikipedia

    en.wikipedia.org/wiki/Ophthalmic_trial_frame

    An ideal trial frame have minimum 3 cells, one each for holding spherical lens, cylindrical lens and other tools like occluder or pinhole. [4] Angle for axis of astigmatism is marked on outermost visible cell There are knobes to adjust pupillary distance, side angle, height and cylindrical lens axis. [5]

  3. Prism sight - Wikipedia

    en.wikipedia.org/wiki/Prism_sight

    A Trijicon 3.5x35 ACOG prism sight with a Trijicon RMR reflex sight mounted on the top.. A prism sight or prismatic sight, sometimes also called prism scope or prismatic scope, is a type of telescopic sight which uses a reflective prism for its image-erecting system, instead of the series of relay lenses found in traditional telescopic sights.

  4. Digital single-lens reflex camera - Wikipedia

    en.wikipedia.org/wiki/Digital_single-lens_reflex...

    A photographer will often use lenses made by the same manufacturer as the camera body (for example, Canon EF lenses on a Canon body) although there are also many independent lens manufacturers, such as Sigma, Tamron, Tokina, and Vivitar, that make lenses for a variety of different lens mounts. There are also lens adapters that allow a lens for ...

  5. Porro prism - Wikipedia

    en.wikipedia.org/wiki/Porro_prism

    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°.

  6. Photochromism - Wikipedia

    en.wikipedia.org/wiki/Photochromism

    A photochromic eyeglass lens, after exposure to sunlight while part of the lens remained covered by paper. 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 ...

  7. Bifocals - Wikipedia

    en.wikipedia.org/wiki/Bifocals

    A bifocal lens with areas of differing magnification Bifocals with separate lenses. In this case, the Swedish ethnologist Jan-Öjvind Swahn . Bifocals are eyeglasses with two distinct optical powers. Bifocals are commonly prescribed to people with presbyopia who also require a correction for myopia, hyperopia, and/or astigmatism.

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