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  2. Fresnel lens - Wikipedia

    en.wikipedia.org/wiki/Fresnel_lens

    The company made small bull's-eye lenses for use on railroads, steamboats, and docks; such lenses were common in the United States by the 1870s. [13] : 488 In 1858 the company produced "a very small number of pressed flint-glass sixth-order lenses" for use in lighthouses—the first Fresnel lighthouse lenses made in America. [56]

  3. Eyeglass prescription - Wikipedia

    en.wikipedia.org/wiki/Eyeglass_prescription

    Eyeglass prescription. Using a phoropter to determine a prescription for eyeglasses. An eyeglass prescription is an order written by an eyewear prescriber, such as an optometrist, that specifies the value of all parameters the prescriber has deemed necessary to construct and/or dispense corrective lenses appropriate for a patient.

  4. Astigmatism (optical systems) - Wikipedia

    en.wikipedia.org/wiki/Astigmatism_(optical_systems)

    An optical system with astigmatism is one where rays that propagate in two perpendicular planes have different foci. If an optical system with astigmatism is used to form an image of a cross, the vertical and horizontal lines will be in sharp focus at two different distances. The term comes from the Greek α- ( a-) meaning "without" and ...

  5. List of Pentax products - Wikipedia

    en.wikipedia.org/wiki/List_of_Pentax_products

    A sixth lens and an adapter were announced in September, 2012. Pentax 01 Standard Prime (2011) — 47 mm equivalent; Pentax 02 Standard Zoom (2011) — 28–80 mm equivalent; Pentax 03 Fisheye (2011) — 17.5 mm equivalent; Pentax 04 Toy Lens Wide (2011) — 35 mm equivalent; Pentax 05 Toy Lens Telephoto (2011) — 100 mm equivalent

  6. Glasses - Wikipedia

    en.wikipedia.org/wiki/Glasses

    Corrective lens shape Modern glasses with a rectangular lens shape. Corrective lenses can be produced in many different shapes from a circular lens called a lens blank. Lens blanks are cut to fit the shape of the frame that will hold them. Frame styles vary and fashion trends change over time, resulting in a multitude of lens shapes.

  7. Helios (lens brand) - Wikipedia

    en.wikipedia.org/wiki/Helios_(lens_brand)

    In 1972, the director of KMZ issued an order to increase the production of Helios-44-2 lenses in Valdai. The lens received a slightly modified lens block, the rear set of lenses was no longer twisted by the block and the lenses simply poured. The serial number was transferred to the lens body. In this form, the lens was assembled until the ...

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