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Cataract surgery is the most common application of lens removal surgery, and is usually associated with lens replacement. It is used to remove the natural lens of the eye when it has developed a cataract, a cloudy area in the lens that causes visual impairment. [4] [10] Cataracts usually develop slowly and can affect one or both eyes. [4]
Heterophoria is an eye condition in which the directions that the eyes are pointing at rest position, when not performing binocular fusion, are not the same as each other, or, "not straight".
The Petzval objective, or Petzval lens, is the first photographic portrait objective lens (with a 160 mm focal length) in the history of photography. [1] It was developed by the Slovak mathematics professor Joseph Petzval in 1840 in Vienna , [ 2 ] with technical advice provided by Peter Wilhelm Friedrich von Voigtländer [ de ] .
Monofixation syndrome (MFS) (also: microtropia or microstrabismus) is an eye condition defined by less-than-perfect binocular vision. [1] It is defined by a small angle deviation with suppression of the deviated eye and the presence of binocular peripheral fusion. [2]
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°.
A waist-level non-metered finder was available, as well as a non-metered pentaprism and three varieties of through-the-lens (TTL) metered prisms (CdS, PD and AE). The metered prisms read the aperture dial through a mechanical coupling on the lens. The standard lens was the 80mm f/2.8 C or the 70mm f/2.8 C E or the 80mm f/1.9 C. [4]
Special purpose lenses included the Micro-Nikkors 55 mm f/3.5 and 55 mm f/2.8, Micro-Nikkor 105 mm f/4 for close-up "macro" photography, the Noct-Nikkor 58 mm f/1.2 for low light photography, the PC-Nikkor 28 mm f/3.5 shifting perspective control lens, the GN-Nikkor 45 mm f/2.8 for automatically setting the proper aperture for flash exposure ...
The light passing through the lens is reflected by the mirror to a focusing screen, usually ground glass. The image formed on this ground glass can be observed directly, giving a waist-level reflex finder, or through a redressing optical device (set of mirrors or prism) for eye-level viewing, giving an eye-level reflex finder.
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