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Magnifiers are typically characterized using a "standard" value of 0.25 m. A magnifying glass operates as the simplest form of optical instrument. It is essentially a hand-held lens that converges light to produce an enlarged, upright image that appears to stand where light doesn't actually converge, known as a 'virtual' image.
A View-Master Model E of the 1950s. The practice of viewing stereoscopic film-based transparencies through a small magnifying viewer dates to at least as early as 1931, when Tru-Vue began to market black-and-white 35 mm filmstrips that were fed through a handheld viewer made of Bakelite.
A traditional handheld refractometer is an analog instrument for measuring a liquid's refractive index. It works on the critical angle principle by which lenses and prisms project a shadow line onto a small glass reticle inside the instrument, which is then viewed by the user through a magnifying eyepiece.
Fresnel lenses are used as simple hand-held magnifiers. They are also used to correct several visual disorders, including ocular-motility disorders such as strabismus. [73] Fresnel lenses have been used to increase the visual size of CRT displays in pocket televisions, notably the Sinclair TV80. They are also used in traffic lights.
A standard illuminated Snellen's chart for distant vision. A set of lenses used in refraction testing. Ishihara Plate 9. Ishihara Plate 23. A phoropter. NdYAG Laser.
A dome magnifier is a dome-shaped magnifying device made of glass or acrylic plastic, used to enlarge words on a page or computer screen. They are plano-convex lenses : the flat (planar) surface is placed on the object to be magnified, and the convex (dome) surface provides the enlargement.
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