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The MNREAD acuity chart or Minnesota low vision reading chart is a text based chart used to measure near visual acuity in people with normal or low vision. [1] It can also be used to measure maximum reading speed, critical print size and the reading accessibility index of a person. [2] Digital and printed types of charts are available. [3]
Reading stone in Archeon, a historical theme park. A reading stone is an approximately hemispherical lens that can be placed over text to magnify the letters, making it easier for people with presbyopia to read. Reading stones were among the earliest common uses of lenses.
The constant 25 cm is an estimate of the "near point" distance of the eye—the closest distance at which the healthy naked eye can focus. In this case the angular magnification is independent from the distance kept between the eye and the magnifying glass.
The magnifying power obtained in this condition is MP 0 = (0.25 m)Φ + 1, where Φ is the optical power in dioptres, and the factor of 0.25 m represents the assumed near point (¼ m from the eye). This value of the magnifying power is the one normally used to characterize magnifiers.
Three Part (Carbonless) – Three sheets are printed on one 105 gsm paper and the other two are printed on 60-70 gsm paper on A4 sheets. The bottom of the first sheet, the top and bottom of the second sheet, and the top of the third sheet are chemically treated so that the impression of the first sheet comes on the second and third sheets.
One of the earliest readers of microfilm was the Coddington Magnifier. Developed by Sir David Brewster, this magnifier was a "simple plano-convex lens of such thickness that the focus of its spherical curvature coincides with the flat surface of the lens. [2] On June 21, 1859, the first patent for a microfilm was issued to Rene Dargon in France.