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2. Eye chart - Wikipedia

   en.wikipedia.org/wiki/Eye_chart

   Landolt C. Lea test. logMAR chart. An eye chart is a chart used to measure visual acuity comprising lines of optotypes in ranges of sizes. Optotypes are the letters or symbols shown on an eye chart. [ 1] Eye charts are often used by health care professionals, such as optometrists, physicians and nurses, to screen persons for vision impairment.

3. Snellen chart - Wikipedia

   en.wikipedia.org/wiki/Snellen_chart

   In the most familiar acuity test, a Snellen chart is placed at a standard distance: 6 metres. At this distance, the symbols on the line representing "normal" acuity subtend an angle of five minutes of arc, and the thickness of the lines and of the spaces between the lines subtends one minute of arc. This line, designated 6/6 (or 20/20), is the ...

4. Lens - Wikipedia

   en.wikipedia.org/wiki/Lens

   For a thin lens in air, the distance from the lens to the spot is the focal length of the lens, which is commonly represented by f in diagrams and equations. An extended hemispherical lens is a special type of plano-convex lens, in which the lens's curved surface is a full hemisphere and the lens is much thicker than the radius of curvature.

5. Here are the specs of Apple’s whole iPhone 12 range

   www.aol.com/specs-apple-whole-iphone-12...

   For the first time in its history, Apple released four iPhones: the iPhone 12 mini, the iPhone 12, the iPhone 12 Pro, and the iPhone 12 Pro Max. There's a lot of learning about these new devices.

6. Optical flat - Wikipedia

   en.wikipedia.org/wiki/Optical_flat

   At 2 inches (5.1 cm) in diameter and 0.5 inches (13 mm) thick, both surfaces are flat to within 1/10 of the wavelength of the light (58.9 nm), as indicated by the perfectly straight fringes. An optical flat is an optical -grade piece of glass lapped and polished to be extremely flat on one or both sides, usually within a few tens of nanometres ...

7. Display size - Wikipedia

   en.wikipedia.org/wiki/Display_size

   Display size. On 2D displays, such as computer monitors and TVs, the display size or viewable image size ( VIS) is the physical size of the area where pictures and videos are displayed. The size of a screen is usually described by the length of its diagonal, which is the distance between opposite corners, usually in inches.