Editing Film speed (section)

====Scheiner{{anchor|Scheinergrade|Sch|Sch.}}====
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The ''Scheinergrade'' (Sch.) system was devised by the German astronomer [[Julius Scheiner]] (1858–1913) in 1894 originally as a method of comparing the speeds of plates used for astronomical photography. Scheiner's system rated the speed of a plate by the least exposure to produce a visible darkening upon development. Speed was expressed in degrees Scheiner, originally ranging from 1° to 20°&nbsp;Sch., with each increment of a degree corresponding to a ''multiplicative'' factor of increased light sensitivity. This multiplicative factor was determined by the constraint that an increment of 19° Sch. (from 1° to 20°&nbsp;Sch.) corresponded to a hundredfold increase in sensitivity. Thus emulsions that differed by 1° Sch. on the Scheiner scale were <math>\sqrt[19]{100} = 1.2742...</math>-fold more (or, less) sensitive to each other. An increment of 3°&nbsp;Sch. came close to a doubling of sensitivity<ref name ="Sowerby"/><ref name="Riat_2006"/> <math>(\sqrt[19]{100})^3 = 2.06914...</math>.

The system was later extended to cover larger ranges and some of its practical shortcomings were addressed by the Austrian scientist [[Josef Maria Eder]] (1855–1944)<ref name="DIN_1934_DIN-4512_Introduction"/> and Flemish-born botanist {{Interlanguage link multi|Walter Hecht|de|3=Walter Hecht}} (1896–1960), (who, in 1919/1920, jointly developed their ''Eder–Hecht neutral wedge sensitometer'' measuring emulsion speeds in ''Eder–Hecht'' grades). It remained difficult for manufacturers to reliably determine film speeds, often only by comparing with competing products,<ref name="DIN_1934_DIN-4512_Introduction"/> so that an increasing number of modified semi-Scheiner-based systems started to spread, which no longer followed Scheiner's original procedures and thereby defeated the idea of comparability.<ref name="DIN_1934_DIN-4512_Introduction"/><ref name="Sheppard_1932_Dresden-Congress"/>

Scheiner's system was eventually abandoned in Germany, when the standardized [[#DIN|DIN]] system was introduced in 1934. In various forms, it continued to be in widespread use in other countries for some time.