Film speed
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Film speed is the measure of a photographic film's sensitivity to light, determined by sensitometry and measured on various numerical scales, the most recent being the ISO system introduced in 1974. A
This film container denotes its speed as ISO 100/21°, including both arithmetic (100 ASA) and logarithmic (21 DIN) components. The second is often dropped, making (e.g.) "ISO 100" effectively equivalent to the older ASA speed. (As is common, the "100" in the film name alludes to its ISO rating.)
A box of Agfacolor Neu with the instruction "expose as 15/10° DIN" (in German)
Weston Model 650 light meter from about 1935
Early Weston Master light meter 1935–1945
Film grain
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Film grain or film granularity is the random optical texture of processed photographic film. Film grain develops due to the presence of small particles of metallic silver, or dye clouds, developed fro
Film speed
…almost always affect image quality. Higher sensitivities, which require shorter exposures, typically result in reduced image quality due to coarser film grain or increased digital image noise. Lower sensitivities, which require longer exposures, will retain more viable image data due to finer grain or less…
Photomicrograph of grain of different photographic plates
Film grain used for artistic effect
Rallycross car pictured on Agfa 1000 RS slide
Detail of the same photo to show the grain better