Film speed
![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.)](/Images/godic/202502/11/Provia_100F_RDPIII_Box_with_ISO_film_speed5026.jpg")
![Film speed conversion table of the 50s](/Images/godic/202502/11/ASA_DIN_conversion_table5026.jpg")
![Classic camera Tessina exposure guide](/Images/godic/202502/11/Tessina_with_exposure_guide_plate5026.JPG")
![ISO 6:1993 method of determining speed for black-and-white film.](/Images/godic/202502/11/ISO6speedMethod5027.png")
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. A closely related ISO system is used to measure the sensitivity of digital imaging systems.