Editing Film speed (section)

===Historic ASA and DIN conversion ===
[[File:ASA DIN conversion table.jpg|thumb|300px|Historic film speed conversion table, 1952<ref name="Singapore_1952"/>]]
[[File:Tessina with exposure guide plate.JPG|thumb|300px|Classic camera [[Tessina]] with exposure guide, late 1950s]]

As discussed in the ASA and DIN sections, the definition of the ASA and DIN scales changed several times in the 1950s up into the early 1960s making it necessary to convert between the different scales. Since the ISO system combines the newer ASA and DIN definitions, this conversion is also necessary when comparing older ASA and DIN scales with the ISO scale.

The picture shows an ASA/DIN conversion in a 1952 photography book<ref name="Singapore_1952"/> in which 21/10°&nbsp;DIN<!-- This convention used up to 1957. --> was converted to ASA&nbsp;80 instead of ASA&nbsp;100.

Some classic camera's exposure guides show the old conversion as they were valid at the time of production, for example the exposure guide of the classic camera [[Tessina]] (since 1957), where 21/10°&nbsp;DIN is related to ASA&nbsp;80, 18°&nbsp;DIN to ASA&nbsp;40, etc. Users of classic cameras may become confused if they are not aware of the historic background of changing standards.