Archived posting to the Leica Users Group, 1999/07/12
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Two points. First, the ASA scale was reworked in 1960 when the "safety factor" was re-evaluated. The actual means of computing the ASA speed remained unchanged, but a safety factor was reduced, effectively raising ASA speeds for the same film. As I recall, Tri-X went from 320 to 400 and Plus-X from 80 to 125, but I'd have to look up the specifics to be certain. It was not a linear transformation: each film had a different increase. See the GEVAERT MANUAL for discussion. Second, ASA ceased to be used as the index for film speeds a decade back and was replaced by the "ISO" index. This is a two-part figure separated by a slash, the first part being the ASA index and the second the DIN index. Hence, Tri-X and 400 Delta and the like are now "400/27" and Kodachrome 64 is "64/19". So, those camera store clerks actually do have to "translate" ASA speeds into the modern ISO index, though they shouldn't have to struggle too manfully with the problem. Marc msmall@roanoke.infi.net FAX: +540/343-7315 Cha robh bas fir gun ghras fir!