How did Iso come about? Some reflections to add to Ian,s
Ian said in this weeks AP that “British standards did not make it to Still Photography.”
I am a little older perhaps than he, and remember quite clearly that that in the 40's and early50's British films were marked in BSI and Scheiner both log scales. Some even gave Weston values which at that time differed to ASA by 1/3 stop. Later models of the Weston meter were calibrated the same as ASA.
The 50's leading into the early 60's was a period of confusion. With films marked in Din (old) and Din (New) Scheiner, BS (arithmetic) and BSI (log), Asa, and Weston., If you bought a Russian camera and exposure meter with a film it was likely to marked in Ghost.
Ilford sold their films marked in BSI and Scheiner. Kodak included ASA depending where they were made.
To confuse matters further in 1959-60 Kodak ( followed by others) recalibrated their black and white films to twice their previous rating. (the films were not changed , only the marked speed).
This was because a majority of photographers preferred the higher quality of print obtainable by not including such a large safety margin in the negative.( colour films were not changed)
The advent of the ISO standard was a godsend as at last both the European and American standards were rationalised into a single combined figure ( 100/21.°)
Kodak packed in with their sheet colour film. “A Batch Data sheet” giving speed/colour, and reciprocity variations, for that particular batch.
67 happy photo years from amateur to professional and back. Caught the bug Young.