Response to Acros in Microphen - and why are ISO ratings inflated?

Phil Davis' "Beyond the Zone System" also confirms that the ISO/ANSI standard uses 0.1 over b+f (when developed to a CI around 0.6) as the speed point.

I checked my TMZ box and indeed, it is an EI 100 film, not an ISO 100 film! On the film cassete (35mm) it just says 100/21 and doesn't mention EI or ISO. On the other hand, Tri-X is ISO 400 and FP4+ and HP5+ are also ISO, as is Acros.

I'm just glad I don't need to shoot my Sensia 100 at EI 50 too! At least slide films are pretty much "as advertised". Of course they use a different standard for film speed too.

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