John Lind wrote
>When a film the nature of Velvia is run through the tests it comes out ISO
>50, however many who have done density and other measurements conclude an
>EI (exposure index) of 40 works better in actual use. Apparently for some
>films, the ISO lab tests end up slightly off (in Velvia's case by 1/3 stop)
>from what provides a more balanced result in practical use.
FWIW, Ilford recommend a speed setting for their b/w films to give the
optimum results, and specifically state that this is *not* necessarily the
ISO speed. For example, Delta 3200 has a recommended meter setting of
3200, but an ISO speed rating of 1000. Quote the Ilford data sheet: "..the
exposure index recommended...is based on a practical evaluation of film
speed and is not based on foot speed as is the ISO standard." Having used
Delta 3200, at 3200, I can vouch for its recommended speed rating.
Richard Ross
Hemel Hempstead, England
rhdesign@xxxxxxxxxxxxx
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