On Sun, 31 Jan 1999 12:36:17 -0800, "Nandakumar Sankaran" wrote:

>First of all, Velvia is rated ISO 50 by Fuji. Only reason for rating it
>otherwise is if you know through prior tests that your METER produces more
>accurate numbers for ISO 50 if it is asked to compute for ISO 40. This is
>called meter calibration. Before you run out and imitate the pros, try a
>test for yourself as John Shaw mentions in his books, on YOUR meter.

Actually, given that my meters are calibrated to produce
proper density for me with all other slide films I've tried
(except the 400-speed Fuji and Kodak [failing...] efforts,
which are closer to 320..., Velvia (with average-lighting/
non-intense-color) looks best at 40... But I do find that
strongly-colored subjects do require exposure compensation
with Velvia, and I rate it (with strong color predominating)
at 50-64 with green, 32 with yellow-orange, and 25 with
red...

>Somebody mentioned as a follow-up to this message that the difference is 1/3
>stop and too small for your eye to notice the difference. Maybe, but many
>meters do not have a finer resolution than 1/2 stop. So even though ISO 40
>is a third of a stop slower, the camera uses this number for its meter
>computation and approximates the numbers to the closest 1/2 stop. So,
>setting the ISO dial does matter in some cases.

Yes - a 1/4 stop difference is quite obvious with the
contrasty Velvia slide film...

>I have an EOS Elan IIE and I rate Velvia at 40 if I am shooting scenes
>darker than middle tone by atleast 1 stop. I rate Velvia at 64 if I am
>shooting scenes brighter than middle tone by atleast 1 stop. Otherwise, I
>leave Velvia at 50. Through tests, I know that this produces best results on
>my Elan IIE.

Then for you the 100-speed slide films may look best at 125,
K-64 at 80, and K-25 at 32... (though the lower-contrast
100-speed films may not obviously show the error...).
(Exposing Velvia at 40 does not require having the processing altered...).