Film Rating

[P3D <TimMaf@xxxxxxx>]

The subject of what speed to rate film at has come up and I'd
like to muddy the waters further. 

The general rule is that slides look better when slightly (1/3
to 1/2 stop) underexposed. Prints will look better when the
negative is slightly (same amount) OVERexposed. The easiest
means of doing this is to alter the film speed on the meter
thus your settings are automatically over or under exposed.

Looking at your meter if I wanted to underexpose Velvia by
1 stop (assume 1/60 at f8) adjust the flim speed until you're
1 stop under (f11). The film speed should now read ISO 100. 
Do the opposite for overexposeing negitives. 

What got this started was a question about Velvia and its
speed. Someone wondered if it should be uprated (higher ISO)
to produce an underexposed more saturated image. Normally
this is the case with chromes but according to many, 
especially those who write about film, Velvia is truely an
ISO 40 film not ISO 50. That would produce an image that is
1/3 stop overexposed compared to Fuji's thinking.

Personally when shooting chromes I find my metering has more
of an impact than the speed so I always shoot at the published
speed. For negatives I'm always 1/3 stop over.

Tim Maffia
Seattle


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