Good point John, but when do you use this procedure much any more? I
experimented with taking some photos of a Wizard A (dry plate 4X5 folding
box camera) this afternoon. Instead of using TTL I set the T20 and T32 on
auto and set the intensity to give a two stop difference between them. I
made sure (by looking at the scale) that the flashes were placed at the
correct distances.
I placed the Wizard on a translucent white plastic with the T20 underneath
and the T32 in an umbrella to the right and slightly behind the Wizard.
Then I bracketed and used a 90mm macro, 70mm (Tokina ATX zoom), 50mm and
24mm lenses to try for different perspectives and dof. Then I started all
over with a clear piece of plastic under the Wizard.
I just don't use the guide numbers much any more. Before TLL metering I had
to correct for filters, magnification ratios, night photos etc., but seldom
even think along those lines now. Now I just choose the correct body
(meter) and film for the light and lenses and situation I plan on shooting
Gregg
From: John A. Lind
> About Guide Numbers:
>
> Note: The GN normally given for a flash unit is for ISO 100 film speed.
> The GN for the same flash changes for different ISO film speeds! The GN
> data should also tell you whether it is for subject distance in meters or
> feet. For instance, the GN for a T-32 running in Manual Mode is 32 in
> meters, and 104 in feet
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