No matter where you set the f-stop ring, the metering you are viewing
actually takes place with the lens wide open and any vignetting effects
will be those of the wide open lens. The lens does not stop down until
the shutter release is pressed and just before the first curtain is
released. With spot metering, you have set the shutter speed that will
be used after the lens is stopped down. With average metering, you are
only looking at an estimate of a shutter speed which will actually be
based on the light coming through the stopped down lens under TTL
exposure control.
Because of these differences, the only way to accurately carry out a
test between the two modes would be to expose film and test the results
with a densitometer. Slight differences should be expected between
different lenses and cameras of the same models due to tolerances in the
coupling mechanisms that tell the camera the f-stop that is set on the
lens and stop the lens down for exposure.
Moose
Thomas Müller wrote:
<>(I did my test at f5.6).
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