>The Zuiko 35-70mm f 3.6 exhibits this behavior as well, even though it is a
>"costant aperture" zoom lens.
>
>regards,
>
>Mahlon
It's more likely, that a zoom with variable maximal aperture doesn't stop
down while changing the focal length. With zooms with constant maximal
aperture, the aperture often (mostly) closes while changing the focal
length (at least with wide angle zooms). With Zuikos, there are two
different ways to do this: the 35-70 1:4 for example closes the aperture
immediately whereas the 1:3,6 keeps the aperture open, but the aperture
simulator moves a little bit. The latter lens stops down then (even with
open aperture), if the DOF button is used or the camera moves the aperture
shaft at 35mm. So the 3,6 is better if used with stored exposure values,
for example spot metering values. But there are of course lenses with
variable aperture, which changes the aperture diameter while changing the
focal length, too (for example the Pentax FA 28-105 1:4-5,6).
Matthias
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