Barry Bean asked about the compact 35-70 3.5-4.5 S zoom:
> 3) When the aperture ring is moved from 3.5 to 5.6 on the wide end
> (35mm), the aperture closes slightly. My other Zuiko zooms are fixed
> aperture, so of course don't do this, but my Sigma/Quantaray
> 28-80/3.5-4.5 doesn't show this behavior. Did I get a defective
> lens, or is this normal behavior in a Zuiko variable aperture zoom
Yes, mine does this too. It's a "real hack."
Minolta and probably some other AF lens mounts do this by
the lens CPU telling the camera what the effective aperture
is, so the meter can be corrected on the fly. That lets you
view wide open and is the "correct" solution. It isn't available
on the OM mount since only the aperture difference (set
minus current wide-open) is sent back to the body. The hack means
you can set exposure on an OM-1 and then zoom without having
to adjust it. It's also useful for flash.
The disadvantage is that you're viewing at f/4.5 rather than
f/4. That half stop is enough to darken the split prism much
more often than with the fixed f/4 zoom.
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