On 22 May 2010 10:04, Adam Maas <[email protected]> wrote:
>
> Actually, it's pretty clear, neither AF or OS will function on bodies
> which don't support SDM (IE the K100D and all earlier bodies). HSM is
> merely Sigma's version of SDM and the OS system is integrated with the
> AF system in most lens-based implementations.
>
Thanks for the clarification, Adam, that makes sense now. Pentax SDM
signals use the old Powerzoom contacts, right? But that doesn't mean
that a Powerzoom capable camera can control SDM, or the piggybacked
OS, where they don't have a controller for those systems, so
Thibouille's statement falls down on that point.
OTOH, and IIRC (sorry, Mr Brewer) it took years for the protocols of
all the KA contacts (and variations) to be deciphered, and Pentax was
only telling service people. It's always possible that there are
undisclosed protocols awaiting future products, and that SIgma has
found and tapped into one of them. After all, how on earth can a
Pentax control in-lens shake reduction when its native SR is in-body?
Either these lenses have internal shake sensors and only need power
through the mount (which makes Thibouille's statement feasible), or
the Pentax bodies are also supplying shake data through the lens
mounts. It has to be one or the other, there can be no free ride.
Just speculating.
regards, Anthony
"Of what use is lens and light
to those who lack in mind and sight"
(Anon)
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