Guys,
This is more aimed at the lens than the body, so I've posted in the lens section.
I was wondering how much, if any, difference the body will make to a Pentax SDM or Sigma HSM lens? Surely the speed at which it changes focal point will be dependent on the speed of the motor in the lens, and not the body? Sure, the body might be able to lock focus or have a more accurate autofocus mechanism, but I'm looking at this from a 'point to point' basis.
The reason I'm asking, is the HSM lenses seem to be pretty rapid indeed - for example:
YouTube - Sigma 50 f/1.4 HSM Hunting on a Pentax K20D
Now this seems quicker than the DA* 55mm to me:
YouTube - DA*55mm F1.4 SDM AF Speed K20D
Then I found this, the 70-200mm f/2.8 which also seemed to be quicker than similar lengthed Pentax equivalents
YouTube - SIGMA 70-200HSM II PENTAX.AVI
Getting back to my original point, here is a demo of the same lens on a Nikon D300:
YouTube - AF speed Sigma 70-200mm HSM Macro II
That seemds very nippy indeed. Given that the Nikon D300 has very quick autofocus, how much of it is the body and how much of it is the lens? Will the Pentax equivalent be as quick as the D300? From the two vids above, it certainly seems possible.