Originally posted by Serkevan The *new* SDM motors on the DFA 15-30/2.8, 24-70/2.8 and Star 50/1.4 seem to be different ring-type motors, so they should only have the name in common. They also appear, from the reviews, to be much faster.
SDM is a name. Obviously the SDM in the DFA 15-30/24-70 is completely different as these lenses are rebadged Tamron lenses. The DFA *50 actually has a ring motor which is very different from the SDMs of the past.
But even within the SDM line up the speed varied. The DA *55 had by far the slowest focusing motor (and you could actually hear it power up when you zoomed). The DA *16-50 seemed a little faster than the 50-135. Anyway, just saying that the bigger question is what motor they are actually using combined with the length of the focus throw (shorter obviously makes for faster AF).
My guess for this lens would be a DC motor though. They could still call it SDM and have it be a similar motor to what is on a lens like the DFA *70-200.
Everyone seems to think the PLM system is awesome, but I'm not totally sold on focus by wire systems where they are unusable, even as manual focus lenses on older cameras. But maybe it is the way of the future...