Originally posted by Clavius To expect a DC motor is unrealistic and it is unfair to burn Ricoh about its absence. A DC motor can not turn that big optical elements. That's why all the other lenses with bigger elements have the SDM.
Most of the latest Pentax lenses with built in motor use DC motor, and the DC motor may even be more powerful (and faster) than SDM.
HD Pentax-D FA 645 90mm F2.8 ED AW SR Macro
HD Pentax-DA 560mm F5.6 ED AW
Both use DC motors, so maybe Pentax even abandoned SDM motor for HD lenses.
But I don't expect built in motor in then new HD DA 55-300 mm lens.