Originally posted by Frogfish SDM makes a noise ? Maybe it varies from lense to lense ? I've absolutely never noticed even a whisper from the DA*300.
I've Never used
SDM myself, but all five
HSM lenses that I have make a very quiet, but audible noise when focusing. But then again, I don't worry about HSM failing
The different manufacturers all have their own implementations of in-lens focusing motors, and they are not all made equal. They may even differ per manufacturer, e.g. one of my Sigma HSM lenses has a micro-motor HSM, while my others have a ring-type HSM.
SDM = Silent Drive Motor (Pentax)
HSM = Hyper-Sonic Motor (Sigma)
USM = Ultra Sonic Motor (Canon)
SWM = Silent Wave Motor (Nikon)
USD = Ultrasonic Silent Drive (Tamron)