Originally posted by BirdDude007 Ya I have read about the SDM going out on this lens, but I see I have the screw drive still if that happens for back up.
Please note that SDM below refers to both SDM and DC.
Be aware that some lenses are SDM only (e.g. DA17-70, your DA18-135 as far as I know) and don't have screw drive; they will become manual focus lenses on (older) cameras that don't support SDM (e.g. K100D).
Also, you can't fall back on screw drive in case SDM (in the lens) fails, even if the lens supports SDM and screw drive. As long as the camera that supports SDM detects a lens with a motor in it, it will insist on using SDM and not screw drive. People here on the forums have been 'requesting' for the option to enable screw drive for a very long time.