does the sx100 have a USM motor? could not find information about that. but it might just be possible that it doesnt support setting zoomspeed. the s-series (s3is, s5is etc) have written USM on the front lens and they support this command. they also have like 128 zoom steps as opposed to like 8 steps in a typical ixus camera. sx100 has 10x zoom, so i guess there are more steps and there COULD be a speed setting, dunno.