catgirl Loc: las vegas

what does USM mean for a lens thank you for your info

BHC Loc: Strawberry Valley, JF, USA

Ultra-Sonic Motor

catgirl Loc: las vegas

thank you, always see it on some lens but not others and didn't how important it was to have it or not

BHC Loc: Strawberry Valley, JF, USA

It means the motor was designed to be quieter than standard motors - so called because operation noise was supposed to be above audible levels. It's not that quiet, but it's better than conventional non-USM lenses.

haroldross Loc: Walthill, Nebraska

There are two basic types of USMs. There is the micro-USMs that are possibly quieter that a non-USM and possibly a little quicker focusing than a non-USM. On these lens I think it is just a marketing term to sell lens.

Then there is the true ring-type USM. These are much quieter and quicker to focus. Most of them offer FTM (full time manual) focus.

True ring USMs have no gears - the armature is integrated into the focus ring and can be very precisely started and stopped, while non-USM and micro-USM mechanisms have a considerably larger amount of mechanical give because of the gears. The older, more complex mechanical mechanism many times will overshoot the focus point more than the simpler ring USM.

catgirl Loc: las vegas

thank you bill41 for the information

catgirl Loc: las vegas

thank you haroldross appreciate the time and information