Question about lenses w/stabilisation built in - USM etc

[andrew00]

Hey,

I was wondering if someone could explain USM lenses to me please, I'm reading they have stabilisation built into the lens. Does this mean it is always in play - regardless of if you are using the stills or video mode?

I've got a Pentax K10D which had it in the body (awesome) and a D90 with old manual lenses which doesn't have any (lame).

I was curious if the USM lenses were worth the extra cash b/c they'd give the video extra, valuable, stabilisation.

Cheers!
a x

[mhood]

IFAIK, USM refers only to the auto focus motor and has nothing to do with IS.

[USLatin]

Yea, I think it is:
USM = Ultra Sonic Motor
IS = Image Stabilization

So USM is something like faster and quieter, possibly more accurate AF. While IS is image stabilization which helps avoid blur from camera movement and allows you to shoot shorter shutter, so better low light performance. For motion I guess it works the same way, right?

[andrew00]

Ah ok so IS = stabilisation.

So in that case, does the IS work for all video too? As it'd be a big plus for the IS lenses if it did.