Expert: John Oliverio - 12/13/2005

Question
Hi i am running a cannon reble, the older style 35mm slr camera, i already have diffrent lenses for it the standeard 28-70 and a 200-300 and am looking at geting a 75-300mm, the question i have is the differnce in operating devices, as one of the lenses uses a DC motor and the other uses USM, everything else on these lenses seem to be identical or pretty close, the lenses are
EF 75-300mm f/4-5.6 III USM
EF 75-300mm f/4-5.6 III
link
http://consumer.usa.canon.com/ir/controller?act=ProductCatIndexAct&fcategoryid=1...

so what are the advantages of using the usm for im assuming it would be the better of the two because it is slightly more expensive but as iam not sure about its functionality, pretty much a comparison between the two and which is better. thanks very much for you time.


Answer
Jonathan,

 USM motors supply more torque for auto-focus and are quiter.  More torque means it focuses faster.  It is also said that USM motors last longer than the DC motors.  However, I've never seen  a DC motor wear out.  If you want to more about USM, the website "howstuffworks.com" used to have an article on them.  They probably still have it up.

John