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DocFrankenstein
22nd of June 2004 (Tue), 02:08
What's the difference?

I don't quite understand it. What are the benefits of the "ultra sonic" or quiet motor compared to non usm lenses?

Do they focus faster or something?

I know it's a noob question, I just can't find any info on this

Cadwell
22nd of June 2004 (Tue), 02:19
Lenses with USM motors are quieter (which may be an advantage under certain circumstances) and they tend to be faster focusing than non-USM.

scottbergerphoto
22nd of June 2004 (Tue), 07:08
USM lenses focus faster, quieter, and allow for full time manual focusing.
Check this out: http://photonotes.org/cgi-bin/entry.pl?id=USM
Regards,
Scott

CyberDyneSystems
22nd of June 2004 (Tue), 13:52
The speed difference can be astronomical. Some USM lenses are fastrer than others.. but any USM lens is faster than a non USM canon lens.. at least from my experience.. I also find them to be much more accurate more often.

With the 50mm f/1.8 and other non USM lenses.. I find that many times the first attempt to AF results in being slightly "off" focus..

drisley
22nd of June 2004 (Tue), 14:25
When I first was looking at buying a DSLR, I seriously thought lenses with USM actually sharpened the picture! :roll:

Jon
22nd of June 2004 (Tue), 15:00
USM lenses focus faster, quieter, and allow for full time manual focusing.


Make that some allow full-time manual focussing. Others will just grind, whine, and moan at the thought.

SeanDempsey
22nd of June 2004 (Tue), 15:15
I have had both types, and the USM is essential to me. They are FAST FAST FAST, and quiet.

Haifidelity
22nd of June 2004 (Tue), 16:14
True Ring-Type USM is FAST, QUIET and allows FTM.

Micro-USM (in the 50mm F/1.4 for example) isn't much faster focussing, at least in my experiences.

Tom W
22nd of June 2004 (Tue), 20:45
USM lenses focus faster, quieter, and allow for full time manual focusing.


Make that some allow full-time manual focussing. Others will just grind, whine, and moan at the thought.

All ring-type USM lenses allow full-time manual focusing. However, there a couple of Micro USM lenses, only one of which allows full-time manual focus. That particular lens is the 50 mm f/1.4.

Also note that the micro USM lenses do not focus as quickly as the true ring USM lenses.

DocFrankenstein
22nd of June 2004 (Tue), 21:46
I don't really care for the silent motion. Not like it's a video camera.

Why won't non USM lenses be able to focus accurately?

Tom W
22nd of June 2004 (Tue), 21:53
I don't really care for the silent motion. Not like it's a video camera.

Why won't non USM lenses be able to focus accurately?

I think that the stop/start is less precise with the non-USM lenses (and maybe even the micro-USM whose motor is separate from the focus ring as well).

True ring USM has no gears - the "armature" is integrel to the focus barrel/ring and can be very precisely started and stopped, whereas non-USM mechanisms have a considerably larger amount of mechanical "slop" not to mention the increased inertia of more moving parts. The older, more complex mechanical mechanism is bound to overshoot the proper focus point more readily than the lighter, simpler ring USM.

That's not to say that non-USM lenses are terrible - they just aren't quite as precise as the USM. Plus, they will hunt more before acheiving focus (probably related to the overshoot and mechanical slop).

DocFrankenstein
23rd of June 2004 (Wed), 00:54
My poor wallet! :cry:

I'm thinking about 10d with some usm lens now.

Tom W
23rd of June 2004 (Wed), 08:51
Fear not, Doc, for there are many ring-type USM lenses that are good, but don't cost an arm and a leg. Here's a couple:

24-85 f/3.5-4.5 USM - $300 US
28-105 f/3.5-4.5 USM - $230 US (watch out for the less capable f/4.0-5.6 version)
28-135 f/3.5-5.6 USM with Image Stabilization - $400 US

There's several more at a reasonable price with USM, including some very good prime (non-zoom) lenses. Take a gander at Canon's web site, then look for some reviews on the net.

ron chappel
23rd of June 2004 (Wed), 09:02
Please note that there are definitely two fundamental types of Ultrasonic motors.
Many above have mentioned ring usm where the motor really is a ring shape.The micro usm in most cheap consumer zooms lookes very much like a normal dc electric motor and also is connected the same way-ie. through a heap of small gears.These types of USM's are basically a marketing thing only!I've seen kit zooms where the non usm version focuses faster than the usm version.The 75-300 lens is one example where usm makes very little improvement-both versions have very slow focus. :lol:
My (just sold :cry: :cry: :cry: ) 100 macro non usm version focused very nearly as fast as the 50/1.8. How on earth does it do that without USM and with all those weighty elements to move?!!
Dead simple-it has a bigger motor :)
So you can't really tell a lens has quiet fast focus just by the USM after the name.....
Sure all the best L lenses and the best primes are USM and are VERY fast focusing,but once you get down into the consumer lenses it's not so clear.Alot of the cheap non usm zooms focus so fast and quiet that most amatuers would be stunned.There's not alot of point paying even a small premium.
With something as slow as a 75-300 on the other hand,you would do well to go usm even for the slight improvement it gives that slow focussing model

DocFrankenstein
23rd of June 2004 (Wed), 09:28
Thanks for the info. Now I have even more questions.

I'm gonna spend a few days/weeks doing lens research :shock:

Tom W
23rd of June 2004 (Wed), 10:22
Please note that there are definitely two fundamental types of Ultrasonic motors.
Many above have mentioned ring usm where the motor really is a ring shape.The micro usm in most cheap consumer zooms lookes very much like a normal dc electric motor and also is connected the same way-ie. through a heap of small gears.These types of USM's are basically a marketing thing only!I've seen kit zooms where the non usm version focuses faster than the usm version.The 75-300 lens is one example where usm makes very little improvement-both versions have very slow focus. :lol:

That is why one should look for the ring-type USM (these usually offer center or rear focus as well, complete with a focus scale and non-rotating front element, but there is no hard-and-fast rule).

My (just sold :cry: :cry: :cry: ) 100 macro non usm version focused very nearly as fast as the 50/1.8. How on earth does it do that without USM and with all those weighty elements to move?!!
Dead simple-it has a bigger motor :)
So you can't really tell a lens has quiet fast focus just by the USM after the name.....

Neither of those lenses is a ring-type USM. My 50/1.4 (micro-USM) focuses reasonably fast, but not as quickly or accurately as my 28-105 or my "L" zooms, all of which share ring USM. It hunts a bit more, but is still pretty doggone good.

Sure all the best L lenses and the best primes are USM and are VERY fast focusing,but once you get down into the consumer lenses it's not so clear.Alot of the cheap non usm zooms focus so fast and quiet that most amatuers would be stunned.There's not alot of point paying even a small premium.
With something as slow as a 75-300 on the other hand,you would do well to go usm even for the slight improvement it gives that slow focussing model

Every one of these lenses focuses faster and more accurately than I can do manually under most conditions. I wouldn't fault a lens for being non-USM, but there are plenty of ring-type fast-focusing USM lenses out there for a reasonable price. The 3 zooms I named are all fast focusing lenses. I've owned 2 of them and still have 1 of those.

I think you'll really have to figure out what range of lens you want, and then research each lens individually - there are overlapping features that may make a lens more desirable, regardless of USM. IOW, as Ron implies, don't throw a lens to the side just because it doesn't have USM or ring-type USM - it is but one of many features that should be considered.

ron chappel
23rd of June 2004 (Wed), 10:30
Not sure if i got the point across but tom's reply to me seemed to sort it :lol:

DocFrankenstein
23rd of June 2004 (Wed), 23:22
Is there a good lens FAQ somewhere? cause I need to get some basic terminology down first, cause if I don't get it, I'm gonna pester people and I don't wanna do that.

That is why one should look for the ring-type USM (these usually offer center or rear focus as well, complete with a focus scale and non-rotating front element, but there is no hard-and-fast rule).
Do u mean that not all canon glass has a range scale on the focusing ring?

What's center focus? What's rear focus?

ron chappel
24th of June 2004 (Thu), 06:49
The focus question i can answer.
All old fashioned lenses used to focus by moving the whole lens glass assembly closer or further away from the camera
Most modern lenses now only move one or several groups of lenses instead of the whole thing which means ,all things being equal,focussing will be faster because there is less weight to move.
Some lenses only need to move the tiny middle or rear elements which is where they get the name 'rear focus' or 'internal focus',etc.

Basically one can safely ignor the marketing names in most cases .Just try to find out from other owners/reviewers how the lens focus speed compares to others.

Most of the cheap canon lenses have no focus scales