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Canon EOS Lens Motors

by Philip Greenspun, 1996


Canon was very smart and put an AF motor in each of their EOS lenses. This means that you always have the correct size motor for your lens and therefore AF will be fast. There are four types of Canon AF motors.

Arc Form Drive (AFD)

This was the original Canon EOS motor. It is relatively noisy and slow. It does not allow simultaneous auto and manual focus. You do not really want a lens with this motor. No new Canon EOS lenses are being designed with this motor, but they are still selling some older designs with the AFD motor. As of November 1996, some lenses with AFD motors include the 50 macros, the 24, 28, and 35 fixed wide angles, and 135 soft focus lens, and the 100-300L zoom.

An even cheaper and crummier motor is the "micro motor", available on the 100 macro, 50/1.8, and two really cheap zoom lenses.

Ring Ultrasonic Motor

Beginning in 1987 with the 300/2.8, Canon has been slowly equipping its best lenses with the ring ultrasonic motor, in which the rotor and stator are big circles around the optics. These are incredibly fast and silent. Even more important, they allow simultaneous use of autofocus and manual focus. You can leave the lens in AF mode all the time and override the camera's decision at any time (or move AF to a separate button as with the EOS 5 body).

This is the "right stuff."

Micro Ultrasonic Motor

If you were a big company and figured out how to make something for 1/3rd the cost but still sold under the same name, wouldn't you? Well, that's what Canon did. The micro ultrasonic motor is a tiny little motor that they stick in the lens and then connect with gears to the focus mechanism. It is tough to see how this is any better than the Minolta/Nikon AF method of driving the lens focus mechanism from a motor inside the lens mount.

A micro USM does not allow simultaneous AF and MF. Thus, the largest user-interface advantage of the ring USM is gone. Much of the noise of a standard motor is back too. The micro USM is noticeably quieter than a regular motor, but not silent like a ring USM.

Canon puts the micro-USM mostly into its new cheap zoom lenses.


Text and pictures (c) Copyright 1991-1996 Philip Greenspun

Article created 1996

Readers' Comments


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Glen Johnson , December 13, 1996; 02:57 P.M.

Right now the only way to tell from Canon literature whether or not a usm lens has the ring style usm motor is to check to see if they claim that it has the FTM feature. ( FTM stands for full time manual focus for those that hate the acronyms.) If a usm lens has FTM, then it has the ring style motor. If a usm doesn't have FTM, then it has the micromotor usm drive instead. If you get a lens with the micromotor usm drive, be very careful when you attach or remove the lens hood. It is possible to apply enough torque during this process to get the little gears in the drive to "jump." This could lead to serious damage to the drive, especially if you do it frequently. To reduce the likelihood of this happening, you may want to switch the lens focus switch to MF before you try to attach or remove a lens hood from any of these lenses. Then be careful.

Glen Johnson , December 26, 1996; 12:30 P.M.

I recently noticed that another acronym for the full time manual focus feature in some of Canon's literature is EM for electronic manual focus. These lenses also have the ring motor.

Hubert Wachter , January 29, 1997; 04:34 P.M.

Please take note that the statement "micro usm does not allow full time manual focus" is not entirely correct. The EF 50mm f1.4 does have a micro usm motor and is perfectly capable of FTM.

Glen Johnson , January 31, 1997; 02:05 P.M.

After Hubert's post, I called Canon to see what they would say about this. The information that I had passed along earlier had come from Canon.

I asked if the 50 f/1.4 had the ring style or the micro motor style usm. The fellow said that he thought it was ring style, but he would check.

He was gone for about 5 minutes. When he returned, he apologized and said that it had the micro style usm. We then discussed this issue of FTM, usm, etc.

The punch line is: Canon apparantly can provide the FTM feature even without the ring style motor. When they don't include it, there is some other reason in play.

If you want FTM, don't assume that all usm lenses provide it. They don't. If you want FTM, you just have to make sure it is present by discussing it with the sales person, playing with the lens in person, reading reviews, or maybe even reading Canon's product literature. :-)

Jaco de Klerk , March 10, 1997; 02:04 P.M.

From a 1993 publication by Canon on the EOS5, I found the following lenses have micro motors:

50mm f/1.8 ii 100mm f/2.8 macro 35-80mm f/4-5.6 35-105mm f/4.5-5.6 75-300mm f/4-5.6 80-200mm f/4.5-5.6

None of these were denoted USM, only MM.

Don Baccus , June 12, 1997; 07:37 P.M.

There are two forms of overridable manual focus implemented for ring USMs. One, the electronic manual focus glen mentions, is supplied on lenses like the big white telephotos.

In lenses with electronic manual focus, the focus ring causes a position signal to be sent to the lens' focus module, which then drives the ring USM motor. The nifty feature of this implementation is that Canon can provide a virtual gearbox, in a sense. You can generally choose between three manual focus speeds. Fast whips the lens around when you twitch the focus ring, while the slow speed alows very fine focus control by requiring a relatively large movement to shift focus significantly.

Then there's the "real" full-time manual focusing lenses. In these, there's an internal focus ring. On one side lies the ring USM motor, on the other the manual focus ring. Via a cute system of rings and wheels, which allow either the ring USM or the manual ring to turn the real focus ring without turning the other component, real full-time manual focusing is provided. It is manual because it is the force of your hand that physically moves the focusing group, rather than signaling to the focus module information which then turns the internal focus ring for you.

How do you tell them apart? One way is to turn your camera off and attempt to manually focus. If it does, it's the "real" manual system. If it doesn't, it's the electronic system.

I don't know offhand which lenses have the electronic form. This was the first form, developed for the 300/2.8. I believe the electronic focus module used in the 300/2.8 is identical to that in the 200/1.8, 500/4.5, 400/2.8, 600/4. They all have identical buttons for using this, down to the beeper button (boo, hiss!).

I believe the 50/1.0 also has electronic manual focusing, but don't know for sure. Perhaps others.

The "real" manual FTM was introduced to, in part, reduce cost, I believe. I think the electronic module is overkill for short focal lengths, anyway. I don't miss the lack of three manual focus speeds on my shorter L zooms with the manual form, anyway.

The above, at least, is how I understand stuff from perusing Canon's "Lens Work" (older edition) some time ago.

George Agasandian , July 17, 1997; 01:59 A.M.

EOS-5 manual says "After autofocusing is completed in One-shot AF mode when using a USM lens equipped with a distance scale window, the lens can be manually focused directly without switching the lens' focus mode switch". Thus MF in AF mode should work fine in combination with Custom Function-4 if your lens has a distance scale window.

Charles G. Ruberto , November 30, 1998; 08:15 P.M.

Those interested in the electronics and mechanics of a Canon USM lens might want to take a look at http://www.photoscene.com/sw/tour/inside.htm. The owner of the page, Steven Weixel, dropped his 28-105 and broke some of the internal couplings; rather than have it repaired, he took it apart and made it the subject of a very interesting "lens tour."

Chu jung , August 04, 2000; 02:48 P.M.

Just bought a EF85mmf1.2 lens which according to Canon has FTM and electronic manual focusing. It turns out that the FTM feature only works in 'one shot' AF mode (i.e. on stationary subjects). In servo mode for moving subjects, FTM does not work (rotating the focus ring manually has no effect on the focus).

According to Canon Tech Services, this was designed into this lens (I suspect this may also be true of the 50mmf1.0). Kind of defeat the purpose of having FTM in the first place, considering that both lenses have SLOW 'front group focusing' instead of IF or RF.

Hubert Wachter , August 11, 2000; 04:30 P.M.

Chu Jung:

Have look at Custom Function 4. It may solve your problem.

Regards, -Hubert

Mark Wrathall , January 30, 2001; 09:48 A.M.

The 28-80/ 2.8-4L also has the electronic manual focusing.

Carl Smith , January 30, 2001; 10:05 P.M.

Of the two lenses I currently have (in my fledgling collection as a poor student as Phil puts it), one has the FTM (full time manual), and the other, to my slight dismay, does not.

the 24-85 3.5-4.5 USM does have the ring motor, and has the wonderful mechanical version, so you can play with it whenever you like. It's amazingly fast too, if I were one of you guys, it would probably make a great beat around lens on a less fancy body.

The other lens I have is the 75-300 4-5.6 IS USM, I suppose this has the micro motor, it's pretty quick, but in low light it takes it a bit longer. It's not as quiet as the other, which is virtually silent. I do like its metal construction and all. I chose it with the Image stabilizer over the version without because it was a happy medium, since I couldn't afford the next step up as far as a faster lens is concerned. And from what I've seen, the IS is great, it really helps for me, and even without it, the lens jsut seems to produce good shots.

Currently I'm trying to amass enough money for the Elan 7E. I have no idea how long itll take, but I'm working on it. I wish there was a review here for it, like the one for the older Elan II (e). but i'll just assume, aside from what I already know, it follows in the IIs footsteps. At B&H it's about $570 for the lens and the grip.

Dave B , April 18, 2001; 02:54 A.M.

How does Sigma's HSM compare to this? More like the Micro Motor???

Hung James Wasson , July 17, 2001; 07:15 A.M.

In response to the inquiry about the Sigma HSM (Hyper-Sonic Motor, I believe): From the reviews I've seen, and from my own experience, the Sigma 70-200mm f/2.8 APO EX HSM is extremely silent & allows for manuall override of the AF, but slower focusing than Canon ring type USM (i.e. 70-200mm f/2.8L), and DOES tend to hunt for focus more. For these reasons it has gotten blasted on many web pages. However, what almost everyone seems to ignore is that although the lens may be Sigma's "Pro" series, it truly competes with mid-level lenses for advanced amateur consumers -- not the Canon L's or Nikkor's that cost 2 to 3 times as much! If you've got the $1500 to $2000 to spend, then by all means go for the best (my wife would probably divorce me if I bought a lense worth more than her car).

I had an opportunity to buy the above Sigma used for $675 US (looked new), but didn't know anything about it. I was trying to decide between the Sigma, an older used Canon 80-200mm f/2.8L (somewhat beat up, not USM, but by all accounts very sharp) for $800 US, and a new Canon 75-300mm f/4.5-5.6 USM (micro-motor, not ring) IS for $520 US. I went to do some research, and rushed back the next day to put a down-payment on the Sigma -- but it was already gone. Yes, I'm kicking myself.

My reasons for deciding on the Sigma HSM? The Canon 80-200mm may be a good lens, but I like FTM override capability on AF, and a silent motor is priceless for grabbing candid shots (my reason for shopping for a medium telephoto zoom in the first place is my young kids find my Canon 24-85mm USM too intrusive sometimes [proximity, not sound]). The Canon 75-300mm IS doesn't have 2 step IS with panning (as it's big brother the 100-400mm f/4-5.6L IS does -- now this is a nice lens! It should be for $1600 US). The micro-motor USM doesn't focus as fast and doesn't allow for FTM, and the front lens element rotates -- playing havoc with polarizers & gradual filters. Those were the cons. The pros were the Sigma EX lens felt solid & well made, it focused very quickly compared to micro-motor competition, and at f/2.8 it was wonderfully bright/fast. I could see focusing in dim light with this lens much better than the Canon 75-300 IS. I've decided to continue to look for a used bargain Sigma f/2.8 HSM, or else save my pennies & buy either the Canon 100-400mm f/4-5.6L IS or Canon 70-200mm F/2.8L with a Canon 2xTC [for times when I could use a 140-400mm f/5.6]. The only question then would be how would I hide one of these big white monsters from my wife? :-)

Here are some links that might help:

http://www.photographyreview.com/reviews/35mm_zoom_lenses/product_4739.asp

http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=000wLP

Hubert Figuiere , June 03, 2002; 09:54 A.M.

How to check if the lens has USM or not when you have the lens in hand?

First, all USM lens sold by Canon do have the "Ultrasonic" logo and trademark printed on it. But that does not mean it is a real USM ring motor inside.

Second: all USM ring motor do have a window were you can read the focusing distance. Some USM micro-motor have it too, like the 75-300 USM II (IS or not). But if it has not the window, then it is not a USM ring motor either. Usually on those lenses, the focusing ring is just on the front element and usually thin. Why? Because the user probably won't focus manually either. It is consumer lens after all...

Third: USM ring motor lenses, when commuted in AF mode (see the switch on the side of the lens, close to the mount), allow focusing manually. That means that if you turn the the focusing ring, the focusing distance you can read behind the small window will change accordingly. If it does not then you don't have a real USM ring motor on the lens.

Jim Mueller , April 10, 2003; 11:02 P.M.

"AFD motors ....you do not want a lens with this motor." That's a pretty broad statement. I own a 24/2.8 with an AFD motor. It focuses faster and more decisive than my 50/1.4 but is noisier. The term "noisier" is a relative term. The AFD on the 24/2.8 sounds roughly like a zipper on a jacket, not obtrusive at all.

Some current Canon lenses (esp. wide angle) come only with the AFD motor. I would not let that stop you from buying one. The 24/2.8 is a superbly sharp lens with internal focusing and a floating element. It's a GEM, AFD or not.

Catchiest Zero , August 27, 2004; 03:00 A.M.

Look for the golden ring near the front of the lens (or the ring around the USM logo in lens brochure) to see whether or not a lens has ring USM. Pro lenses have a red line/margin instead of the golden one.

Look for FTM in the lens brochure to see if a lens provides full-time-manual focusing.


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