yakim_peled1 Posted June 8, 2012 Share Posted June 8, 2012 <p>Based on what is currently known, does anybody understands how STM is better than Ring-USM?<br /><br />Happy shooting,<br />Yakim.</p> Link to comment Share on other sites More sharing options...
bobatkins Posted June 8, 2012 Share Posted June 8, 2012 <p>It's possibly cheaper?</p> <p>Otherwise ring USM is supposed to be silent, so I don't really see why STM (stepping motor) would be better.</p> <p>Maybe Canon will eventually tell us.</p> Link to comment Share on other sites More sharing options...
denisgermain Posted June 8, 2012 Share Posted June 8, 2012 <p>sounds like the "STep down Version Motor"</p> Link to comment Share on other sites More sharing options...
yakim_peled1 Posted June 8, 2012 Author Share Posted June 8, 2012 <p>Hummm.... cheaper than ring USM and better than AFD and Micro-USM. I think you got it Bob. 10X. <br /><br />Happy shooting,<br />Yakim.</p> Link to comment Share on other sites More sharing options...
colin carron Posted June 8, 2012 Share Posted June 8, 2012 <p>Stepper motors are often used where high precision positioning is required.</p> <p>http://en.wikipedia.org/wiki/Stepper_motor</p> <p>don't know if that makes them better, worse, cheaper or more expensive - just a well-known technology for precise applications.</p> Link to comment Share on other sites More sharing options...
massimo_foti Posted June 8, 2012 Share Posted June 8, 2012 It's hard to say... Could be it's only about cost optimization, or maybe Canon is also paving the way to some mirrorless camera with different and/or hybrid AF system that would be EF compatible but work better with STM lenses? Could be both Link to comment Share on other sites More sharing options...
HenryUK Posted June 8, 2012 Share Posted June 8, 2012 <p>A stepper motor is an open loop device. The contoller tells it to move 100 steps and that's what it does, unless it is overloaded.<br> The ultrasonic motor and the micromotor are open loop devices and require a position feedback device (encoder) to tell the controller that they have reached the desired position.<br> This means that a stepper motor is a cheaper solution, especially if it is a linear motor, so it can eliminate a gear train and an encoder.</p> <p>What I want to know is how the phase detect AF works with the image sensor. I though you had to have field lenses in the optical path to form the secondary images on the focus sensor arrays.</p> <p>Henry</p> Link to comment Share on other sites More sharing options...
yakim_peled1 Posted June 8, 2012 Author Share Posted June 8, 2012 <p>Thanks for the detailed explanation Henry.</p> <p>Happy shooting,<br />Yakim.</p> <p> </p> Link to comment Share on other sites More sharing options...
jim_larson1 Posted June 8, 2012 Share Posted June 8, 2012 <p>Theoretically, if you don't need/use feedback, focusing can be faster. Might be relevant for video applications.</p> Link to comment Share on other sites More sharing options...
ilkka_nissila Posted June 8, 2012 Share Posted June 8, 2012 <p>Movie mode autofocus?</p> Link to comment Share on other sites More sharing options...
cabbiinc Posted June 8, 2012 Share Posted June 8, 2012 <p>The ONLY thing I know about them is that they are required for the new autofocus mode during video.</p> Link to comment Share on other sites More sharing options...
leopoldstotch Posted June 8, 2012 Share Posted June 8, 2012 <p>A <a href="http://itlounge.eu/hands-on-review-canon-ef-40mm-f2-8-stm/">hands-on preview</a> of the lens from today has some info about how the STM compares to other lens motors out there.</p> <p>In short, USM>STM when it comes to stills, and that's straight from the horse's mouth.</p> Link to comment Share on other sites More sharing options...
Marcus Ian Posted June 8, 2012 Share Posted June 8, 2012 <p>another native advantage of a stepper motor is that it can spin relatively freely, I'd expect Canon to make the lenses with it FTM capable. So I suppose for the cost of a DC motor, one has a motor which is almost as good as a USM.</p> Link to comment Share on other sites More sharing options...
bobatkins Posted June 8, 2012 Share Posted June 8, 2012 <p>Just another thought. With a stepper motor you have very fine and easy control over focus speed. You can make it slow or fast. With USM it may be more difficult to slow the motor down (though I'm sure it can be done).</p> <p>As mentioned above, for still shots you want the fastest possible focus. For video, that may not be desirable and a slower focus shift may look better than "snapping" focus between subjects at different distances.</p> <p>For high end use it would surprise me if at some point Canon release a body and lens combination that is USM fast for stills, but with control over the speed of AF in video mode. I'd say it's also possible we'll see a lens with power zoom added to the system. Today it seems that it's "all about video" when it comes to new camera features, possibly because still capability is already so well developed. There's a lot more room for innovation in video, whether people want it or not - and most people do seem to want it.</p> Link to comment Share on other sites More sharing options...
Marcus Ian Posted June 8, 2012 Share Posted June 8, 2012 <p>Bob is absolutely right, I had forgotten about that... even though Ring USM can go slow, fine, <em>and dynamic</em>, control of speed is nearly impossible, so where a USM has to 'snap' to a new plane of focus, then go 'slow' to make precise adjustments, an STM would be able to adjust it's speed dynamically based on how much OOF you were, then slow down as it approaches the new 'ideal' plane of focus... it also has to stop before it changes speed.<br> In video, smoothness is King - I don't think I ever thought that the reason that Canon's AF for video was essentially their stable of lenses... and all their lenses were designed for blindingly <em>fast</em> AF... not smoothness...</p> <p>Given the price $200, and stealthy size, I think I'll be picking one up... :-)</p> Link to comment Share on other sites More sharing options...
alan_bryant1 Posted June 8, 2012 Share Posted June 8, 2012 <p>The price on the 40/2.8 is slightly amazing. I checked prices and it appears to be the fourth cheapest lens Canon makes -</p> <p>50/1.8 - $109<br />EF-S 18-55/3.5-5.6 IS II - $139<br />75-300/4-5.6 III - $159<br />40/2.8 - $199</p> <p>I sure didn't see that coming. I mean it's got a metal mount. And after the recent 24/2.8 IS and 28/2.8 IS lenses were announced, I assumed we'd seen the last of sub-$500 lenses from Canon.</p> <p>Has anyone seen whether STM supports full-time-manual focusing? That's one of my favorite features of ring USM.</p> Link to comment Share on other sites More sharing options...
scott_ferris Posted June 8, 2012 Share Posted June 8, 2012 <p>The MkI EF super telephotos all had variable speed USM motors, you can adjust the focus speed on the side via a switch. The big drawback is if you lose the motor you can't manually focus.</p> Link to comment Share on other sites More sharing options...
steve_dunn2 Posted June 8, 2012 Share Posted June 8, 2012 <cite>Has anyone seen whether STM supports full-time-manual focusing? That's one of my favorite features of ring USM.</cite> <p>Somewhere (and I don't recall where, maybe one of Canon's sites, maybe another photography site) I saw mention that at least one of these two lenses uses electronic FT-M, like a few of Canon's other lenses have. This doesn't use a mechanical connection between the focus ring and the actual focusing hardware, but rather detects what you're doing to the focus ring and drives the focus motor accordingly.</p> Link to comment Share on other sites More sharing options...
peter_langfelder Posted June 8, 2012 Share Posted June 8, 2012 <p><em>Has anyone seen whether STM supports full-time-manual focusing? That's one of my favorite features of ring USM?</em><br> <em><br /></em>According to the specifications on dpreview.com, both STM lenses support FTM (so this seems official), and according to what I read also there, focusing is by wire (this may be unofficial).</p> Link to comment Share on other sites More sharing options...
Marcus Ian Posted June 8, 2012 Share Posted June 8, 2012 <blockquote> <p>The MkI EF super telephotos all had variable speed USM motors, you can adjust the focus speed on the side via a switch. The big drawback is if you lose the motor you can't manually focus.</p> </blockquote> <p>So would you say reliability was an issue ;-) ?<br> <em>"A key observation in the study of ultrasonic motors is that the peak vibration that may be induced in structures occurs at a relatively constant vibration velocity regardless of frequency." </em><br> The implication is that only a very finite number of speed would be achievable in such a setup, further, it may be damaging to the stator to change motor speed while the motor is running. <br> Also, a stepper motor's speed can be adjusted simply w/ PWM something that is a) easy to program , b) requires no additional mechanics (cost), and c)does not require stopping.<br> ...though a stepper is a bit louder than USM...</p> <p>I too saw that on dpreviews site, they mentioned that it had FTM focus. Odd that Canon's page didn't include it.</p> Link to comment Share on other sites More sharing options...
scott_ferris Posted June 8, 2012 Share Posted June 8, 2012 <blockquote> <p>"So would you say reliability was an issue ;-) ?"</p> </blockquote> <p>Yes. Canon don't have the parts for these lenses now and if/when the focus motor dies you have a multi thousand dollar paperweight. With later lenses if the focus motor dies you can manual focus, if the aperture dies you can use it wide open (where many of them live anyway), and if the IS dies then it doesn't stop the rest of the lens working. I am staggered every time I see 200 f1.8 lenses sell for $3,000+ when they are unrepairable. </p> Link to comment Share on other sites More sharing options...
yakim_peled1 Posted June 9, 2012 Author Share Posted June 9, 2012 <p>Leopold, thanks for the link.</p> <p>Happy shooting,<br> Yakim. </p> Link to comment Share on other sites More sharing options...
jim_larson1 Posted June 10, 2012 Share Posted June 10, 2012 It can't become a multi-thousnand dollar paperweight because the purchase cost of these lenses is scant hundreds. The 40/2.8 is a "mere" $200. More significant is the fact that the STM motors appear to be preferred for video AF. I don't think you can ignore this factor. I don't know how good the 4ti video AF is, but by the time we have a 5D-IV, it is likely to be decent. Look for a new series of L primes soon. Link to comment Share on other sites More sharing options...
neuro_anatomist Posted June 10, 2012 Share Posted June 10, 2012 Regarding varying the AF speed with ring USM, keep in mind that's a feature currently available on th MkII supertele lenses, with the Power Focus mode specifically intended for video: http://cpn.canon-europe.com/content/education/infobank/autofocus/power_focus.do Link to comment Share on other sites More sharing options...
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