New SDM lenses

<p>Anyone else notice the new lenses that are apparently rebadged (very good) lenses from Tamron have been outfitted with SDM AF motors? These are the D-FA 15-30mm f/2.8, D-FA 24-70mm f/2.8, and DA 18-270mm f/3.5-6.3, all SDM. Those newly issued which originate from Pentax, like the D-FA 70-200mm f/2.8, the DA 16-85mm f/3.5-5.6, the D-FA 28-105mm f/3.5-5.6, the DA 20-40mm f/2.8-4 Limited, and still others of recent Pentax origin, have DC AF motors.</p>

<p>Assuming that Tamron is actually assembling and/or supplying components for these lenses, presumably the tech they're using for AF motors is similar to what Pentax has used in its SDM models so that naming convention was adopted. It's not clear that one type is considered by Pentax to be generally superior to another or more appropriate for high-end models as they've been putting DC motors even in high-priced lenses like the DA560 and D-FA150-450 as well as DFA645 90/2.8 (the other modern 645 lenses used SDM).</p>

<p>I figured Pentax switched to DC because of past reliability problems with at least some SDM models. Maybe you are onto something, Andrew, the 3rd party AF system is simply rebadged as "SDM" since it is not DC. </p>

<p>The "SDM" from the D-FA 15-30 f/2.8 and the D-FA 24-70 f/2.8 is Tamron's USD ring-type motor (and on the 18-270 there should be the corresponding consumer Tamron motor).<br>

Why it's called "SDM"? Because it's an "ultrasonic" piezo motor, just like on the DA*s. Besides that, the motor in these two D FAs has nothing to do with the tiny micromotor from the DA*s.<br>

It's the same as with Canon, where USM is used to denote from the smallest (DA*-like) micromotor to ring-type motors found in their top lenses.</p>

<p>Very good! This is the kind of information I was hoping for- a differentiation from the original Pentax SDM AF motor. Andrew is essentially also right, the rebadging includes the Tamron motor. Thanks, Alexandru, for such insightful and very detailed information.</p>

<p>SDM is essentially the same as USM. they both use ultrasonic vibrations. </p>

<p>I was under the impression the actual implementation of Canon, Nikon, Sigma, and Tamron versions of piezoelectric vibration motors were quite different in order for each to avoid the patents of others that came before it. </p>