DC vs SDM?

REM · 09-20-2010, 07:50 AM

I saw from a quick blurb about the new announced 18-135 WR lens and how it uses a DC (direct current) motor for autofocus. The DC is part of the lens name.

How is this different from SDM, or is it exactly SDM? The 17-70, and DA* have SDM in the lens name. Why not just have SDM in the lens name? Or is it to differentiate between DA* (fast lens+WR+SDM) lenses and consumer (slower) lenses ?

Adam · 09-20-2010, 08:06 AM

From my understanding, the DC motor is a type of motor used for the SDM system. Doubt it stands for direct current, though.

Perhaps it's faster!

deadwolfbones · 09-20-2010, 08:27 AM

It does stand for Direct Current, per the official Pentax page for it.

REM · 09-20-2010, 09:01 AM

Yes, it says Direct Current on the spec page for the lens on pentaximaging.com. just the thing to find out later is:

Is DC just a marketing term? (DC is same SDM technology, just used to separate DA* from DA WR lenses with SDM).

or is DC a new/different/updated SDM technology(SDM 2.0)?

Given the current state of SDM, I hope it is more reliable first, faster speed an extra perk!

Entropy · 09-20-2010, 12:27 PM

To me, a DC motor implies a brushless DC micromotor, not an ultrasonic ring motor like found in higher-end in-lens focusing systems.

womble · 09-20-2010, 02:08 PM

Here is the patent application for the new motor: ROTARY ACTUATOR

Aegon · 09-20-2010, 02:43 PM

Originally posted by womble

Here is the patent application for the new motor: ROTARY ACTUATOR

Thanks womble.

Originally posted by the Patent Application:

According to the present invention, a rotary actuator is achieved, in which torque in the circumferential direction is produced by magnetic force between the coil body and the multi-polar magnet by controlling currents supplied to the coil body. Accordingly, a reduction gear device becomes unnecessary, and miniaturization and a weight reduction of the actuator become possible. In addition, a high-voltage circuit for driving a motor such as an ultrasonic motor becomes unnecessary. Therefore, in the case where a rotary actuator according to the present invention is used as a drive source for an AF mechanism of a photographic lens, miniaturization of the AF mechanism becomes possible, so that miniaturization and a weight reduction of the photographic lens can be achieved.

So the new motor has more torque so it doesn't need a gearbox. And it can operate at lower voltages so it requires fewer electronic parts.

09-20-2010, 07:50 AM	#1
REM Forum Member Join Date: Sep 2009 Location: Houston, TX Posts: 78	DC vs SDM? I saw from a quick blurb about the new announced 18-135 WR lens and how it uses a DC (direct current) motor for autofocus. The DC is part of the lens name. How is this different from SDM, or is it exactly SDM? The 17-70, and DA* have SDM in the lens name. Why not just have SDM in the lens name? Or is it to differentiate between DA* (fast lens+WR+SDM) lenses and consumer (slower) lenses ?

09-20-2010, 08:06 AM	#2
Adam Administrator Site Webmaster Join Date: Sep 2006 Location: Arizona Photos: Gallery \| Albums Posts: 51,594	From my understanding, the DC motor is a type of motor used for the SDM system. Doubt it stands for direct current, though. Perhaps it's faster! Adam PentaxForums.com Webmaster (Site Usage Guide \| Site Help \| My Photography) PentaxForums.com server and development costs are user-supported. You can help cover these costs by donating or purchasing one of our Pentax eBooks. Or, buy your photo gear from our affiliates, Adorama, B&H Photo, KEH, or Topaz Labs, and get FREE Marketplace access - click here to see how! Trusted Pentax retailers:

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09-20-2010, 08:27 AM	#3
deadwolfbones Veteran Member Join Date: Sep 2007 Location: La Crescenta, CA Posts: 7,450	It does stand for Direct Current, per the official Pentax page for it.

09-20-2010, 09:01 AM	#4
REM Forum Member Join Date: Sep 2009 Location: Houston, TX Posts: 78 Original Poster	Yes, it says Direct Current on the spec page for the lens on pentaximaging.com. just the thing to find out later is: Is DC just a marketing term? (DC is same SDM technology, just used to separate DA* from DA WR lenses with SDM). or is DC a new/different/updated SDM technology(SDM 2.0)? Given the current state of SDM, I hope it is more reliable first, faster speed an extra perk!

09-20-2010, 12:27 PM	#5
Entropy Veteran Member Join Date: Jun 2007 Location: Owego, NY Posts: 976	To me, a DC motor implies a brushless DC micromotor, not an ultrasonic ring motor like found in higher-end in-lens focusing systems.

09-20-2010, 02:08 PM	#6
womble Pentaxian Join Date: Apr 2010 Location: Hertfordshire Photos: Gallery Posts: 4,324	Here is the patent application for the new motor: ROTARY ACTUATOR

09-20-2010, 02:43 PM	#7
Aegon Site Supporter Join Date: Jan 2008 Location: Portland, OR Posts: 1,416	Originally posted by womble Here is the patent application for the new motor: ROTARY ACTUATOR Thanks womble. Originally posted by the Patent Application: According to the present invention, a rotary actuator is achieved, in which torque in the circumferential direction is produced by magnetic force between the coil body and the multi-polar magnet by controlling currents supplied to the coil body. Accordingly, a reduction gear device becomes unnecessary, and miniaturization and a weight reduction of the actuator become possible. In addition, a high-voltage circuit for driving a motor such as an ultrasonic motor becomes unnecessary. Therefore, in the case where a rotary actuator according to the present invention is used as a drive source for an AF mechanism of a photographic lens, miniaturization of the AF mechanism becomes possible, so that miniaturization and a weight reduction of the photographic lens can be achieved. So the new motor has more torque so it doesn't need a gearbox. And it can operate at lower voltages so it requires fewer electronic parts.

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