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09-20-2010, 07:50 AM   #1
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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
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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!

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09-20-2010, 08:27 AM   #3
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It does stand for Direct Current, per the official Pentax page for it.
09-20-2010, 09:01 AM   #4
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Yes, it says Direct Current on the spec page for the lens on 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
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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
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Here is the patent application for the new motor: ROTARY ACTUATOR
09-20-2010, 02:43 PM   #7
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QuoteOriginally posted by womble Quote
Here is the patent application for the new motor: ROTARY ACTUATOR
Thanks womble.

QuoteOriginally 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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