PentaxForums.com - View Single Post - Pentax Announces New DA* Lenses and Other Accessories

Alvin · 02-21-2007, 10:43 PM

Originally Posted by wmmk

sorry to sound like a n00b, but what is SDM?

No worries.

SDM = Supersonic Direct-drive Motor

It's a motor in the lens that drives the focusing mechanism, much like the Supersonic-Wave Motor (SWM) in recent Nikon lenses, or UltraSonic Motor (USM) for Canon.

Older lenses would have the focus driven by a screw in the body. On the K mount, you will see the drive screw at around the 5:00 position.

What the SDM hopes to achieve is quicker focus times, and quieter focus mechanisms. As you may already know the body driven focus motors are noisier. Try a kit 18-55 (uses SWM) on a Nikon D50 or D70, then bolt on an older screw driven 75-300 on and you'll hear what I mean.

02-21-2007, 10:43 PM	#5
Alvin Pentaxian Location: Mississauga, Ontario, Canada Gallery Photos: 7 Posts: 2,532	Originally Posted by wmmk sorry to sound like a n00b, but what is SDM? No worries. SDM = Supersonic Direct-drive Motor It's a motor in the lens that drives the focusing mechanism, much like the Supersonic-Wave Motor (SWM) in recent Nikon lenses, or UltraSonic Motor (USM) for Canon. Older lenses would have the focus driven by a screw in the body. On the K mount, you will see the drive screw at around the 5:00 position. What the SDM hopes to achieve is quicker focus times, and quieter focus mechanisms. As you may already know the body driven focus motors are noisier. Try a kit 18-55 (uses SWM) on a Nikon D50 or D70, then bolt on an older screw driven 75-300 on and you'll hear what I mean. Last edited by Alvin; 02-21-2007 at 10:51 PM.