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10-14-2013, 07:46 AM   #46
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QuoteOriginally posted by cbope Quote
Although the Sigma gets a point for the extra stop of speed, the DA gets a point for longer reach, so in my book they balance out, assuming the optical and AF performance are similar. Anyone who has owned both lenses care to comment, assuming price is not a deciding factor? Which lens would you go for?
My DA 17-70 never had issues with hunting, and was quick to lock focus in light and dark situations, when the focusing motor worked. The problem with it was SDM. I purchased the lens shortly after its release and three months later it was dead. Pentax replaced the entire SDM assembly and that one didn't last much longer.

Perhaps, if Pentax really has upgraded SDM parts it would be a great lens. I haven't owned the Sigma 17-50, but during my quest to find the best wide zoom some years ago, I owned the DA 18-55, DA 17-70, DA 16-45, and DA*16-50 all at the same time. The 17-70 was by far the best performer optically for me in every situation compared to the others, even the DA*. It also has the best zoom range of those I compared. In the end I went with the 16-45 and sold the 17-70 and 16-50 solely because of SDM issues at the time.

10-14-2013, 08:21 AM   #47
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QuoteOriginally posted by builttospill Quote
Perhaps, if Pentax really has upgraded SDM parts it would be a great lens.
And here lies another problem. If Pentax has upgraded the SDM components in this or any other lens, how am I as a buyer supposed to know that the lens I am buying online or even in a camera shop has the upgraded internals? It's practically impossible to know for sure, unless Pentax were to publish a serial number list which we all know they are not going to do.
10-14-2013, 12:30 PM   #48
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QuoteOriginally posted by cbope Quote
And here lies another problem. If Pentax has upgraded the SDM components in this or any other lens, how am I as a buyer supposed to know that the lens I am buying online or even in a camera shop has the upgraded internals? It's practically impossible to know for sure, unless Pentax were to publish a serial number list which we all know they are not going to do.
Agreed but note that not a single SDM lenses came out since the first DC lens (18-135) was announced.
Even the 560 is a DC lens. Says a lot to me.

They'll either market a SDM II or use a different term (DC anyone?).
10-14-2013, 01:04 PM   #49
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QuoteOriginally posted by thibs Quote
Agreed but note that not a single SDM lenses came out since the first DC lens (18-135) was announced.
Even the 560 is a DC lens. Says a lot to me.
(...).
I'm afraid your statement isn't totally accurate. Announced in September 2012, DA 18-270 f/3.5-6.3 is a SDM lens.

10-14-2013, 01:23 PM   #50
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QuoteOriginally posted by Mistral75 Quote
I'm afraid your statement isn't totally accurate. Announced in September 2012, DA 18-270 f/3.5-6.3 is a SDM lens.
But that lens is made by Tamron so it probably has the same pzd AF (Piezo Drive) as the versions for Canonikon with Tamron on it.
10-14-2013, 01:33 PM   #51
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SDM and DC are two different kinds of motor mechanisms. SDM itself does not refer to a single motor type - for example, the SDM in the 50-135 is not the same as the SDM in the 16-50 and is not the same as the 55 f1.4. The SDM motor is supposed to be an ultrasonic motor, similar to the Silent Wave Motor of Nikon, and the Ultra Sonic Motor of Canon. The DC motor is a complete different type of motor (I am not entirely clear what it is, supposedly it is a ring-type motor, maybe piezoelectric?).

If the DA 18-270 has the same piezoelectric motor as the Tamron, it would be a misuse of the SDM name, as far as the historical context goes. So either Pentax is no longer defining SDM as an ultrasonic motor designation, or the DA 18-270 has an actual ultrasonic motor instead of Tamron's piezoelectric motor.
10-14-2013, 02:23 PM   #52
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QuoteOriginally posted by Mistral75 Quote
I'm afraid your statement isn't totally accurate. Announced in September 2012, DA 18-270 f/3.5-6.3 is a SDM lens.
Pentax also released the 90mm SDM lens for the 645D after the 18-135. I'm not sure when they released the 25, but the designation is the same as the 90 and 55 SDM for the 645.
10-14-2013, 10:26 PM   #53
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True forgot about thé 645 lenses.<br />
Thé Tamron is really a Tamron lens so no 'proper Pentax sdm'.<br />
<br />
@JinDesu: SDM was NEVER an ultrasonic motor. It has always been micromotors.

10-14-2013, 10:54 PM   #54
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My SDM DA 17-70 started to refuse to focus after first turning on the camera. It needs manually to refocus
and than things go normal. Up to the next starting the camera. (with K200D and with K-5).
10-15-2013, 12:29 AM   #55
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QuoteOriginally posted by JinDesu Quote
(...)The SDM motor is supposed to be an ultrasonic motor, similar to the Silent Wave Motor of Nikon, and the Ultra Sonic Motor of Canon. The DC motor is a complete different type of motor (I am not entirely clear what it is, supposedly it is a ring-type motor, maybe piezoelectric?).
(...)
As already stated by thibs, SDM and DC are not that different from one another: both are micro-motors, neither are ring-type motors such as ring USM (Canon), SWM (Nikon) or SSM (Sony).
10-15-2013, 01:16 AM   #56
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This ongoing discussion confirms that I will likely order the Sigma EX 17-50 f/2.8 now, and wait to see what Pentax announces in this area in the future. I can always sell the Sigma and get the Pentax if it proves to be good optically (at least as good as the Sigma and better than the DA*16-50) and reliable (no SDM issues). I want to like the DA 17-70 f/4, but I can't thanks to the albatross that is SDM.

As I don't live in the US or Japan and don't have convenient access to a local Pentax repair facility, I'm not taking a chance on SDM.
10-15-2013, 02:05 AM   #57
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QuoteOriginally posted by thibs Quote
True forgot about thé 645 lenses.<br />
Thé Tamron is really a Tamron lens so no 'proper Pentax sdm'.<br />
<br />
@JinDesu: SDM was NEVER an ultrasonic motor. It has always been micromotors.
Ultrasonic does not automatically mean a ring-type motor. SDM is an ultrasonic micromotor.
10-15-2013, 02:29 AM   #58
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The optical quality of the Pentax SDM DA 17-70 is very, very good. But who placed this SDM inside?
10-15-2013, 04:24 AM   #59
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QuoteOriginally posted by starbase218 Quote
Ultrasonic does not automatically mean a ring-type motor. SDM is an ultrasonic micromotor.
<br />
<br />
No, it is a plain simple micromotor.
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