[thibs]

Chasseur d'Images gives 4stars to 18-135 (including 4 stars for performance, 4 for price/perfs) and btw 4 stars to the 35/2.4 for perfs, 5 stars for price/perfs.

[audiobomber]

Chasseur d'Images gives 4stars to 18-135 (including 4 stars for performance, 4 for price/perfs) and btw 4 stars to the 35/2.4 for perfs, 5 stars for price/perfs.

Interesting, that's a pretty credible source. Would you be able to summarize their conclusions?

[thibs]

Yep although I didn't buy the thing what I remember is:
* too expensive (surprise huh?)
* for what it is, very credible performance
* Excellent build, fast AF
* IQ lower in the Telephoto part of the lens.

I can't say much more but will try to read more carefully next time I enter the book store

[GingerBeer]

So I got into a bit of a discussion (in the marketplace section of all places) about DC versus SDM. It probably wasn't the best place to be debating the difference so I thought I'd ask some more questions about the differences here instead.

So it is my understanding that the trademark for the SDM designation for lenses refers to lenses driven with a supersonic motor. And the DC in the name of the DA 18-135mm lens refers to a direct current motor.

Yet Pentax, in the media release about the DA 18-135mm describes the lens as:
"3. Extra-smooth SDM autofocus operation
A DC motor built into the lens’ AF (autofocus) unit assures extra-smooth autofocus operation."

There seems to be plenty of instances of SDM being interpreted as being short for silent drive motor yet I have never seen any evidence of Pentax (Hoya) using the SDM with this meaning - only their name for ultrasonic lenses.

Yet Pentax (in the media release about the DA 18-135mm) has clearly linked the DC motor to the SDM autofocus system. I haven't pulled apart the lens, but it seems to me that most of the evidence suggests that the direct current motor is a conventional DC micro-motor, although I note that Falk Lumo suggested that it was a "new, faster ultrasonic focus motor". Can someone definitively say that it is a conventional DC micro-motor? And if so, why are Pentax using SDM for a non ultrasonic AF lens? Have they broaden their definition of what SDM refers to?

[thibs]

Pentax has no Ultrasonic motors if your point of comparison are high end verion of USM/SSM/HSM etc. Pentax SDM is more like Sony SAM or low end Canon (EF 50/1.8, noisy as hell), micro motors. Plain and simple.

[GingerBeer]

I'm getting more confused. SDM is a trademark designation for lenses driven by a supersonic motor and you say that Pentax has no ultrasonic motors, yet the K-5 manual talks about "DA lenses with an ultrasonic motor".

Don't both "supersonic" and "ultrasonic" just refer to soundwaves with a frequency above the human hearing range? So SDM lenses, driven by supersonic motors are by definition driven by ultrasonic motors, surely?

[twitch]

Pentax have no ring motors, only micro motors. Canon uses USM to refer to ring motors.

SDM does appear from pentax marketing to cover both what we know as sdm (those mechanisms in the da* glass and the da17-70) as well as the different mechanism in the 18-135 refered to as DC. However when we talk on this forum we refer to sdm as different from DC, which they are, even though pentax likes to refer to them both as being a type of sdm.

Maybe we need to talk of SDM-POS, and SDM-DC. But that's too hard, so it's just sdm or dc here. So the question as to whether the 18-135 is SDM I'd say no it isn't, because when people ask that they don't care about what a marketing broucher says, they want to know whether what drives the 18-135 is the same poor excuse of a mechanism that also drives the 16-50 say, and the answer is they are different mechanisms. That matters because DC motors seem reliable thus far, but SDM is anything but.

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Last edited by twitch; 06-12-2011 at 06:09 AM.

[mbukal]

prošli mjesec kupio sam rabljeni 17-70, stari 1,5 godina, mogu li očekivati probleme kakvih ima 16-50 - nepouzdan SDM?, sada radi super i nemam prigovora

[MSM]

Pentax have no ring motors, only micro motors. Canon uses USM to refer to ring motors.

SDM does appear from pentax marketing to cover both what we know as sdm (those mechanisms in the da* glass and the da17-70) as well as the different mechanism in the 18-135 refered to as DC. However when we talk on this forum we refer to sdm as different from DC, which they are, even though pentax likes to refer to them both as being a type of sdm.

Maybe we need to talk of SDM-POS, and SDM-DC. But that's too hard, so it's just sdm or dc here. So the question as to whether the 18-135 is SDM I'd say no it isn't, because when people ask that they don't care about what a marketing broucher says, they want to know whether what drives the 18-135 is the same poor excuse of a mechanism that also drives the 16-50 say, and the answer is they are different mechanisms. That matters because DC motors seem reliable thus far, but SDM is anything but.

Great post. You made me laugh with the SDM sub-categories. I think this sums up the state of SDM motors at Pentax today. I personally love the DC motor whether it is a ring or micromotor. The only thing that matters to me is that it is fast, quiet, reliable. 2/3 so far and (knock on wood) the third point is looking good too. Bottom line, I am going to avoid all SDM-POS motors...until they come out with SDM-POS Mark II.


I would also say that if the DC is a micromotor it is not the same noisy mechanism in the cheap Can*n micromotor lenses like the 50/1.8.

[thibs]

Yep. I checked and Canon 50/1.8 is is not marked as being usm which means micro motors. Yeaterday a friend of mine used used his canon 50/1.8 and it's micro motorsarenoisy asPentax screwdriven AF. Very noisy. And slow to focus (on an Eos 1000D).

[ogl]

Great post. You made me laugh with the SDM sub-categories. I think this sums up the state of SDM motors at Pentax today. I personally love the DC motor whether it is a ring or micromotor. The only thing that matters to me is that it is fast, quiet, reliable. 2/3 so far and (knock on wood) the third point is looking good too. Bottom line, I am going to avoid all SDM-POS motors...until they come out with SDM-POS Mark II.
I would also say that if the DC is a micromotor it is not the same noisy mechanism in the cheap Can*n micromotor lenses like the 50/1.8.

DC or SDM are micro-motors. Pentax has no ring-motors.
It's not funny. Ring-motor is SPEED. Pentax SDM and DC are smoothness and quiet.
Not speed.

[elho_cid]

Pentax have no ring motors, only micro motors. Canon uses USM to refer to ring motors.

Canon uses USM to refer to both micro USM and ring USM. SDM is similar to Canon micro USM in both speed and silency.
It is true that Pentax never had something like ring USM, but on the other hand Pentax never had anything as bad as conventional micromotors.

[philbaum]

Its important to note that the chronic SDM problems are associated with the 16-50 and the 50-135. Very few if any problems with the rest of the SDM lenses. Personally i have only the 50-135 and the DA-300 and no problems with either over the last 2+ years.

Why some people have had multiple problems and others have had none is a mystery. It would be interesting to correlate reported SDM problems with weather conditions in the locations where problems are reported from. But Hoya isn't talking, and thats a shame.

[Blue]

Pentax have no ring motors, only micro motors. Canon uses USM to refer to ring motors.

SDM does appear from pentax marketing to cover both what we know as sdm (those mechanisms in the da* glass and the da17-70) as well as the different mechanism in the 18-135 refered to as DC. However when we talk on this forum we refer to sdm as different from DC, which they are, even though pentax likes to refer to them both as being a type of sdm.

Maybe we need to talk of SDM-POS, and SDM-DC. But that's too hard, so it's just sdm or dc here. So the question as to whether the 18-135 is SDM I'd say no it isn't, because when people ask that they don't care about what a marketing broucher says, they want to know whether what drives the 18-135 is the same poor excuse of a mechanism that also drives the 16-50 say, and the answer is they are different mechanisms. That matters because DC motors seem reliable thus far, but SDM is anything but.

I have to ask . . . did Hoya TM or patent the SDM-POS.

[ntv1211]

It is very good lens for daily. Nice to have it in bag.