DC motor or ultrasonic?

In the 150-450mm lens thread I noted that in a recent comparison the Pentax was unique in using a DC motor for focusing whereas the other manufacturers (Nikon, Canon, Sigma, Tamron, Sony) all use an ultrasonic system. Does it have anything to do with the quick-shift system? I presume there are good reasons Pentax are making this choice for their new lenses, does anyone know why this is?

Do other makes have a quick-shift system?

The DC motors have proved to be quick and reliable. I expect that each lens is kitted out in a way appropriate to its design. It will be interesting to see if DC replaces SDM in all future lenses.

SDM Lenses

I have a battery of DA*Lenses and I have up to now not found anything optically better in Telephotos. (in wider primes their are very good options as their are in some zooms some of which are Ricoh / Pentax).

However the SDMs are prone to failure in early releases of the DA*range and I have had one fail twice (DA*50-135) both on new lenses (the second a replacement provided by Pentax for the first ,which failed with in a year).
I must say that whilst they are definately my most used and reveered lenses the SDMs and focus in general is definately very good when it is "behaving" but is at best tempramental at worst unreliable; two of my DA*s are newish and I have learned two tips that keep them functionin;

1. Always keep the contacts clean, carefully buffing frequently
2. Always carry a small flat head scew drinver as "twiddling" the small drive sprocket on the lens seems to "wake them up " when they decide to have "day off".

This was a tip that came via PU some years ago and for me it works.

I have just bought the HD 150-450 which has the DC motor and apart from the now well reported "blistering" optical performance I am glad to say the focus is definately crisp, wholly reliable and spot on.

Coupled with, (in my view) the "undersold improvements " on the K3II this combination has made redundant most other lenses I have in the telephoto range.

I am usually deflated by the actual functional performance of new Lenses and Cameras that are hyped up so much butin this case, whether it is the DC motor, the improved K3 II, or the combination of both: the functional performance has consigned my K3 and the DA*s (300, 200 and 60 -250) to the cupboard for the time being.

So if the DC motor stands the test of "work and time" and maintains it's functionality as it is now, then I for one would not be sorry to see the SDM technology superceded.

Interestingly someone in another current post/ thread mentioned what a fan they were of the much underrated 18-135, well so am I, and that is not SDM either, it is DC: mine (18-135) is optically wonderful and has been hammered; yet it just goes on and on like the day I bought it, interestingly that lens focusses like lightening on the K3II as well, maybe that is another pointer about the way to go.

A bit of research shows that on new Nikon lenses there is a switch for M or M/A in addition to the selection switch on the camera body which seems an unnecessary duplication. M/A allows manual focusing whilst in Autofocus. Same arrangement for Canon lenses.

Good to hear Canikon are catching up

As long as Pentax don't bring out a lens with an AC Motor I couldn't care less...... although I'm never far from a 13 amp socket even when I'm down at the pub

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Pentax had an ultrasonic motor (SDM) and it was notoriously unreliable (particularly with the flagship DA* 16-50 and DA* 50-135 zooms). Dropping that was one of the essential pre-requisites to reviving the brand.

My DA* F4 300mm is an early one, whisper quiet and works fine. I read heat from early cramped circuit boards and fragile gearing were the big enemies of the 16 - 50 and 50 - 135mm models. Shame they never did a proper recall and a clearly identifiable fixed MKII of such. My 18 - 135 zoom is DC and does make a noise. Wide zooms such as my 12 24 F4 and wide primes like the DA 15mm are fine as screw drive as they have little focus travel. The question is will the, uncommunitive in the UK, Ricoh continue to revamp the APSC lens range include the SDM star series or concentrate on the 35mm frame models?