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View Poll Results: which SDM implementation would you prefer?
Ring SDM: very fast and precise, incompatible with *ist D/DS/DL, K100D 4683.64%
Micro SDM (current implementation): much slower however lenses compatible with all bodies 916.36%
Voters: 55. You may not vote on this poll

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01-31-2008, 06:40 AM   #1
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Another SDM poll

There are two types of ultrasonic in-lens autofocus drive implementation:

1) Ring ultrasonic motors, drive shaft AF is dropped completely. Ring type ultrasonic motors are very fast and precise, they are much faster than conventional "skrewdriver" autofocus motors. However this implementation leaves out conventional AF mechanism, so such lenses won't focus on bodies without SDM support (i.e all *ists and K100D, all out of production now).

2) Micro ultrasonic motors which are hooked up to conventional "skrewdriver" AF mechanism. Such motors are underpowered and not so precise. In fact lenses with micro ultrasonic motors they are even slower than driven by conventional AF (user tests proved that K10D focuses faster with conventional AF than with SDM).
This is current Pentax SDM implementation in DA★ lenses. Such lenses autofocus on all bodies.

So, my question is: which implementation would you prefer?

1) Ring type SDM -- very fast, precise and incompatible with *ist D/DL/DS and K100D;

or

2) Micro SDM (current implementation) -- not so fast (slower than conventional AF) and compatible with all bodies.

01-31-2008, 07:08 AM   #2
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A tough call, Edvinas. I think I'd like to see Pentax maintain backwards compatibility with the older digital bodies just a little bit more than I'd lust for the ring USM, even though my K10D would be just that little bit quicker and more precise. Still, the existing SDM works well enough for my needs, so I'd just as soon have SDM lenses that work with earlier bodies for the sake of fellow Pentaxians.
01-31-2008, 07:18 AM   #3
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Even though I have an *istD along with the K10D, I think there is not an issue of compatibility, because when the time comes to purchase my next lens, I will have already bought a thrid DSLR and the K10 can work as a back up for SDM motors. The *istD will become primairly a MF and K mount platform.
01-31-2008, 02:35 PM   #4
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QuoteOriginally posted by christinelandon Quote
A tough call, Edvinas. I think I'd like to see Pentax maintain backwards compatibility with the older digital bodies just a little bit more than I'd lust for the ring USM, even though my K10D would be just that little bit quicker and more precise. Still, the existing SDM works well enough for my needs, so I'd just as soon have SDM lenses that work with earlier bodies for the sake of fellow Pentaxians.
I personally think that the future lies in ring motors. I do understand why Pentax equiped the first SDM lenses with micro motors, but I think that it is only a temporary solution. I don't doubt that many people will say "bad bad Pentax" when they'll equip new DA lenses with ring SDM only - remember crippling K-AF mount but I think that it is inevitable. DA lenses are not (mostly) designed for full-frame bodies, they are designed for cropped digitals - and *ist and K100D are out of production. So, the benefit of keeping compatibility in this direction doesn't impress me, ring SDM seems (at least to me) to be the greater benefit.

On the other hand, I also expect that Pentax will keep in-body drive still for a long time, probably longer than the other companies. There are too many good lenses and Pentax cares about the compatibility (well, sometimes too much as I noted above). IMHO, for some kinds of compact lenses (like the famous pancakes) is the in-body drive necessity - maybe another reason why to keep it.

I would be pleased, if the in-body drive remained, while new DA lenses were born mostly with ring SDM.

Anyway, if Sigma fulfills what has been just announced, the market will tell soon whether the in-body drive compatibility is really so necessary. I'm really looking forward to 70-200 f/2.8 with HSM for Pentax!

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