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12-29-2008, 11:44 AM   #1
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Are you satisfied with the SDM?

I have only one SDM lens - DA* 16-50mm. It has provide me great images, and seem often very versatile, but still I often don't quite trust the capabilities of the ultra sonic autofocus of the SDM motor. It sometimes works very well, but sometimes it just does not get the focus, or lock, regardless of lighting situation.

My screw focus lenses never fail to works unless it is very dark and no contrast is to be found.

What are your experiences with SDM?


Last edited by gawan; 12-29-2008 at 11:51 AM.
12-29-2008, 11:58 AM   #2
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I agree, my kit lens tends to lock onto stuff in a really obvious way, whereas the 16-50 tends to shift around and not quite hit the focus straight on first time.
A lot of the time i zoom in, focus, then zoom out again to actually get an accurate lock
12-29-2008, 12:23 PM   #3
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I like the 50-135 a lot but the SDM is not on the top of the list as to why. The AF is good enough at most times. But on the K10D, the AF can be a little antsy at times. Perhaps it's due to the longer focus throw.

I'd like to test the 50-135 up against the Sigma 50-150 to see which has the shorter focus throw. I think it would be interesting.
12-29-2008, 01:55 PM   #4
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Sadly, I manual focus Da* 16-50 f2.8 quite a bit lately. The manual focus ring in this lens is rather too loose, not dampened but I still prefer to do this for a faster focus and better result.

SDM can be silent but I found little use even on k20d in 16-50mm focal range.

I hope pentax body has a focus beam support to better the autofocus ability in the dark. It is not so expensive to do so.

12-29-2008, 01:56 PM   #5
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I'm satisfied with the SDM. Its not as fast as the screw focus mechanism in some lenses, but its dead silent, which is nice for taking candid photos.

The 16-50 seems to focus very quickly, the 50-135 is slower, but it also has a large throw.

I did not purchase these lenses based on SDM, I based my decision on the sample photo's that I saw from both, and I would buy them again without SDM.
12-29-2008, 02:48 PM   #6
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QuoteOriginally posted by apeman Quote
The 16-50 seems to focus very quickly, the 50-135 is slower, but it also has a large throw.
that's the problem w/ pentax's AF tech. it seems that instead of using faster and more (probably) reliable ring motors they use the old micromotors. to compensate this in the later lenses, they shorten the focus throw to an amount that isn't very useful for MF, like the DA* 60-250
12-29-2008, 11:14 PM   #7
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Works ok for my lens

The only SDM lens i have is the DA 300 and it works fine in a variety of conditons. I have noticed in dimmer indoor situations (ok, it was raining :-)), the SDM may take a coupla tries to hit the focus correctly. I've also noticed that with a TC on outdoors, the lens also starts missing the focus in lower light situations. My Tamron 18-250 is about the same speed at the wider end, and the SDM seems better than its AF.
12-30-2008, 12:34 AM   #8
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QuoteOriginally posted by apeman Quote
I'm satisfied with the SDM. Its not as fast as the screw focus mechanism in some lenses, but its dead silent, which is nice for taking candid photos.
.
This has become an issue for me. One thing that is nice about candids/street with a good p&s is essentially silent operation. The clack of a dSLR isn't so bad in most cases, but the damn screw drive, especially when the lens is hunting, can disrupt the moment. I love how the SDM is quiet (basically bringing it on-par with my 5 year old low-end Nikon setup). It isn't especially fast, but tends to be pretty accurate with my 50-135*.

12-30-2008, 02:49 AM   #9
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QuoteOriginally posted by k100d Quote
that's the problem w/ pentax's AF tech. it seems that instead of using faster and more (probably) reliable ring motors they use the old micromotors
What do you mean by old micromotors? How does the Pentax SDM work? Are you saying that it is not even a piezoelectric motor but simple electromagnetic motor? I really searched the web but couldn't find specifications on Pentaxes SDM - from wiki I understood that it is some kind of piezoceramic drive, but you confused me greatly.

I was just thinking about getting the DA 17-70 but after this thread I am rethinking this choice....

Thanks!
12-30-2008, 08:47 AM   #10
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In my opinion the best SDM focusing lens that I've tried out on my K20D is the DA* 200mm f/2.8.
12-30-2008, 08:49 AM   #11
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i'm no electronics expert at all, but i do know that what Pentax uses isn't what Canon, Nikon, Sigma or Sony use in their best lenses which are ring motor type motors.
12-30-2008, 08:52 AM   #12
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QuoteOriginally posted by gawan Quote
I
What are your experiences with SDM?

When I owned the DA* 16-50, one of my complaints was the SDM. I found it to be very sluggish.

There always seemed to be just a bit of a hesitation in it when attempting to autofocus.

I did not find it to be as fast as the screw drive and it did not seem to help the camera lock on as fast.

Those issues, and the sheer bulk of the lens, were the reasons I sold it and went back to the DA 16-45.
12-30-2008, 01:26 PM   #13
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Thank you for the comments! One thing I have noticed is that my SDM does seem to get more unsure when the temperature drops. I did not notice this last winter, so there may be some "development" in the history on my specific lens...
12-30-2008, 02:59 PM   #14
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QuoteOriginally posted by gawan Quote
Thank you for the comments! One thing I have noticed is that my SDM does seem to get more unsure when the temperature drops. I did not notice this last winter, so there may be some "development" in the history on my specific lens...

Man, I thought it was just me. I noticed the same thing with my 50-135. I thought it was all just in my head but apparantly not. This is my first winter with the lens and I'm noticing the unsure autofocus as well, even in good light. Seemed faster in the spring. I'm thinking about dropping it for the Sigma 50-150 if I can find some feedback on that lens.
12-30-2008, 07:16 PM   #15
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This is an interesting thread, as I've thought about exchanging the 16-45 for the DA17-70 for the SDM capability, along with the increased zoom range. Now I'm beginning to question the wisdom of doing that, as faster focusing is more important to me than quiet focusing.

Heather
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