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12-22-2013, 10:46 AM   #1
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DA* SDM vs DA DC Motor AF (Auto Focus) Speed ?

For those of you who have both technologies, the SDM AF (DA*) and the DC Motor AF (DA), how would you compare the AF speed?, currently I have the 18-135mm Lens and I am thinking on buying the DA* 16-50mm and the DA* 50-135mm for lens and optics quality and f/2.8 constant across the Focal length. I think the 18-135mm AF is good, but I don't think is blazing fast. Comments and opinions are welcome, thanks.

12-22-2013, 10:48 AM   #2
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The 18-135 is very quick to focus - on par with most screwdrive lenses.Having played a little with the DA*16-50 and the DA*50-135, they are much slower.
12-22-2013, 10:50 AM   #3
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QuoteOriginally posted by JinDesu Quote
The 18-135 is very quick to focus - on par with most screwdrive lenses.Having played a little with the DA*16-50 and the DA*50-135, they are much slower.
Would you say that "screwdriver" AF is the fastest technology available on Pentax today?, the concerns I have with screwdriver AF is the level of noise it creates, even on the Pancake Limited lenses is very noisy, what's your opinion?
12-22-2013, 11:17 AM   #4
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QuoteOriginally posted by brosen Quote
Would you say that "screwdriver" AF is the fastest technology available on Pentax today?, the concerns I have with screwdriver AF is the level of noise it creates, even on the Pancake Limited lenses is very noisy, what's your opinion?
Screwdrive AF is the fastest focusing system on Pentax lenses. This is partly because the fastest focusing lenses for Pentax are screwdrive and have also the shortest focus throws. That combination makes screwdrive lenses the fastest. An equivalent screwdrive lens and SDM lens would have the screwdrive winning - see the threads where people convert their SDM 16-50 and SDM 50-135 to screwdrive.

DC is pretty quick and will be on par with most screwdrive lenses. Sigma HSM is about as quick as DC.

12-22-2013, 11:55 AM   #5
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I think SDM isn't that much different from screw drive as far as speed. The problem with most of the lenses with SDM is that they have pretty long focus throws. The 18-135 is pretty fast because it has a short focus throw. The 50-135 and 55 are really bad in this regard.
12-22-2013, 01:47 PM   #6
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Interesting... I'd actually expect that to be the opposite. I know that Ed did a spot on his Photouniverse channel about the Tamron 70-200mm f/2.8 and that the screwdrive is fast. I'd have to agree.
Is it faster than SDM or DC - I don't know - I'll find out when I try out the 18-135WR (vs. my Sigma 18-200mm w screwdrive).
The only thing I notice with screwdrive - it 'can' hunt a bit at the end (i.e. it'll be close - then zoom in/out a couple of times before locking) in which one can perceive that its slow. Again - I'll try this out soon.
I've also read that the AF motors in general on Pentax are relatively slow compared to say... Canon/Nikon. Since I'm generally not shooting sports, I don't care. For me - the screw drive is plenty fast, and VERY reliable (has anyone had a screwdrive failure ? There are reports of SDM failure, haven't seen any on DC )

Someone actually posted this on YouTube - 50-150 vs. 18-135 vs. 50mm

12-22-2013, 02:02 PM   #7
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QuoteOriginally posted by formercanuck Quote
Interesting... I'd actually expect that to be the opposite. I know that Ed did a spot on his Photouniverse channel about the Tamron 70-200mm f/2.8 and that the screwdrive is fast. I'd have to agree.
Is it faster than SDM or DC - I don't know - I'll find out when I try out the 18-135WR (vs. my Sigma 18-200mm w screwdrive).
The only thing I notice with screwdrive - it 'can' hunt a bit at the end (i.e. it'll be close - then zoom in/out a couple of times before locking) in which one can perceive that its slow. Again - I'll try this out soon.
I've also read that the AF motors in general on Pentax are relatively slow compared to say... Canon/Nikon. Since I'm generally not shooting sports, I don't care. For me - the screw drive is plenty fast, and VERY reliable (has anyone had a screwdrive failure ? There are reports of SDM failure, haven't seen any on DC )

Someone actually posted this on YouTube - 50-150 vs. 18-135 vs. 50mm
Actually after looking at the video the 18-135mm lens has a pretty fast and silent AF
12-22-2013, 02:17 PM   #8
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Someone actually posted a video with SDM 18-270 - couldn't believe how quiet it was. At the price it is - I wouldn't get the 18-270mm SDM anyways, and its not even WR!



12-23-2013, 09:14 AM   #9
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In my experience the AF on the 18-135 is noticably faster than on my screw drive lenses (da 15, 35, 70, Tam 70-200), especially in low light. You hit the AF button and the focus is just there and its accurate too. The 50-135 is often a bit slower than most others (except the da 35 2.8) but I would still consider it adaquate.
12-27-2013, 05:10 AM   #10
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QuoteOriginally posted by TopherTheME Quote
In my experience the AF on the 18-135 is noticably faster than on my screw drive lenses (da 15, 35, 70, Tam 70-200), especially in low light. You hit the AF button and the focus is just there and its accurate too. The 50-135 is often a bit slower than most others (except the da 35 2.8) but I would still consider it adaquate.
How indicative is the speed from close range to infinity? Focus accuracy, focus tracking, ... are probably much ore interesting.
SDM focus is a nice add-on for DA* lenses. Less noise and typically much more interesting optical formulae. Pentax SDM is not the fastest AF, but still defines the state of the art in Pentax land. Going backwards to screwdrive AF makes little sense.
12-27-2013, 02:22 PM   #11
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QuoteOriginally posted by JinDesu Quote
Sigma HSM is about as quick as DC.
But it is not as fast as screwdriver. I have old Sigma 50-500 with screwdriver AF and modern 50-500 OS with HSM only. The HSM version is remarkable slow as an older lens.
12-27-2013, 02:53 PM   #12
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QuoteOriginally posted by formercanuck Quote
Interesting... I'd actually expect that to be the opposite. I know that Ed did a spot on his Photouniverse channel about the Tamron 70-200mm f/2.8 and that the screwdrive is fast. I'd have to agree.
Is it faster than SDM or DC - I don't know - I'll find out when I try out the 18-135WR (vs. my Sigma 18-200mm w screwdrive).
The only thing I notice with screwdrive - it 'can' hunt a bit at the end (i.e. it'll be close - then zoom in/out a couple of times before locking) in which one can perceive that its slow. Again - I'll try this out soon.
I've also read that the AF motors in general on Pentax are relatively slow compared to say... Canon/Nikon. Since I'm generally not shooting sports, I don't care. For me - the screw drive is plenty fast, and VERY reliable (has anyone had a screwdrive failure ? There are reports of SDM failure, haven't seen any on DC )

Someone actually posted this on YouTube - 50-150 vs. 18-135 vs. 50mm

Pentax Autofocus Test 18-135 - YouTube
I also believe that the Pentax "screwdriver" is tad slow. Of course, this is comparing DSLR's of the same year.

I'd be curious to know if the new improved screwdriver of the K-3 is up to canikon levels...and how good is AF locking at low light.
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