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04-27-2011, 06:20 AM   #1
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af speed comparison

Hello,

is there an af-speed comparison between different screw driven lenses somewhere?
The kit lens i have is relatively fast but i want to upgrade and i couldn't find information on af speed of the upgrade options on the net.

cheers,

derrdaniel

04-27-2011, 06:45 AM   #2
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I don't know if there is a comparison chart somewhere. However, I can say that some screw-driven lenses have faster AF than others. The speed depends on how long or short the focus throw is.
04-27-2011, 07:40 AM   #3
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so focus speed is inverse proportional to the number of turns the screw drive needs to do to focus from infinity to near focus? (e.g. 10 Turns are faster than 20 turns)

maybe we should start a database here or add the information to the lens review section...(counting the turns should be easy if you manually turn the screw while the lens is unmounted)
04-27-2011, 08:28 AM   #4
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Well at least in my collection the DA 40mm/f2.8 Ltd is the fastest lens in AF.

04-27-2011, 08:29 AM   #5
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Well, I don't think it's that simple. I'm sure other factors must come into play too including the largest aperature available, the weight of the elements that need to be turned, etc.
04-27-2011, 09:20 AM   #6
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QuoteOriginally posted by jake14mw Quote
Well, I don't think it's that simple. I'm sure other factors must come into play too including the largest aperature available, the weight of the elements that need to be turned, etc.
At the end of the day, I think the OP is trying to find a lens that can be brought into focus on the intended subject as quickly as possible. Achieving this goal requires good performance on the part of both the lens and the camera body.

When evaluating the ability of a lens to respond to the commands issued by the camera's AF system, you should also consider what distance range is relevant to the type of shooting you are interested in. Some lenses (notably the DA 35 Macro Limited) have a very short focus throw for subjects between (say) 5 feet and infinity, but much longer to get down to the minimum focus distance.
04-27-2011, 09:29 AM   #7
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QuoteOriginally posted by RonHendriks1966 Quote
Well at least in my collection the DA 40mm/f2.8 Ltd is the fastest lens in AF.
Wouldn't it be nice every lens could AF like a DA40?
04-27-2011, 09:49 AM   #8
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QuoteOriginally posted by JHD Quote
Wouldn't it be nice every lens could AF like a DA40?
That would be great and more intelligent AF-system in our camera.

04-27-2011, 04:41 PM   #9
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QuoteOriginally posted by RonHendriks1966 Quote
That would be great and more intelligent AF-system in our camera.
I agree. It would be nice to see pentax take sports photography a little more serious... not that it is all I do, but it is nice to have something that can track a subject very fast and effectively

cheers
04-28-2011, 09:24 PM - 1 Like   #10
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I just made a video and article on the full focus speed (keeping the lens cap on the camera) as well as how each lens sounds when auto-focusing with all of the lenses I had available to me.

Pentax Lenses: Auto-Focus (AF) Sound Test Roundup | photographybanzai.com

That was fun. Of course, the screw-drive AF lenses are louder and the DA 40mm f2.8 Limited is crazy fast.
04-29-2011, 04:41 AM   #11
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QuoteOriginally posted by sjwaldron Quote
That was fun. Of course, the screw-drive AF lenses are louder and the DA 40mm f2.8 Limited is crazy fast.
And I really thought that making pictures of brickwalls was the craziest thing to do

Fun to watch and you have a nice lenscollection.

Reputationpoints for this silly video
04-29-2011, 07:40 AM   #12
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Now we get the idea of the "S" in SDM stands for - slow... sleepy... sluggish... sloth... spiritless...
04-29-2011, 08:55 AM   #13
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QuoteOriginally posted by JHD Quote
Now we get the idea of the "S" in SDM stands for - slow... sleepy... sluggish... sloth... spiritless...
At least the 55mm, the 300mm spins around pretty fast for such a big lens.
04-29-2011, 09:13 AM   #14
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QuoteOriginally posted by RonHendriks1966 Quote
And I really thought that making pictures of brickwalls was the craziest thing to do
Fun to watch and you have a nice lenscollection.
Reputationpoints for this silly video
Haha, maybe it was fun in the sense of making a video and a first time at using an external microphone.
04-29-2011, 09:24 AM   #15
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Screw-driven is almost always focus faster than SDM, except DA 55-300mm which is ridiculously long focus throw.

Screw-driven AF in F, FAJ or FA lens series are faster than in DA, DAL and DFA series.

DSM in DA 17-70mm AF is much faster than DA* 55mm and DA 50-135mm because of its very short focus throw.
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