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03-25-2010, 04:55 PM   #1
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AF speed: Lens or body?


Not yet considering SDM, What determines AF speed? the body or the lens? If I take the exact same lens in my K100DS and put it in say a K7 or K-x, will it focus faster? Much faster?


03-25-2010, 05:18 PM   #2
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It actually depends on both.

But to answer your hypothetical, using a K7 or Kx will focus faster than a K100DS using the same lens.
03-26-2010, 07:41 AM   #3
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AF speed is mainly body I believe. The lens helps but definitely body dependent.
03-26-2010, 07:48 AM   #4
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Along with AF issues such as front focus & back focus are dependant on the body.

03-26-2010, 09:02 AM   #5
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QuoteOriginally posted by epqwerty Quote
AF speed is mainly body I believe. The lens helps but definitely body dependent.
The lens is also part of the equation. Put a slow motor in a lens or a long focus throw and the focusing time will be slow.
03-26-2010, 05:25 PM   #6
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AF depends on both the body and the lens being used. Even with body based AF, the lens has great impact on AF speed because every lens has different lens travel (the amount the focus ring has to turn).
03-27-2010, 01:15 AM   #7
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K-7 or K-x paired with lenses like 18-55, 16-45, 12-24, 10-17 (lenses with short focus throw) will be very fast.

I did an unscientific comparison between my K-7 & DA18-55wr and Nikon D80 & AF-S 18-55. My combo was faster!

Ok, the Nikkor 18-55 is not a great lens, but its the kit lens, as is the DA18-55wr.
03-27-2010, 03:30 AM   #8
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Short answer: Both body and lens.

Long Ans: Body - stronger motor will turn the lens faster, couple with a good AF sensor in the body will make it better. Weak AF sensor w strong motor will just have a faster lens hunting

Lens - lighter lens has less load to the body motor, so it can turn faster. Focus throw distance in a lens will also affect the speed, as a quater turn throw should be faster than a half turn. Modern AF lenses usually have short throw to optimise AF speed, but that make manual focus harder.

In your case, K7 has a stronger motor and better AF sensor than K100DS, so all your lenses should be faster. I think KX is the same, just the motor is not as strong as K7. Thats my subjective assessment, as I own both.


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