Busting the Lens dictates Focus Speed Myth

Started Mar 22, 2013 | Discussions thread
Matt
Senior MemberPosts: 2,338Gear list
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In reply to Sovern, Mar 23, 2013

I notice a big difference between Ring USM L lens AF and the AF of shitty lenses ...

AF speed depends on the AF motor in the lens and the amount of lenses it has to move over how much of a distance. Here is where primes may have an advantage...

For reasons that arent too clear to me, the body also affects lens speed. That said, if your body is the limiting factor then that may be why you dont see a difference

Sovern wrote:

Why is that I hear so much on this forum and other forums that more expensive lenses especially primes AF faster than cheaper lenses and the kit lens a long with other cheap but more than capable lenses are such a bad lens for AF speed?

I have one of Canon's fastest focusing lenses (Canon 85 1.8 USM) and the kit lens and they both AF at the speed speed no manner the lighting conditions.

I have also had the Tamon 17-50 2.8 and 50 1.8 in the past and have never felt a difference in AF speed between any of these lenses they all lock on focus very fast.

Is this "This lens has faster AF" a myth sort of like how people claim that their $2,000 prime is "sharper" than a $350 primes or zoom (myth in my opinion)?

From what I have read the AF focusing system built on the camera determines the AF speed and not the lens itself (besides cycling between MFD and infinity being a minor difference obviously).

Whats your take on it?

Personally I'm not convinced.

I believe from my own personal experience that the body determines AF speed as my 40D AF's faster than my xsi but all of my lenses AF just as fast/precisely no manner the lighting conditions from my own experience using them myself.

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Canon EOS 400D
Sigma 24-70 HF
Canon 50 f1.8

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