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Author Topic: Auto Focus Technology for Low Light Moving Subject Shooting  (Read 6948 times)  bookmark this topic!
427l
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Auto Focus Technology for Low Light Moving Subject Shooting
« on: September 20, 2008, 02:08:10 AM »

I am new to the forum and could not find any previous discussion on this topic. I have a 40D and enjoy shooting wildlife in low light conditions. Does one manufacturer (i.e. nikon, canon, sony) have "better" AF technology than the other for this application? By better I mean faster, more consistent focuses? I have read that the "cross-type" AF points are best for tracking moving objects and that prosumer/pro Nikon's use more of these points (15 vs 9 w/ f/5.6 or faster lenses) than Canon's 40D/1D MKIII. I understand that all these cameras utilize a principal called "phase detection" to auto focus themselves however Nikon also talks about how they use "color" to detect "3D movement", Canon doesn't mention this. I'm not sure if this is Nikon marketing stuff or a real difference/advantage? I have never shot with Nikon and I have have had good luck thus far with my 40D's AI Servo AF mode although I'm not sure if I've maximized the 40D's capability in my shooting thus far. I've been renting lenses up til now and I'm considering buying something like a 70-200mm L series lens. Before I begin to really invest in one brand I wanted to understand if these manufacture's AF technologies (nikon vs. canon vs. sony, etc) are something I should consider prior to buying more Canon products. I guess real world performance is what matters and I'm hoping some in this forum have more experience on this issue.

427L
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Bob Atkins
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Re: Auto Focus Technology for Low Light Moving Subject Shooting
« Reply #1 on: September 20, 2008, 12:26:30 PM »

It's a good question and one I don't know the answer to. I don't know of any comparative ,quantitative, tests of autofocus under low light conditions between Nikon and Canon.

The only empirical evidence is that there's a pretty even split between Nikon and Canon when it comes to the equipment used by professional sports and nature photographers, two groups of users who often need fast and accurate AF, sometimes in less then ideal lighting. Perhaps Canon has slightly more users, but probably for reasons other than AF performance. If either system had a significant advantage you'd see photographers who depend on accurate AF for their living shifting to one or other system.

I know in one published test that the Canon EOS 1D MkIII showed better tracking AF (servo AF) accuracy on a moving target (approching runner) than the Nikon D3, but the test was done in good light. But that's just one test under one specific set of conditions with two specific cameras.

I suspect that the Nikon and Canon AF systems are pretty close in performance. You can never say they are identical, but I don't see any evidence that either one is significantly better when taken over a set of typical operating conditions.

In general, at least with Canon, you get the best AF performance with the center AF zone selected and a fast (f2.8 or faster) ring-USM lens. That allows the use of the center cross sensor in high precision mode.
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yayas
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Re: Auto Focus Technology for Low Light Moving Subject Shooting
« Reply #2 on: February 23, 2009, 07:45:25 AM »

I have question concerning the high precision AF.
I read an EF 50/2.5 Compact Macro review that stated the lens is one of the exceptions of high precision (cross type?) AF.
So I would assume that my older 50/1.8 Mk-I is excluded too.

Would a Tamron or Sigma /2.8 benefit from this high precision AF?
Or it's exclusive for fast-Canon-USM lenses?

Thanks.

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Bob Atkins
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Re: Auto Focus Technology for Low Light Moving Subject Shooting
« Reply #3 on: February 23, 2009, 10:15:00 AM »

I wasn't aware that the macro 50/2.5 won't activate the f2.8 high precision AF sensor. At full macro (1:1) I can see how it might not siince the effective speed of the lens would drop below f2.8 due to the amount of extension involved. However at normal focus distances I would have thought it would be like any other fast lens.

I'm sure the 50/1.8 (II) can use the high precision sensors and as far as I'm aware all other lenses f2.8 and faster (including 3rd party lenses) are the same.
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