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DPChallenge Forums >> Hardware and Software >> Focus: The camera or the lens?
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Panasonic Lumix DMC-GH4
Panasonic Lumix 20mm f1.7 ASPH
 04/25/2012 04:59:23 AM · #1
This is one of those things I must have skipped over...and really should already know.

When one is doing something like sports photography, and sets his camera to AF...is it the lens or the body that determines how fast it can track the moving subject? OR is it a combination of both. Until now, I've always set my camera focus at center and waited for the *beep* before pushing for the snapshot. I've never actually tried to follow a moving subject allowing the camera or lens to try and track the subject...in fact, I'm not certain how I would set that up (AI servo I believe).

This is something I should know, but don't. So I ask DPC...the answer to all my questions!!
Canon EOS-5D Mark II
Tamron SP 24-70mm f/2.8 Di VC USD Canon Mount
04/25/2012 06:02:52 AM · #2
The camera determines how quickly it can determine the focus. This is based on the available light, sensitivity/accuracy of the focus points, etc. Some camera will be much better than others at this. The focus motor of each lens performs differently as well. So the ability of the lens to attain the focus the camera tells it to will be dependent on the lens selection.

So the answer is both.

When tracking a subject you want al servo. You focus on a subject and the camera will follow and maintain focus. The speed at which it does that is dependent on the body/lens combo used.

Message edited by author 2012-04-25 10:58:25.
Canon EOS R5
Canon RF 24-70mm f/2.8 L IS
 04/25/2012 10:30:39 AM · #3
As Mike stated, the answer is definitely "both." The performance is determined by the interaction between the lens and AF system, and there are a lot of variables, such as the max aperture of the lens (f/2.8 lenses will enable faster, more accurate focus on many bodies), the type of focus motor, the AF detector, the AF processing system capability... the list goes on.
Canon EOS-5D Mark II
Tamron SP 24-70mm f/2.8 Di VC USD Canon Mount
04/25/2012 11:19:47 AM · #4
also remember before you shoot the lens is wide open and then drops the aperture down to where its set when you shoot. so like kirbic said, faster lenses will allow faster more accurate AF.

this is important as the more accurate cross point AF points on the bodies aren't actually cross type unless you are using faster glass. cross point sensors have two sensors that are 90 degrees to each other and one of those sensors usually requires a larger aperture to work, something like 2.8 and wider.

using an f4 lens wont gain you any benefit of the cross point AF points, but a 2.8 lens will.

but, note that in some cases really fast glass can take longer to focus if the dof is too shallow, even though the available light is more.

so to summarize:

the body needs to be able to track and gather info as fast as possible and the lens needs to provide as much data as possible and be able to quickly do what the camera tells to to do.

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