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Old Dec 11, 2003, 12:16 AM   #1
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Default 10D AF question

I've read this fact about the 10D in several places:

The 10D does not guarrenty where in the Depth Of Field (DOF) the AF point will be, only that it will be within the DOF.

Recently I saw it stated on another forum and others did not dispute this. I know that I've repeated it here on several occasions.

Recent discussions I've had have lead me to doubt this. Does anyone really know if this is true? Have you read it any where other than said by me?

Steve, do you have any idea?

Eric
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Old Dec 11, 2003, 8:37 AM   #2
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Eric

Think in term of the sensor... How does it know what the DOF is (especially when the lens is wide open)? It jobs is to only perform the best AF as it possibly could regardless of what the DOF is going to be the seconds the lens is stopped down and captured by the sensor...

I'm sure the manufacturers are smarter than this and probably include 3D maps in the lens to fine-tune modulation characteristic or transfer function (much like a car engine) for each lens, but even so a user can add a 1.4x/2x TC or diopter close-up adapter to mess up the whole equation so there you have it... Focusing with relation to DOF is probably anecdotal! ops:
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Old Dec 12, 2003, 12:35 AM   #3
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The f-stop point is a very good one. If the camera focuses at f2.8, and then stops down to f8 and takes the picture... that stopping down will change the DOF (from all I've read.) So how does it get it right? It must try to focus in such a way that it doesn't matter how much you stop down, or it can calculate how the DOF will change when it stops down and takes that into account when it announces it's in focus.

But that still doesn't mean that the camera can't place the focus point further into the DOF on a camera with a better AF subsystem. Once you find out where the DOF is, I would bet you can calculate its depth and then place the focus point as far in as you want (i.e. as precisely as you want.) One camera could place it further in than another. Why not?

Ahh, as you say, because you can add a TC or some other thing that would lie (like you can tape pins on the 1.4xTC.) The camera will take longer to focus, but it will still AF correctly even when the aperture is reported incorrectly to the body. Why doesnít the lying cause it to miss focus?

Humm. Maybe this isn't a fact after all. Pity. Itís one of the improvements I was hoping to get when (in how many years) I upgrade to a camera with a better AF system. I'm really sick of a badly place DOF.

Eric
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