Caution ! Dynamic AF versus single point AF... !

Started Jan 13, 2013 | Discussions thread
Mako2011
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You read it wrong
In reply to rubank, Jan 16, 2013

rubank wrote:

Mako2011 wrote:

Mako2011 wrote:

rubank wrote:


If the camera is set to AF-C and S (no dyn area) it has no problem to focus on a dear, an elk, a rabbit or whatever - yet it does shift focus to a "better contrast target" when dynamic area AF is set (as explained above).

You saying that if you focus on a medium contrast target, while using one of the dynamic AF-Area modes, the camera will switch focus to a stronger contrast target if one falls under the FOV of any of the other focus arrays. I haven't seen any indication of this. So far, they seem pretty good at maintaining lock on the subject one keeps the primary array on. Otherwise, panning would be impossible.

If the camera decides it can´t focus on your chosen target it all by itself decides to focus on something else -instead of letting you know it can´t focus.

Yes, if the primary array can no longer maintain lock due to loss of contrast, it will transition to another contrast if it is adjacent to the primary focus point. That has always been the case with the latest generation of Nikon bodies when using any of the dynamic AF-Area modes.

The dynamic AF-Area modes are not designed (or intended) to track a target as AF-Area mode 3D does. They are designed to aid the photographer in keeping lock on the target in the FOV of the focus point he selects. They help you PAN..not track. Just as the manual indicates. If the target briefly leaves the FOV of the point...the Dynamic AF-Area modes will help maintain lock..but only briefly. The bigger the Area mode (9 vs 21 vs 39 vs 51) the farther the initial target can get before the system reverts back to the primary point. The systems helps you pan not track across the frame. It helps only briefly and in 9pt..not very far. Thinking it's supposed to track...gives many here the false impression that it has picked a new target. In reality, it has given up and assumed the shooter wants something else so looks at the primary point, and if it finds no contrast there, will check the 8 immediately adjacent sensors before giving up completely. I think

You think wrong. I think.
The purpose of AF-C "predictive follow-focus" is to track moving subjects (regardless of which dynamic mode you´ve chosen).

True, but you might note that "predictive follow-focus" is never used to describe the 3 dynamic AF-Area modes in a way that suggests tracking in the way AF-Area mode 3D does. The real quote is as relating to :

"...camera will engage predictive focus tracking to predict final distance to subject and adjust focus as necessary".

This relates only to the focus distance to the subject and not the lateral position of the target as in tracking. You're mixing up terms and usage. You have simply misinterpreted the meaning in the manual much like the OP mus-understood the block diagram. Easy mistake as The manual doesn't do a great job.

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