Hi folks. I'm on a bit of a learning curve with my new D700 and just want to check I've understood this part of the AF system correctly.
If I'm photographing something like birds in flight or other fast moving subject and I have the following settings on my camera:
a1 AF-C priority selection Release + focus
a3 Dynamic AF area set to 51 points (3D-tracking)
a8 AF point selection AF11 11 point
I set the front focus switch to C, for AF-C to let me continuously focus
I select the back focus switch to dynamic area mode.
As I understand it, if all of the above are set, I can select a focus point of the 11 central ones manually by using the selector dial and press the shutter half way down. Therefore, if I've used, for example the centre point, to focus on the bird's eye. As long as I keep the shutter half depressed the dynamic area focus should track the bird through all 51 points.
Your only slight misunderstanding is that it's not the central 11 AF points you can choose from with those settings - it's a subset of the full 51, but spread across most of the AF array. Exactly which 11 is illustrated on page 289 of the D700 manual.
I tend to set a3 to 9- or 21-points for birds in flight, as I find using 51-point can slow down AF tracking - but it really depends on the size of the bird and how much of the frame it fills. If you're less confident about keeping the selected AF point on the bird, 21 tends to be better than 9.
Thanks Brian, I got the relevant part of the manaul now.
Am I right in assuming that once I select an AF point on the bird, the 3D tracking will try and move with it as it flies so that even if I can't keep the selected point on the bird the system should follow it?