Nikon D6 Reference Manual page 214

D
Using Autofocus in Live View
•
The camera may take longer to focus in live view than during viewfinder
photography. The camera may be unable to focus if:
- The subject contains lines parallel to the long edge of the frame
- The subject lacks contrast
- The subject in the focus point contains areas of sharply contrasting
brightness
- The focus point includes night-time spot lighting or a neon sign or
other light source that changes in brightness
- Flicker or banding appears under fluorescent, mercury-vapor,
sodium-vapor, or similar lighting
- A cross (star) filter or other special filter is used
- The subject appears smaller than the focus point
- The subject is dominated by regular geometric patterns (e.g., blinds
or a row of windows in a skyscraper)
- The subject is moving
•
The monitor may brighten or darken while the camera focuses.
•
The focus point may sometimes be displayed in green when the camera
is unable to focus.
•
Use an AF-S or AF-P lens, as the desired results may not be achieved
with other lenses or teleconverters.
A
f : The Center Focus Point
In all AF-area modes except [Subject-tracking AF], a dot appears in the
focus point when it is in the center of the frame.
162
Choosing How the Camera Focuses (Focus)