DUsing Autofocus in Live View

Autofocus is slower in live view and the monitor may brighten or darken while the camera focuses. The camera may be unable to focus in the situations listed below (note that the focus point may sometimes be displayed in green when the camera is unable to focus):

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, or the subject is lit by spot lighting or by 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

In addition, the subject-tracking AF may be unable to track subjects if they move quickly, leave the frame or are obscured by other objects, change visibly in size, color, or brightness, or are too small, too large, too bright, too dark, or similar in color or brightness to the background.

Live View 173