Canon EOS-1D X Mark II DSLR Camera (Body Only) - Manual (Page 334)

3 Menu Function Settings
334
Movie Servo AF Speed
You can set the Movie Servo AF’s AF
speed and its operation conditions.
This function is settable when [ Movie
Servo AF ] is set to [ Enable ] and [ AF
method ] is set to [ FlexiZone - Single ].
Additionally, the function is enabled
when using a lens supporting slow focus
transition during movie shooting*.
When active : [ Always on ] sets the AF adjustment speed to take effect
at all times for movie shooting (before and during movie
shooting). [
During shooting ] sets the AF adjustment
speed to take effect only during movie shooting.
AF speed : You can adjust the AF speed (focus transition speed)
from standard speed to slow (one of seven levels) or
fast (one of two levels), to obtain the desired effect for
movie creation.
* Lenses supporting slow focus transition during movie shooting
USM and STM lenses released in and after 2009 are compatible. For
details, refer to Canon Web site.
Setting [ AF method ] to [ u +Tracking ] gives the same effect as [ AF speed ]
set to [ Standard (0) ].