This option controls how autofocus adjusts to changes in the distance to the subject when AF-C is selected during viewfinder photography.
Blocked Shot AF Response
Choose how quickly focus responds when something passes between the subject and the camera. Choose from values between 5 (Delayed) and 1 (Quick). The higher the value, the slower the response and the less likely you are to lose focus on your original subject. The lower the value, the quicker the response and the easier it is to shift focus to objects crossing your field of view. Note that 2 and 1 (Quick) are equivalent to 3 when 3D-tracking or auto-area AF is selected for AF-area mode.
Select Steady for smooth focus when photographing subjects that approach the camera at a steady pace, or Erratic for improved response when photographing subjects prone to sudden starts and stops.