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Focusing Essentials                                            77


           This uses the same algorithms as Center Lock-On AF shown earlier, with
           two key differences:
           •   It will only show you a tracking rectangle if it detects a face.

           •   You  don't  have  to  overtly  tell  the  camera  "This  is  my  subject"  and
               press the center button.  Instead, the camera locks onto the subject in
               the usual way, and then uses that as a starting point for analyzing the
               live view feed, identifying what the subject looks like, and then tries to
               track it as previously described.
           To see the difference in behavior, place your subject in the middle of the
           frame (I told you to choose "Lock-on AF CENTER, for a reason!), press
           the shutter release button halfway down, and then move the camera left and
           right,  up  and  down,  just  as  before.    Although  the  same  subject  tracking
           algorithms are at work, it won't show you a white rectangle – however, you
           CAN see the active focus points illuminate over your subjects, regardless of
           where your subject moves to in the frame.

           This can be a very useful tool in shooting sports, but as discussed earlier, it
           will  either  work  brilliantly  or  will  quickly  default  to  the  "focus  on  the
           closest thing in your defined focus area" if the camera can’t keep up with
           your subject.  Do some tests in your particular shooting conditions before
           relying on it to shoot an important event.

           3.4.1    OTHER FOCUS AREA CHOICES

           So  far  we’ve  talked  about  three  of  the  MENU       3    Focus  Area
           settings:  Center  (one  spot  in  the  center  of  the  viewfinder),  Flexible  Spot
           (where you can choose any one of the 79 focus points), and Lock-On AF
           (which  is  used  in  conjunction  with  any  of  the  focus  area  choices  and
           augments the focus tracking algorithm by analyzing the live view feed.)

           What do the other focus area choices do?  A quick overview appears below,
           and you can actually see the differences in Figure 3-7.

             Wide  –  Automatically  choose  from  the  camera’s  79  focus  points
              (Section 5.14.1)
             AF Area Points – If 79 is too many, concentrate on just the center 61
              (Section 6.12)
             Center – Just use the one in the very center.
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