Canon DIGITAL IXUS860IS User Manual page 26

Various Shooting Methods I 99
Changing the AF Frame Size
When the [AF Frame] is set to [Center], the AF frame can be resized
to correspond to the subject. Select [Small] to constrict the focal
frame to suit a small subject or to focus on a particular area of a
subject.
Select [AF Frame Size].
1. Press the _ button.
2. In the [r'_] menu, use the 4, or
41,button to select [AF Frame
Size].
,2 Accept the setting.
1. Use the 4- or ,_ button to select
[Normal] or [Small].
2. Press the _ button.
_] he setting is configured to [Normal] when the digital zoom
or digital tete-converter is used.