Pentax K10D Operating Manual page 135

Setting the Focus Position in the Viewfinder
1
Select j (Select) with the AF
point switching dial.
2
Look through the viewfinder and
check the position of the subject.
3
Use the four-way controller (2345) to select the desired
AF point.
The AF point lights red in the viewfinder (Superimpose AF Area) and you
can check where you set the AF point.
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4