Pentax K-7 Operating Manual page 72

Subjects that are Difficult to Focus on
The autofocus mechanism is not perfect. Focusing may be difficult
when taking pictures under the following conditions. These also apply
to manual focusing using the focus indicator II in the viewfinder.
(a) Extremely low-contrast subjects such as a white wall in the
focusing area.
(b) Subjects which do not reflect much light within the focusing
area.
(c) Fast moving objects.
(d) Strongly reflected light or strong backlighting (bright
background).
(e) If repeating vertical or horizontal line patterns appear within
the focusing area.
(f) Multiple subjects in the foreground and background within the
focusing area.
If the subject cannot be focused automatically, set the focus mode
lever to MF and use the manual focus mode to focus on the subject
with the aid of the matte field in the viewfinder. (p.127)
iii
Subject may not be focused even when O (focus indicator) is displayed
when (e) and (f) above app!y.