All 3 Uses of

focus
in
The Grapes of Wrath

Grampa focused his eyes fiercely until he recognized Casy.
Chpt 8

focused = adjusted (to see clearly)

And still the family stood about like dream walkers, their eyes focused panoramically, seeing no detail, but the whole dawn, the whole land, the whole texture of the country at once.
Chpt 10 *

Definitions:

(1) (focus as in: Turn your focus to question #2.)
verb: to concentrate, look at, or pay attention to

noun: the act of concentration, or the ability to concentrate

(to concentrate is to direct attention or effort towards a single thing)
(2) (focus as in: The focus of our study is...)
where attention is concentrated or directed
(3) (focus as in: bring into focus; or out of focus)
a state where something has come into view or can be seen clearly; or an adjustment made to permit a clear view
(4) (focus as with technical usage)
technical usage typically involves some sense of center or concentration such as:
- physics — a point where things come together such as the point where light rays meet
- geometry — a fixed reference point (as of a parabola)
- geology — the point of origin of an earthquake
See a comprehensive dictionary for other less common meanings.