All 4 Uses

focus
in
Fahrenheit 451
(Edited)

Each time he made the turn, he saw only the white, unused, buckling sidewalk, with perhaps, on one night, something vanishing swiftly across a lawn before he could focus his eyes or speak.
p. 3.3

focus = adjust (to see clearly)
The old woman's eyes came to a focus upon Beatty.
p. 33.6 *

focus = look closely
And so when houses were finally fireproofed completely ... They were given the new job, as custodians of our peace of mind, the focus of our understandable and rightful dread of being inferior;
p. 56.3 *

focus = center (where attention is concentrated)
They didn't show the man's face in focus.
p. 143.1 *

in focus = so it could be clearly seen

Definitions:

(1) (focus as in: Turn your focus to question #2.)
to direct attention or effort toward a single thing; or the ability to do so without getting distracted
(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.
(5) (meaning too rare to warrant focus)