Both Uses

focus
in
The Curious Incident of the Dog in the Night-time
(Edited)

I decided that my best plan would be to wait for a really sunny day and then use my glasses to focus the sunlight on a piece of my clothing and start a fire.
Chpt 23 *

focus = concentrate at one spot
And the advert said "DREAM HOLIDAY, THINK KUONI IN MALAYSIA" and behind the writing there was a big photograph of 2 orangutans and they were swinging on branches and there were trees behind them but the leaves were blurred because the camera was focusing on the orangutans and not the leaves and the orangutans were moving.
Chpt 223 *

focusing = with lens adjusted for a clear image

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)