obtrusive

As an adjective obtrusive

is sticking out; protruding.

As a noun focus is

(countable|optics) a point at which reflected or refracted rays of light converge.

As a verb focus is

to cause (rays of light, etc) to converge at a single point.

As adjectives the difference between abstruse and obtrusive

is that abstruse is concealed or hidden out of the way; secret while obtrusive is sticking out; protruding.