Short sighted people can't focus on objects far away (distant objects) > their far point is closer than infinity.
Short sight is caused by the eyeball being too long, or the cornea and lens system being too powerful- the eye can't prduce a focused image on the retina.
Images of distant objects are focused in front of the retina.
Correcing short sight > diverging lens (negative power) in front of the eye. This diverges the light before it enters the eye, so the lens can focus it on the retina.
Long sighted people can't focus on close objects (near objects> > their far point is further away than normal (25cm +).