The Human Eye
The human eye can focus on objects at different distances from the eye within a certain range – between the near point and the far point. It does this by changing the shape of the eye lens. If it becomes fatter, then more refraction takes place at objects nearer to the eye can be brought into focus. This is called accommodation. The eye can only properly focus for a certain distance at a time – objects at other distances become blurred.
The near point is the least distance between the eye and an object such that the eye can bring that object into focus without strain or aid from a lens. It is often taken to be 25 cm.
The far point is the distance between the eye and the furthest object that can be brought into focus. This is effectively infinity for normal vision – you can focus light from distant stars to a point, be they ever so many light years away.
