Why do pupils dilate when looking at a far object

i know they constrict when looking at a near object...because that allows less light to enter eye so you can focus on the object...but can someone explain these in a more detailed way? both dilation and constriction...far and near objects?

Rays of light from a far away object are almost perfectly parallel and by the time they reach your eye, these rays are quite weak, so the pupils dilate to let as much light in from the object as possible..
Rays of light from a close up object are diverging and the rays are very strong, so the pupil constricts, restricting the amount of light entering your eyes to prevent damage.