Question

When we look at distant object the ciliary muscles contract and the lens become thinner and the focal length increases. When we look at a nearer object the ciliary muscles relax and the lens become thicker and the foc?

Answer 1

The human eye is a sense organ adapted to allow vision by reacting to light. The cornea and the crystalline lens are both important for the eye to focus light.

The eye focuses light in a similar way to when you use a magnifying glass to concentrate the Sun’s rays onto a piece of paper. The distance from the magnifying lens to the piece of paper is the focal length.

For the eye, light from distant objects is focused onto the retina at the back of the eye.
The eye is about the size of a table tennis ball, so the focal length needs to be about 2.5 cm.