Question

What shape are your eye-lenses: 

when you look at a distant tree? 

Answer 1

When we look at a distant tree, the eye lens is thin. When we look at a far-off object, the eye is in a relaxed state. The eye lens becomes thin or less convex because a small converging power of the eye lens is sufficient to focus the parallel light rays from the distant object (the tree) to form an image on the retina.