Draw a ray optics diagram, except now replace the magnifying glass with your human eye lens, and replace the leaf with your retina that rests at the back of your eyeball. Once again, label s, s’, and f with symbols.

Given that the distance between the eye’s lens and the retina is around 2cm, relabel s, s’, and f with their exact distances. (Note: you can automatically know the focal length (converging strength) of your human eye when you look at something far away, because you can approximate the object distance as infinitely far away.)

Explain why we need a lens in our human eye in order to focus light from an object onto our retina. (ie: an invertebrate with photoreceptors but no lens would see a brighter spot where the light is, but would not be able to focus the edges of the panels and rectangular shape of the light holder.)