The Eye Eye Dissected The eye is an

The Eye

Eye Dissected ] The eye is an optical lens system. • Two single lenses ] The goal of the eye is to focus an image on the retina.

Corneal Lens ] The cornea is a curved membrane with fluid behind it. • • • Two indices of refraction ncorn = 1. 376 naq = 1. 336 ] This is roughly the refraction from air to water. • Eye works poorly underwater

Crystalline Lens ] The lens is a denser material for fine focusing. • nlens = 1. 406 at maximum ] Relaxed muscle provides little additional focus. • For distant objects ] Contracted muscles provide more focus. • Relaxes tension and creates a bulge • For near objects

Accommodation ] The focusing by the lens is ] The moon subtends an angle called accommodation. of about 0. 009 rad as seen from the earth. ] The size of the moon on the retina comes from the image triangle. ] The relaxed lens forms a combination with the cornea. • Object focus 15. 6 mm in front of cornea • Image focus 24. 3 behind • Optical center 17. 1 mm in front of the retina ] Typical shifts in accommodation are a few mm.

Retina ] The retina is the screen for the eye. • Light sensitive cells • Neurons for signal transmission ] Ideally it should be at the focal plane. • Otherwise image is blurred

Pinhole Camera ] A pinhole opening can act as a single lens. • Forces ray convergence at the opening point • Iris in eye can act as pinhole lens ] A pinhole camera is a box with a pinhole opening to focus light.

Single Lens Reflex ] A single lens reflex (SLR) camera acts much like an eye. • • • Shutter like iris Lens fixed Adjust distance to screen next