Unit 16 – Part 2 notes continued Given: 4-18 and 4-19

Lens Aberration - distortion of image - lines are bowed - some areas are fatter or wider than they should be Aberrations occur when you change the shape of your glasses, especially if you have been wearing a particular shape lens for many years. EX:

Hand out -Parts of the Human Eye Wksht

Definitions of human eye structures

cont.cont. Vitreous Humor - the transparent gelatinous substance in the posterior chamber of the eye between the back of the lens and the retina Iris - the circular muscle structure that opens and closes to form the pupil, therefore controlling the amount of light that enters the eye. Lens – the structure in the eye that is responsible for sharpening images for near and distance, by becoming more thick in the middle( for near vision ), and more thin in the middle ( for distance vision) Known as accommodation. *Aqueous Humor – the watery substance in the anterior chamber located between the back of the cornea and the front of the lens. * No line is drawn for this structure. I will show you where to draw the line to include this structure. FYI- Intraocular pressure is created by the continual renewal of the fluids within the eye. Eye Structures cont.

Astigmatism Astigmatism ( Analogy ) Cornea or lens is shaped more like a football then like a spherical basketball, which is the same in every meridian.

Presbyopia ( just part of getting older ….) Caused by the natural aging process of the lens in the eye ( Loss Of Elasticity makes the lens less pliable and it tends to stay in the distance range focal area.) Accommodation goes from 15 diopters to >5 diopters Use of Readers, or Bifocals to magnify images Monovision contact lenses Myopic individuals like to take their glasses for distance off and use their natural nearsightedness to read small print.

Diffraction and Interference Diffraction – bending of light around corners Diffraction grating demo ( What do you see ? ) Monochromatic (light)- light of a single color  only the constructive interference patterns - produces light thru pinholes or slits, destructive interference patterns – no light is produced Iridescence – a phenomenon where all colors are produced by the interference of mixed frequencies on thin films. Different colors correspond with cancellations of their complementary colors.

Lasers Incoherent ( light ) –EX: light from a lamp - chaotic, random emission of light & out of phase - spreads out farther as it gets away from source - becomes less intense (intensity is associatied with?) - amplitude Coherent ( light ) – EX: light produced by LASER Light Amplification by Stimulated Emission of Radiation - light wave emitted by 1 atom  stim. emis. of other atoms in a cascading fashion so that crests of each wave coincide. Constructive Interference in layers.

Incoherent vs. Coherent Visual Incandescent Bulb  Laser 

Hologram “ Holo “ comes for the Greek word ? “whole” “Gram” comes for the Greek word for ? “message” Def’n  3 dimensional version of a photo produced by interference patterns of laser beams on photographic film. They are difficult to reproduce  that is why they put them on credit cards.