Week 9 Flashcards
Light is an electromagnetic wave (EM) (meaning)
light is self-propagating combination of oscillating electric and magnetic fields
The speed of light (or any electromagnetic wave) for observers:
It is the same for all observers, regardless of their direction or speed.
Visible light lies on the spectrum
between about 380 nm and 750 nm
refraction -
phenomenon of when a ray of light is transmitted obliquely through the boundary between two materials of unlike index of refraction, the ray bends
absolute index of refraction of a material:
n = speed of light in vacuum / speed of light in the meterial = c/v
For any two material, the relative index of refraction of material 1 with respect to material 2 is:
relative index = n1/n2,
n - the absolute refractive indices of the two materials
If n2 > n1, the ray bends
toward the normal
If n2 < n1, the ray bends
away from the normal
if n2 = n1, refraction
does not bend the light beam
Snell’s Law:
The way in which a ray refracts at an interface between materials with indices of refraction ni and nr
ni x sinΘi = nr x sinΘr
reflection -
when light hits the surface of almost any material, some of that light ‘bounces back’ off the surface
law of reflection:
reflected light leaves the surface at the same angle that the incident light falls on it
Specular reflection -
happens when light hits a very flat, reflective surface, such as a mirror => all light coming from a single direction is reflected in a single direction.
diffuse reflection
when the surface is rough, the light is reflected in a wide range of directions
Converging or positive lenses:
- thicker at the center than at the rim
- converge a beam of parallel light to a real focus
Diverging or negative lenses
- thinner at the center than at the rim.
- diverge a beam of parallel light from a virtual focus
Converging lenses form
inverted real images of objects located outside the principal focus
Diverging lenses produce
only virtual, erect and smaller images of real objects
Within the eye the cornea and crystalline lens are what kind of lenses?
positive lenses, because they need to form a real image on the retina.
radius of curvature, r, is positive when
its center of curvature lies to the right of the surface
radius of curvature, r, is negative when
its center of curvature lies to the left of the surface
for positive focal lengths, lenses can be:
biconvex, planoconvex (one side flat) or positive
meniscus
for negative focal lengths, lenses can be:
biconcave, planoconcave (one side flat), or negative meniscus
isolated cornea is what type of lens?
negative meniscus lens
crystalline lens is what type of lens?
an asymmetric biconvex lens
Why is cornea transparent?
because it is uniform in structure, avascular except in the extreme periphery, and relatively dehydrated
layer of tears covering cornea - how thick and fn?
7–10 µm thick
smoothens over optical irregularities and supplies the cornea with oxygen
diameter of the pupil is controlled by
opposing pair of smooth muscles
formation of an image on the retina is determined by (2):
- the indices of refraction of each eye component that the light passes through and
- by the shapes of the surfaces of these elements
focusing elements in the eye
cornea and crystalline lens
performance of focusing in the eye:
cornea performs about two-thirds of the focusing and the crystalline lens the remaining one-third
rod cells: how many, characteristics, fn, where, sensitivity in nm
- about 120 million rod cells per retina
- high sensitivity, low spatial acuity
- night vision, peripheral vision
- relatively more numerous in the periphery of the retina
- sensitivity of rods peaks near 500 nm => vision using only rods results in various shades of gray.
cells: how many, characteristics, fn, where, sensitivity in nm
- about 6.5 million cone cells per retina
- low sensitivity—about 1.000× lower than rods—high spatial awareness
- concentrated in the fovea
- blue cones: 445 nm, green cones 535 nm, red cones 570 nm
Most of the light from 300 to 400 nm is absorbed by
crystalline lens
accommodation -
The ability to control the focal length of the crystalline lens
Decreasing the pupil size affects vision in several ways (3):
- Decreasing pupil size decreases light transmission to the retina.
- The size of the diffraction-limited spot varies inversely with opening diameter.
- Decreasing pupil size lessens the effect of lens aberrations.
depth of field
range in object distances over which good images are formed
Myopia is corrected with a
diverging lens
hyperopia is corrected w/
Converging lenses
Keratoconus
condition in which the cornea thins near the center to form a cone and can be locally wavy because of corneal scarring
