(OPT 111 OOPS) Intro to Geometrical Optics and Vergence Notes Flashcards
Refractus means what in latin
To bend
How does a refraction occur
Due to light traveling at different speeds through different medias
Speed of light in a vacuum or air
3x10 ^8 m/s
Is the speed of light slower or quicker in denser mediums?
Slower. Causes light to take a different path.
Index of refraction describes what
How much light is slowed down
Index of refraction equation
n= c/Vm
n= index of refraction (no units. both cancel out) c= speed of light in vacuum (3x10^8 m/s) Vm= velocity of light traveling in media (m/s)
What is n ( index of refraction) for most common ophthalmic lenses?
1.5-1.6
What does “rectilinear propagation of light” mean?
Light will travel in a straight line unless something interferes
Snells law
(n1)(sin Theta 1) = (n2)(sin theta 2)
Describes how much light bends depending on the change of index of refraction between the 2 objects.
What is an object?
- Anything that gives off light and can be viewed.
- Can be an original source of light (light bulb, star)
- Can be seen by reflecting light off of it (people, apples, etc)
- Object sends light INTO a lens
point object and point __ are the same thing
source
Where do point sources emit light
In all directions. 3D. Same speed and index in all directions and light wave propagates energy.
Rays
Drawn perpendicular to light wave fronts and represented as an arrow
Pencil
Collection of rays in 2D
The farther the wavefront travels from the point source, the ____ the wavefront becomes
Flatter
Longer radius of curvature = ___ surface
Shorter radius of curvature= ___ surface
Flatter
More curved/steep
What does the surface look like if the curvature is infinitely long?
Completely flat
Divergent rays represents wavefronts getting
Flatter
Flat wavefronts is another word for
Plane waves
By the time waves travel __ feet (__ meters) from a point/object source, the waves are “flat enough” for clinical purposes.
20 feet or 6 meters. This is “optical infinity” and divergence (diopters) is so small it’s insignificant.
Convergent rays represents wavefronts getting
Stepper/curvier
- Real object
- Virtual object
- Real image
- Virtual image
- Rays diverging and headed into optical system
- Rays converging and headed into optical system
- Rays converging and coming out of optical system (Can be seen after optical system)
- Rays diverging and coming out of optical system. (Can be traced back before optical system)
Physically real image
An image that is produced due to a converging real image and is either displayed on a screen or creates the image before it reaches a screen (therefore, the image is not displayed, but it is still physically there)
Optically real image
When a real image is blocked by a screen before the image is formed at the image point. Therefore, the image is not produced so it is not physically there.
Vergence quantifies
Convergence or divergence
Related to the curvature of the wavefront at a given point
Assume what when discussing Vergence
Uniform media, spherical wavefronts
Diopter (unit)
Reciprocal of the distance you are away from a point source or object source (Diverging, minus)
Reciprocal of the distance you are away from the focus point or point image(Converging, hyperopia, plus)
Relationship between a ray’s distance and vergence
Longer the ray = less vergence or curving
Shorter the ray = more vergence or curving
Equation to calculate vergence using index of refraction and distance
vergence = index of refraction light is traveling through/distance in meters
L= n/l
Will diverging light have a + or - vergence
-
Will converging light have a + or - vergence
+
True or false: light rays always diverge from a real object
True
Directly at the object or source, the vergence is
infinite
Index of refraction in
- Air
- Water
- CR-39
- Crown Glass
- 1.00
- 1.33
- 1.49
- 1.523
If a lens has a virtual object, then it has ____ rays coming out of the lens
Diverging
