general T.O topics 2 Flashcards
states that in a homogeneous optical medium, light travels along a straight path
Law of Rectilinear Propagation of Light
Proofs of Law of rectilinear propagation of light
- Shadow of an opaque object with a point source of light
- Shadow of an opaque object with an extended light source
- Pinhole camera
- Eclipses
an object placed between a point source of light and screen will cast a shadow with a sharply defined boundary, the boundary line is the intersection of the screen with the conical surface that touches the surface of the obstacle and has its apex at the source
Shadow of an opaque object with a point source of light
is the smallest possible source of light
Point source
dark image formed by intercepting the light rays; formed if you block the rays of light
Shadow
The region of complete shadow formed on the screen
UMBRA
when an opaque disk is interposed between an extended light source and a screen, part of the screen is illuminated by one extremity of the source, another part is illumination by the other extremity, the shadow of the sphere will not be clearly define
Shadow of an opaque object with an extended light source
the region of partial shadow, which receives light from only a portion of the source
Penumbra
- where an inverted real image is formed
- the size of the image depends on the length of the camera and the distance of the object from it
Pinhole Camera
the natural phenomenon that illustrates the formation of shadows
Eclipses
the visual angle formed at the nodal point of the eye by the object
Apparent Height or Angular height
2 apparent height factors:
- the distance of the object from the observer
- the size of the object
science of measuring and comparing light quantities
Photometry
instrument used for measuring and comparing light quantities
Photometer
3 aspects of Photometry
- the Luminous flux or flow of light from the source
- the luminous intensity of the source
- the illuminance or brightness of a surface
- rate of flow of luminous energy from a source
- radiant energy which is emitted by a source per unit time which causes the sensation of sight
Luminous Flux
unit if luminous flux
Lumen
- quantity of light emitted by a source in one given direction
Luminous Intensity
the unit of luminous intensity
candle or candle power
- measure of the illumination
- brightness of the surface
Illuminance
states that the illumination of a surface placed perpendicularly to he direction in which the light is traveling varies inversely as the distance of the surface from the source
Inverse square law
states that the illumination of a surface varies as the cosine of the angle of incidence
Cosine Law of illumination
states that the candle powers of two light sources are directly proportioned to the squares of their distances from the screen of a photometer.
Law of intensity
for an extended light source, like fluorescent lamps, the illumination decreases as the inverse first power of the distance
Luminance of Extended Sources
Law that states the angles which the incident and reflected rays make, respectively with the normal reflecting surface, are equal
Laws of Reflection
2 Types of reflection:
- Specular (regular) reflection
- Diffuse (irregular) reflection
- reflection that occurs only on smooth surfaces such as glass, mirror, mercury where most of the energy is reflected
- reflected rays travel in the same direction
Specular (regular) Reflection
- reflection that occurs on rough and uneven surface like wood where most of the energy is absorbed
- reflected rays spread out in different directions
Diffuse (irregular) Reflection
- reflection that occurs on rough and uneven surface like wood where most of the energy is absorbed
- reflected rays spread out in different directions
Diffuse (irregular) Reflection
Portion of a sphere which was sliced away and then silvered on one of the sides to form a reflecting surface
Spherical Mirrors
silvered on the inside of the sphere
the curve is away from the observer
Concave mirrors
- silvered on the outside of the sphere
- the reflecting surface is curved towards the observer
Convex mirrors
Line passing through the center of the sphere and attaching to the mirror in the exact center of mirror
PRINCIPAL AXIS
the point in the center of sphere from which the mirror was sliced
Center of Curvature
the point on the mirror’s surface where the principal axis meets the mirror
Vertex
midway between the vertex and the center of curvature
Focal point
distance from the vertex to the center of curvate
Radius of Curvature
distance from the mirror to the focal point
Focal Length
usable rays in construction of images: Ray#1 ?
Ray #1 - ray parallel to principal axis passes through F after reflection
usable rays in construction of images: Ray#2 ?
Ray #2 - ray passing through F will be reflected parallel to the principal axis
usable rays in construction of images: Ray #3 ?
Ray #3 - ray passing through C will follow the same path back after reflection
usable rays in construction of images: Ray #4 ?
Ray #4 - ray incident to the vertex of the mirror will be reflected according to the laws of reflection
images produced by CONCAVE MIRRORS: Case #1 ?
Case 1 - Object at an infinite distance from the mirror
A point image is formed at the PRINCIPAL FOCUS
images produced by CONCAVE MIRRORS: Case #2 ?
Case 2 - Object at a finite distance beyond the center of curvature
image is REAL, INVERTED, and MINIFIED, located between the CENTER OF CURVATURE and the PRINCIPAL FOCUS
images produced by CONCAVE MIRRORS: Case #3 ?
Case 3 - Object at the center of curvature
image is REAL, INVERTED, and has the SAME SIZE OF THE OBJECT located at the CENTER OF CURVATURE
images produced by CONCAVE MIRRORS: Case #4 ?
Case 4 - object between the center of curvature and the principal focus
image is REAL, INVERTED, and MAGNIFIED located beyond the CENTER OF CURVATURE
images produced by CONCAVE MIRRORS: Case #5 ?
Case 5 - Object at the principal focus
NO IMAGE FORMED
images produced by CONCAVE MIRRORS: Case #6 ?
Case 6 - object between principal focus and mirror
image is VIRTUAL, ERECT and MAGNIFIED, located BEHIND THE MIRROR
images formed by CONVEX MIRROR:
always VIRTUAL, ERECT, and MINIFIED
image is BEHIND THE MIRROR within its PRINCIPAL FOCUS
image formed in PLANE MIRROR:
VIRTUAL, ERECT, SAME SIZE
SAME DISTANCE as the object from the mirror
image formed in PLANE MIRROR:
VIRTUAL, ERECT, SAME SIZE
SAME DISTANCE as the object from the mirror
refers to the ratio of image length to object length measured in planes that are perpendicular to the optical axis
Linear magnification
bending of light as it goes from one medium to another of different density
Refraction
Laws of refraction:
A ray of light striking a refracting surface perpendicularly is _____
Undeviated
Laws of refraction:
A ray of light which passes obliquely from a RARER to a DENSER medium is bent ______ the normal.
TOWARDS (decrease speed)
Laws of refraction:
A ray of light which passes obliquely from a DENSER to a RARER medium is bent _____ from the normal.
AWAY (increase speed)
Laws of refraction:
the incident ray, normal and refracted ray, all lie in the _______.
Same plane at the point of reference
Laws of refraction:
law in which Sine of the angle of incidence is to the sine of the angle of refraction as the inverse ratio of their indices
Snell’s Law
ratio of the speed of light in empty space or vacuum (air) to the speed of light in some other optical medium
Absolute index of refraction
ratio of the speed of light of two optical media, of which neither is air or when such is the case that light does not originate from air
Relative index of refraction
refractive index of air:
1.0
refractive index of water:
1.33
refractive index of ethyl alcohol:
1.36
refractive index of crown glass:
1.523
refractive index of Polycarbonate:
1.58
refractive index of Diamond:
2.417
an optical medium having two refractive sides, both of which are plane and parallel
Plane refractors
Light passing through a plane refractor suffers no _____, and
merely a ______.
permanent deviation, displacement
the displacement suffered by the ray is dependent upon:
- the angle of incidence
- thickness of plane refractor
- indices of refraction
an angle of incidence at which the angle of refraction makes an angle of 90 degrees with the normal angle of incidence, which just transmit a ray of light in a dense medium to pass out into a rare medium
Critical Angle
when the incident ray coming from a dense medium subtends an angle with the normal to the refracting surface, greater than the critical angle for the substance, it does not pass out into the rare medium but suffers _____.?
TOTAL INTERNAL REFLECTION
defined as a portion of a transparent substance bounded by two polished surfaces, both of which may be curved, or only one may be curved and the other plane.
LENS
grounded using a minus tool
spherical PLUS curvature
grounded using a plus tool
spherical MINUS curvature
wedge shaped portion of a refracting medium contained between two plane polished surfaces which are not parrellel to each other
PRISM
a ray of light passing through a prism is bent towards the _____
BASE
- It forms a magnified image of an object held within its focus
- when moved, an object viewed through it appears to move in opposite direction
CONVEX LENS
- it diminishes the apparent size of an object seen through it
- when moved, an object viewed through it appears to move in opposite direction
CONCAVE LENS
standard forms of Plus and Minus Lenses:
- Plano convex/Plano concave
- Bi convex- Bi concave
- Equi-convex/Equi-concave
- Plus/minus Meniscus
- Periscopic Lenses
the back surface is plane, all the power being provided by the front surface:
Plano convex/Plano concave
both surfaces having same curve but of different power
Bi convex/Bi concave
both surfaces having the same curvature and power
Equi-convex/Equi-convave
the front is convex, the back surface is concave
Plus/minus meniscus lens
this lens is the form in which mass-produced lenses are now made
Plus/minus meniscus lens
all the plus lenses have back surface power of -1.25 D and all minus lenses have a front surface curve of +1.25 D
Periscopic lens
the line joining the center of curvature of the two sphere or lens
OPTIC AXIS
point through which rays of light pass unrefracted
OPTIC CENTER
line drawn perpendicular to the optic axis passing through the optic center, from which the object and image distances may be measured
Principal of Bending plane
images produced by convex lenses:
- Object at an infinite distance from the mirror
a REAL IMAGE is produced at the FOCUS
images produced by convex lenses:
- object is placed at a distance greater than twice the focal length
image is
- REAL,
- INVERTED,
- DIMINISHED
images produced by convex lenses:
- object at a distance twice the focal length
- REAL IMAGE,
- INVERTED,
- SAME SIZE AS THE OBJECT
images produced by convex lenses:
- object at a distance between 2f and f
- REAL IMAGE
- INVERTED
- MAGNIFIED
images produced by convex lenses:
- object at the principal focus
NO IMAGE FORMED
images produced by convex lenses:
- object between the principal focus and the lens
VIRTUAL IMAGE
ERECT
MAGNIFIED
image produced in concave lens:
ALWAYS VIRTUAL, ERECT AND DIMINISHED
This relation holds for any case of image formation by a convex or concave lens
Thin lens Equation and Linear magnification
The power of a surface lens depend upon its _____ and ______.
RADIUS OF CURVATURE and INDEX OF REFRACTION
have two different curves on a single refracting surface on or within the eye
ASTIGMATISM
General classes of cylinder lenses:
- Simple cyl
- Compound cyl
- mixed cyl
- Cross-cyl
cyl with no spherical equivalent
Simple cyl
cyl having plus or minus power in both meridians
(cyl
Compound cyl
cyl having plus power in one meridian and minus power in the other
(cyl >sph)
Mixed cylinder
cyl having two similar or dissimilar cyl crossed at right angle
Cross-Cylinder
it is defined as changing the form of a lens prescription without changing its value
Transposition
types of transposition:
- Flat transposition
- Toric Transposition
applicable to cylinder prescriptions, and by of any cylinder prescriptions may be changed to plus cylinders, minus cylinder or cross cylinder
FLAT TRANSPOSITION
process of finding the power or strength of the refracting elements which make up an unknown lens
NEUTRALIZATION
Purpose of transposition:
- to simplify the expression of a lens formula
- to aid in changing or combining lenses in a trial frame
- to facilitate the use of lenses to be used
Methods of neutralization:
- By measurement of the focal length of lens
- By determining the curvature of each of the surfaces of the lens
- By computing the thickness difference between the center and edge of the lens
- Hand neutralization
- By the use of vertex power instrument
used for determining the curvature of each of the surfaces of the lens
LENS MEASURE
used for computing the thickness difference between the center and edge of the lens
CALIPER
used for hand neutralization of the lens
TRIAL LENSES
used for the use of vertex power instrument
LENSMETER/LENSOMETER
is measured from the lens to the image or focal plane with the source of light originating from infinity
FOCAL LENGTH
other term for lens measure
- Geneva lens measure
- Lens clock
other term for Lensmeter:
- Focimeter
- Vertometer
Types of mires:
- Circle of Dots (sphere lens)
- 2 sets of lines perpendicular to each other (cylinder lens)
- consist of two straight lines drawn at right angles to each other and representing the principal meridians of a lens or lens combinations.
OPTICAL CROSS
- describes the manner in which the lens is made
- depends on the use of definite base curve and all the other curves of the lens being determined by using the selected base curve as a point of reference
TORIC TRANSPOSITION
- – curvature upon which a series of power is ground
- power from which the other powers of the lens surface may be calculated
BASE CURVE
- Lens in which base curve is always the lowest [powered curve on the front surface
SV LENS
- base curve is always a sphere
- Lens in which The base curve is always on the same surface as the segment
BIFOCAL LENS
- The base curve on the segment side must be spherical in nature
- The cylinder element in bifocals is always ground on the surface opposite the segment side
FUSED BIFOCAL TORIC TRANSPOSITION
The deviation produced by a prism is expressed in terms of its?
PRISMATIC POWER
- Causing deviation of light without changing its vergence.
PRISM
Prisms do not affect the vergence because their surfaces are ____, the surface have _____.
FLAT, NO DIOPTRIC POWER
prism has converging surfaces which meet in a line called _____?
APEX
the prism’s divergent extremities are connected by a surface called the _____?
BASE
Ray of light passing through a prism are bent toward the _____?`
BASE
An object observed through a prism is displaced apparently toward the _____?
APEX
An eye looking through a prism is turned towards the _____?
APEX
A prism that deviates a light ray 1.00 cm at a distance of 1 m is said to have a power of _____?
1 prism diopter
- Are used to alleviate symptoms associated with disorders of binocular vision by deviating light to fall on the foveas of both eyes. But it does not solve the underlying problems.
PRISM IN SPECTACLES
prisms Cause reduction in visual acuity due to
chromatic abberation
is created when the patient looks away from the optical center of any plus or minus lens
PRISMATIC EFFECT
THE PRISMATIC POWER ______ AS THE DISTANCE FROM THE OPTICAL CENTER OF THE LENS AND OR THE LENS POWER _______.
increases, increases
The greater the prism power, the more the image is _____?
displaced
There is no prismatic power along the _____ of the lens. ( a ray of light travels along the ______ is not deviated)
OPTICAL AXIS
A LENS has both ____ power and _____ power
DIOPTRIC AND PRISM
_____ power due to the curvature of the lens surfaces is manifest as a change in the vergence of light rays.
DIOPTRIC POWER
_____ power is manifest as a displacement of the image toward the apex of the prism.
PRISMATIC POWER
a result of inappropriate positioning of the optical centers,
UNWANTED prismatic effect
Prismatic effect can be computed using:
PRENTICE RULE
_____ is the distance from the center of the lens to the point in question.
displacement
A cylinder decentered along its axis will give _____ effect.
NO prismatic effect
A cylinder decentered perpendicular to its axis will give a _____ equivalent to a sphere of the same power.
prismatic effect
Incorporating a Prism in Prescription are achieved by:
- ACTUAL GRINDING
- DECENTRATION OF LENS
Incorporating a Prism in Prescription are achieved by:
- ACTUAL GRINDING
- DECENTRATION OF LENS
If prisms are combined with their base-apex line parallel, and with their bases in the same direction, then their effects are considered to be additive or called ____?
THIN PRISM COMBINATIONS
If the two prism to be combined are NOT PARALLEL, then the single effective prism can be produced by ______.
resolving the two prisms
A circle viewed through a prism appears slightly oval and with the upper and lower edges faintly blurred. The blurring occurs along the base-apex line; distinct along the axis.
Prism aberration
optical effect that occurs when an object viewed through a prism appears displaced toward the apex.
Produce an Optical Illusion
rotating a prism on its base-apex line or axis as the observer looks through it at an object causes the object to be distorted and the distortion is spoken of as ______?
Metamorphopsia
when a beam of solar light is made to pass through a prism of rock crystal or flint glass is broken up into its constituent parts.
Dispersion of Light