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fall optics 2 Flashcards

1
Q

untreated surface

A

reflectance is govered solely by refractive indeces of the media
-usually between air (n=1)

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2
Q

treated surface

A

NOT based on index (n does not matter)

-the reflectance (aka transmission) is used instead

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3
Q

transparent material has bulk transmittance of?

A

100% or 1.00 because all light goes through

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4
Q

external transmittance is what?

A

T(e)= T12TbT23

- if in air, then T12= T23 and equation will be squared

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5
Q

in a glass filter, where is the greatest part of the incident energy falling on?

A

-greats E @ transmitted in T1

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6
Q

how does the reflectance R1 and R2 comapre with each other and to T1?

A
  • R1 and R2 will equal each other roughtly

- both will add up to be SMALLER than T1

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7
Q

Does the total of all reflectance and transmission add up to the incident intensity? why/why not?

A

-no, some E will be absorbed by the material itself EXCEPT when it’s 100% transmittance.

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8
Q

In all cases that the intensity transmitted through a filter is same or different in BOTH directions?

A

-same! and will be the same in any order

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9
Q

when calculating reflectance or transmission in a transparent filter, what is T(B) assumed to be for a given material n=1.7?

A

T(b) = zero for ALL transparent surfaces

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10
Q

what are the general math rules of density filters and their transmittence rate?

A

can add density, but multiply transmittence

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11
Q

If I change thickness of a filter, what will happen? I.e 2mm thick= 0.8, going to 3mm thick=?

A
  • exponential rule
  • 2mm=0.8
  • 3mm= 0.8 * 0.8=0.16
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12
Q

a light beam in the vertical position is removed, then the light beam is linearly polarized in the ___ direction?

A
  • horizontal polarizer
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13
Q

when is light completely linearly polarized?

A

when all waves are vibrating in one direction vs. the perpendicular direction

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14
Q

what is an analyzer in polarized light?

A

analyzer= determines the state of polarization of a light beam by inspecting with an ideal polarizer

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15
Q

what’s an ideal polarizer? what are 2 properties it needs?

A
  1. transmits 100% of light vibrating in its direction of polarization
  2. transmits 0% of the light vibrating in the perpendicular to the polarized direction
    * *BOTH must be met?
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16
Q

what is Malu’s Law? what category does it refer to?

A

no light is transmitted when 2 polarizers are placed 90 degrees to each other

  • if they are NOT @ 90 degrees from eachother, the equation “I2= I1 * (cos squared)
  • I1= light intensity from 1st polarizer
  • I2= light intensity from 2nd polarizer
  • theta angle is angle between the polarizers
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17
Q

what are the 2 ways a polarizer can fail being “ideal”?

A
  1. transmits LESS than 100% in the direction of polarization

2. lets through some light in the direction perpendicular to the direction of polarization

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18
Q

If a polarizer transmits 80% in the vertical plane and 20% in the horizontal plane, what direction is the polarization?

A
  • vertical—always in direction of most transmission of light
  • polarized in same direction it allows light into
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19
Q

are sheet polarizers ideal polarizers? (Sheet polarizer= light passing a tinted polarizer)

A
  • NO, not ideal polarizer because most have less than 50% transmission= they absorb some of the light in both polarized directions
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20
Q

is scattering a process that results in ideal polarized light?

A
  • NO, not ideal because only a small part of light is redirected from the incident beam.
  • it may be highly polarized in some directions, but it does not represent all the light taht’s vibrating in the direction of the incident beam
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21
Q

Is Bewster’s angle polarizer and ideal polarizer?

A

-NO, not ideal because even though it IS 100% polarized, it does NOT represent all the light of the incident beam. Some light actually passes straight through the material

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22
Q

what would be the transmittance of an ideal polarizer if it is illuminated with UNpolarized light?

A
  • 50% in both directions since it will not be bending in just one direction
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23
Q

what would be the transmittance of an ideal polarizer if it is illuminated with leght polarized in the SAME direction as the polarizer?

A

100% as all light will pass through the direction of the polarizer

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24
Q

what is an “unpolarized or randomly polarized light?

A

a beam of light whose waves are resolved into 2 equal components

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25
Q

what is the definition of Brewster’s angle?

A

all the reflected light is vibrating in the “S” direction (perpendicular to incidence)
–this means Rs= 100% polarized | Rp= 0% polarized, BUT there is still some transmission that goes through known as “angle of refraction”

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26
Q

what is happen with reflected light and reflectence @ Brewster’s angle in the S direction?

A
  • 100% reflected light is vibrating in S direction (Rp= 0)

- BUT reflectance for the “s” vibration is NOT 100%—most of the light is transmited into material!

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27
Q

what is happening with reflected light and reflectance @ Brewster’s angle in the P direction?

A
  • reflectance P = 0, so transmittance= 100%

-

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28
Q

what is the relationship between reflectance and transmission for anything at Brewster’s angle?

A

R (s) + R (p)= 1
and vibration will be equal in both directions: I (o)= 0.5* I (s) + 0.5 I (p)

-if given Rs, then you will know Ts etc.

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29
Q

what type of glasses are regular polarized sunglasses? 2. vectographic VT materials? and for 3D vision?

A
  1. regular polarized sunglasses= polarized LINEAR only
  2. use with vectographic VT
  3. 3-D movies use circularly polarized glasses
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30
Q

what is randomly polarized light? aka UNpolarized light when regarding “natural light”

A
  • there are e- magnetic charges that vibrate and create electromagnetic waves
  • has electric waves vibrating (oscilating) in all directions that is PERPENDICULAR to travel
  • if light travels in “z” then the vibrations of the elctric field will lie in the x-y plane
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31
Q

are oscillating particles charged? how?

A

-YES! In direction perpendicular to direction of travel

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32
Q

what type of polarized light does oscillating charge produce?

A
  • LINEARLY

- vibrating in the direction of the oscillating charge and radiate in the perpendicular direction

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33
Q

what are the 2 processes involved in light scatter?

A
  1. a charged particle is set into oscillation by an incoming light wave- vibration
  2. the charged particle then radiates light waves as it oscillates/vibrates
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34
Q

what is “scattered light?”

A

the RE-EMMITED light (diff from incident light) from the vibrationing particles radiate in all directions that is PERPENDICULAR to the charged particle itself

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35
Q

what makes the color of the sky blue?

A

due to particles in the air that scatter light

- mainly oxygen and nitrogen

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36
Q

why are clouds white, then pink sometimes?

A
  • white= when sun is high and there’s less “Stuff” to travel through and clouds will reflect whatever color shines on them, which is why light
  • pink during sunrise/sunset because there’s a longer distance from
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37
Q

what is Raleigh scattering?

A
  • scattering by SMALL particles is more effective at SHORT wL vs. long wL
  • the effectiveness of the scattering is inversely porportional to wL to 4th power
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38
Q

what does “small” particles refer to in Raleigh scattering that makes it more efficient?

A

-the scattering particles are small compared to the wL of light—-such as oxygen and nitrogen

E inversely = 1/ wL^4

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39
Q

why are the clouds pink while sky is blue?

A
  • clouds reflect whatever shines on it
  • the blue sky is from sun light that is scattering short wL (blues/greens) while the clouds are reflecting the longer wL light (red/orange) that is taking a longer time to get to the atmosphere
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40
Q

what is transmittance of an ideal polarizer with randomly polarized light?

A

-50% in each direction (I0/2)

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41
Q

how many cycles of dark/light occur in one complete revolution of a polarizer when based through 2 filters and one can rotate?

A

-2 cycles (or 2 light + 2 dark)

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42
Q

how many cycles of light/dark is observed when middle polarizer of a 90/180 polarizer is placed?

A
  • 4 cycles (every 45 degrees, it changes color so you have 4 of each changes)
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43
Q

Is light INTENSITY greater/less after passing through 2 polarizers vs. one? what about % polarization? (in NON-deal conditions)

A
  • light intensity= decreases
  • % polarization= increases
  • more light is allowed to pass through, but they are less bright?
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44
Q

If a reflected light is inspected w/ an ideal polarizer and found to be 42%, what is % polarized of the INCIDENT light? what about the % of light transmitted INTO glass? ( light intensity= 3.5 mW)

A
  • BOTH % polarized of incident light hitting glass and amount that goes into the material will be 43%
  • because Rs and Rp are equal in the incident beam
  • *APPLIED ONLY TO NORMAL incident, which means angle is zero**
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45
Q

what is a wave front?

A

a surface of constant phase
- starts from emitted light in all directions coming from a point source and after a certain time, there is a “sphere” of light around the point source all with the SAME “in phase” dynamic

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46
Q

in a sine-wave pattern, wht is considered “ 1 cycle?”

A

peak to peak or low to low

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47
Q

what is the process of “young’s experiment?” what was it looking at?

A
  • plane wave front (basically zooming in on the “sphere of light” emitted from a point source) using a collimating lens
  • it showed that light was a “wave”
48
Q

what is the phase relationship change with? what’s the aka of the dark/light bands?

A
  • aka “finges”
  • ON midline= in phase and bright band @ at midline
  • OFF midline: the paths taken by the light are different and may not be “in phase” so it may be a dark “fringe”
49
Q

what is the change in P mean in the equation change P= P1- P2?

A
  • change in P is how much “out of step” the filter is from the screen
  • if it’s a whole number, then likely a BRIGHT band vs. if 0.5= likely dark band
50
Q

what will increase the distance between the dark bands? 1. changing wL 2. increase slit distances between each other 3. increase distance to the screen

A
  1. increasing the distance to the screen
    - the distance between dark bands is based on (K + 0.5)*L (wL/d), so we must increase the L as K itself is the # for bright/dark bands per cycle and will not change and wL is dependent on light given while d will make it closer
51
Q

what happens if you increase the distance between the slits?

A
  • increasing the distance between the slits= “d” measurement in equation means you must make the L smaller, or effectly walk closer to the screen to achieve same results
52
Q

why do we usually look at REFLECTED light vs transmitted light?

A
  • good cancellation is obtained in relfected light but not in transmitted.
  • since reflected light will be equal in reflection, the bright should be BRIGHT and dark will be extra DARK vs. in transmitted light it would only be partial
  • *easier to see interference when the dark bands are VERY dark.

-recall that 2 reflected rays (R1 + R2) are about equal to each other, but both are still LESS than T1,

53
Q

what criteria needs to be met to get cancellation of 2 waves?

A
  • must be out of phase from each other

- must be of EQUAL amplitude (if not equal, will get incomplete cancellation)

54
Q

what optometric instrument is made based on the Michelson photometer/interpherometer?

A

OCT machine= optical coherence tomography

-looks at the layer of the retina

55
Q

what are Newton rings? where are they?

A

circular rings that appear using “sphere wavefront”

  • dark bands turn circular
  • the center will be DARK due to phase shift deconstruction interference
56
Q

In Newton’s Rings, what happens to the spacing of the radii as you increase k? (aka what happens to the ring spacing as you go outwards on the sphere?)

A

-increasing K will DECREASE the spacing, so the rings get closer and closer to each other.

57
Q

why do soap bubbles have different colors?

A

interference colors are viewed through reflected light

–change with varing thickness of the bubbles as the liquid drops from top to bottom of the bubble

58
Q

how do we view a soap bubble where part of it is reflecting color and the other half is “invisible?”

A

-half wL phase shift= one reflected ray and other does not reflect rays (invisible!)

59
Q

how do anti-reflective coatings work on glasses?

A
  • a thin transparent layer to the lens surface that causes DESTRUCTIVE interference between the light rays reflected from the 2 surfaces (the lens)
  • *thickness of this layer matters!
  • want thickness that allows rays reflected from the two sides of the layer to be 1/2 wL out of phase (canceling rays out essentially)
  • the 2nd layer will go through 2 trips through the A/R so THICKNESS MUST BE 1/4wL
60
Q

what are the conditions for complete DESTRUCTIVE interference?

A
  • *principle of superposition**
    1. same amplitude
    2. 1/2 wL or 180 degrees out of phase
61
Q

In a YOung’s double slit experiment, it’s found that 2 consecutive DARK bands are separated by 3mm, what is the dist. between LIGHT bands?

A

same, 3mm.

-Young’s experiment has all bands equally spaces, so the dark will be equally apart as bright from each other

62
Q

In Young’s experiment, if given wL is changed from 400nm to 600nm (increase in wL) what is the change to the radii?

A

proportional difference!

  • increaseing wL will increase radii per
  • same as decreasing d (dist. between slits is smaller)

equation= the separation of 2 successive dark bands is DIRECTLY dependent on L*(wL/ d) so more wL makes whole answer bigger

63
Q

if you have double dark bands that are 2mm separated, how many dark bands are there in 1 cm?

A
  • make units the same: 2mm= 0.2cm
  • how many 0.2 can fit in 1cm?= 1/0.2=5
  • *answer is 5 dark bands are present
64
Q

why is A/R coating called the 1/4 wavelength coating?

A
  • since we’re causing a DESTRUCTIVE interference between light rays reflected from the 2 surfaces of this A/R layer
  • the R2 will have to go through the A/R twice, so the thickness must be 1/4 of that to account for being 1/2 out of phase AND that one ray has to travel twice
65
Q

why is A/R coating only max. effective at ONE given wL?

A
  • needs to be exceedingly THIN
  • needed to adhere reliably to the surface, but still be close enough to the ideal coating index
  • if you alter the wL that can be affected, you will need to change the index or the coating will be really thick
    • one way is to add layers of A/R
66
Q

if you have a wedge interference apparatus that already has 1 material plaed between the wedge, what happens to the number of bright bands if you add a SECOND filter material to the already existing one?

A

if separator is twice as thick= bands will become twice as CLOSE together

“d”= separation thickness. By increasing “d,” the over all separation will become SMALLER= closer together.
**mathematically making a denomenator bigger= smaller outcome

67
Q

in a wedge interference, if the first bright band is seen at 0.2cm from the edge of the plates, how far is the 3rd DARK band?

A
  • know that it starts off DARK band (k=0)
  • therefore k=2 for the 3rd band
  • 0.2 is a bright band, so 0.2*2= 0.4= 2nd dark band placement (k=1)
  • For k=2, it’ll be 0.4*2=0.6cm from the edge
68
Q

what is diffraction?

A

spreading of a collimated light beam when the light encounters an obstacle

–young’s double slit experiment

69
Q

what is Airy’s disc? where do you see this?

A
  • foudn in CIRCULAR aperture’s circular image that has a bright center and dark/bright bands around it
  • Airy’s = the bright center= alpha= 1.22* (wL/d)
70
Q

what is Rayleigh’s criterion? what natural phenomenon for vision is this related to?

A
  • how to tell stars apart (resolve them)
  • 2 stars are resolved if the airy discs are half overlapped over each other

-AKA: if the edge of one disc is at the center of the other (stacked half way on top)

71
Q

what is the equation for the resolving power proportional to if they have circular aperture?

A
  • via Rayleigh’s, the resolving power is angle “alpha”
  • resolving power= inversely proportional to diameter of entrance aperture of instrument
  • *all angles
72
Q

how does our pupil resolving power compare with our retinal mosaic?

A
  • pupil resolving power= 1.9e-4
  • retinal mosaic (cones)= 3e-3/ 17mm of nodal distance of retina= 1.7e-4

** the 2 are close, meaning evolution of eye results in eyes that can work together

73
Q

what are the diffraction effects of a pinhole camera?

A
  • slit opening must be SMALL for crisp image, but cannot be “randomly small”
  • brightness of image depends on aperture size
  • diffraction effects become increasingly important as aperture is reduced

**decreasing aperture=image improves, BUT the diffraction compromises the image–must find a “middle ground”

74
Q

how does a pinhole occluder make vision “better?”

A
  • pinhole allows distortions to bypass (including refractive error, moderate cyl, cataracts)
  • so if your vision changes with pinhole, then you know it’s likely due to these factors. if it does NOT change, then it’s something else as pinhole is not affected by other things
75
Q

what are diffraction bands?

A

faint bands of light and dark reaching into the shadow region when light is shined onto a wall–NOT a sharp drop off around the edges as expected via geometric optics

-Airy’s disc is at the center= bright circle @ middle with bands around it

76
Q

what is the relationship of airy’s disc to the angle alpha in diffraction equation

A

-angle alpha= anglular radius of the disc which also represents the resolving power between the center and the dark band next to it

77
Q

what does resolving power have to do with optometry?

A

-need resolving power so that we can tell things apart from one another. An optical instrument on a chart like Snellen must meet certain resolving power so we can tell the “E” as not just a black blob, but as a letter

78
Q

what does airy disc depend on? (optical property)

A

-diameter of the entrance aperture of the instrument

79
Q

what is the relationship between Airy’s disc and Rayleigh’s criterion for resolving power of an optical instrument?

A

we can “resolve” something as separate if the Airy disc is on top of the center part of another

80
Q

what is an ideal lens have? (3 properties)

A
  1. for a point source object= point source image in image space
  2. series points in 1 plane= images in image space would also be in 1 plane
  3. the mag would be the SAME for any pair of points, no matter where they are in the object space
81
Q

what is the line of path for something in “primary gaze?”

A
  • optic axis passes through center of rotation of the eye
  • eyes are straight ahead looking through the pole of the lens

** here optic axis and line of sight coincide= 1-point image

82
Q

when is magnification constant?

A

for object points lying very close to the axis and must be MORE than just one point

83
Q

what are paraxial rays?

A

when light rays are parallel to each other AND parallel to the optic axis of the lens and close to the optic axis–> F’ = where rays would normally focus

**allows us to use small angle approx. and not care about “tan”–happens only @ primary gaze

84
Q

what are aberrations regarding the visual system?

A
  • when eyes are OFF-AXIS due to eye turn etc.
  • light rays are no parallel to lens axis anymore
  • how this model FAILS= “aberrations”
85
Q

what does the power of any lens depend on? where do chromatic aberrations come from?

A
  • radius of curvature of its surface

- refractive index (short wL-blue= bigger index vs. long wL-reds=smaller)—leads to “chromatic aberrations”

86
Q

what is SPHERICAL aberration and when’s it used/why it’s special?

A
  • primary gaze & only one that’s ON-AXIS
    light rays are parallel to optic axis, but NOT close to the optic axis.
    -paraxial rays are focused on 1 point vs. rays that pass through the lens farther from the pole are focused closer to the lens
87
Q

what is the AKA of spherical aberrations and what are some consequences of its paraxial image?

A
  • aka= aperture dependent
  • will get halo of light that increases with larger aperture (diameter dependent)
  • *usually negligible in spec lens design
  • *felt by pt. when dilated (mydrasis) and VA=blurry
88
Q

what is a COMA aberration? what are its consequences

A
  • off axis counter of spherical aberration
  • happens when eye is not in primary gaze–eye turned/head turned etc
  • rays not parallel to optic axis of spec lens
  • consequence= unsymmetrical halos= looks like a comet with bright head (paraxial focus) with diffuse tail
89
Q

what is COMA aberration dependent on?

A
  • aperature dependent (like spherical)

- not important in spec design

90
Q

what is RADIAL astig? what are its consequences? what is it’s AKA?

A
  • AKA= marginal astigmatism/oblique/meridonal astig (NOT due to toric optical element)
  • a point source is imaged as a pair of mutally PERPENDICULAR lines, separated in space.
91
Q

what is “astigmatic interval”..which aberration is it part of?

A
  • part of radial astig. abberation

- separation between 2 images–similar to interval of sturn for spherical lenses

92
Q

is radial astig important in lens design? why?

A
  • yes

- the size of the astig interval does NOT depend on the aperture of the lens OR the diameter of the bundle of rays

93
Q

when does radial astig happen?

A
  1. bundle of rays is incident parallel to optic axis, but DISPLACED from the axis

OR
2. ray is incident anywhere on the lens, but at an angle from the optic axis

** all these occur when head is turned

94
Q

does the sagittal focus or the tangential focus lie in the optic axis? where does the other lie?

A
  • saggital focus= includes optic axis

- tangential focus= perpendicular to the plane

95
Q

what is special about placement of sag/tangential focus in a (+) lens?

A

in a (+) lens, the tangential place (perpendicular one) lies CLOSER to the lens than the sag focus

96
Q

what are the things that affect astigmatism?

A
  1. viewing distance= dist. of eye to object
  2. “stop” dist= eye’s center to center of lens
  3. oblique turn= angle where the eye turns off-axis
  4. refractive index of material
  5. back vertex power
  6. base curve of lens
97
Q

what is the Tschening ellipse?

A

when values of the BC of a lens is plotted against the BACK VERTEX P
tells us what BC to use for an Rx

  • -creates an “oval” shape
  • -unique for each refractive index, oblique-ness, and stop distance
98
Q

what 3 things is the Tschening ellipse uniquely dependent on?

A
  1. refractive index (n)
  2. obliqueness (amount of turn)
  3. stop distance- eye to center of lens
99
Q

how does “far point sphere” relate to curvature of field?

A
  • curvature of field allows for the “sweeping” motion of the far point (F) when we turn our head
  • a sphere is created when the eye “sweeps” many circles as it moves in all directions a certain degree
100
Q

how do we utilize Corrected Curve Lenses to minimize blur produced by aberrations?

A

combine calculations for correction of RADIAL astig + correction of curvature of field (not aperture dependent)

101
Q

when does Distortion happen? why?

A
  • when image appears to have a shape different than the actual object
  • due to a change in magnification change across the lens (like ray bending in spherical aberration)
102
Q

with a (+) lens, when do you get a pincushion distortion? when do you get barrel distortion?

A
  1. pincushion= INCREASE in mag (like wearing readings, but slight distortion
  2. barrel= decrease in mag (stretching of image
103
Q

for lens UV proofing, how does CR-39 compare with glass in UV-A and UV-B preventing?

A

CR-39: transmits most UV-A, but not UV-B

glass: transmits ALL UV-A and some UV-B

104
Q

for a given light wave that passes through a LINEAR polarizer, which direction are the rays ABSORBED?

A
  • perpendicular to transmission axis direction is absorbed

- only allows parallel side to “go through”

105
Q

what is a filter?

A

device which changes the intensity and also the spectral distribution of light passing through it

106
Q

what is transmittence?

A

for a SPECIFIC wL, it’s a ratio

transmitted radiant flux : incident radian flux

107
Q

what is reflectance?

A

for a SPECIFIC wL, it’s a ratio

reflected radiant flux : incident radian flux

108
Q

what is a transmission curve?

A

graph where the transmittance is plotted against the wL

109
Q

what is a “bulk” tint (what’s this AKA?)

A

AKA a regular solid tint= incorporated throughout the material

110
Q

what is a surface tinted lens?

A

a lens where only the surface layer has an equi-tint effect (even coloration)

**not thickness dependent as it’s just a single layer added

111
Q

in real eyes, what is spherical aberrations affected by? (what gives you LESS SA)

A
  1. small pupil size
  2. aspheric cornea&lens
  3. gradient refractive index (n) of the lens
112
Q

for a coma aberration, what is the difference between a (+) and (-) coma aberration?

A

(+): focus is further AWAY vs. chief ray’s focus= and brightest ray is at the BOTTOM

(-): focus is BEFORE/CLOSER than chief ray’s focus= brightest ray is at the TOP (close to chief ray focus)

113
Q

if you have a (+) SA and the stop is in front of the lens, what type of coma aberration will you have?

A

you will get a NEGATIVE coma where the brightest ray will be towards the TOP, closest to the F’ focus point

114
Q

for radial/oblique astig. aberration, what happens to the astig as you increase the angle between off-axis ray&optic axis?

A

you’ll have MORE oblique astig.

115
Q

what is the “teacup and saucer” image shell mean?

A
  • refers the radial astig. where off-axis rays from all meridians will create…
    1. tangential ray formed image in FRONT= teacup–creates the “radius” of teacup
    2. saggital ray formed image BEHIND= saucer of the teacup–creates the “circular outline” of the saucer
116
Q

how do we quantify the magnitude of radial astig?

A
  • the difference between the tangential & saggital foci

- the further away the object positions are, the more radial astig you’ll have

optics2 (2 decks)

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