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Ophth. Optics II > Lens Coatings > Flashcards

Lens Coatings Flashcards

1
Q

describe the modern AR system

A

combo scratch coat and AR layers per side ; includes quatz like layers with outer hydrophobic layer

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2
Q

What % of lenses in the US are AR coated

A

30% ( AR lenses more popular in Europe, Canada , and Japan)

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3
Q

the purpose of this coating is to increase the amt of light transmitted through the lens ; reduce unwanted reflections

A

AR coating

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4
Q

majority of light striking a lens surface is _______

A

refracted

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5
Q

small portion of reflected light can cause ?

A

ghost images, falsification of image position, haze and loss of contrast

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6
Q

what are some methods for reducing surface reflections

A

base curve selection, pantoscopic tilt, changing vertex distance, selecting smaller lens size , AR coatings

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7
Q

which coating works on the principle of interference

A

AR coatings

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8
Q

what two things can we get whenever two waves of equal intensity /amplitude are superimposed by a monochromatic source

A

neutralization or reinforcement

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9
Q

this is negative interference; this occurs if the path diff. is an odd number of half wavelengths

A

neutralization

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10
Q

this is positive interference; this occurs if the path diff is an even number of half wavelengths

A

reinforcement

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11
Q

light striking the front surface of a lens with an AR coating creates which two reflecting waves

A

front surface of the lens coating and the interface between the coating and the lens

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12
Q

when do two reflecting waves cancel one another

A

if waves are of equal amplitude ( amplitude condition) and if waves are 1/2 wavelength out of phase ( path condition)

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13
Q

with AR, how much light is transmitted versus reflected

A

> 98 % transmission and

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14
Q

T or F: the higher the refractive index of lens material , the greater the incidence of reflections and glare

A

T

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15
Q

how does Cr39 lens work with AR

A

1/2 wavelength out of phase so reflection is cancelled

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16
Q

this determines the index of refraction for the coating; intensity of the reflection from the air coating interface must equal the intensity of the reflection for the coating lens interface

A

amplitude condition

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17
Q

what is the amplitude condition equation

A

n(c) = √ nL

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18
Q

what is the path condition for AR coatings

A

2 waves out of phase by 1/2 a wavelength at the point of interference ; determines the thickness of the AR coating; bc the wave reflected from the lens-coating interface transverses the coating twice , the wave will be 1/2 wavelength out of phase with the reflected wave at the air-coating interface if the coating is made with an optical thickness of 1/4 wavelength

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19
Q

with amplitude condition equation what is the n(c) for crown glass

A

1.234 ( a coating with 1.234 is too soft so usually MgFl 1.38 is used as an AR coating for glasses lenses )

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20
Q

T or F: path condition will only work for one monochromatic wavelength

A

T

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21
Q

reflections increase toward what end of the spectrum

A

towards thr red and violet ends of the spectrum

22
Q

what properties of AR coatings repels water and makes the lens surface easier to clean

A

hydrophobic properties

23
Q

what properties of AR coatings repels oil, dirt, and dust and helps reduce fingerprints, smudges, and grease

A

oleophobic properties

24
Q

what properties of AR coatings repels dust, dirt, and debris by giving the lens surface anti-static properties

A

anti-particulate properties

25
Q

which AR coating repels dust, fingerprints , oil , grease, and water, blocks UV

A

crizal alize

26
Q

which AR coating is improved version with scotchguard; twice as scratch resistant as crizal alize lenses

A

crizal avance

27
Q

which AR coating is improved with no glare performance; best cleanability ( no smudges, water , or dust); best scratch resistance ( scotchgard)

A

crizal sapphire

28
Q

which AR coating is improved AR coating with 99% luminous transmittance ; cleaner with improved anti-static technology ; tougher with improved scratch resistance and improved slick coat

A

Teflon elite

29
Q

what are some probs with AR coatings

A

soft and scratch easily; they display grease and smudges

30
Q

this is a layer of silicone added as the outermost layer to the lens; it causes water and grease to form smaller droplets ; increases hardness of lens surface

A

hydrophobic coatings

31
Q

how many layers is the typical AR coating

A

Many AR coatings have 5-6 layers

32
Q

how does essilor monitor the quality of AR coating

A

in every batch of lenses that goes through the AR process, 2 non dispensable lenses are included. Those lenses are sent to Essilors main lab in Dallas everyday for quality control checks

33
Q

What are the tests for quality AR lenses

A

Ar craze, anti static test, bayer test, crosshatch adhesion test, and tumble test

34
Q

what is usually the outer layer of the AR coating

A

hydrophobic layer

35
Q

why do people get AR

A

reduce reflections noticed by observers; reduce the glassines of the lens appearance ; can be applied to all types of lenses ; doesn’t interfere/degrade polarized or photochromic lens performace

36
Q

the goal of this coating is to enhance reflections

A

mirrored coatings

37
Q

this effect is created by constructive interference at the lens surface

A

mirrored coatings

38
Q

this coating is usually for cosmetic enhancement ; created by depositing powdered oxides or compounds onto the surface of a tinted spectacle lens

A

mirrored coatings

39
Q

what are the two basic types of mirror treatments

A

metallic and dielectric

40
Q

this type of metallic tx reduced visible light transmission by 25-35% ; solid, reflective one way mirror… cant see wearers eyes ; usually gold, silver, or blue

A

metallic mirrors

41
Q

this type of metallic tx has less metallic coating, reduces visible light transmission by 8-12%; used more for fashion

A

flash mirrors

42
Q

Which coating is typically put on the front and back surfaces of the lenses

A

scratch resistant coatings

43
Q

how do AR layers enhance scratch coatings

A

by including three SiO2 layers

44
Q

the outermost layer of scratch coating is a ________ layer to ease cleaning

A

hydrophobic layer

45
Q

with the lens abrasion test, which lenses withstood the steel wool abrasion test

A

GEMCOAT beat out crizal

46
Q

which AR coating eliminates more glare than most other AR coatings and has superior scratch resistance

A

Teflon

47
Q

this coating resists oil, water, and dust ; superior hydrophobic and anti-statis properties

A

Teflon coating

48
Q

What does the clear coat on the crizal alize coating do

A

reduce static electricity

49
Q

the production sequence of this AR on what type of material involves thorough lens cleaning; lenses baked for 2 hours to remove water; lens heated in a vacuum to 100 degrees Celsius; Na dioxide used with electron beam evaporation for outer layer

A

plastic lenses AR production sequence

50
Q

the production sequence of this AR on what type of material involves thorough lens cleaning; lens heated in a vacuum to 300 degrees Celsiu; Mg Fl heated to 2500 degrees Celsius causing vaporization and deposition on the lens surface

A

Glass lens production AR

51
Q

which process takes 4-10 hours; thin layers of low medium and high index materials are alternately applied

A

AR coating process

52
Q

final thickness of AR coating is about __________ width of human hair

A

1/5000th

Ophth. Optics II (7 decks)

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