Lens Coatings Flashcards
describe the modern AR system
combo scratch coat and AR layers per side ; includes quatz like layers with outer hydrophobic layer
What % of lenses in the US are AR coated
30% ( AR lenses more popular in Europe, Canada , and Japan)
the purpose of this coating is to increase the amt of light transmitted through the lens ; reduce unwanted reflections
AR coating
majority of light striking a lens surface is _______
refracted
small portion of reflected light can cause ?
ghost images, falsification of image position, haze and loss of contrast
what are some methods for reducing surface reflections
base curve selection, pantoscopic tilt, changing vertex distance, selecting smaller lens size , AR coatings
which coating works on the principle of interference
AR coatings
what two things can we get whenever two waves of equal intensity /amplitude are superimposed by a monochromatic source
neutralization or reinforcement
this is negative interference; this occurs if the path diff. is an odd number of half wavelengths
neutralization
this is positive interference; this occurs if the path diff is an even number of half wavelengths
reinforcement
light striking the front surface of a lens with an AR coating creates which two reflecting waves
front surface of the lens coating and the interface between the coating and the lens
when do two reflecting waves cancel one another
if waves are of equal amplitude ( amplitude condition) and if waves are 1/2 wavelength out of phase ( path condition)
with AR, how much light is transmitted versus reflected
> 98 % transmission and
T or F: the higher the refractive index of lens material , the greater the incidence of reflections and glare
T
how does Cr39 lens work with AR
1/2 wavelength out of phase so reflection is cancelled
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
amplitude condition
what is the amplitude condition equation
n(c) = √ nL
what is the path condition for AR coatings
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
with amplitude condition equation what is the n(c) for crown glass
1.234 ( a coating with 1.234 is too soft so usually MgFl 1.38 is used as an AR coating for glasses lenses )
T or F: path condition will only work for one monochromatic wavelength
T
reflections increase toward what end of the spectrum
towards thr red and violet ends of the spectrum
what properties of AR coatings repels water and makes the lens surface easier to clean
hydrophobic properties
what properties of AR coatings repels oil, dirt, and dust and helps reduce fingerprints, smudges, and grease
oleophobic properties
what properties of AR coatings repels dust, dirt, and debris by giving the lens surface anti-static properties
anti-particulate properties
which AR coating repels dust, fingerprints , oil , grease, and water, blocks UV
crizal alize
which AR coating is improved version with scotchguard; twice as scratch resistant as crizal alize lenses
crizal avance
which AR coating is improved with no glare performance; best cleanability ( no smudges, water , or dust); best scratch resistance ( scotchgard)
crizal sapphire
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
Teflon elite
what are some probs with AR coatings
soft and scratch easily; they display grease and smudges
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
hydrophobic coatings
how many layers is the typical AR coating
Many AR coatings have 5-6 layers
how does essilor monitor the quality of AR coating
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
What are the tests for quality AR lenses
Ar craze, anti static test, bayer test, crosshatch adhesion test, and tumble test
what is usually the outer layer of the AR coating
hydrophobic layer
why do people get AR
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
the goal of this coating is to enhance reflections
mirrored coatings
this effect is created by constructive interference at the lens surface
mirrored coatings
this coating is usually for cosmetic enhancement ; created by depositing powdered oxides or compounds onto the surface of a tinted spectacle lens
mirrored coatings
what are the two basic types of mirror treatments
metallic and dielectric
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
metallic mirrors
this type of metallic tx has less metallic coating, reduces visible light transmission by 8-12%; used more for fashion
flash mirrors
Which coating is typically put on the front and back surfaces of the lenses
scratch resistant coatings
how do AR layers enhance scratch coatings
by including three SiO2 layers
the outermost layer of scratch coating is a ________ layer to ease cleaning
hydrophobic layer
with the lens abrasion test, which lenses withstood the steel wool abrasion test
GEMCOAT beat out crizal
which AR coating eliminates more glare than most other AR coatings and has superior scratch resistance
Teflon
this coating resists oil, water, and dust ; superior hydrophobic and anti-statis properties
Teflon coating
What does the clear coat on the crizal alize coating do
reduce static electricity
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
plastic lenses AR production sequence
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
Glass lens production AR
which process takes 4-10 hours; thin layers of low medium and high index materials are alternately applied
AR coating process
final thickness of AR coating is about __________ width of human hair
1/5000th
