Lens Coatings Flashcards
What percent of lenses are AR coated in US?
34%
What is the purpose of anti-reflective coatings?
Reduce reflections and increase light transmitted through the lens which can increase contrast.
What are the 5 methods of reducing surface reflections?
1) Base curve selection
2) Adjusting the pantoscopic tilt
3) Changing the vertex distance
4) Selecting a smaller lens
5) Antireflective coating
The higher the refractive index of a lens, the ____________ incidence of reflections and glare.
greater
occurs if the path difference is an ODD number of half wavelengths
neutralization
occurs if the path difference is an EVEN number of half wavelengths
Reinforcement
Two reflecting waves cancel one another if:
1)Waves are equal amplitude
2)Waves are 1/2 wavelength out of phase
repels oil, dirt and dust and helps reduce
fingerprints, smudges and grease
Oleophobic
repels dust, dirt and debris by giving the
lens surface anti-static properties
Anti-Particulate
What molecule is responsible for AR in glass lenses?
magnesium flouride
What molecule is responsible for AR in plastic lenses?
sodium dioxide (quartz)
What are some problems with AR coatings?
soft, scratch easily, show grease and smudge marks more
How does Essilor check the quality of its AR coatings?
In a batch of lenses, they take two nondispensable lenses and test them.
What is the typical sequence of lens coatings applied to a lens for AR?
hydrophobic coating (outermost)
AR coating
Hardcoat
Lens (middle)
Hardcoat
AR
hydrophobic coating (Outermost)
4 benefits of AR coating
1) Reduces Distracting glare
2) Reduces reflection noticed by observers
3) Reduces glassiness of the lens
4) Increases light transmission
Is the AR coating applied before or after putting the tint on sunglasses?
AR after the tint
Is the AR coating on the frontside or backside of sunglasses?
backside
What two materials make up the mirrored appearance of mirrored coatings?
Metals
Dielectrics
Would a dielectric mirrored coating transmit more or less light than metallic treatments?
More transmission
How much do solid mirrored coatings reduce transmission?
25-35%
How much does a flash mirror coating reduce light transmission?
8-12%
What is the steel wool scratch test?
Used on AR coatings. Steel wool rubbed 200 cycles with 5 pound weight.
Does scratch resistant and AR increase or decrease impact resistance for lenses?
Decrease
What percent loss of strength is caused by adding a hard coating?
45%
What percent loss of strength is caused by adding an AR coating?
20%
