Lens Coatings Flashcards

1
Q

What percent of lenses are AR coated in US?

A

34%

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2
Q

What is the purpose of anti-reflective coatings?

A

Reduce reflections and increase light transmitted through the lens which can increase contrast.

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3
Q

What are the 5 methods of reducing surface reflections?

A

1) Base curve selection
2) Adjusting the pantoscopic tilt
3) Changing the vertex distance
4) Selecting a smaller lens
5) Antireflective coating

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4
Q

The higher the refractive index of a lens, the ____________ incidence of reflections and glare.

A

greater

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5
Q

occurs if the path difference is an ODD number of half wavelengths

A

neutralization

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6
Q

occurs if the path difference is an EVEN number of half wavelengths

A

Reinforcement

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7
Q

Two reflecting waves cancel one another if:

A

1)Waves are equal amplitude
2)Waves are 1/2 wavelength out of phase

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8
Q

repels oil, dirt and dust and helps reduce
fingerprints, smudges and grease

A

Oleophobic

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9
Q

repels dust, dirt and debris by giving the
lens surface anti-static properties

A

Anti-Particulate

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10
Q

What molecule is responsible for AR in glass lenses?

A

magnesium flouride

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11
Q

What molecule is responsible for AR in plastic lenses?

A

sodium dioxide (quartz)

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12
Q

What are some problems with AR coatings?

A

soft, scratch easily, show grease and smudge marks more

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13
Q

How does Essilor check the quality of its AR coatings?

A

In a batch of lenses, they take two nondispensable lenses and test them.

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14
Q

What is the typical sequence of lens coatings applied to a lens for AR?

A

hydrophobic coating (outermost)
AR coating
Hardcoat
Lens (middle)
Hardcoat
AR
hydrophobic coating (Outermost)

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15
Q

4 benefits of AR coating

A

1) Reduces Distracting glare
2) Reduces reflection noticed by observers
3) Reduces glassiness of the lens
4) Increases light transmission

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16
Q

Is the AR coating applied before or after putting the tint on sunglasses?

A

AR after the tint

17
Q

Is the AR coating on the frontside or backside of sunglasses?

A

backside

18
Q

What two materials make up the mirrored appearance of mirrored coatings?

A

Metals
Dielectrics

19
Q

Would a dielectric mirrored coating transmit more or less light than metallic treatments?

A

More transmission

20
Q

How much do solid mirrored coatings reduce transmission?

A

25-35%

21
Q

How much does a flash mirror coating reduce light transmission?

A

8-12%

22
Q

What is the steel wool scratch test?

A

Used on AR coatings. Steel wool rubbed 200 cycles with 5 pound weight.

23
Q

Does scratch resistant and AR increase or decrease impact resistance for lenses?

A

Decrease

24
Q

What percent loss of strength is caused by adding a hard coating?

A

45%

25
Q

What percent loss of strength is caused by adding an AR coating?

A

20%