Lens Coatings Flashcards
(52 cards)
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
