01-19-2010, 07:23 AM
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Member
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Join Date: Jan 2010
Posts: 33
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Disvantages of increased indices
First,it means increased chromatic abrration amongst other things;second,poorer light transmission and increased backside and inner-surface reflections(see fresnel reflection equation)increasing importance of anti-reflective coating;thirdly,manufacturing defects have more impact on optical quality;finally,off-axis optical quality degrades(oblique astigmatic error).In practice this degradation should be perceptible-current frame styles are much smaller thatn they would have to be for these aberrations to be noticeable to the patient,the aberration occurring some distance away from optical centre of the lens(off-axis)
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