Please answer

[majucalicut]

Dear Friends,

Please help me to clarify below doubts:

1. Why plastic lenses(CR 39) turn yellow in color (when exposed to sunlight or kept in stock for a long period). Will it affect vision?

2. Is there any instrument to measure the Refractive index and Abbe number of a lens?

Helping with answers will be highly appreciated

[Chris Ryser]

Dear Frien

Please help me to clarify below doubts:

1. Why plastic lenses(CR 39) turn yellow in color (when exposed to sunlight or kept in stock for a long period). Will it affect vision?

Since 1980 CR39 monomer conatins UV absorbers to prevent the lens from yellowing. Every decent brand name lens does not yellow anymore. I assume that some manufacturerer i China is saving money.

[Jacqui]

If your CR-39 lenses are turning yellow, just dip in lavender tint for a few seconds to neutralize it.