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192 Ophthalmic Lenses

Fig. 13.6: Varieties of tinted lenses
grey is produced. If the absorption is different for different wavelengths,
then the tint has a particular colour. Tinting resin lenses are relatively simple
procedure. The lenses are placed in a suitable bath of hot colour dye for an
appropriate length of time. Excess darkness can be reduced and light colour
can be made darker. Full colour and graduated colours are all possible.

Fig. 13.7: Mirror coating

Glasses can also be coated by vacuum process which has a unique
advantage of uniform tint throughout the lens surface which is otherwise
not possible in glass lenses.