2. PROPERTIES
 Refractive index
 Abbe value
 Density

3. Refractive index
 The ratio of the velocity of light of a given
wavelength in air, to the velocity of light of
the same wavelength in refracting medium
 n = velocity of light in air
velocity of light in medium

4.  ABBE VALUE
 It is reciprocal of dispersive power
 It is denoted by “V”
 V = _______1______
__nf – nc____
1 - nd
 V = ____1 - nd________
 nf - nc

5. DENSITY
mass per unit volume
D = ____MASS___
VOLUME
UNIT = g/cm³

6.  SPECIFIC GRAVITY
 the ratio of the density of material to the
density of water at 1⁰ centigrade
∫ = _____density of material______
density of water

7. Type of lens material
 GLASS MATERIAL
1. crown glass
2. barium crown glass
3. flint
 PLASTIC MATERIAL
1. CR 39
2. PMMA
3. Polycarbonate
4. Trivex

8. CROWN GLASS
Another name soda lime silica glass
composition
silica 70%
soda 25%
lime 15% (calcium carbonate)
trace of other material borax, potasium, antimony
, arsenic which improve the quality of glass by
acting as a refining agent

9.  Refractive index 1.523
 Abbe value 59
 Specific gravity 2.5
 Density 2.5 g/cm³

10. Barium crown glass
Composition
 silica = 35%
 Barium oxide = 30%
small percentage of lime , zinc, antimony,
boron, zirconium

11. FLINT
 COMPOSITION
PbO₂ = 80%
silicon = 30%
soda & potash = 8%
small percentage of arsenic & antimony
If increase the percentage of PbO₂ in
material increase refractive index as
well as dispersive power specific
gravity and density also increase

12. CONTINUE
 Refractive index 1.6
 Abbe value 42
 Specific gravity 2.6
 Density 2.6

13. Plastic material
 Polymethylmehtacralyate (PMMA) &
CR39 are principal plastic material that
emulate the crown glass
PROPERTIES PMMA CR39
REAFRACTIVE INDEX
1.49 1.498
ABEE VALUE
58 57.6
DENSITY 1.19 1.32
SPECIFIC GRAVITY 1.19 1.32

14. Trivex
 New lens material, contain three good
lens characteristic
 Also known as phoenix , trilogy
 REFRACTIVE INDEX 1.532
 ABBE VALUE 45
 DENSITY 1.1
 SPECIFIC GRAVITY 1.1

15. QUALITIES
 Lightest weight among plastic material
 Impact resistance (bullet prove)
 Excellent Abbe value
Block UV ray

16. POLYCARBONATE
 Alternate plastic material
 Block ultra voilet rays
Refractive index 1.586
Abbe value 30
Density 120
Specific gravity

17. NAME OF MATERIAL
REFR
INDEX
ABBE
VALUE
DENSITY
SPECIFI
C
GRAVITY
PLASTIC MATERAIL
CR39 1.498 57.6 1.35 1.35
PMMA 1.49 58 1.19 1.19
PLYCARBONATE 1.586 30 120 120
TRIVEX 1.532 45 1.1 1.1
GLASS
CROWN 1.523 58 2.5 2.5
FLINT 1.6 42 2.6 2.6