1. A plastic meniscus lens of index 1.50 has a front radius of curvature of 8 cm and a back radius of curvature of 22.22cm. What is its dioptric power?

                      n - 1           n - 1
       DN = 
                       r1                r2
where:
   DN = ?
   n = 1.50
   r1 = 8 cm = 0.08 m
   r2 = 22.22 cm = 0.2222 m

                      0.50        0.50
       DN = + - 
                     0.08       0.2222
(A meniscus lens has a convex or positive front surface and a concave or negative back surface)
       DN = +6.25 - 2.25 = +4.00D
 

2. A barium meniscus lens, n = 1.60, has a front radius of curvature of 12cm and a back radius of curvature of 7.5cm. What is its dioptric power?

                      n - 1           n - 1
       DN = 
                       r1                r2
where:
   DN = ?
   n = 1.60
   r1 = 12cm = 0.12 m
   r2 = 7.5 cm = 0.075 m

                      0.60        0.60
       DN = + - 
                     0.12       0.075
(A meniscus lens has a convex or positive front surface and a concave or negative back surface)
       DN = +5.00 - 8.00 = -3.00D
 

3. A flint meniscus lens, n = 1.70, has a front radius of curvature of 11.2 cm and a back radius of curvature of 175 mm. What is its dioptric power?

                      n - 1           n - 1
       DN = 
                       r1                r2
where:
   DN = ?
   n = 1.70
   r1 = 11.2cm = 0.112 m
   r2 = 175 mm = 0.175 m

                      0.70        0.70
       DN = + - 
                     0.112      0.175
(A meniscus lens has a convex or positive front surface and a concave or negative back surface)
       DN = +6.25 - 4.00 = +2.25D
 

4. What is the power of a plano-convex polycarbonate lens with a front surface radius of curvature of 500mm?

                      n - 1           n - 1
       DN = 
                       r1                r2
where:
   DN = ?
   n = 1.586
   r1 = 500 mm = 0.50 m
   r2 = infinity

                      0.586       0.586
       DN = + - 
                     0.50         inf.
(A flat surface has an infinite radius. Any number divided by infinity is 0.)
       DN = +1.17 - 0 = +1.17D which rounds to +1.12 D.
 

5. What is the power of a plano-concave crown glass lens with a back surface radius of curvature of 45mm?

                      n - 1           n - 1
       DN = 
                       r1                r2
where:
   DN = ?
   n = 1.523
   r1 = infinity
   r2 = 45 mm = 0.045 m

                      0.523        0.523
       DN = + - 
                        inf        0.045
       DN = 0 - 11.62 = -11.62 D
 

6. What is the power of a bi-convex high-lite lens (n = 1.70) with a front surface radius of curvature of 70cm and a back surface radius of curvature of 1.5m?

                      n - 1           n - 1
       DN = 
                       r1                r2
where:
   DN = ?
   n = 1.70
   r1 = 70 cm = 0.70 m
   r2 = 1.5 m

                      0.70        0.70
       DN = + - 
                     0.70       1.5
(A bi-convex lens has two convex or plus surfaces.)
       DN = +1.00 + 0.47 = +1.47D, which rounds to +1.50 D.
 

7. What is the power of a biconcave CR39 lens with a front surface radius of curvature of 250mm and a back surface radius of curvature of 37.5cm?

                      n - 1           n - 1
       DN = 
                       r1                r2
where:
   DN = ?
   n = 1.498
   r1 = 250 mm = 0.250 m
   r2 = 37.5 cm - 0.375 m

                      0.498       0.498
       DN = - - 
                     0.250       0.375
(A bi-concave lens has two negative surfaces.)
       DN = -1.99 - 1.33 = -3.32 D which rounds to -3.37 D.

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