Biomedical Engineering Reference
In-Depth Information
Both surfaces of the equiconvex lens have the same power,
+
8.08 DS. For the
front surface,
n
′
−
n
F
=
r
1.52
−
1.00
+
8.08 D
=
r
r
= +
0.064 m
6.4 cm
and for the back surface, -6.4 cm. From Figure F-1, we see that the front surface of
the flint glass lens has the same curvature as the back surface of the crown glass lens.
The power of the front surface of the flint glass lens in air is
The radius of curvature for the front surface of this equiconvex lens is
+
n
′
−
n
F
=
r
1.62
−
1.00
F
=
−
0.064 m
F
= −
9.69 D
Since the total power of the flint glass lens is -10.17 D, the power of its back
surface is -0.48 D. Its radius of curvature is
n
′
−
n
F
=
r
1.00
−
1.62
−
0.48 D
=
r
r
= +
1.29 m
The radii of curvature of all four surfaces of the
+
6.00 D achromatic doublet are
given in Figure F-1.
Although the calculations give the powers of the lenses in air, these lenses are
fused to each other. To convince ourselves that the fused doublet has a total power
of
6.00 D, let's add together the powers of the three interfaces. For the first inter-
face (air/crown glass) the power is
+
8.08 D; for the third interface (flint glass/air),
the power is -0.48 D. To complete this calculation, we must determine the power
at the crown glass/flint glass interface as follows:
+
n
′
−
n
F
=
r
1.62
−
1.52
F
=
−
0.064
F
= −
1.56 D
