Biomedical Engineering Reference
In-Depth Information
Appendix F: Correction
of Chromatic Aberration
LONGITUDINAL CHROMATIC ABERRATION
While we're usually not concerned with the longitudinal chromatic aberration
produced by spectacle lenses, this aberration can be an important consideration
in the design of certain optical systems. To minimize longitudinal chromatic
aberration, we can combine a lens of a given refractive index with a lens of another
index to form an
achromatic doublet
. The component lenses of the doublet are
in contact with each other. As illustrated in Figure F-1, one lens has a positive
refractive power and the other a negative refractive power. The formulae used to
calculate the powers of the component lenses are given below:
F
Lens1
υ
Lens1
F
Lens2
υ
Lens2
=
−
F
Ach
=
F
Lens1
+
F
Lens2
where
F
Lens1
is the power of the first lens in air,
F
Lens2
is the power of the second
lens in air,
v
Lens1
is the constringence of the first lens,
1
v
Lens2
is the constringence of
the second lens, and
F
Ach
is the total power of the achromatic doublet.
Let's apply these formulae.
Using a plus crown glass lens with a constringence of
59.0 and a minus flint glass lens (n
=
1.62) with a constringence of 37.0, design
a
6.00 D achromatic doublet that minimizes longitudinal chromatic aberration.
Specifically, what are the powers of the component lenses?
+
1. Recall from Chapter 15 that the terms constringence and Abbe value are interchangeable.
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