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Correction of secondary spectrum using standard glasses

The correction of secondary spectrum has generally been achieved by the use of special optical materials having non- normal relative partial dispersions, such as fluorite. These optical materials are expensive, unobtainable in large pieces and difficult to work to a good polish. For these reasons the use of these special optical materials is not common in optical systems. In 1955, E.L. McCarthy discovered that an optical system may be substantially or completely freed of secondary spectrum by using standard glasses only. Later, in 1977, C.G. Wynne discussed that the classical theory of first-order chromatic aberrations, which neglects terms of paraxial order in aperture and powers higher than the first in glass dispersions, had led to the erroneous conclusion that in order to correct the secondary spectrum it was necessary to use special optical materials. And in 1978, C.G. Wynne extended the theory of first-order chromatic aberrations in order to consider those previously neglected terms. Up till now the extended-theory developed by C.G. Wynne has not been applied to the design of optical systems corrected of secondary spectrum by using normal glasses. It is the purpose of this paper to develop the algorithm for the evaluation of secondary spectrum contribution on each surface as well as to apply the algorithm to the design of optical systems. Some examples are given.