For example, the condition for achromatism (4) for two thin lenses in contact is fulfilled in only one part of the spectrum, since do /dn 1 varies within the spectrum.
He concluded that there could be no refraction without dispersion, and hence that achromatism was impossible of attainment (see Aberration).
He concluded that there could be no refraction without dispersion, and hence that achromatism was impossible of attainment.
If all three constants of reproduction be achromatized, then the Gaussian image for all distances of objects is the same for the two colours, and the system is said to be in " stable achromatism."
In uniting three colours an " achromatism of a higher order " is derived; there is yet a residual " tertiary spectrum," but it can always be neglected.
James Gregory and Leonhard Euler arrived at the correct view from a false conception of the achromatism of the eye; this was determined by Chester More Hall in 1728, Klingenstierna in 1754 and by Dollond in 1757, who constructed the celebrated achromatic telescopes.
Leonhard Euler in 1747 had suggested that achromatism might be obtained by the combination of glass and water lenses.
Newton failed to perceive the existence of media of different dispersive powers required by achromatism; consequently he constructed large reflectors instead of refractors.
The absence of this error is termed achromatism, and an optical system so corrected is termed achromatic.
The whole history of his researches proves how fully he was aware of the conditions necessary for the attainment of achromatism in refracting telescopes, and he may be well excused if he so long placed implicit reliance on the accuracy of experiments made by so illustrious a philosopher as Newton.
This artifice is specially adopted in objectives for astronomical photography ("pure actinic achromatism").