The design problems of high aperture triplet objectives

An investigation has been made of the roots of a certain cubic equation f(Yob) = 0, which arises in the theory of the type-111 triplet photographic objective. It has been shown that with the residuals and the parameter values such as might be used in the type 111 triplet, this equation gives three positive roots of which only one leads to a practical solution. It was shown that if certain parameters which enter into the coefficients of Yob in this cubic equation are given values much greater than is usual in a type 111 objective, a second root of the equation leads to a practical solution. In this way, a new region of triplet solution has been opened - up characterised by low powers for the components in the initial thin lens arrangement. It was expected that this region would provide a basis for the development of high aperture objectives. The general physical principles underlying the achievement of these high values of initial parameters has involved a careful study of the properties of thick meniscus shaped cemented triplet components of negative power. A procedure for the design of a type 131 objective, which is the simplest form of objective incorporating these principles, has been developed and is described with numerical examples. A study of more complex objectives is needed to exploit the principles which have been opened up in this work. The time available for the investigation has not permitted the study of type 133 and other objectives from this point of view.