Four Cooke triplet systems have been designed for an 85-mm focal length and f/2.8 relative aperture for use as a 35-mm slide projector objective. Two designs use the existing glasses. In the other two designs the EDF glass of the negative lens was replaced by hypothetical low-index high-dispersion glasses. The performance of the triplet systems is found to improve considerably by using low-index high-dispersion glasses for the middle negative lens.

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A new design for a five-element lens system has been developed at a focal length of 100 mm and relative aperture of f/1.9 for use as a 35-mm cinematograph projector objective. Another design of a double-Gauss system having a five-element configuration which is in current use has also been developed using superior glasses. The performances of the two designs have been compared. The new design is found to have better potential for aberration correction.

A new Cooke triplet derivative of a five-element configuration is proposed, in which both the front and the rear lenses of the triplet are split into two separated positive lenses. The designs of this new lens and the conventional Pentac lens have been developed for use as a 35-mm camera lens under identical conditions. The performance of the two lens systems is compared, and it is found that the aberrations of the new lens system are better corrected.

Designs of three lens systems of the Cooke Triplet family with four-element configuration-Split Front, Split Back, and Tessar-have been developed with the help of a lens optimization program in identical conditions of optimization for use as 35-mm camera lenses. To evaluate the relative performance of these designs, their aberrational characteristics have been compared and contrary to popular belief, it is found that the Tessar is not the best among the four-element lenses of this family.