The effects of changing the center flint glass of a Cooke triplet anastigmat from the optimum glass type are investigated in an attempt to determine how many different glass types are necessary. To this end, about 90 triplets were designed, each with a flint glass displaced from its optimum index and dispersion. Sixteen different combinations of field and aperture and three different crown glass types were used. Variations of performance with flint changes are presented. An ‘‘acceptable’’ variation of the flint glass V value appears to be approximately ±2.