The K2NixCo(1-x)(SO4)(2)center dot 6H(2)O (KCNSH) mixed crystals were grown from solutions of different composition by the temperature difference technique with continuous solution feeding. The schemes of the solution supply and condensate extraction were calculated, which allowed maintaining the constant composition of the crystals. The real structure and optical properties of the crystals obtained were studied. The experimental samples of optical filters were made from KCNSH mixed crystals and their optical characteristics had been studied. Their high optical quality is shown.