A new theory explaining the intensity of f-f transitions and the crystal field using an approximation of a strong configuration interaction is proposed. The theory enables the anomalous influence of excited configurations with charge transfer on some multiplets of the f shell to be taken into account. With the help of this theory, a satisfactory description of the absorption transitions and luminescence branching ratios from 1
2 and 3
0 multiplets for the Pr3+ ion in double molybdates has been achieved for the first time. For further validation the theory, was used to provide a description of Stark splitting of Pr3+ - multiplets in elpasolites and determine the covalence parameters; these parameters were found to be in good agreement with values obtained by the other methods.