The perturbation to the cubic crystalline field at rare-earth ions substituting the cation in CaF₂ is treated as a point-charge Coulomb field of the compensating ion. The cubic field energy states and the local charge compensation have enabled the author to calculate the wavefunction and g-values of Yb³⁺ and Ce³⁺ with tetragonal symmetry in CaF₂. The results for Yb³⁺ turn out to be in reasonable agreement with experimental g-values, while those for Ce³⁺ seem not unsatisfactory.