Self-imaging effects are an important mechanism for phase-locking of laser arrays. The self-imaging cavities include the one with phase corrector (Lau cavity) and the other one without phase corrector (Talbot cavity). In this paper, the Talbot cavity is analysed in terms of the Fox-Li treatment. It is shown that the diffractive losses of the in-phase mode and the out-of-phase mode have a cross over point with respect to the cavity interval.