The analysis of the losses in a Fabry-Perot resonator, worked out by Bergstein and Schachter, is considered and commented upon. It is shown that, at large values of the Fresnel number, it yields results in agreement with those of other authors, if the mathematics involved is correctly developed.
L Ronchi, "The Asymptotic Expression for the Resonant Mode Losses of a Fabry-Perot Open Resonator," Appl. Opt. 9, 733-736 (1970)