  The anomalous dimensions of operators in the purely gluonic SU(2,1|2) sector
of any planar conformal N=2 theory can be read off from the N=4 SYM results by
replacing the N=4 coupling constant by an interpolating function of the N=2
coupling constants, to which we refer to as the effective coupling. For a large
class of N=2 theories we compute the weak coupling expansion of these functions
as well as the leading strong coupling term by employing supersymmetric
localization. Via Feynman diagrams, we interpret our results as the relative
(between N=2 and N=4) finite renormalization of the coupling constant. Using
the AdS/CFT dictionary, we identify the effective couplings with the effective
string tensions of the corresponding gravity dual theories. Thus, any
observable in the SU(2,1|2) sector can be obtained from its N=4 counterpart by
replacing the N=4 coupling constant by the universal, for a given theory,
effective coupling.
