  The effects of electromagnetic interactions on pseudoscalar decay constants
are investigated. Using a compact QED and QCD action we are able to resolve
differences of about 0.1 MeV. We obtain the preliminary results f_pi^0-f_pi^+/-
=0.09(3) MeV and f_D^0-f_D^+/- =0.79(11) MeV for light and charmed pseudoscalar
decay constants on a N_f=2 nonperturbatively improved Sheikholeslami-Wohlert
ensemble.
