  In the optical, the spectrum of symbiotic binaries consists of contributions
from the cool giant, symbiotic nebula and the hot star. Strong emission lines
are superposed on the continuum. In this paper we introduce a simple method to
extract individual components of radiation from photometric UBV magnitudes. We
applied the method to classical symbiotic stars AX Per, AG Dra, AG Peg and Z
And, the symbiotic novae RR Tel and V1016 Cyg and the classical nova V1974 Cyg
during its nebular phase. We estimated the electron temperature and emission
measure of the nebula in these systems and the V magnitude of the giant in the
symbiotic objects. Our results are in a good agreement with those obtained
independently by a precious modelling the UV-IR SED.
