  The amplitude ratios of vector-meson production by heavy photons on spinless
targets are shown to can be explicitly expressed in terms of the
spin-density-matrix elements (SDMEs) only if the lepton beam is longitudinally
polarized. Making use of the amplitude ratios as free fit parameters instead of
the SDMEs reduces the number of the real parameters in data description from 23
to 8. The exact formula for $R = \frac{d \sigma_L}{d t}/\frac{d \sigma_T}{d t}$
in terms of the SDMEs is obtained for spinless targets and the new approximate
formula for $R$ is proposed for nucleon targets.
