  A self-consistent analysis of pion scattering and pion photoproduction within
a coupled channels dynamical model is presented. In the case of pion
photoproduction, we obtain background contributions to the imaginary part of
the S-wave multipole which differ considerably from the result based on the
K-matrix approximation. Within the dynamical model these background
contributions become large and negative in the region of the S_{11}(1535)
resonance. Due to this fact much larger resonance contributions are required in
order to explain the results of the recent multipole analyses. For the first
S_{11}(1535) resonance we obtain as a value of the dressed electromagnetic
helicity amplitude: A_{1/2}=(72 +/- 2) * 10^{-3} GeV^{-1/2}. Similar values can
be derived from eta photoproduction if one takes the same total width
Gamma_R=95 +/- 5 MeV) as in pion scattering and pion photoproduction. The
combined analysis yields considerable strength at invariant mass W>1750 MeV,
which can be explained by a third and a fourth S_{11} resonance with the masses
1846 +/- 47 and 2113 +/- 70 MeV.
