  The spectral, imaging, and polarimetric behavior of Fabry-P\'erot etalons
have an influence on imaging vector magnetograph instruments based on these
devices. The impact depends, among others, on the optical configuration
(collimated or telecentric), on the relative position of the etalon with
respect to the polarimeter, on the type of etalon (air-gapped or crystalline),
and even on the polarimetric technique to be used (single-beam or dual-beam).
In this paper we evaluate the artificial line-of-sight velocities and magnetic
field strengths that arise in etalon-based instruments attending to the
mentioned factors. We differentiate between signals that are implicit to
telecentric mounts due to the wavelength dependence of the point-spread
function and those emerging in both collimated and telecentric setups from the
polarimetric response of birefringent etalons. For the anisotropic case we
consider two possible locations of the etalon, between the modulator and the
analyzer or after it, and we include the effect on different channels when
dual-beam polarimetry is employed. We also evaluate the impact of the loss of
symmetry produced in telecentric mounts due to imperfections in the
illumination and/or to a tilt of the etalon relative to the incident beam.
