A circular analyzer has been used at the focal plane of a telescope in days of absence of instrumental polarization to simultaneously record I±V spectrograms at two different wavelength ranges: ≡6300 Å and ≡3930 - 3970 Å. The observations have been analyzed within two, also different, frames: on the one hand, an empirical relationship between brightness temperature and the magnetic field strength has been found for sunspot umbrae, which allows a determination of the Wilson depression; on the other, estimates of the chromospheric longitudinal component of the magnetic field (magnetic flux if the filling factor is not unity) in two umbrae, in a penumbra, and in a plage have been found by using profiles of the resonance lines H and K of Ca II. A ratio of order 2 - 3 between the longitudinal components of the field at the chromospheric height of formation of the Ca II lines and the photospheric height of formation of the 6302.5 Å Fe I line is also found in umbrae.