CAFOS spectrum of 3C 120 obtained on Oct. 27th 2009. For illustration, the band passes of the filters used for the photometric monitoring are shaded (blue B-band, green V-band). The transmission of the narrow band ([OIII] 5007 Å filter) is indicated by the red dotted line. While narrow band catches the redshifted Hβ line, its flux is composed of about 50% Hβ line (red shaded) and 50% the continuum (black shaded). Note that for actual flux calculations the filter curves are convolved with the transmission curve of the Alta U16 CCD camera.