The Culgoora magnetograph (Ramsay et al., 1970) produces simultaneous filtergrams in opposite circular polarizations at a wavelength selected by a filter bandwidth 0.005 nm (Ramsay et al., 1970). In the blue wing of the 610.27 nm line of CaI, regions of magnetic fields in strong or weak plages are very obvious in one or other polarization, depending on polarity, even before subtraction; in one polarization they are bright, but almost invisible in the other. They are more difficult to discern at equal intervals from the line centre in the other wing (Figure 1). When subtractions are carried out to yield magnetograms of the same sense, the two magnetograms from opposite wings give results which appear to be much the same. An example is shown in Figure 2. Similar results are obtained over a wide range of positions in the wings of the 610.27 nm line.