Relative intensity response functions. Top panel: intensity response of synthetic Ca imaging data for filters with FWHM of 0.03 nm, 0.22 nm, 0.3 nm and 1 nm, respectively (red/orange/blue/purple lines). Green-dash-dotted line: intensity response for the FALF profile transmitted through a 0.3 nm filter. Black line: intensity response of the 630.25 nm line core. Bottom panel: response for a 0.3 nm filter and the 630.25 nm line core normalized to maximal response (blue/black line), and their difference (red line).