This means that the spectral resolution for point sources is higher than for extended sources, in a ratio that is affected, of course, by diffraction . See section 6.3 for more information on this. There the monochromatic detector images just fill the slit width. With the spectral channeling by the FPs, a subtle interplay arises between spectral and spatial properties. Effectively, the spatial resolution may increase due to the narrowness of the FP resonance.
Point sources have less leakage in unwanted FP orders than extended sources.
Spatial extent does not influence the spectral resolution of the FPs. Along the y-axis, the effective size of the aperture is determined by the projection of the detector array on the sky. For the FP bands 5A to 6, the aperture is effectively as wide as a detector image on the sky, i.e. either 10 or 17 . To derive the position angle of an aperture, information on the spacecrafts position on the sky must be used. See also section 8.10 .