Intrinsic half light radii of galaxies and QSOs in the 70 μm blue band as a function of redshift. Symbols or limit for QSOs are encircled in green. The blue line indicates the physical size corresponding to the half width at half maximum of the PACS point spread function at that wavelength. Pink symbols mark results for close doubles/pairs. These are not used below unless explicitly mentioned. The most local galaxies have been placed at z = 0.002 to limit plot size. A number of galaxies with very compact FIR regions are identified. For many bright and large targets, error bars are smaller than the symbol size. Lower redshift galaxies with typically higher S/N can be resolved to smaller fractions of the PSF than the fainter QSOs.