Comparison of the optical depth for primary γ-rays for sources at cosmological redshifts in CRbeam, CRPropa and ELMAG. In all cases, the EBL model of Franceschini et al. (2008) is assumed. Top panels show the optical depth as a function of γ-ray energy for a range of redshifts. Bottom panels show discrepancies between the code calculations and the analytical model. For CRPropa, the differences between the analytical model and code calculations are not shown for redshifts of >0.3 because they exceed 50%.