Dust extinction: the flux ratio F(Hα/Hβ ) in blue galaxies with U_e − R_e < 2.2. Three different redshift difference cuts  | Δz |  are pictured for the pairs, top:  | Δz |  = 0.001, middle:  | Δz |  = 0.006, bottom:  | Δz |  = 0.012. The individual errors are unweighted in the calculations of mean values and error bars. Only objects with emission line fluxes that are greater than three times the measured error are included.