Example of the growth curve analysis of source ID 018 (photo-z = 0.39). The cluster’s redshift and luminosity are close to the median values of the entire sample. The curves show the encircled cumulative flux as a function of radius (PN: blue curve, combined MOS: red, dot-dashed). The PN and MOS curves are in good agreement. Dashed lines mark the flux measurement error bars which include the Poisson noise and an additional 5% systematic error from the background estimation. The estimated plateau flux is F_plat = 5.19 × 10^-14 erg s^-1 cm^-2 (horizontal line), reached at r_plat ~ 90 arcsec. The vertical line signifies the estimated r₅₀₀ radius of the source, r₅₀₀ = 0.6 Mpc (~117 arcsec). In this case, the plateau radius is slightly smaller than r₅₀₀ and the flux and luminosity for r₅₀₀ had to be extrapolated from their plateau values. The required extrapolation is only  ~2% in this case. See Sect. 3.3 for details.