Dependence of the CCF on concentration ratio of the two binding partners for which the concentration of the particles were varied according to c_a = 2.5 nM,c_a = 0.5 … 10 nM, c_ab = 1.25 nM^-1 (c_a × c_b). We assumed identical detection volumes for both channels with axial radii of 260 nm, and axial radii of 1.3 μm, corresponding to observation volumes of 0.5 fl; the brightness of the two particles was set to 1500 counts/second in their respective channel, and 10% cross-talk from particle a into the detection channel B and 1% cross-talk of particle b into detection channel A; the diffusion times for the two particles were set to τ_Da = 3 ms, τ_Db = 0.3 ms.