Regions of star cluster parameter space where aperture photometry meets the required accuracy. The grey areas and regions with blue or red squares indicate the cluster mass and age combinations containing at least 50% (out of ∼1300) of clusters satisfying the photometric error threshold, σ_t. Top row: results for the F475W passband. Middle row: results for F336W−F475W. Bottom row: results for F475W−F814W. Left column: results for different background fields, using R_ap = 1.5×R₅₀ and the error threshold σ_t≤0.05 mag. Middle column: results depending on the σ_t threshold value for the B3 field, using R_ap = 1.5×R₅₀. Right column: results depending on the aperture size for the B3 field and the error threshold σ_t≤0.05 mag. Results are based on artificial clusters with half-light radii of R₅₀ = 0.25″−1.00″.