Standard deviations of errors. σ_err for different FOV sizes and CAs. Red: r₀ = 20 cm; Green: r₀ = 10 cm; Blue: r₀ = 7 cm. N × N-pixel subfields. Diamonds (◇): image scale 0″̣41/pixel, varying N =  {16,24,36}  as labeled in the plots; Down triangles (▿): 0″̣29/pixel, N = 24; Up triangles (▵): 0″̣53/pixel, N = 24. Symbols below the dotted line correspond to data without noise, above the line with 1% noise. Note different vertical scales.