Shear selection bias introduced by SEXTRACTOR detection as a function of the measured magnitude. Upper panel: multiplicative bias m along the PSF direction and at 45° to it. Lower panel: additive bias in PSF frame, for PSFs with ⟨|ϵ_PSF|⟩ ∼ 0.025. Faint galaxies can exhibit a shear bias as large as −0.05 after the detection step, prior to shape measurements. The points are slightly offset in the horizontal direction for visual clarity.