Characterization of the KCWI point spread function. Example for the standard star (Feige66) where the first and second rows show the size measurement at Mg II (≈ 3790 Å) and [O II] (≈ 5045 Å) wavelengths of the corresponding science object observed (J1256+4509), respectively. First panel: Narrow-band image at the wavelengths of interest (≈ 1000 km s⁻¹ wide or 13 Å at z = 0.35). The white and orange contours corresponds to SB levels of 10⁻¹⁴, 10⁻¹³, and 10⁻¹² erg s⁻¹ cm⁻² arcsec⁻² for the data and Moffat best-fit model, respectively. Second panel: Fit residuals of the Moffat best-fit model. Third panel: Radial SB profiles of the standard star data (black), Gaussian best-fit model (blue) and Moffat best-fit model (orange). The best-fit model parameters are shown in the bottom left. Forth panel: Zoom-in on the inner profiles. A Moffat model better describes both the core and wings of the PSF for our KCWI observations.