(A) Images of 2-µm-diameter fluorescent beads obtained with a 0.5-NA Gaussian and a 0.3-NA Bessel focus, respectively, through a 1-mm-diameter doublet GRIN lens. Insets: zoomed-in views of beads at the FOV center (green square). (B) Axial intensity profiles of the Gaussian and Bessel foci used in (A). (C) Signal variation across FOVs in (A); horizontal orange line indicates 10% of signal at the center, thus the border of the FOV. (D–F) Same measurements as (A–C), but for a 0.5-mm-diameter singlet GRIN lens of inferior imaging quality. (G, H) Gaussian image stacks of beads (upper panel) at FOV center (cyan square in A and D) and (lower panel) away from FOV center (purple square in A and D, 82 µm and 89 µm from center), respectively. Scale bars: 20 µm in (A, D), 2 µm in (G, H).