Fig. 4.

(a) Measurement of the focal spot size (without prism) by the knife-edge method. (b) The $x$ and $y$ diameters of imaging resolution (with prism) by scanning across the edge of an agar at the incident angle $\alpha$ of 30 deg, respectively. (c) The prism rotating about point $D$ and (d) the image resolution versus the angle $\alpha$.