Fig. 2
From: Round robin comparison study on the form measurement of optical freeform surfaces
Design form and deviation from the best-fit sphere for the three specimens: The top row shows (from left to right) the design form of the two-radii specimen (left), the convex toroidal surface (middle) and the concave toroidal surface (right). The bottom row shows (from left to right) the corresponding deviations from the best-fit sphere for the two-radii specimen (left), the convex toroidal surface (middle) and the concave toroidal surface (right)