We claim the ornamental design for a spherical lens for a camera, as shown and described.
FIG. 1 is a front view of the spherical lens for a camera, wherein oblique line shading indicates transparent outer body surfaces, and wherein the back side, left side and right side views of the lens assembly are mirror image/symmetrical relative to each other;
FIG. 2 is a top side view of the spherical lens for a camera;
FIG. 3 is a bottom side view of the spherical lens for a camera; and,
FIG. 4 is a left side perspective view of the spherical lens for a camera.
Any broken line(s) shown are for illustrative purposes only and form no part of the claimed design.