Consider an infinitely long cylinder of radius $r$ oriented with its
axis along the $y$-axis. The cylinder has a Lambertian surface and is
viewed by a camera along the positive $z$-axis. What will you expect to
see in the image if the cylinder is illuminated by a point source at
infinity located on the positive $x$-axis? Draw the contours of constant
brightness in the projected image. Are the contours of equal brightness
uniformly spaced?