5
z=15 r=1 g=1 b=1 rad=10   A big dull sphere for camera background.
z=0  rad=40               And another for behind the camera.
z=1  rad=.33 refl=.9      A reflective sphere in front.
x=.33 rad=.17  r=0 g=0 b=0  Another to the side.
x=0 y=-.67 z=0 rad=.33  r=.5 g=.5 b=.5  And another we see only in reflection.