Question: Contourplot3d in Spherical Coordinates


     I would like to plot a potential on a sphere, with colours and equipotential lines too. I can easily get the colours with this

f:=(psi-Pi/2)^2 + (theta-.5)^2;
plot3d( 1,psi=0....2*Pi,theta=0..Pi,coords=spherical,scaling=constrained, style=patchnogrid, color =f ,lightmodel=none,contours = 60,numpoints=6000);

but cant get the contours to be the level sets of f.  I tried 2dcontour, contourplot3d, etc, but in spherical cordinates they dont seem to work well...

I'm going for a plot something like this



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