An axially symmetric optical lens made of isotropic material produces
a transverse shift DELTAx is-proportional-to sigmalambda/2pi of the fo
cal spot ''center of gravity'' under the switch of circular polarizati
on sign sigma = +/- 1 of a plane incident wave (e(z) + isigmae(y))exp(
ikz). This can be accomplished if most of the upper half (y > 0) of th
e input plane is illuminated. This simple effect is discussed in the g
eneral context of the spin-orbit interaction of the photon.