  A special subclass of shear-free null congruences (SFC) is studied, with
tangent vector field being a repeated principal null direction of the Weyl
tensor. We demonstrate that this field is parallel with respect to an effective
affine connection which contains the Weyl nonmetricity and the skew symmetric
torsion. On the other hand, a Maxwell-like field can be directly associated
with any special SFC, and the electric charge for bounded singularities of this
field turns to be ``self-quantized''. Two invariant differential operators are
introduced which can be thought of as spinor analogues of the Beltrami
operators and both nullify the principal spinor of any special SFC.
