  The properties of the hollow beam produced by a conical lens are studied in
detail. In particular, the impact of a rounded vertex is examined. It is shown
that it could lead to drastic changes in the transverse distribution of the
hollow beam, determined by the ratio between the transverse size of the
incident beam and the size of the blunt area. An adequate choice for this ratio
allows us to either minimize the losses or optimize the distribution symmetry.
