  Using the method of separation of variables and a new approach to
calculations of the prolate spheroidal wave functions, we study the optical
properties of very elongated (cigar-like) spheroidal particles. A comparison of
extinction efficiency factors of prolate spheroids and infinitely long circular
cylinders is made. For the normal and oblique incidence of radiation, the
efficiency factors for spheroids converge to some limiting values with an
increasing aspect ratio a/b provided particles of the same thickness are
considered.
  These values are close to, but do not coincide with the factors for infinite
cylinders. The relative difference between factors for infinite cylinders and
elongated spheroids ($a/b \ga 5$) usually does not exceed 20 % if the following
approximate relation between the angle of incidence $\alpha (in degrees)$ and
the particle refractive index m=n+ki takes the place: $\alpha \ga 50 |m-1| + 5$
where $1.2 \la n \la 2.0$ and $k \la 0.1$. We show that the quasistatic
approximation can be well used for very elongated optically soft spheroids of
large sizes.
