  We present a new class of magnetically shaped deformable liquid mirrors made
of a magnetic liquid (ferrofluid). Deformable liquid mirrors offer advantages
with respect to deformable solid mirrors: large deformations, low costs and the
possibility of very large mirrors with added aberration control. They have some
disadvantages (e.g. slower response time). We made and tested a deformable
mirror, producing axially symmetrical wavefront aberrations by applying
electric currents to 5 concentric coils made of copper wire wound on aluminum
cylinders. Each of these coils generates a magnetic field which combines to
deform the surface of a ferrofluid to the desired shape. We have carried out
laboratory tests on a 5 cm diameter prototype mirror and demonstrated defocus
as well as Seidel and Zernike spherical aberrations having amplitudes up to 20
microns, which was the limiting measurable amplitude of our equipment
