  We investigate the point spread function of a multimode fiber. The distortion
of the focal spot created on the fiber output facet is studied for a variety of
the parameters. We develop a theoretical model of wavefront shaping through a
multimode fiber and use it to confirm our experimental results and analyze the
nature of the focal distortions. We show that aberration-free imaging with a
large field of view can be achieved by using an appropriate number of segments
on the spatial light modulator during the wavefront-shaping procedure. The
results describe aberration limits for imaging with multimode fibers as in,
e.g., microendoscopy.
