  MAVIS (MCAO-Assisted Visible Imager and Spectrograph) is an instrument
proposed for the VLT Adaptive Optics Facility (AOF), which is currently in the
phase-A conceptual design study. It will be the first instrument performing
Multi-conjugate adaptive optics at visible wavelengths, enabling a new set of
science observations. MAVIS will be installed at the Nasmyth platform of VLT
UT-4 taking advantage of the already operational Adaptive Optics Facility that
consists of 4 LGS and an adaptive secondary mirror with 1170 actuators. In
addition, two post-focal deformable mirrors and 3 Natural Guide Stars (NGS) are
foreseen for the tomographic reconstruction and correction of atmospheric
turbulence. The MAVIS AO module is intended to feed both an imager and a
spectrograph that will take advantage of the increased resolution and depth
with respect to current instrumentation. In this paper we present the trade-off
study for the optical design of the MAVIS AO module, highlighting the
peculiarities of the system and the requirements imposed by AO. We propose a
set of possible optical solutions able to provide a compact and efficient
implementation of the different subsystems and we compare them in terms of
delivered optical quality, overall throughput, encumbrance, ease of alignment
and residual distortion.
