an infinitely large mirror will
reflect only half of the visible
world for it is impossible for the
mirror to reflect itself unless it is
reflecting a mirror identical to itself
in which case the reflection would
not be of the opposite mirror but
of the mirror's own reflection
in the opposite mirror; a mirror
cannot reflect what is directly behind
itself, what is effectively invisible
& technically unknown but which
is supporting the mirror in place;
an infinitesimally small mirror
will reflect its entire surrounding;
gazing at a microscopic mirror through
a microscope will reveal the entire
visible world in its reflection;  
while an infinitely large mirror
will reflect only a portion of it