The Collaborative International Dictionary of English v.0.48:

Megascopic \Meg`a*scop"ic\, Megascopical \Meg`a*scop"ic*al\, a.
   1. (Physics) Of or pertaining to the megascope or the
      projection upon a screen of images of opaque objects.
      (b) Enlarged or magnified; -- said of images or of
          photographic pictures, etc.
          [Webster 1913 Suppl.]

   2. (Geol.) Large enough to be seen; -- said of the larger
      structural features and components of rocks which do not
      require the use of the microscope to be perceived. Opposed
      to microscopic.
      [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

megascopic
    adj 1: visible to the naked eye (especially of rocks and
           anatomical features) [syn: megascopic, gross]