Sean Breheny wrote:

> Yes, what you describe is exactly what I plan on doing. I was planning
> on using cardboard, painted black, as the barrier.

  I'd suggest the opposite, at least for the "guides".  Use silvered
foil to maximise gain.  The four photocells mount at the very inside
corners, with a black barrier behind:


           XXXX|XXXX
         XXXXXX|XXXXXX
        XXXXXX,|,XXXXXX   <-- sensors
       --------+--------         in
        XXXXXX`|`XXXXXX   <-- corners
         XXXXXX|XXXXXX
           XXXX|XXXX
               ^--------- reflective baffles

  As for lensing; I suspect that a custom nosecone could be moulded to
function as a lens.

  An alternate sensor mounting of course could be on the four sides of
the fuselage behind the nosecone, using the fuselage itself as the
baffle.
--
  Cheers,
        Paul B.