Index: trunk/Mars/msimreflector/MFresnelLens.cc
===================================================================
--- trunk/Mars/msimreflector/MFresnelLens.cc	(revision 19611)
+++ trunk/Mars/msimreflector/MFresnelLens.cc	(revision 19612)
@@ -264,5 +264,5 @@
 
     const double so    = rc / sqrt(rc*rc + F*F);
-    const double alpha = atan(so / (1-sqrt(n0*n0 - so*so)));
+    const double alpha = atan(so / (1-sqrt(n0*n0 - so*so))); // alpha<0
 
     //             theta                   peak_z
@@ -276,5 +276,5 @@
         return -1;
 
-    // Propagate to the hit point
+    // Propagate to the hit point at z=dz (dz<0)
     p.PropagateZ(u, dz);