diff --git a/vcg/math/shot.h b/vcg/math/shot.h
index 0eeda9cf..6ab6def0 100644
--- a/vcg/math/shot.h
+++ b/vcg/math/shot.h
@@ -127,7 +127,7 @@ public:
   void SetViewPoint(const vcg::Point3<S> & viewpoint);
 
   /// GET fov from focal
-  float GetFovFromFocal();
+  float GetFovFromFocal() const;
 
   /// look at (point+up)
   void LookAt(const vcg::Point3<S> & point,const vcg::Point3<S> & up);
@@ -256,7 +256,7 @@ void Shot<S,RotationType>::SetViewPoint(const vcg::Point3<S> & viewpoint)
 
 /// GET fov from focal
 template <class S, class RotationType>
-float Shot<S,RotationType>::GetFovFromFocal()
+float Shot<S,RotationType>::GetFovFromFocal() const
 {
   double viewportYMm= Intrinsics.PixelSizeMm[1]* Intrinsics.ViewportPx[1];
   return 2*(vcg::math::ToDeg(atanf(viewportYMm/(2*Intrinsics.FocalMm))));