{
   TCanvas *c1 = new TCanvas("glcanvas","Geometry Shapes",200,10,700,500);

// Define the geometry

   TGeoManager *geom = new TGeoManager("geom","Optics Demo");
   TGeoMaterial *vacuum = new TGeoMaterial("vacuum",0,0,0);
   TGeoMaterial *Fe = new TGeoMaterial("Fe",55.84,26.7,7.87);
   TGeoMixture *glass = new TGeoMixture("Glass",2,0.6);
   glass->DefineElement(0,28.09,14,0.4674655);
   glass->DefineElement(1,16,8,0.5325345);
   glass->SetTransparency(30);

   TGeoMedium *Air = new TGeoMedium("Air",0,vacuum);
   TGeoMedium *Iron = new TGeoMedium("Iron",1,Fe);
   TGeoMedium *Glass = new TGeoMedium("Glass",2,glass);

   TGeoVolume *top = geom->MakeBox("top",Air,100,100,100);

   geom->SetTopVolume(top);
   geom->SetTopVisible(0);

   TGeoTranslation *t1= new TGeoTranslation("t1",0,0,-55);
   t1->RegisterYourself();
   TGeoTranslation *t2= new TGeoTranslation("t2",0,0,55);
   t2->RegisterYourself();

   TGeoVolume *s1 = geom->MakeSphere("S1",Glass,0,75,0,90,0,360);
   TGeoVolume *s2 = geom->MakeSphere("S2",Glass,0,75,90,180,0,360);
   TGeoCompositeShape *convex = new TGeoCompositeShape("convex","(S1:t1)*(S2:t2)");

   TGeoVolume *lens1 =  new TGeoVolume("LENS1",convex);

   top->AddNode(lens1,2,new TGeoTranslation(0,0,0));
   TGeoVolume *m2 = geom->MakeBox("m2",Iron,75,75,5);
   top->AddNode(m2,3,new TGeoTranslation(0,0,-75));


   geom->CloseGeometry();

   geom->SetVisLevel(4);
   geom->SetNsegments(25);
   top->Draw();
   c1->Update();

}