diff --git a/src/experimental/note.md b/src/experimental/note.md
index a4b4c44d..0bd941d8 100644
--- a/src/experimental/note.md
+++ b/src/experimental/note.md
@@ -1,6 +1,6 @@
 to_do:
 
-- doc: sf add convexity
+- doc: sf, stereographic_extrude add convexity
 
 new:
 
diff --git a/src/stereographic_extrude.scad b/src/stereographic_extrude.scad
index 9de0d73d..c284db57 100644
--- a/src/stereographic_extrude.scad
+++ b/src/stereographic_extrude.scad
@@ -8,7 +8,7 @@
 *
 **/
 
-module stereographic_extrude(shadow_side_leng) {
+module stereographic_extrude(shadow_side_leng, convexity = 1) {
     half_side_length = shadow_side_leng / 2;
     outer_sphere_r = half_side_length / 3;
     a = atan(sqrt(2) * half_side_length / (2 * outer_sphere_r));
@@ -25,7 +25,7 @@ module stereographic_extrude(shadow_side_leng) {
                 circle(inner_sphere_r * cos(a));
         }
      
-        linear_extrude(outer_sphere_r * 2, scale = 0.01) 
+        linear_extrude(outer_sphere_r * 2, scale = 0.01, convexity = convexity) 
             children();
     }