Mirror: Lets try to just copy projectionMatrix. See #12080

examples/js/Mirror.js

@@ -156,15 +156,10 @@ THREE.Mirror = function ( width, height, options ) {
 		mirrorCamera.up.reflect( normal );
 		mirrorCamera.lookAt( target );
 
-		mirrorCamera.fov = camera.fov;
-		mirrorCamera.zoom = camera.zoom;
-
-		mirrorCamera.aspect = camera.aspect;
-		mirrorCamera.near = camera.near;
-		mirrorCamera.far = camera.far;
+		mirrorCamera.far = camera.far; // Used in WebGLBackground
 
 		mirrorCamera.updateMatrixWorld();
-		mirrorCamera.updateProjectionMatrix();
+		mirrorCamera.projectionMatrix.copy( camera.projectionMatrix );
 
 		mirrorCamera.userData.recursion = 0;