PerspectiveCamera: More robust fov. See #5364.

src/cameras/PerspectiveCamera.js

@@ -92,10 +92,12 @@ THREE.PerspectiveCamera.prototype.setViewOffset = function ( fullWidth, fullHeig
 
 THREE.PerspectiveCamera.prototype.updateProjectionMatrix = function () {
 
+	var fov = THREE.Math.radToDeg( 2 * Math.atan( Math.tan( THREE.Math.degToRad( this.fov ) * 0.5 ) / this.zoom ) );
+
 	if ( this.fullWidth ) {
 
 		var aspect = this.fullWidth / this.fullHeight;
-		var top = Math.tan( THREE.Math.degToRad( ( this.fov / this.zoom ) * 0.5 ) ) * this.near;
+		var top = Math.tan( THREE.Math.degToRad( fov * 0.5 ) ) * this.near;
 		var bottom = - top;
 		var left = aspect * bottom;
 		var right = aspect * top;
@@ -113,7 +115,7 @@ THREE.PerspectiveCamera.prototype.updateProjectionMatrix = function () {
 
 	} else {
 
-		this.projectionMatrix.makePerspective( this.fov / this.zoom, this.aspect, this.near, this.far );
+		this.projectionMatrix.makePerspective( fov, this.aspect, this.near, this.far );
 
 	}