diff --git a/source/viewer/navigation.js b/source/viewer/navigation.js
index a4a290d..53c1de6 100644
--- a/source/viewer/navigation.js
+++ b/source/viewer/navigation.js
@@ -397,8 +397,13 @@ OV.Navigation = class
 		let moveDiff = this.mouse.GetMoveDiff ();
 		let mouseButton = this.mouse.GetButton ();
 		if (mouseButton === 1) {
-			let orbitRatio = 0.5;
-			this.Orbit (moveDiff.x * orbitRatio, moveDiff.y * orbitRatio);
+			if (ev.ctrlKey) {
+				let zoomRatio = 0.005;
+				this.Zoom (-moveDiff.y * zoomRatio);
+			} else {
+				let orbitRatio = 0.5;
+				this.Orbit (moveDiff.x * orbitRatio, moveDiff.y * orbitRatio);
+			}
 		} else if (mouseButton === 2 || mouseButton === 3) {
 			let eyeCenterDistance = OV.CoordDistance3D (this.camera.eye, this.camera.center);
 			let panRatio = 0.001 * eyeCenterDistance;