diff --git a/changelog.txt b/changelog.txt
index e416df23..5ff344fb 100644
--- a/changelog.txt
+++ b/changelog.txt
@@ -56,6 +56,7 @@ OPENSEADRAGON CHANGELOG
 * Fixed an issue with zero size viewers in IE8 (#609)
 * Fixed: Cross Origin policy not working (#613)
 * Optimized tile loading by clearing the queue on a re-draw when imageLoaderLimit is set (#616)
+* Now animating zoom spring exponentially (#631)
 
 1.2.1:
 
diff --git a/src/spring.js b/src/spring.js
index 3320ecc2..2c89ee07 100644
--- a/src/spring.js
+++ b/src/spring.js
@@ -38,10 +38,14 @@
  * @class Spring
  * @memberof OpenSeadragon
  * @param {Object} options - Spring configuration settings.
- * @param {Number} options.initial - Initial value of spring, default to 0 so
- *  spring is not in motion initally by default.
- * @param {Number} options.springStiffness - Spring stiffness.
- * @param {Number} options.animationTime - Animation duration per spring.
+ * @param {Number} options.springStiffness - Spring stiffness. Must be greater than zero.
+ * The closer to zero, the closer to linear animation.
+ * @param {Number} options.animationTime - Animation duration per spring, in seconds.
+ * Must be greater than zero.
+ * @param {Number} [options.initial=0] - Initial value of spring.
+ * @param {Boolean} [options.exponential=false] - Whether this spring represents
+ * an exponential scale (such as zoom) and should be animated accordingly. Note that
+ * exponential springs must have non-zero values.
  */
 $.Spring = function( options ) {
     var args = arguments;
@@ -52,7 +56,7 @@ $.Spring = function( options ) {
         options = {
             initial: args.length && typeof ( args[ 0 ] ) == "number" ?
                 args[ 0 ] :
-                0,
+                undefined,
             /**
              * Spring stiffness.
              * @member {Number} springStiffness
@@ -72,6 +76,17 @@ $.Spring = function( options ) {
         };
     }
 
+    $.console.assert(typeof options.springStiffness === "number" && options.springStiffness !== 0,
+        "[OpenSeadragon.Spring] options.springStiffness must be a non-zero number");
+
+    $.console.assert(typeof options.animationTime === "number" && options.springStiffness !== 0,
+        "[OpenSeadragon.Spring] options.animationTime must be a non-zero number");
+
+    if (options.exponential) {
+        this._exponential = true;
+        delete options.exponential;
+    }
+
     $.extend( true, this, options);
 
     /**
@@ -83,10 +98,13 @@ $.Spring = function( options ) {
     this.current = {
         value: typeof ( this.initial ) == "number" ?
             this.initial :
-            0,
+            (this._exponential ? 0 : 1),
         time:  $.now() // always work in milliseconds
     };
 
+    $.console.assert(!this._exponential || this.current.value !== 0,
+        "[OpenSeadragon.Spring] value must be non-zero for exponential springs");
+
     /**
      * @member {Object} start
      * @memberof OpenSeadragon.Spring#
@@ -108,6 +126,12 @@ $.Spring = function( options ) {
         value: this.current.value,
         time:  this.current.time
     };
+
+    if (this._exponential) {
+        this.start._logValue = Math.log(this.start.value);
+        this.target._logValue = Math.log(this.target.value);
+        this.current._logValue = Math.log(this.current.value);
+    }
 };
 
 $.Spring.prototype = /** @lends OpenSeadragon.Spring.prototype */{
@@ -117,8 +141,17 @@ $.Spring.prototype = /** @lends OpenSeadragon.Spring.prototype */{
      * @param {Number} target
      */
     resetTo: function( target ) {
+        $.console.assert(!this._exponential || target !== 0,
+            "[OpenSeadragon.Spring.resetTo] target must be non-zero for exponential springs");
+
         this.start.value = this.target.value = this.current.value = target;
         this.start.time = this.target.time = this.current.time = $.now();
+
+        if (this._exponential) {
+            this.start._logValue = Math.log(this.start.value);
+            this.target._logValue = Math.log(this.target.value);
+            this.current._logValue = Math.log(this.current.value);
+        }
     },
 
     /**
@@ -126,10 +159,18 @@ $.Spring.prototype = /** @lends OpenSeadragon.Spring.prototype */{
      * @param {Number} target
      */
     springTo: function( target ) {
+        $.console.assert(!this._exponential || target !== 0,
+            "[OpenSeadragon.Spring.springTo] target must be non-zero for exponential springs");
+
         this.start.value  = this.current.value;
         this.start.time   = this.current.time;
         this.target.value = target;
         this.target.time  = this.start.time + 1000 * this.animationTime;
+
+        if (this._exponential) {
+            this.start._logValue = Math.log(this.start.value);
+            this.target._logValue = Math.log(this.target.value);
+        }
     },
 
     /**
@@ -139,6 +180,27 @@ $.Spring.prototype = /** @lends OpenSeadragon.Spring.prototype */{
     shiftBy: function( delta ) {
         this.start.value  += delta;
         this.target.value += delta;
+
+        if (this._exponential) {
+            $.console.assert(this.target.value !== 0 && this.start.value !== 0,
+                "[OpenSeadragon.Spring.shiftBy] spring value must be non-zero for exponential springs");
+
+            this.start._logValue = Math.log(this.start.value);
+            this.target._logValue = Math.log(this.target.value);
+        }
+    },
+
+    setExponential: function(value) {
+        this._exponential = value;
+
+        if (this._exponential) {
+            $.console.assert(this.current.value !== 0 && this.target.value !== 0 && this.start.value !== 0,
+                "[OpenSeadragon.Spring.setExponential] spring value must be non-zero for exponential springs");
+
+            this.start._logValue = Math.log(this.start.value);
+            this.target._logValue = Math.log(this.target.value);
+            this.current._logValue = Math.log(this.current.value);
+        }
     },
 
     /**
@@ -146,15 +208,31 @@ $.Spring.prototype = /** @lends OpenSeadragon.Spring.prototype */{
      */
     update: function() {
         this.current.time  = $.now();
-        this.current.value = (this.current.time >= this.target.time) ?
-            this.target.value :
-            this.start.value +
-                ( this.target.value - this.start.value ) *
+
+        var startValue, targetValue;
+        if (this._exponential) {
+            startValue = this.start._logValue;
+            targetValue = this.target._logValue;
+        } else {
+            startValue = this.start.value;
+            targetValue = this.target.value;
+        }
+
+        var currentValue = (this.current.time >= this.target.time) ?
+            targetValue :
+            startValue +
+                ( targetValue - startValue ) *
                 transform(
                     this.springStiffness,
                     ( this.current.time - this.start.time ) /
                     ( this.target.time  - this.start.time )
                 );
+
+        if (this._exponential) {
+            this.current.value = Math.exp(currentValue);
+        } else {
+            this.current.value = currentValue;
+        }
     }
 };
 
diff --git a/src/viewport.js b/src/viewport.js
index ff91ad29..b882580e 100644
--- a/src/viewport.js
+++ b/src/viewport.js
@@ -127,6 +127,7 @@ $.Viewport = function( options ) {
         animationTime:   this.animationTime
     });
     this.zoomSpring    = new $.Spring({
+        exponential: true,
         initial: 1,
         springStiffness: this.springStiffness,
         animationTime:   this.animationTime
diff --git a/test/coverage.html b/test/coverage.html
index fe75c797..9d61c48f 100644
--- a/test/coverage.html
+++ b/test/coverage.html
@@ -72,6 +72,7 @@
     <script src="/test/modules/tilecache.js"></script>
     <script src="/test/modules/referencestrip.js"></script>
     <script src="/test/modules/tilesourcecollection.js"></script>
+    <script src="/test/modules/spring.js"></script>
     <!-- The navigator tests are the slowest (for now; hopefully they can be sped up)
     so we put them last. -->
     <script src="/test/modules/navigator.js"></script>
diff --git a/test/modules/spring.js b/test/modules/spring.js
new file mode 100644
index 00000000..b627f832
--- /dev/null
+++ b/test/modules/spring.js
@@ -0,0 +1,77 @@
+/* global module, asyncTest, $, ok, equal, notEqual, start, test, Util, testLog, propEqual, console */
+
+(function () {
+
+    var originalNow;
+    var now;
+
+    module("spring", {
+        setup: function () {
+            now = 0;
+            originalNow = OpenSeadragon.now;
+
+            OpenSeadragon.now = function() {
+                return now;
+            };
+        },
+        teardown: function () {
+            OpenSeadragon.now = originalNow;
+        }
+    });
+
+    asyncTest('regular spring', function() {
+        var spring = new OpenSeadragon.Spring({
+            initial: 5,
+            animationTime: 1,
+            springStiffness: 0.000001
+        });
+
+        equal(spring.current.value, 5, 'initial current value');
+        equal(spring.target.value, 5, 'initial target value');
+
+        spring.springTo(6);
+        equal(spring.current.value, 5, 'current value after springTo');
+        equal(spring.target.value, 6, 'target value after springTo');
+
+        now = 500;
+        spring.update();
+        Util.assessNumericValue(5.5, spring.current.value, 0.00001, 'current value after first update');
+        equal(spring.target.value, 6, 'target value after first update');
+
+        now = 1000;
+        spring.update();
+        equal(spring.current.value, 6, 'current value after second update');
+        equal(spring.target.value, 6, 'target value after second update');
+
+        start();
+    });
+
+    asyncTest('exponential spring', function() {
+        var spring = new OpenSeadragon.Spring({
+            exponential: true,
+            initial: 1,
+            animationTime: 1,
+            springStiffness: 0.000001
+        });
+
+        equal(spring.current.value, 1, 'initial current value');
+        equal(spring.target.value, 1, 'initial target value');
+
+        spring.springTo(2);
+        equal(spring.current.value, 1, 'current value after springTo');
+        equal(spring.target.value, 2, 'target value after springTo');
+
+        now = 500;
+        spring.update();
+        Util.assessNumericValue(1.41421, spring.current.value, 0.00001, 'current value after first update');
+        equal(spring.target.value, 2, 'target value after first update');
+
+        now = 1000;
+        spring.update();
+        equal(spring.current.value, 2, 'current value after second update');
+        equal(spring.target.value, 2, 'target value after second update');
+
+        start();
+    });
+
+})();
diff --git a/test/test.html b/test/test.html
index f1f1716c..ae4863e8 100644
--- a/test/test.html
+++ b/test/test.html
@@ -37,6 +37,7 @@
     <script src="/test/modules/tilecache.js"></script>
     <script src="/test/modules/referencestrip.js"></script>
     <script src="/test/modules/tilesourcecollection.js"></script>
+    <script src="/test/modules/spring.js"></script>
     <!-- The navigator tests are the slowest (for now; hopefully they can be sped up)
     so we put them last. -->
     <script src="/test/modules/navigator.js"></script>