diff --git a/gtsam/geometry/Cal3_S2.h b/gtsam/geometry/Cal3_S2.h
index d7640cc15..25337deb0 100644
--- a/gtsam/geometry/Cal3_S2.h
+++ b/gtsam/geometry/Cal3_S2.h
@@ -36,6 +36,8 @@ namespace gtsam {
 
 	public:
 
+		typedef boost::shared_ptr<Cal3_S2> shared_ptr;  ///< shared pointer to calibration object
+
     /// @name Standard Constructors
     /// @{
 
diff --git a/gtsam/slam/ProjectionFactor.h b/gtsam/slam/ProjectionFactor.h
index 73d18a7e6..b09b148b0 100644
--- a/gtsam/slam/ProjectionFactor.h
+++ b/gtsam/slam/ProjectionFactor.h
@@ -101,6 +101,11 @@ namespace gtsam {
       return z_;
     }
 
+    /** return the calibration object */
+    inline const Cal3_S2::shared_ptr calibration() const {
+      return K_;
+    }
+
 	private:
 
 		/// Serialization function
diff --git a/gtsam/slam/StereoFactor.h b/gtsam/slam/StereoFactor.h
index 729b9fff1..8d1e360d9 100644
--- a/gtsam/slam/StereoFactor.h
+++ b/gtsam/slam/StereoFactor.h
@@ -100,6 +100,12 @@ public:
 	  return z_;
 	}
 
+  /** return the calibration object */
+  inline const Cal3_S2Stereo::shared_ptr calibration() const {
+    return K_;
+  }
+
+
 private:
 	/** Serialization function */
 	friend class boost::serialization::access;