How to zoom in smoothly with orthographic camera?

Hello, i currently making a camera system for Human anatomy like rotating object, zoom in when i clicked certain object, etc. Basically, i want my camera move like Human Anatomy Atlas.

what i already achieved is:

1. Camera Rotation around target

2. Double click on object to focus camera on it

but here the problem, i want to camera to focus & zoom smoothly to double clicked object. i already tried vector3.lerp but i don't understand it very well (sorry im still noob at this).

here my code :

 using UnityEngine;
 using System.Collections;
 
 public class CameraController : MonoBehaviour {
 
     public Transform target;
     public float zoomDistance = 0.4f;
     public float distance = 5.0f;
     public float xSpeed = 120.0f;
     public float ySpeed = 120.0f;
     
     public float yMinLimit = -20f;
     public float yMaxLimit = 80f;
     
     public float distanceMin = .5f;
     public float distanceMax = 15f;
     
     public float smoothTime = 2f;
     
     float rotationYAxis = 0.0f;
     float rotationXAxis = 0.0f;
     
     float velocityX = 0.0f;
     float velocityY = 0.0f;
 
     // double click variable
     float lastClick = 0;
     float catchTime = .25f;
 
     // Vector3.Lerp Variable
     public float speedLerp = 1.0f;
 
     private Transform startMarker;
     private Transform endMarker;
     private float startTime;
     private float journeyLength;
 
     // Use this for initialization
     void Start()
     {
         Rigidbody rgdbody = GetComponent<Rigidbody> ();
 
         Vector3 angles = transform.eulerAngles;
         rotationYAxis = angles.y;
         rotationXAxis = angles.x;
 
         // Make the rigid body not change rotation
         if (rgdbody)
         {
             rgdbody.freezeRotation = true;
         }
 
         startTime = Time.time;
     }
 
     void Update () {
         if (Input.GetMouseButtonDown (0)) {
 
             Ray ray = Camera.main.ScreenPointToRay (Input.mousePosition);
             RaycastHit hit;
 
             // Vector3.Lerp
             startMarker = transform;
             endMarker = target;
             journeyLength = Vector3.Distance (startMarker.position, endMarker.position);
             // end Vector3.Lerp
 
             // double click check
             if (Time.time - lastClick < catchTime) { // if double click
                 if (Physics.Raycast (ray, out hit)) { // if click on object
                     target = hit.transform; // camera will rotation around new target
                     distance = zoomDistance; // camera will zoom clicked object
 
                     // Vector3.Lerp
                     float distCovered = (Time.time - startTime) * speedLerp;
                     float fracJourney = distCovered / journeyLength;
                     transform.position = Vector3.Lerp(startMarker.position, endMarker.position, fracJourney);
                     // end Vector.Lerp
 
                 } else {
                     distance = 5f; // if clicked on blank space, it will zoom out
                 }
                 print ("its double click");
 
             } else {
                 print ("its normal click");
             }
             lastClick = Time.time;
         }
     }
 
 
     // Camera Rotation / Position / Zoom
     void LateUpdate() {
         if (target) {
             if (Input.GetMouseButton(0)) {
                 velocityX += xSpeed * Input.GetAxis("Mouse X") * distance * 0.02f;
                 velocityY += ySpeed * Input.GetAxis("Mouse Y") * 0.02f;
             }
             
             rotationYAxis += velocityX;
             rotationXAxis -= velocityY;
             
             rotationXAxis = ClampAngle(rotationXAxis, yMinLimit, yMaxLimit);
             
 //            Quaternion fromRotation = Quaternion.Euler(transform.rotation.eulerAngles.x, transform.rotation.eulerAngles.y, 0);
             Quaternion toRotation = Quaternion.Euler(rotationXAxis, rotationYAxis, 0);
             Quaternion rotation = toRotation;
 
             distance = Mathf.Clamp(distance - Input.GetAxis("Mouse ScrollWheel") * 1, distanceMin, distanceMax);
             Camera.main.orthographicSize = distance; // zoom with orthographic camera
 
 //            RaycastHit hit;
 //            if (Physics.Linecast(target.position, transform.position, out hit))
 //            {
 //                distance -= hit.distance;
 //            }
 
             Vector3 negDistance = new Vector3(0.0f, 0.0f, -distance);
             Vector3 position = rotation * negDistance + target.position;
             
             transform.rotation = rotation;
             transform.position = position;
             
             velocityX = Mathf.Lerp(velocityX, 0, Time.deltaTime * smoothTime);
             velocityY = Mathf.Lerp(velocityY, 0, Time.deltaTime * smoothTime);
         }
         
     }
 
     public static float ClampAngle(float angle, float min, float max) {
         if (angle < -360F)
             angle += 360F;
         if (angle > 360F)
             angle -= 360F;
         return Mathf.Clamp(angle, min, max);
     }
 }