void Update() { //paste it in your Update method

    if (Input.GetKeyCode(KeyCode.Z)) {

        StartCoroutine(WaitThenCallThisConstantly(0.0005f,0.0075f,counter,maxTimes));
    }
}

IEnumerator WaitThenCallThisConstantly(float time,float smoothTime,int counter,int maxTimes) {

    yield return new WaitForSeconds (time);

    float zoom = 4.25f; float smooth = 5.0f;
    float normal = 4.95f; //increase this to a bigger value to zoom out even more


    counter++;
    if (counter < maxTimes) {

        mainCamera.orthographicSize = Mathf.Lerp(mainCamera.orthographicSize,normal,Time.deltaTime * (counter/2.0f) *smooth);
        StartCoroutine(WaitThenCallThisConstantly(time,smoothTime,counter,maxTimes));

    }
}