Smooth change of camera zoom

Hi everyone. I need to change my camera zoom using its ortographic size smoothly during time. I have levels and at each level I want to change the initial zoom speed and the max zoom speed so during time my zoom speed It will increase. But when I change my max zoom speed into a greater value the zoom speed jump directly into the new maximum value. How can I do that?

ZoomSpeedPerTime = (ZoomSpeed * Time.time);

     ZoomSpeedPerTime = Mathf.Clamp (ZoomSpeedPerTime,0f,MaxZoomSpeed);

     Camera.main.orthographicSize = Mathf.PingPong(ZoomSpeedPerTime * Time.time,MaxZoom-MinZoom)+MinZoom;