Orthographic camera movement using mouse for RTS game

Hi,

I am very new to unity as well as 3D programming. I am trying to move the camera using mouse but the movement is not perfect . I guess i am doing some calculation mistakes but not able to figure it out. My Script :

Code (csharp):

1.  
2.         if (Input.GetMouseButtonDown(0))
3.         {
4.             mouseDownPoint =Input.mousePosition;
5.         }
6.  
7.  
8.         if (Input.GetMouseButtonUp(0))
9.         {
10.             mouseDownPoint = Vector3.zero ;
11.         }
12.  
13.  
14.         if (!mouseDownPoint.Equals(Vector3.zero))
15.         {
16.             Vector3 diff = mouseDownPoint - Input.mousePosition;
17.             Camera.mainCamera.transform.Translate(diff);
18.             mouseDownPoint = Input.mousePosition;
19.             return;
20.         }

 

that really doesn't tell us anything... how is it working? how do you want it to work? describe the actual problem you are getting...

 

The panning is too fast , I can multiply diff variable to a factory to make the movement slower but this factor is not consistent and it depends on the orthographicSize of the camera ,

This is the demo with the problem

https://dl.dropboxusercontent.com/u/64306446/Unity/City Builder/Unity/Unity.html

 

I just want my camera to move with the same speed as my mouse cursor , With the above implementation camera moves at a higher speed than the mouse