Re: rise or fall

[zxiong@xxxxxxxxxxxxxxxxxxxxxx]

I think a little optical illustration may help.  I hope this will display
properly in plain text mode.


     Scene                 lens         image on film (upside-down)

       ___
        |
        |
   shift-up view                               ---
        |                                       |
        |                                 shift-down image
       ---                                      |                            
        |                                      ---
        |                   /\                  |
    no shift               |  |            non-shift image
        |                  |  |                 |
        |                   \/                 ---
       ---                                      |
        |                                 shift-down image
        |                                       |
  shift-down view                              ---
        |
        |
       ---


In one word, shift changes the angle of view.  It has two functions.
1, raise/lower the horizon on film; and 2, provide a higher/lower angle of 
view without tilting the camera so that the object (such as building) and the
focal plane (film) remain parallel and thus vertical lines stay vertical on 
film (not converging lines which you'll get pointing your camera up).

One good example is that when you shoot with a wide angle lens, you can pull
in a toll building by stepping backward a few steps, not by climing a ladder. 
With a normal lens there may not be enough room for you to move back.  
Think shift as changing to a wider angle lens and you capture only part of 
the image of that wider angle.