Cut and paste from dpreview.com...


The author uses a combination of downward tilt and downward shift.


[url="http://www.dpreview.com/lensreviews/canon_24_3p5_tse_c10/page5.asp]http://www.dpreview.com/lensreviews/canon_24_3p5_tse_c10/page5.asp[/url]



<h3 class="H3-ruler"]Depth of field control using tilt movements</h3>


The
second major application for a perspective control lens is the use of
tilt to manipulate depth of field. When using a wideangle, this is most
widely used for extreme near-far compositions (common in landscape
photography) which require the depth of field to extend from a few
inches in front of the lens to the far distance. Use of downward tilt
can achieve such depth while still shooting at the lens's optimum
aperture.


The samples below illustrate this. On the left
is conventional shot with the lens set straight at F8 - the foreground
is in focus, but the background isn't. Apply downward tilt, and both
the foreground and background can be brought into sharp focus
simultaneously. In this particular shot, we've also used considerable
downwards shift to maintain the verticals of the church in the
background.
<table class="table-std6px" align="center" border="0" width="200"]
<tbody>
<tr>
<th>
<div style="font-weight: bold;" align="center"]No tilt</div>
</th>
<th>
<div style="font-weight: bold;" align="center"]Downward tilt</div>
</th>

</tr>
<tr>
<td>
<div align="center"][url="http://www.dpreview.com/lensreviews/canon_24_3p5_tse_c10/Samples/applications/0T7H8233.jpg][/url]</div>
</td>
<td>
<div align="center"]</div>
</td>
</tr>
</tbody>
</table>