When using depth map shadows, the map resolution is very important to the quality of the shadow.
Sometimes, when your spotlight has a very wide cone angle, the map resolution will not be large
enough to cover the entire angle with decent quality results. The image below shows an example of this problem.
It is not always possible to get rid of this problem by simply increasing the map resolution. That solution can take a lot of memory and render time. However, if you are only concerned with shadows being cast
from objects that are in the center of interest of the spotlight, there is a feature called "auto focus" that can save the day. The image below shows the situation with this spot light. The green circle is the spot's cone angle.
(You can see this view by selecting the spot, then panel->look through selected).
Go to the spot's attribute editor and turn off "Use Dmap Auto Focus," and set the focus angle to just cover the objects that cast shadows. (In the spot view, you can play with cone angle to determine this value interactively).
Normally, auto focus sets the focus angle to cover cone angle + penumbra angle.
The image below shows the result. Auto focus was the only value that changed.
