Throw Your Strobe To Great Lengths Using a Poor Man's Better Beamer
It is not really possible to defy the inverse square law. I know I tried and failed miserably. But you can stretch it.
A better beamer is a device that does just that, it extend the distance the light from your strobe travels. So while the inverse square law is still in effect, it stretches over a greater distance.
Physics bla-bla aside, it means that light coming from your strobe will go further. Some strobes, like the SB900 has an impressive zoom functions that does just that.
Flickr used lonelyhome contrapted a poorman's better beamer using a cheapo Fresnel lens (around $1) and some plastic (I assume cardboard will do too).
The picture is really self explanatory.
and the test shows that it actually works improving exposure by 1 stop over distance
If you are out there planning to shoot far away birds, this may be just the stop that is missing