You want to make sure that the
instrument is properly focused. If your focus is too soft, the dramatic effect will be compromised. Also, try to avoid harsh shutter cuts. I would choose the narrowest degree of instrument possible (such as a
Source Four 19 degree). If you choose a 26 or 36 degree, you might have to
iris it down with a
gobo or something. I guess it doesn't matter if the beam of light is square or round. Also, if you put a donut in the fixture, the halation will be reduced. I would add some background color, such as blue to enhance this effect. If you add some pars overhead, you can get a nice moonlight effect. A deep-colored
cyc is also nice. To add texture to your scenery, try throwing some softly-focused breakup gobo patterns gelled in no-color blue. This will look like moonlight shining through trees, if they are suggested in your show. Hope this helps some.