David,
Its all about the
SIZE of the light source rather than if it is flash or continuous. A studio head just gives a larger area of light than a camera flashgun. Now you can fire a camera flash gun into a brolly to increase the area of the light but you will sacrifice a fair bit of the flash guns power due to the distance it needs to be from the reflective surface for its beam to adequately cover the reflective surface. A studio head with its bigger light can be so much closer to the brolly so less light is lost. Perhaps I need to do a couple of graphics but in the mean time have a look at this early thread on diffusion.
http://www.worldphotographyforum.com...ead.php?t=1852
Can it be done on the cheap - yes. Not the tidiest, but in this link I used 2 guns to increase the power and even the light spread ( first image ), a silver brolly, and a bit of horticultural fleece ( third image ). Check the shadow hardness ( fourth image ). To replicate that with studio units, it would have only required one light in place of the two camera flashguns.
http://www.worldphotographyforum.com...ead.php?t=1878
I will look at doing a new explanitory graphic tomorrow of studio light and brolly and camera flash and brolly.
Don