Anyway the duration of an electronic flash is simply a result of the R/C (resistance/capacitance) time function of the flash tube and capacitor bank. And is easily calculated from the formulas available in any basic electronics reference. Small strobes usually have rather short durations, and large powerful one have longer durations. Most older studio and 200+w/s portables have durations of 1/200 of a second or so. Dinky things like my Vivitar 252 have a duration of maybe 1/2000 of a second or less.
There are various ways of limiting the output and thus the duration of a flash. The most comon nowadays is the thyrister circuit which cuts the power after the desired light level is obtained without fully discharging the capacitors. One of the older circuits cut the main flash tube out of the circuit while the rest of the energy was discharged trough another (hidden) flash tube.
Anyway the original poster (I have lost track of who that was) will probably find useful information if he does a search on "stroboscope photography" which is the term usually used for the very short flash durations he is asking about.
graywolf http://www.graywolfphoto.com "Idiot Proof" <==> "Expert Proof" -----------------------------------
