Flash Duration Results for the Pentax AF-540FGZ Flash - and the Neewer SF-01 Slave Flash
AF-540-FGZ Power levels of 1/32 and 1.64 and the Neewer Slave Flash
David B. Shaffer Ph.D.
1/32 power: the flash is quenched even sooner (compare on the superposed graphs).
At 1/32 power: t-0.5 75 microseconds or 1/13000 seconds
t-0.1 134 microseconds or 1/7460 seconds
P50 44 microseconds or 1/23000 seconds
P90 134 miscroseconds or 1/7460 seconds
1/64 power: the flash is now quenched long before it reaches full power.
at 1/64 power: t-0.5 54 microseconds or 1/18500 seconds
t-0.1 107 microseconds or 1/9300 seconds
P50 34 microseconds or 1/29000 seconds
P90 89 microseconds or 1/11000 seconds
t-0.1 here is a bit over 100 microseconds. This will be fast enough to freeze a lot of action, but seems to me to be substantially short of some comments credited to Pentax that the flash duration is 1/20000 second! The Pentax site is mum on flash duration in their presentation of AF-540FGZ specifications.
I also measured the times for the Neewer slave flashes which are (or at least, were!) available for a ridiculously low price on Ebay (I paid $10 each, including shipping, for a pair).
I loaded one of these with freshly-charged NiMH batteries and made similar measurements. The results are shown here (coming real soon!). Although the total light output of these flashes is somewhat less than for the 540, the flash duration is quite short, and, as described on the last page of this report, generally adequate for water drop photography.
