Hi all high speed Flashers,
There is a guy interested in high speed flash (see huecandela.com) who
recommends the Vivitar
283/285s as doing a particularly good job of short duration flash when set to
minimum power.
He claims they get to about 1/16,000sec, and when feeding back the light to the
sensor it gets to
close to 1/30,000sec. He uses multiple units synced together (electronically
not optically I
think).
Really high speed flashes (and true stroboscopes) use a different kind of flash
tube which has an
internal trigger contact instead of the external wire contact on consumer
camera flashes. In
consumer camera flashes I would guess the delay before flash fires depends on
the trigger
autotransfomer and associated capacitor which causes a delay before the trigger
voltage reaches
the 5kV or so needed to trigger. Adding a remote optical trigger adds more
delay. The old self
powered triggers were very slow as they depended on photovoltaic cells. If you
search on the web
there is lots of do it yourself literature on remote triggers, this appears to
be a favourite do
it yourself project!
Auto flashes of course, extend out the flash duration by adding a series
inductor in the flash
circuit to get durations out to a few milliseconds. This reduces the current
for the electronic
switches and more importantly the circuitry does not have to respond in a very
short time to
"quench" the flash in auto mode. In non-auto flashes the flash duration tends
to be much shorter
(if comparing full power) as it is limited mainly by capacitor and lead
inductance and circuit
wiring resistance. The flashes are often designed so the inductor and flash
tube form aa
approximately critically damped circuit. (see EG&G/PerkinElmar website for
details)
The F280 (according to the Rochester institute research paper tests) runs at
about 20kHz, as far
as I remember, so each mini flash is significantly lesss less than 1/20000 sec.
According to
Clint this is the same flash tube as used in the T32.
Although the flash duration is often qouted, it is a bit misleading as the
light output is not at
all constant and looks more like a distorted bell shaped curve when not
quenched. So effective
movement stopping duration (at full output) can be shorter than quoted.
The high power Metz CT60-4 has a claimed flash duration of ~5mS with the
shortest duratioon quoted
as 1/20,000.
Regards,
Tim Hughes
TimHughes@xxxxxxxx
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