lexjenkins@xxxxxxxxxxx writes:
<< Purely out of ignorance and speculation I'm wondering whether a
conventional
electronic flash unit can be modified to emit a single burst of long
duration, or whether this simply isn't feasible. I can imagine this would
wear out the unit and batteries pretty quickly, but for certain photo uses
it'd be worthwhile.
>>
The new blue looking high intensity headlamps on BMW's etc are a type of
discharge lamp, but normal flashtubes in electronic flashes are not designed
for continous operation at the energy level used in a single flash discharge.
One reason is, that they would overheat and crack, apart from issues like
metal sputtering at the electrodes. The reason the flashtubes have a (sun
like) color temperature of 5800 deg Kelvin is that the plasma arc runs at
about 5800 K = 5517 deg C, many times the melting point of glass or metal.
The radiation very roughly approximates that of a black body radiator at
5800K. If you take a T32 as an example, it puts out 70Joules/flash on manual
with a flash duration of about 2mSec. If this were flashed
repeatedly/continuously the power used would be 70/(2/1000) = 35000
Joules/sec or 35 Kilo Watts. You would require an elephant to carry the huge
battery ! A car battery can put out about 4kW for a short period so about 9
car batteries should suffice. To put this in perspective, in the US the
domestic wall outlet is rated at 15A,110V or 1600 Watts maximum. You would
need to use 22 outlets in parallel for continuous operation.
Obviously at high shutter speeds you only need to supply energy for
the shutter travel time or about 1/60sec for most OM's. So to maintain the
full T32 guide number you would need to supply a total of at least
35000/60=580Joules roughly the energy of a medium sized (line operated)
studio flash or a bank of 9 T32's.
Regards,
Tim Hughes
>>Hi100@xxxxxxx<<
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