john@xxxxxxxxxxxxxxxx wrote:
On Sat, 14 Dec 2002 10:56:56 +0800, "C.H.Ling" <chling@xxxxxxxxxxxxx>
wrote:
>>I remember the Metz 45T series flash was 1/300s at full power output,
rather slow when compared to the 1/1000s T32 do.<
You're absolutely right - I hang my head on this one, especially as I
*have* a Metz 45CT4!
<<
This is not a fault it's a design feature!! (sort of)
Automatic flashes all extend the flash duration out, so they can cut it off
more easily, when they have integrated enough light measured from the scene.
They do it by adding an air core series inductor in the lead to the flash tube.
If they did not do this it would be tough for them to cut the light off soon
enough when the flash is close to the subject. It is also why there is a
minimum auto flash distance below which they can't respond quick enough to cut
off the light without some overexposure. Extending the flash duration also
helps reduce peak current so extending flash tube life, as well as making it
easier for the high power electronics needed to cut off the flash. A typical
auto flash must interupt about 200-300Amps though the flash tube when cutting
it off on auto. The thyristors used as tube switches, are special flash rated
devices with a guaranteed minimum number of flash interuptions at full rated
energy (typically ~70Joules for larger on camera flashes) with a sp!
ecified series inductor. By making the flash duration longer Metz traded of
frieze movement versus distance range of auto flash and flash tube life.
Regards,
Tim Hughes
TimHughes@xxxxxxxx
|