RE: Filter/Speed/Meter & DON'T meter using a Nikon Camera

["Brewer, Kevan" <kevan.brewer@xxxxxxxxxxxxxx>]

> 
> > Ah, they aren't operated like flash tubes. Flash tubes are 
> connected to a
> > source of high voltage on a capacitor. When it's time to 
> flash, there's a
> > second system to start the ionization in the flash tube, 
> which then allows
> > the capacitor to discharge through the tube. I'm not sure 
> how variable
> > intensity flash circuits work, since the discharge isn't to 
> empty the
> > capacitor, but is regulated by some other circuit.
> 
> In some cases a scr is used to stop the flow of electricity 
> to the flash
> tube.
> Some studio flash units do this now. In other cases banks of 
> capacitors
> are switched in and out of the circuit in parallel. In other cases
> the capacitors are  only allowed to charge to a certain voltage.
> 
> 
> 
> 
> 
> > LEDs in remotes are driven by integrated circuits at relatively low
> > voltages, and don't depend on capacitive discharges. But 
> the key you hold
> > down determines the exact pulse pattern for the function the key
> represents.
> 
> 
> 
> yeah but they sure are a lot brighter than when you just hook 
> a battery up
> to  the
> leds at therated voltage.
> 
> 
> plug a photocell into the audio - in jack of an amp and enjoy :)
> 

They are normally driven by a transistor and have a low value resistor
in series which gives a current through the LED of about twice the rated
continuous current of the device. Because the LED is driven with a
square wave, it's only on for half the time (less because of the coding)
and so it doesn't get over-rated.

Flashes are indeed controlled by SCRs (aka Thyristors hence why some flash
guns have the word 'Thyristor' on). Auto flashguns work by measuring the
amount of light reflected from the subject and once a threshold is reached
the Thyristor is triggered cutting of the supply to the tube.

Apologies that this thread is getting rather technical. It might be better
to take it off list if there is any more to be said?

Kevan
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