radio trigger issues

I am an absolute newbie to these kind of lights, only used them for about six hours. Im guessing flash tail is the last part of the flash duration? When the capacitor is nearing the end of its discharge? I think i read somewhere cheaper units suffer from a long, sine pattern as the capacitor has to totally discharge??? And better ones cut off sooner??. I used to be into making electronic music and understand wave patterns and the the effect that attack, cut off and sustain has on different waves. might be totally off track lol
 
Yes, that's more or less it. Cheaply made lights economise on capacitors, this result in fairly long flash durations at full power and increasingly long flash durations as the power is reduced.
Some of the better flash units have a number of capacitors that are switched out (off) as the power is reduced from say full to half, half to a quarter, etc - but cheaper ones often only have two capacitor and maybe only one, so the only way of reducing the power is by means of a potentiometer, which is the main cause of the problem.

Basically what's happening in your case is that if you are using a shutter speed too high for the shutter to be fully open at one point, the moving slit caused by the second curtain closing is still doing the job up to a point because the flash duration is so long.

If you photograph say a grey wall, you'll see that the exposure is very uneven and that the colour will change as the flash power starts running down the curve. Mind you, with those particular lights you'll get a fair amount of variation anyway
 
Wot Garry said, innit ;)

The clue is that as you wind the shutter speed up you are getting less and less light in. Just like you would if you had a continuous light. In fact for the shutter duration your flash is producing continuous light.

FWIW Damian Lovegrove "discovered" this anomaly a while back and there's an interesting thread somewhere on his site about it. IIRC he went off to take some cool (non test) pictures using this trick buy I don't recall seeing any.

That quote FITP found is almost certainly the same thing. "FP mode" seems to trip the flash earlier in the exposure than normal which means you benefit from the continuous flash light. Ordinarily with "high speed" flash the shutter can be closed before the flash actually fires.
 
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