Eileen:The manual's not very clear on this point (to me at least).
There are two tables on the same page. The first is called 'Max. number of continuous firings' and tells you how many flashes (at 6fps) can be made before you need to switch the speedlight off to cool down. Using TTL or manual at 1/1 or 1/2 power it allows up to 15.
The second is called 'Synchronisation during continuous flash shooting (at 6fps)'. This says you can take up to 4 shots at 1/8 power, 8 at 1/16 and so on before you need to switch the flash off.
It looks as though you can only synchronise at 6fps continuous shooting with the flash set to manual (or only using low power). The section on repeating flash in the D300 manual will allow up to 2 flashes at 1/4, 2-5 at 1/8, and so on.
So there doesn't seem to be any option that allows synchronised or repeating flash at settings above 1/8 or 1/4. Which makes the reference to 15 full power flashes in the first table puzzling. Perhaps it makes sense to someone else?
Nah - it's clear enough to me
Let's take the 2nd point first. I don't really understand electrics but water makes sense to me....
In your flash gun is a capacitor. It's a bit like a big tank of water with a ball valve in it. Any time it's less than full the valve opens and more water (power from the batteries) flows in. If the tank is empty then it takes about 4 seconds to fill it. The only way to speed this up is use a fatter pipe (the high speed charge socket) or pressurise the filler tank (more / more powerful batteries).
OK on to the flash bit. A full power flash = empty the tank and a 4 second wait to refill. Half power = half drained - you can squeeze off another flash "instantly" but then it will be empty. 1/4 power = 4 etc. There will come a point where the tank can refill in 1/6 second so that you can keep up with the motor drive but you won't get much flash for that.
As for why Nikon say 2 X 1/4 etc - either they are being conservative or some water sloshes out when you fire the flash. Probably both.
Back to the first part. Fire the flash at full power and it will take about 4 seconds to recharge. When you fire it, it gets very hot. When it's not firing it cools. The trick is you can recharge it faster than it cools. So fire as fast as you can and after shot 2 it is hotter than shot 1. Do that enough times and it will reach the point where it's so hot it will explode. That's a number over 15. And it's messy.
BTW - the 4 second thing? You can reduce this a bit by using fresh NiMHs, the 5th battery, an SD-8A etc. but you probably get the point.
Kidography. It's like photography. But more fun.