
Here's the final product and the circuit functions as expected.
The LED gives quite a bright flash but it's not bright enough to trigger the slave flash.
Any thoughts?
You may find that the LED is not getting driven at full power.
LED's need a very precise voltage to work or more correctly current.
A Cree XR-E for example produces full power at 1 amp of current and will require about 3.7 volt.
Too much voltage will make the LED draw too much current and the LED will blow.
Since we are talking about a single flash of very short time ( How long are the LED's turning on for?) you can probably run them at double their current rating which may only require a few 1/10s of a volt increase.
The reason others may get away with a 6 volt power source is because they may be using small batteries that simply cant supply enough current.
Also if you using a MOSFET and a 3v battery you may find the MOSFET is not fully turning on and not supplying enough current to the LED.
Instead of using a MOSFET and resistors you could probably get away with using AMC 7135 driver chips. These are about the size of a resistor but will regulate current to the LED to 350ma per AMC7135. Simply add as many AMC's as you want and no other components will be needed except LED and a battery of voltage from about 3.3volt(depending on LED) up to 6 volt.