The way that this circuit works is as follows. The AC line voltage is
rectified by D1 and D2 which connects to a voltage doubler circuit made
up of the two 22uf capacitors. The Flash Freq. Pot and the 10uf
capacitor charge up which triggers the Diac and causes the triac to turn
on. This allows the trigger transformer T1 to send a very High Voltage
to the flash tube and lighting it. The flash timing is adjusted by the
flash freq. pot.