Background for those who haven't investigated how a strobe works:
The flash tube is directly across the storage capacitior that provides the power for the flash, but 330 volts isn't enough to ionize the gas in the tube. Most strobes use a small trigger transformer (think TV flyback) to generate the ionization voltage for the flash tube. The current in the trigger circuit is small (but still supplied from the 330 volt source), so almost any device rated for the voltage should work. A high voltage optocoupler would be ideal to protect the PICAXE.
The rate between flashes is limited by the DC/DC inverter that charges the flash capacitor. The DC/DC converter in an old flash camera is typically designed to work on a couple of AA cells and the maximum flash rate is limited by the power that the AA cells can deliver. If you plan to replace the AA cells with a more powerful supply in hopes of increasing the flash rate, be sure to check for overheating of the DC/DC converter components and the flash tube itself: both have duty cycle limitations. The flash tube also has a limited lifetime - they are usually rated in number of flashes - but this is not likely to be exceeded with a film camera (although digital cameras may be a different story entirely).
In the original intended use, the time between flashes is limited by the user - time to compose the image and press the button. The PICAXE trigger will not have those limits, so it will always be ready before the DC/DC converter has fully recharged the flash capacitor.
You can increase the flash rate without exceeding the duty cycle of either the DC/DC converter or the flash tube if you replace the capacitor for the flash tube itself with a smaller value (i.e., replace a 50ufd with a 10ufd). The light output will be lower, but the capacitor will recharge faster and the smaller discharge through the flash tube will increase its life.
John
