@Robert quick question: what’s the reason you are trying to use an opto-coupler? Is it because you’re worried about false triggering your flash or because you are worried about vibrations or G-forces? No wrong answer here. I just remember always hearing a relay snap just before being blinded. I know you need to stay away from reed relays because on high currents they will wield themselves closed, but Omron makes a 5 volt relay that will not act like a transformer (sending noise back into your control logic- though you might still want your opto-coupler to control your relay through a Darlington transistor and a diode across the relay pointing to the positive side of the power) and they are rated for 2 amps at 110 V. It might be a good plan B. Sorry, I don’t have my Omron data book anymore.