Wanting to get a old Vivitar flash to sync with the other flash / strobes, I put together this simple DIY for a Remote flash trigger with opto-isolator cause the old flash probably had a trigger voltage which would blow out modern cameras or triggering devices
I put it there to adjust for the ambient light / master flash , i.e. if the flash is not getting triggered than dialing down the pot would help. Adjustment is hit and trial.