#include <avr/interrupt.h>pinMode(2, INPUT_PULLUP);attachInterrupt(digitalPinInterrupt(2), buttonPressed, FALLING);
#include <avr/interrupt.h>pinMode(2, INPUT);attachInterrupt(digitalPinInterrupt(2), buttonPressed, FALLING);
The input was floating and slight touch of the UNO or the camera trigger would create a false positive.
This is not evidence for a floating input.The way you have it wired, with an interrupt triggered by a falling edge, that observation suggests that grounding the input with a relatively low resistance circuit (including your sweaty finger) produces that falling edge.
Power Arduino with a battery so it doesn't share ground with anything?
I don't think I can externally pullup the trigger signal as it works on its own circuit and trying to run a separate current through the camera controller makes it malfunction.