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Things to remember
Lumix GH5S Remote shutter release:
https://www.norwegiancreations.com/2018/07/controlling-a-camera-shutter-remotely-with-an-arduino/
I used this circuit with the 4N25 optocoupler: http://wei48221.blogspot.com/2016/06/how-to-use-4n25-optocoupler_27.html
To use this with a 3.3V trigger signal, the resistor going to input 1 on the optocoupler should be around 50Ω.