I still haven't given up on this, my goal is to try and be completely confident in my understanding before trying it out...
I'm going with the transistor option.
I found this quite detailed and helpful tutorial and he is also using the same transistor as me which highlighted the calculations you were doing Nick:
I'm probably not understanding something here but could I for e.g. use my multimeter in amp mode - make the short with the multimeter - measure the current - then perform the calculations done in the video and by nick to select the best possible resistor for on the base? Or could that be a bad idea considering I know nothing of the camera internal circuit?
Could someone also advise me about common grounding? I find myself slightly puzzled between for example a battery with +/- terminals and my arduino with its GND pins.
Now the standard google response is its a common reference point for voltages..... but that doesn't really click in my head.
What is actually under the GND pins on the Arduino and why for example when I take my 5v to resistor to led and touch the other end to for e.g. a metal mic stand I get nothing. What is under those GND pins that make the electricity flow but not when touching a mic stand on the actual ground? (you may tell me this was a silly idea but I had to try)
This question is popping up because the camera has a battery with + and - and the arduino has +5v pins and GND and I'm just wanting some clarity on how the two layouts can mix. How does GND pins interact with batteries, is the - on bat just a GND?
Again thanks for all the input and patience. My understanding is growing and it will all click sooner or later!