G5 and third party flashguns
Can anybody tell me if a "basic" flashgun i.e. one with just the
one centre terminal will work with a G5.
It depends. First check the trigger voltage isn't above 6V as this can fry the circuits in your camera.
If that's OK then put it on the camera and see! It depends on the type of flash it is - clearly it's not going to have E-TTL compatability - some flashes have their own detectors which adjust the flash duration, assuming you have the aperture and ISO setting that the flash gun expects. On others you just have to set the flash to max duration and experiment with the camera aperture to get the right exposure.
Another option is a slave flash unit mounted on a flash bracket, set off using the camera's onboard flash - this means you don't have to worry about trigger voltage, and if you already have a reasonably powered older flashgun can be a much cheaper alternative than a dedicated flash unit.