EDIT: Looks like Godfrey answered most of it while I was messing about. Here's what I wrote anyway tho:
I dunno specifically (others might) but I guess it will fire fine. I have a buttload of National PE-3550 and PE-3057 units I got locally for $5 each (untested - but they all worked fine) and the GH1 can use them np at all. The PE-3057 has it's own fill-mode sensor that exposes beautifully (bounced or direct) if the camera is set appropriately. The trouble is with the GH1 that as soon as the camera thinks there is a strobe attached the shutter speed is limited (in all modes) to 1/160. So, assuming the the G3 is similar, if you want faster speeds than the sync limit (I think) you have to get the camera and flash to fire simultaneously without the camera knowing that a flash is being used. The only way I can think of is to buy one of those $50 Hong Kong remotes that are able to fire the shutter and also slaved (remote) flash(s).
Originally Posted by gardenersassistant
I dunno, while these particular flash guns do have a light sensor and a built-in auto mode, and are actually geared for film cameras so should be mostly too bright I can usually just shoot without too much thought or effort using the guide on the back. I shoot only manual lenses anyway so I'm not losing much without the automation. I still get plenty of aperture leeway even with that very restrictive Xs ~ 1/160s. Here's some I just took right now just for fun:
I would lose TTL flash in Av mode though. I don't use that very often, but when I do ..... Grrr, it's all so complicated and difficult to get my head around with so many pluses and minuses for each option.
Auto: 1/30, Bounce 0º, f/11
Auto: 1/30, Bounce 45º, f/8
Auto: 1/30, Bounce 75º, f/4
Macro in the wild, sounds like a diffuser situation. Same things apply. But again if you want higher than max-sync on a Panasonic M4/3 I think yo have to trigger the flash and camera separately or pay Panasonic's lunar based prices.
Given my particular working methods (long story) I'm not sure how practical it would be for my macro work, which is all done "in the wild". Still, it's an interesting alternative that I hadn't thought of. Would this work faster than 1/160 sec though? I thought the problem there was that at shutter speeds faster than a camera's sync speed the shutter is never fully open, the second curtain starting out before the first curtain finishes - and so with the flash being almost instantaneous, not all of the image gets flash illumination. And hence FP/HSS mode, where the flash is doing "microbursts" all the while the shutter is open.
Also Godfrey did a good job of explaining things I thought. Flashes can and do burn longer than "instantaneous" - up to about 1/2 a second. The problem is just telling your camera that you're not so stupid as to expect the flash and the SS to be the same and all metered for you and stuff. Most other camera manufactures allow access to the FP mode in the camera body. Panasonic, in an effort to sell more flashes I am sure, puts access to that mode in the flash itself. So either you need to fool the camera into thinking there is no flash or pay thru the nose.