I have been building up studio kit over the past few months, studio flash, soft boxes, beauty dishes, and a Sekonic L-478D light meter.
The meter can be used for flash, in fact the reason I bought it, but it does of course read ambient light as well. This meter can be profiled to match the cameras dynamic range for it claimed more accurate results.
So today I did some tests and created a profile for shadow or cloudy conditions. This revealed a dynamic range of 8.7 on the GH3. That's if I did the job correctly, I had a few failed attempts which suggested a dynamic range of well over 9 at one stage.
Next step was to photograph something, I chose a whit Lilly.
First exposure was made using the meters default setting, next my profiled setting. The third was using he cameras meter in aperture priority then shutter priority both in spot metering mode, then in multi-metering mode, both aperture and shutter settings.
I was very surprised to find in spot metering mode the camera gave slightly different results between aperture (very slightly more exposure) than shutter priority. Using multi metering mode the results were both the same in shutter or aperture priority being much the same as the aperture setting using spot metering and also the best of the camera exposures.p
The Sekonic exposure setting gave slightly different results again using the default profile a shade better than the previously mentioned camera exposures. The very best came from the custom profile I made.
It must be said that any of these resulting files were exceptionally good and the user would pleased with any, we are talking slight variations between the best and least good, but that was really good anyway.
My conclusion is the cameras exposure system is truly excellent, but a tiny bit more quality may be gained by a hand held meter under some conditions. I certainly wouldn't recommend anyone buying a hand held meter for out and about use unless they want a meter for flash which can then be used for out and about, particularly landscape or outdoor portraiture.