(discussion in dpreview's Panasonic forum)
Wendy B...
I am talking about the electronic viewfinder being so dark you can't see anything if it is in manual {exposure} mode.Adrian Ashfield (Parallel)...
To sum up the problem with using external flash.
In full manual mode the evf is too dark to see anything.
In S shutter priority mode, although you can select any speed, the aperture defaults F2.8. This results in over-exposure with some flash units and a near subject.
In A aperture preferred mode, the shutter defaults to 1/60, which doesn't allow for freezing a moving object there is much ambient light.
The best work-around for me is to use aperture preferred and deliberately set the flash to suit a small aperture like <F5.6, so that ambient light has less effect. This tends to fully discharge the flash and makes recycling take longer. As far as I can tell there is little or no improvement in resolution when decreasing the aperture.
What we really need is for the evf to stay bright in full manual, so that one has control over both the aperture and shutter speed without the `feature' of the evf getting too dim to be usable.
{Picture below `Porvette' by Adrian Ashfield. Taken with FZ10 flash. If you look at Adrian's galleries using the link below or above, you can find many other examples of FZ10 photographs taken under low-light conditions.}
With an external flash, you can also use Shutter priority and set the shutter speed to 1/1000 (sometimes even faster). The viewfinder remains relatively bright, the camera selects f/2.8, and 1/1000 will freeze just about anything, as well as eliminating the white balance problem caused by yellow room lighting.
As Wendy has said, the real problem is that some of us would like to be able to use full Manual mode, knowing that we've pre-set the camera and/or external flash to provide enough light. The only way to do that right now is to set aperture/shutter in Manual mode, then switch to Program mode to manually focus and compose, then switch back to Manual mode and press the shutter. And that only works if the subject is stationary and the camera is on a tripod.
{Picture below `Peering through beveled glass'. Taken by Charlie Howard with FZ10. Not a flash photograph!}