phily_guy (dpreview, Panasonic forum, 1 March 2004)...
I tried all the flash modes of the built in flash and it does do a pre-flash (see sectionClint `Clint751' (dpreview, Panasonic forum, 2 March 2004)...) on all of them. You can try a mirror test where you fire the built in flash and your slave unit. Check the picture if both flashes fired.
...the FZ10 does use a preflash. I have a Digiflash 3000 which has two settings for slaving -- one for a single flash and one for use with preflash (it will fire on the second (main) flash. I found that it worked fine with the FZ10 aperture set to 2.8 but not with smaller apertures. At smaller apertures it seems there is too much time lag between the preflash, the closing of the iris and then the main flash -- the slave seems to interpret that as two Single flashes so it doesn't fire. If it is set to single flash mode it will fire on the preflash and not the main flash :-(. However, I did find a work around: I have to enable the red-eye reduction, then the Digiflash (set to work with preflash) ``sees'' the first flash as a single main flash (because of the time lag) but sees the red-eye reduction flash as a preflash and then the main flash following it is close enough in time that it causes the Digiflash to fire at the proper time. This technique is useful if I want to use the flash off-camera on a bracket instead of on the hotshoe. If I am fairly close to the subject and don't want the extra exposure of the on-camera flash I just cover most of the camera flash with a bit of opaque tape so that only enough light escapes to trigger the Digiflash.
{Picture above taken by Clint with FZ10, flash and ?macro-lens}phily_guy (dpreview, Panasonic forum, 2 March 2004)...
...if you really want to supress the output of the built in flash but still trigger the slave, you can use a piece of unexposed film in place of the opaque tape. the unexposed film is supposed to only allow infra-red light to pass through which the slave will fire on.
