How can I trigger an external flash for portraits with the HX-100V?

Well, I have to make a soft black bag and cover the internal flash and the trigger to shield the flash from other shooters in event shooting like a concert...since I shoot hx100 too.

Hx100 does have pre-flash under most flash mode(havent test them all yet, but in my experience anything you can pick from A/S/M will give you an unpleasant pre-flash before the real exposure)

I tested the slave 1 & slave 2 mode of yn560 flash with internal flash as trigger, it works fine. Sync is not a problem under slave 2 mode at all as long as you got a flash like yn560 which supports pre-flash cancel mode(just her slave 2 mode) even at 1/2000s (1/4000s not tested yet since in my experience it only appears under S Mode which is not very good for flash photography and it forces you to use F 5.6 and slower aperture which might be a waste of your precious GN of the external flash or force your flash drains its batteries faster).

Of course under slave 1 which yn560 simply flash according to the first flash, it never joins the real exposure.And thats the chance for an stand-alone optical trigger.

As you can see, 2 sources of flash(built-in and external) were captured by the camera, which proves my external flash escaped from the pre-flash by using slave 2 mode.

The sad news, however, is that the syk-5 they send me was a flop. It just wont trigger my external flash when I boarded it on the hotshoe of syk-5. The one I received might be a faulty one as the rear cover was too loose to stick to the trigger and it fell off from the body of the trigger. Sorry I cannot test the syk-5 for you guys before I got a replacement from the vendor. I will keep trying as this will offer me an opportunity to use radio transmitter to trigger more external flash off-camera to make more complicated flash lighting, which may help hx100v with its weakness-----portrait, partially for its depth of field control as a DC...

Keep trying mates!