No flash at all, at least I wasn't able to see it, since normally the headset starts with a dark image including pimax logo, the lines can't almost be seen at this moment. However, as soon SteamVR starts, they are clearly visible.
I've read that adjusting brightness may help, but it's still not okay, imho.
Unfortunately, at this very moment I have pretty hectic times at my office, so no time to play with the HMD as well as taking any pictures.
Will update as soon I get my hands on it again.