Quote Originally Posted by Prof_Pixel View Post
If I remember correctly, FP bulbs were bayonet-base, gas filled fast peak bulbs designed to be used with X sync at faster shutter speeds. Regular flash bulbs didn't work well at high shutter speeds because you only got to use a small part of the burn (and thus got a low guide number).

There were long peak bulbs designed for focal plane shutters; I think they were all screw-base.
I understand FP to stand for focal plane. However, regarding X-sync- I have several cameras with separate sockets for X sync and FP sync.
So it would appear they were not designed for X sync.