Does anyone have knowledge of or experience with a Dormitzer Synctron Model 260 "Zephyr?" The Crown Graphic outfit I inherited from a favorite uncle came supplied with such a flash, and SUCH a flash it is. It still works, and I think it would melt the chromium off a truck bumper, or light up the night sky, since it is such a monstrous bright flash. But what in the world would you use for guide numbers?

Assuming this wonder is electronic flash, just find a friend with [or take it to a camera shop with] a flash meter. Make settings for your commonly used films, then fire that sucker off [outdoors at night the way you describe it]. Keeping careful notes of the flash reading on the meter, and the distance from flash to meter, then make your computations for future use.