I am using a YONGNUO YN685 N GN60 2.4G on my Nikon 7100 and would like the flash to deliver a series of 0.25 sec flashes. On the flash unit I have it set to show MULTI 4 1Hz 1/4Sec duration. If I read this right it should deliver four 0.25 sec flashes, 1 second apart. In fact it delivers a very short, single, flash. If anyone is familiar with this flash, I would really appreciate help with getting the settings to provide what I need.