Nikon D90 Light Writing Help

[Modernmoriendi]

Hello! I'm a somewhat experienced photographer who's experimenting with his d90 doing light writing for the first time. I'm trying to get my camera to flash at the end of my exposure so I can position my model at the right time without blurring the photo, just using the built in flash. The problem is the pre-flash. I cannot get it to not go off. If anyone knows how to fix this, I would be very grateful.

It should be noted I tried using the rear option and custom setting button to "flash off" to cut out the pre-flash, but instead it just takes the flash out all together, even when I let go of the button.

Any help would be much appreciated!
Thank you!

 

[liviudumitru]

Pre-flashes are in TTL mode. Have you tried to use the flash in manual mode ?

 

[2WheelPhoto]

The flash will always pre-fire in CLS mode