Time between Nikon i-TTL preflash to main flash?

[BeBu Lamar]

How much time is between a Nikon i-TTL flash (like the SB-800) fires the preflash before it fires the main flash?

[Edwin Barkdoll]

Well, as a lark I took a "Slo-Mo" video using my iPhone (240 fps) of my SB-800 (1/1) on my Z7. Looking at the resulting video step-by-step yielded a crude estimate of 60-70 ms delay between the preflash and the main flash.

In the past I've been frustrated by this delay when trying to take photos of hovering deer flies: their reaction times are shorter than the delay so that by the time the shutter trips and the main flash fires, the flies have moved significantly.

[BeBu Lamar]

Thank you!

I use a Minolta Booster II connected to an oscilloscope and I measured it to be 67mS. Which agrees with what you said.

[rodeo_joe1]

To confirm: Here is a DSO trace of an SB-800 being fired in i-TTL mode. 

The shorter vertical line is the pre-flash and the taller line the main flash. 

The cursor function of the 'scope gives a time between the two of 60.4 ms with the camera shutter speed set at 1/200th s.

The delay may well vary slightly between flash/camera models and shutter settings; allowing for variations in mirror-lift time, etc. 

The above was with a D7200 camera.

FWIW. The sensor used to input the flash to the 'scope was a fast-acting photodiode with a measured rise/fall-time of less than 1 microsecond. The pre-flash itself has rise and fall times of over 48 and 21 us, respectively. 

Edited August 20, 2023 by rodeo_joe1