-JAY- wrote:
You could use a pass-through trigger as your AF assist. The YongNuo 622N has a built in auto assist that works well, and will send a pass-through signal to whatever triggers you're using to trigger your flashes.

I have a colleague who uses this method at weddings, we tested the  AF in total darkness and it would lock every time!  Plus they are a great remote trigger... :-)

Paul

GRMACK wrote:
You can go into "Custom" settings on the SB-800 flash menu and turn "Off" the AF Assist light beam feature.  Doing so turns the camera's AF assist light back on.

However, if you have a fast lens (i.e. A large diameter.) I find the camera's AF assist light also gets covered by the lens or its hood so even it is worthless to use.

Another issue is the body I have (D800E) uses a white AF light, and the Nikon speedlights uses a red or IR assist light.  They do not agree in AF (Color issues?) as to where my lenses land at.  The speedlight's one if far worse for focusing misses (I think it back-focused mostly?).  That alone caused me to shut the AF off on the speedlight forever - short of tuning the AF in the menu for AF Fine tuning for use with the SB-900 speedlight and then going back to the normal tuning when I don't use the speedlight.

So now I use a Surefire U2 flashlight (A dimmable 5 watt LED.) as my AF assist light in circumstances where I know the AF will fail.  I point the thing to where my viewfinder's AF square is at and shoot.

Good luck!

I just checked it out, I use the 24-70 which is too big for the auto focus light on the camera.  But I think it will work fine on the 24-85 lens