the sb-800 af assist does not work on all focus points. i did a test a while back to work out which. i think it is the middle column then skips the column beside that, then is the next column and lastly the far sides.

you will need to check which spots activate the af assist (leave your lens cap on). the big grid auto af thingy always works for the af assist, but misses you intended focus often.

@sevencrossing

crude said:
thanks for the reply, i think the flash is securely locked in because it is quite firm when locked no movement what so ever... im using a nikon d50, sb800 flash, 35mm 1.8.

which camera are you using

I would clean the contacts with a rubber eraser. Also, make certain the battery contacts are cleaned the same way. If this is completed, and the battery charge is good, and the batteries are new, the fault most likely would be some internal failure or poor connection. My opinion only.

One other possibility is that the AF assist illumination comes on only when the light is dim. Could it be, there is somehow a light source hitting your flash and causing the flash unit to think it is brighter than it really is? Or the light sensor for the non-TTL flash is somehow feeding information to the unit and it thinks it is brighter in the room than it is. Taping over the sensor might correct the problem.

this problem happened again last night, as advised i stopped and checked all of the settings which were fine, im not too sure what to do now......

crude said:
i think the flash is securely locked in because it is quite firm when locked no movement what so ever...

if the fault is it intermittent that leave two possibilities

you accidentally switched the focus to manual (easily done in the dark)

dirty wet /contacts

if the fault occurs again, stop, do not remove the flash, take the camera in doors and check your settings

sevencrossing said:
yes this can cause problems if the gun is not locked securely in place or contacts get wet
by the way which, Nikon are you using ?

thanks for the reply, i think the flash is securely locked in because it is quite firm when locked no movement what so ever... im using a nikon d50, sb800 flash, 35mm 1.8.

msmoto said:
Or contact points between camera/flash.

yes this can cause problems if the gun is not locked securely in place or contacts get wet
by the way which, Nikon are you using ?

The battery charge level may affect this. Or contact points between camera/flash.

Thanks guys,
i just powered up the camera to do a test shot in low light the af assist from the flash worked no problem, i didn't have to change anything..... i find this a bit strange one dat it works and another it didn't why but either way i checked the focusing it was already on s not c.... what do you guys think i should do if this problem still occurs.

Crude

softer light? don't see how you'd get that from the 910, but anyway, its another option.

and for even more power and softer light the SB 910

yes, probably the atuofocus as stated.

if you dont need the extra power of the sb800 i would look at an sb700. it af illumes on all points and the pattern it emits is better for locking on (a cross like a plus vs a line like a minus).

i have tested both extensively for this purpose and the sb700 is the hands down winner.

Also remember than the SB-800's AF assist light might not come on, depending on what focus point you are using.

I suspect your camera foccusing is set to c rather than s. focus assist will not work on continuous focusing

hiya guys,
im fairly new to the photography scene and i mainly cover clubs and bars, so my sb-800 is a vital part of my gear. So last weekend i took out my gear from my bag and put the lens on and the flash took a quick test shot and i was puzzled why the red grid normally displayed by the flash gun to assist the auto-focus did not apear, this problem carried on all night long and i couldn't find out why. it was working perfectly the night before and i just didn't know what to do.
has anybody else come across this problem and know how to solve it.

thanks crude