Backfill light not affect picture... Weird???

TXBui · Dec 2, 2013

I am stumped. I am using the Nikon D90 built-in flash as my main flash. Just to add fill light, I have a hot shoe slave flash detector unit attached to my external Sunpak flash placed behind the main subject. When the built-in goes off, the slave flash goes off. I can confirm this from the sound and the batteries recharging the slave flash unit. Yet, I cannot see the difference between a picture with a fill flash on, and a picture without fill flash. I can't figure out why this is so. I experimented at different shutter speeds, from 1/15 through 1/200 sec. No change. I am guessing that the slave unit is triggered about 1/10,000 second after the built-in flashes, so that 1/30 shutter speed should be open plenty long to capture the slave flash. But no. I can't get the fill flash to show up any where in the picture, even shining directly in the main subject's face in slave mode. What am I doing wrong?

Derrel · Dec 2, 2013

You're probably having issues with the following, very common scenario. My suggestion would be to set the D90's in-built flash to a MANUAL flash output setting in the menu of the camera. I suspect the D90's on-board flash is in a TTL metering mode or other automatic metering mode, and that it is firing a pre-flash, reading that, and then firing the flash and using the pre-flash data as the basis for computing ther amount of flash power/duration required for the REAL exposure. The slaved flash is firing with the pre-flash, and so...the slaved unit is not actually having any effect on the actual exposure...since the slave flash has already been fired.

Your scenario is pretty common, and this might be the twentieth time I've seen similar posts.

TXBui · Dec 2, 2013

arrrrgggg!!! That was it! Brain fart on my part. Thank you. Though am perplexed now. If my built-in flash is set to -.3 for example, does it not mean that I am controlling its power output, thus putting the flash in manual already?

Derrel · Dec 2, 2013

NO, you're just telling the flash to "automatically" subtract .3 EV off of its automated calculations. The Manual flash output is in the menus on Nikons. Setting Flash Exposure Compensation, commonly abbreviated as FEC, is still under the umbrella of automatic flash control and metering systems.